Performance, Metabolic and Hormonal Alterations during ... · Alterations in heart rate variability, adrenaline and heart rate in response to intensified training that resulted in

Performance, Metabolic and

Hormonal Alterations during

Overreaching

A thesis submitted for the degree of

Doctor of Philosophy

to

Queensland University of Technology

School of Human Movement Studies

Shona L. Halson

B.App.Sci (Hons)

2003

II

Table of Contents Preface VI

Original Authorship statement VII

Acknowledgments VIII

Abstract X

Keywords XI

Abbreviations XII

List of Publications XIII

Chapter 1: General Introduction 1

Background 2

The research problem 3

Objectives of the study 3

Specific aims of the study 4

Research progress linking the manuscripts 7

Chapter 2: Literature Review 8

Introduction to homeostasis, stress and fatigue 9

Introduction to overtraining and overreaching 10

Terms and definitions 10

Causes of overtraining and overreaching 12

Symptoms of overtraining and overreaching 14

Incidence of overtraining and overreaching 19

Changes in variables that occur with overreaching / overtraining 20

Performance 20

Physiological measures 21

Biochemistry 24

Mood disturbance 28

Immune system 31

Neuroendocrine function 39

Autonomic nervous system 47

Central and peripheral fatigue 53

Neuropeptides and immune function interaction 64

Problems associated with overtraining and overreaching research 65

III

Chapter 3: Time course of performance changes and fatigue markers during intensified training in trained cyclists 100

Introduction 103

Methods 105

Results 114

Discussion 127

Conclusion 134

Chapter 4: Mood disturbance, immunological responses and changes in prolactin responses to exercise and pharmacological challenge during overreaching in cyclists 140

Introduction 144

Methods 150

Results 159

Discussion 171

Conclusion 183

Chapter 5: Effects of intensified training on heart rate variability and hormonal indices of neuroendocrine function 195

Introduction 198

Methods 202

Results 205

Discussion 216

Conclusion 222

Chapter 6: Effects of carbohydrate supplementation and dietary intake on performance and substrate utilization following intensified training 230

Introduction 232

Methods 236

Results 241

Discussion 257

Conclusion 262

IV

Chapter 7: General Discussion 265 Research problem revisited 266

Performance Changes 267

Mood Disturbance 269

Physiological and Biochemical Markers 270

Immune Function 274

Substrate Utilisation and Dietary Intake 276

Neuroendocrine Function 281

Blood Hormones 286

Serotonergic System 291

Heart Rate Variability 280

Chapter 8: Summary 286 Mechanisms of Overtraining: Integration of Results and Hypothesis 287

Markers of Overtraining 288

Limitations 289

Future Research 294

Summary 299

V

Preface This thesis for the degree of Doctor of Philosophy is in the format of published and/

or submitted manuscripts and abides by the rules set out in Section 14 of the

Queensland University of Technology 2002 Handbook. All manuscripts included in

this thesis are closely related in subject matter and subsequently form a cohesive

research narrative.

During the course of this study, seven publications and/or manuscripts for

publication, in which the candidate is the first author, have been prepared. These are

initially brought together by a general introduction, which provides background

information, an explanation of the research problem and the aims of the study. The

literature review provides an overview of overreaching and overtraining research.

The methodology related to individual projects is included within each manuscript.

Thereafter follows a presentation of the manuscripts, in a logical sequence following

the development of research ideas in this investigation. A general discussion

integrates the main features of each manuscript and the final summary Chapter

outlines limitations and future research possibilities.

The published and submitted manuscripts adhere to the style of the journal and

therefore variations in formatting are apparent. Figures, tables and reference

numbering in all manuscripts have been retained. A joint authorship statement of the

contribution made by each author precedes each submitted and published

manuscript.

VI

Original Authorship Statement The work contained in this thesis has not been previously submitted for a degree or

diploma at any other institution of higher education. To the best of my knowledge and

belief, this thesis contains no material previously published or written by another

person except where due reference is made.

Signed:

Date:

VII

Acknowledgments The completion of this thesis would not have been possible without the guidance,

support and encouragement that I have received from numerous people.

Dr Asker Jeukendrup has had the greatest immediate influence on this research and

my PhD experience and so deserves to be recognised first. I am extremely thankful

for his advice, expertise, enthusiasm and especially for the opportunity to perform my

research in his laboratory. However, I am equally thankful for his friendship and

support during my time in Birmingham and for making my experience there so

enjoyable.

I would also like to thank Dr David Rowbottom and Associate Professor Andrew Hills

for their assistance in the earlier and latter stages of my candidature, respectively.

I am also indebted to the athletes who volunteered to participate in the studies. The

athletes completed the difficult and time consuming studies with great enthusiasm,

humour and dedication.

Additionally, I would like to acknowledge and thank the following people for their

contribution to this work:

Professor Michael Gleeson for his advice and assistance while performing many of

the biochemical and immunological assays and for his thoughtful comments on my

written work.

Professor David Jones, Dr Anita Sharma and Dr Matthew Bridge for their assistance

and guidance during the buspirone challenge tests and subsequent interpretation of

results.

Professor Romain Meeusen and Bart Busschaert for assistance with measuring

catecholamine concentrations in Study 1.

A very special thankyou goes to Graeme Lancaster for his friendship, humour,

dancing inability and frequent use of the Australian accent. I am certain we were not

supposed to have so much fun performing such a difficult and time consuming study

and I can only hope that we will work together again soon.

VIII

I would also like to thank a group of friends who are or have been postgraduate

students during my PhD. From QUT/UQ: Rebecca Hill, Lisa Atkin, Dr Kate Green and

Chris Brammer. From the University of Birmingham: Dr Juul Achten, Graeme

Lancaster, Dr Matthew Bridge, Dr Roy Jentjens, Luke Moseley and Jimmy Carter.

Additionally I would like to thank Juul Achten and Antoinette Jeukendrup for being

great friends and companions, for making me feel at home in Birmingham and of

course your continued friendship.

Thanks must also go to my friends outside of university life, who aren’t really sure

what I have been doing for the past three and a half years, but who keep me sane

and happy.

Finally, I sincerely thank my family for their love and support and for the constant

reminder of the really important things.

IX

Abstract Many athletes incorporate high training volumes and limited recovery periods into

their training regimes. This may disrupt the fragile balance and the accumulation of

exercise stress may exceed an athlete’s finite capacity of resistance. A state of

elevated fatigue, increased mood disturbance and decreased exercise performance

can result. This is commonly known as overreaching and if increased training and

limited recovery is continued, it is believed that the more serious state of overtraining

may develop. This is relatively commonly experienced in athletes, however little

scientific investigation has been conducted to determine the characteristics and

underlying mechanisms. The overall aim of this thesis was to gain a greater

understanding of the state of overreaching and to specifically provide new

information on potential markers of this state as well as possible mechanisms. To

study the cumulative effects of exercise stress and subsequent recovery on

performance changes, fatigue indicators and possible mechanisms, the training of

endurance cyclists was systematically controlled and monitored in two separate

investigations. A number of variables were assessed including performance,

physiological, biochemical, psychological, immunological and hormonal variables. In

addition heart rate variability and serotonergic responsiveness were also assessed.

Some of the more pertinent effects of overreaching included an increase in heart rate

variability, a reduction in carbohydrate oxidation, an increase in serotonergic

responsiveness and a reduction in stress hormone concentrations. These results

suggest that autonomic imbalance in combination with decreased hormonal release

appears to be related to the decline in performance and elevated fatigue apparent in

overreached athletes. Additionally it also appears that alterations in the

hypothalamic-pituitary adrenal axis may occur in overreached athletes.

X

Keywords Buspirone challenge test

Carbohydrate supplementation

Central fatigue hypothesis

Cortisol

Cycling performance

Cytokine hypothesis

Glutamate

Glutamine

Glycogen depletion

Growth hormone

Heart rate variability

Immune function

Intensified training

Mood state

Overreaching

Overtraining

Power output

Prolactin

Time course

Time domain analysis

Time trial

XI

Abbreviations

AD Adrenaline

BCT Buspirone Challenge Test

CFH Central Fatigue Hypothesis

CHO Carbohydrate

CORT Cortisol

DALDA Daily Analysis of Life Demands of Athletes

GH Growth Hormone

Gln Glutamine

Glu Glutamate

HFP High Frequency Power

HPA Hypothalamic-Pituitary-Adrenal

HRmax Maximal Heart Rate

HRV Heart Rate Variability

IL-6 Interleukin-6

IT Intermittent Test

ITP Intensified Training Period

LFP Low Frequency Power

MT Maximal Oxygen Uptake Test

NA Noradrenaline

POMS Profile of Mood State

PRL Prolactin

RPE Rating of Perceived Exertion

SAM Sympathetic Adrenal Medullary

TNF-α Tumor Necrosis Factor- α

TP Total Power

TT Time Trial

URTI Upper Respiratory Tract Infection

VO2max Maximal Oxygen Consumption

Wmax Maximal Power Output

XII

List of Publications

Journal Articles Halson S.L, M.W. Bridge, R. Meeusen, B. Busschaert, M. Gleeson, D A. Jones and

A.E. Jeukendrup. Time course of performance changes and fatigue markers during

intensified training in trained cyclists. Journal of Applied Physiology, 93 (3), 947-56,

2002.

Halson S.L, G.L Lancaster, A.E. Jeukendrup and M. Gleeson. Plasma cytokines and

immunological responses to overreaching in cyclists. Accepted Medicine and Science in

Sports and Exercise, May 2003.

Halson S.L, M.W. Bridge, A. Sharma, D.A. Jones and A.E. Jeukendrup. Changes in

prolactin responses to exercise and pharmacological challenge in overreached

cyclists. Submitted Experimental Physiology

Halson S.L and A.E. Jeukendrup. Altered mood state following intensified training in

cyclists. In Preparation

Halson S.L, G.I. Lancaster, M. Gleeson and A.E. Jeukendrup. A double-blind

crossover study on the effects of a high carbohydrate diet on underperformance

during overreaching. In Preparation

Halson S.L, G.I. Lancaster, M. Gleeson and A.E. Jeukendrup. Alterations in heart

rate variability, adrenaline and heart rate in response to intensified training that

resulted in overreaching. Submitted Journal of Applied Physiology

Whitham M, S.L. Halson, G.I. Lancaster, M. Gleeson, A.E. Jeukendrup and A.

Blannin. Leucocyte heat shock protein responses to exercise protocols before and

after heavy training. Submitted Journal of Applied Physiology

Lancaster G.I, S.L Halson, Q. Khan, P. Drysdale, M.T. Drayson, A.E. Jeukendrup

and M Gleeson. The effects of acute exhaustive exercise and intensified training on

type 1/type 2 T cell distribution and cytokine production. Submitted Journal of

Leukocyte Biology

XIII

Achten J, S. L. Halson, L. Moseley, M. Drayson, A. Casey and A.E Jeukendrup.

Effect of diet on symptoms of overreaching in runners during a period of intensified

training. In Preparation

Review Halson SL and A.E. Jeukendrup. Does overtraining exist? A critical review of

overreaching and overtraining literature. Submitted Sports Medicine

Book Chapter Halson, SL and Jones, DA. Overtraining. In: ‘High Performance Cycling’. Edited by

AE Jeukendrup. Human Kinetics, Champaign, IL, 2002.

Abstracts Halson S.L, M.W. Bridge, M. Gleeson, R. Meeusen and A.E. Jeukendrup. Time

course of performance changes and markers of overreaching in cyclists. Medicine

and Science in Sports and Exercise. 2002, 34(5), p.S274.

Halson S.L, M.W. Bridge, A. Sharma, A.E. Jeukendrup and D.A. Jones . The effect

of overtraining and recovery on hypothalamic serotonergic 5-HT1A receptor

sensitivity. Medicine and Science in Sports and Exercise. 2001, 33(5), p.S288.

Gleeson M, S.L. Halson, M.W. Bridge, D.A. Jones, G.I Lancaster, N. C. Bishop and

A. E. Jeukendrup. Plasma cytokines, saliva immunoglobulin A and indices of

overtraining during a period of intensified training in trained cyclists. Medicine and

Science in Sports and Exercise. 2001, 33 (5), no. 44.

Whitham, M, Halson, S, Lancaster, G.I and Blannin, A.K. Leukocyte Heat Shock

Protein responses to standard exercise protocols before and after heavy training.

Proceedings 7th Annual Congress, European College of Sports Science. 2002,

P860.

Jeukendrup A.E and S.L. Halson. Simple markers of overtraining. Proceedings 7th

Annual Congress, European College of Sports Science. 2002, P1070.

XIV

Award American College of Sports Medicine- International Student Award 2002. ACSM

Annual Conference, St Louis, Missouri.

_____________________________________________________

Chapter 1: General Introduction _____________________________________________________

Chapter 1 General Introduction

2

Background

Of major concern to the modern athlete is the maintenance of the strenuous training

regimes required to optimise and enhance elite performance. It is generally accepted

that increased training loads correlate to improvements in performance. Yet, it is this

increase in training load in a bid to improve performance that may consequently

result in prolonged fatigue and a decreased performance capacity, or as it is

commonly known, overtraining. When exercise stress is prolonged and excessive in

the presence of inadequate recovery, the positive physiological adaptations that

usually occur with training are absent. Chronic maladaptations occur as a result of

continual exposure to stress and a disruption in internal homeostasis. This imbalance

between training stress/stimulus and recovery can lead to major declines in

performance and signs and symptoms of fatigue and mood disturbance.

The quantity of training stimuli that results in either performance enhancement or a

chronic fatigue state is presently unknown. As it is difficult to ascertain the volume of

training that will result in overreaching or overtraining, it is necessary to identify

markers that distinguish between acute training-related fatigue and overtraining.

Similarly, much of our knowledge about overtraining is derived from cross sectional

studies and anecdotal information. Whilst a number of studies have used a

longitudinal approach, in many cases failure to adequately monitor performance

means we know little about the time course of changes of potential indicators of

overreaching and early phases of the overtraining syndrome.

There are a plethora of changes reported to be associated with overtraining and

range from altered physiological responses, biochemical abnormalities, mood

disturbances, immune dysfunction and neuroendocrine imbalance. However, no

single parameter has been identified and it is essential that overtraining research


3

take a multi-disciplinary approach to investigate a variety of considerations and

factors that may indicate and/ or cause overtraining.

The research problem

Overtraining has been reported to occur in around 10-20% of all elite endurance

trained athletes (1). Given the dramatic and substantial effects that overtraining can

have on performance, this relatively high incidence of overtraining in athletes

contrasts strongly with the lack of knowledge in this area. Much of the information on

overtraining available to athletes, coaches and scientists is experientially based and

lacks scientific investigation. The absence of reliable and consistent markers of

overtraining stems from a number of problems associated with research in this area.

Firstly, there are numerous constraints and difficulties in performing overtraining

research and as such very few scientific investigations have been performed.

Secondly, athletes respond in an individual manner to training stress. Thirdly, it is

often difficult to determine if previous research has indeed initiated a state of

overtraining due to methodological considerations and/or discrepancies in

terminology. Finally, a lack of understanding of the underlying mechanism(s) of

overtraining makes it difficult to develop a suitable diagnostic test.

Objectives of the study

The aim of the series of investigations included in this thesis was to scientifically

examine the state of overtraining in a rigorous and controlled manner. By

systematically controlling and monitoring increases in training intensity, the effects of

this training stress on numerous parameters were determined. A multi-disciplinary

approach was taken to assess such parameters from a variety of scientific

perspectives. These perspectives include alterations in performance, physiology and

metabolism, biochemistry, immunology and neuroendocrinology.


4

Examining the changes that occur in such variables in response to intensified training

allows for the determination of markers that can be utilised to indicate the early

development of overtraining and/or may be used to accurately diagnose the

condition. Exploring alterations that occur alongside performance deterioration may

give clues regarding the underlying mechanism/s.

It has previously been hypothesised that the fatigue experienced by overtrained

athletes is the result of glycogen depletion caused by intensified training with

inadequate recovery. The effects of a high carbohydrate diet versus a normal

carbohydrate diet on performance can give an indication of the effect of carbohydrate

intake on overreaching. Additionally, carbohydrate and fat oxidation rates were

calculated from gaseous exchange. This can provide information on the role of

glycogen depletion as a cause of overreaching.

An additional aim was to describe the time course of changes in performance during

a period of increased training load. Concurrently, the time taken to induce

performance decrements and mood disturbance was also determined.

Specific aims of the study

Chapter 3- Time course of performance changes and fatigue markers during

intensified training in trained cyclists

The aims of this investigation were:

• To identify the time course of changes in selected physiological, biochemical

and psychological parameters during two weeks of intensified training and

two weeks of recovery in trained cyclists. In order to ascertain the time course


5

and fluctuations of these changes, repeated performance tests were

conducted.

• To outline markers of overreaching will be outlined by describing changes in

variables that occur alongside decreases in performance and increased mood

disturbance.

Chapter 4- Mood disturbance, immunological responses and changes in

prolactin responses to exercise and pharmacological challenge during

overreaching in cyclists

This chapter summarizes the effects that intensified training has on changes in mood

state, immunological responses and serotonergic responsiveness. The specific aims

of the study were:

• To examine the relationship between changes in performance and changes in

mood state.

• To examine the use of mood state to identify the amount of time taken to

induce a state of overreaching in the subject group studied.

• To investigate the cytokine hypothesis of overtraining by examining any

changes in plasma cytokine concentration in response to overreaching and

recovery.

• To determine changes in the glutamine: glutamate ratio (Gln/Glu) during

intensified training.

• To examine other possible indicators of overreaching using a range of

immunological, biochemical and haematological parameters.

• To determine if prolactin responses to buspirone administration are altered

following a period of intensified training. This assessment examines the

sensitivity of the serotonergic system.


6

• To compare the PRL response to buspirone to the prolactin responses during

exercise.

Chapter 5- Effects of intensified training on heart rate variability and hormonal

indices of neuroendocrine function

This examination was undertaken to:

• Determine whether intensified training that results in overreaching is

accompanied by changes in heart rate variability.

• In addition, submaximal heart rate and plasma lactate, glucose, cortisol and

catecholamine concentrations were determined to identify possible changes

that may reflect autonomic balance.

Chapter 6- Effects of carbohydrate supplementation and dietary intake on

performance and substrate utilisation following intensified training

This purpose of this investigation was to:

• Determine if carbohydrate supplementation can prevent or minimise the

negative effects of overreaching.

• Additionally, substrate oxidation, glycerol, free triglycerides and free fatty

acids were measured to gain further insight into fuel utilisation and

metabolism.


7

Research progress linking the manuscripts

This research project evaluated the effects of overreaching on numerous aspects

that are linked to decreased performance, mood disturbance and heightened

sensations of fatigue. To achieve this, two separate research projects were

undertaken, both of which successfully induced a state of overreaching in the

athletes studied. Chapters 3 and 4 document the changes in performance, mood

state, immune function and the serotonergic system, respectively. Due the difficulties

in performing overtraining and overreaching studies, examination of these variables

was performed within the one investigation.

As a result of the implications of Study 1 (namely the inference of altered

neuroendocrine function), Study 2 examined the changes in heart rate variability and

autonomic tone in response to intensified training that resulted in overreaching

(Chapter 5). Study 2 also examined substrate oxidation and the effects of

carbohydrate supplementation on symptoms of overreaching (Chapter 6).

The research undertaken in this thesis aimed to comprehensively investigate

changes in a variety of fatigue-related variables that occur with overreaching. There

are several novel aspects of each of the studies, including the determination of the

time course of performance changes, examination of cycling economy and efficiency

following overreaching, examination of the cytokine hypothesis of overtraining,

changes in serotonergic receptor sensitivity and hormone release in response to

overreaching, the effect of dietary manipulation on performance during overreaching,

examination of substrate oxidation during overreaching and an examination of the

neuroendocrine system following overreaching. Independently and collectively,

these studies contribute to the current understanding of overreaching.


8

REFERENCES

1. Budgett, R., E. Newsholme, M. Lehmann, C. Sharp, D. Jones, T. Peto, D.

Collins, R. Nerurkar, and P. White. Redefining the overtraining syndrome as

the unexplained underperformance syndrome. Br. J. Sports Med. 34:67-68,

2000.

_____________________________________________________

Chapter 2: Literature Review

_____________________________________________________

Chapter 2 Literature Review

9

Introduction to homeostasis, stress and fatigue

External or internal forces or stressors continually challenge the maintenance of

human body systems. If a state of equilibrium is reached, a physiologically constant

internal environment or homeostasis is achieved (78). The increasing and ever-

changing demands and challenges of daily life have resulted in the need for the

human body to adapt to maintain its milieu interieur when placed in states of

threatened homeostasis (33).

The term homeostasis, meaning the maintenance of a complex, dynamic equilibrium,

was first coined by Walter Cannon, who extended the previous work of Claude

Bernard and his notion of the milieu interieur recognised over 150 years ago. Cannon

and later Hans Selye borrowed the terms ‘stress’ and ‘strain’ as they are referred to

in physics. Stress was considered the force that tends to deform a solid and the

resultant deformation is strain. This deformation is elastic until a ‘limit of

proportionality’ is reached and beyond this further deformation is plastic. Excessive

or prolonged exposure to stress was suggested to result in weakness and fatigue

(78). Hans Selye extended this concept with the development of the General

Adaptation Syndrome (GAS). The GAS was suggested to be triphasic in nature and

begins with the alarm phase, or as Cannon described, elastic deformation (78). This

is followed by a stage of resistance (analogous to physical reinforcement) and finally

the stage of exhaustion (fracture) is reached.

Selye referred to stress as ‘the state manifested by a specific syndrome which

consists of all the non-specifically induced changes within a biological system’ (126).

Selye’s research into both biochemical and environmental stressors was the first to

examine the effects of such stressors on the hypothalamus, pituitary gland, the


10

adrenal glands, stomach, lymphatic system and white blood cells. Selye’s work also

gave rise to the notion of ‘diseases of adaptation’. These diseases were defined as

those in which imperfections in the GAS played a significant role. Selye continued to

suggest that ‘many diseases are actually not so much the direct results of some

external agent (an infection, an intoxication) as they are consequences of the body’s

inability to meet these agents by adequate adaptive reactions, that is, by a perfect

GAS (126).

As a result of Selye’s pioneering research on the harmful effects of stress, a number

of disorders that are associated with dysfunction of the ‘stress system’ have been

identified. These include: severe chronic disease, anorexia nervosa, melancholic

depression, panic disorder, obsessive-compulsive disorder, chronic active

alcoholism, alcohol and narcotic withdrawal, chronic excessive exercise, malnutrition,

hyperthyroidism, premenstrual tension syndrome, vulnerability to addiction (in rats),

atypical depression, Cushing’s syndrome, seasonal depression, hypothyroidism,

obesity (hyposerotonergic forms), posttraumatic stress disorder and an increased

vulnerability to inflammatory disease (in rats) (126).

It is possible that the mechanisms responsible for the maintenance of homeostasis

have failed to adapt in response to changes in demand. Thus, the many relatively

recent discoveries of ‘disorders of the stress system’ may be a consequence of the

failure of appropriate adaptation to stress (33). An accumulation of stress, either from

exercise, psychological stress or illness without appropriate recovery or regeneration,

is suggested to result in a state of fatigue.

The term fatigue is a complex and common one. Common, as it is often the result of

daily living, illness and/or exercise and complex due to its multifaceted nature and the


11

confusion surrounding its use and definition. The effect of both this prevalent usage

and ambiguity is that the term fatigue is often used undifferentiated in both colloquial

and scientific contexts.

Scientifically, appropriate use of the term fatigue varies depending upon the context

within which it is used. Thus, to physiologists, pathologists, psychologists and

ergonomists the definition of fatigue is specific to their field of investigation. Fatigue

within the domain of exercise physiology is often defined as an inability to maintain a

required force or power output. On the basis of this definition, fatigue can be

classified as either peripheral (metabolic/muscular) or central (central nervous

system). Peripheral and central fatigue processes are differentiated by their

relationship to the neuromuscular junction. Fatigue processes distal to the

neuromuscular junction are considered as peripheral sites of fatigue, while fatigue

that is proximal to this junction and often residing in the brain is referred to as central

fatigue.

Introduction to overtraining and overreaching

Terms and definitions

The term overtraining is often used inconsistently in the literature. Previous terms

used interchangeably include: overtraining, overreaching, overload training,

staleness, burnout, overfatigue, short term overtraining and overtraining syndrome

(122). In general, scientists in the Unites States have labelled this state as staleness,

while Europeans have typically used the term overtraining (102). To clarify this

situation intensified training will be considered the process, while a state of

overreaching or overtraining may be the resultant product of this training.


12

The lack of common and consistent terminology in the study of overtraining is one of

the many problems associated with research in this area and the ability to compare

research studies is hindered. For the purpose of this thesis the following definitions

will be used:

OVERTRAINING: An accumulation of training and non-training stress resulting in

long-term decrement in performance capacity with or without related physiological

and psychological signs and symptoms of overtraining in which restoration of

performance capacity may take several weeks or months (80).

OVERREACHING: An accumulation of training and non-training stress resulting in

short-term decrement in performance capacity with or without related physiological

and psychological signs and symptoms of overtraining in which restoration of

performance capacity may take from several days to several weeks (80).

These definitions suggest that the difference between overtraining and overreaching

is the amount of time needed for performance restoration, and not by the type or

duration of training stress or the degree of impairment (122). It also implies that there

may be an absence of psychological signs associated with the conditions. For these

reasons the above definitions are not entirely satisfactory. However, at present these

definitions provide the most accurate description of the conditions and are commonly

cited in the literature.


13

Causes of overtraining and overreaching

The underlying cause/s of overtraining remain unknown. What is clear is that

overtraining is secondary to the stress of training (25). The process of overtraining is

often viewed as a continuum (Figure 1).

Figure 1- Overtraining Continuum

Initially, increased training stress or overload results in a disruption of homeostasis

and a temporary decrease in function (107). This acute fatigue can result in a positive

adaptation or improvement in performance provided appropriate recovery is allowed.

This is considered a normal training response and this progressive increase in

training load followed by sufficient recovery results in enhanced performance and is

the basis of effective training programs. However, if the balance between appropriate

training stress and adequate recovery is disrupted an abnormal training response

may occur and a state of overreaching may develop (Figure 1).

Increasing state of fatigue

Continual intensified training with inappropriate recovery

Increasing severity of symptoms

Single training session Overreaching Overtraining


14

Thus, if athletes undergo periods of intensified training in the absence of appropriate

recovery, the athlete may not adequately recover (25) and progressive fatigue and

decreased performance can ensue. Once a state of overreaching has occurred one

of two outcomes may occur. Firstly, the athlete/ coach may recognise the symptoms

associated with overreaching and provide appropriate rest and recovery for the

athlete. Following this, full recovery may occur and the process of overreaching may

have stimulated ’supercompensation’ and performance may increase to a level

higher than previously attained (107). The second possible outcome following

overreaching may be the progressive development of a state of overtraining. The

underperformance that occurs as a consequence of overreaching may be the

stimulus for an increase in training in a bid to improve the diminished performances.

Thus, if high levels of training persist and/or rest and recovery is inadequate, the

more serious overtraining syndrome may develop. Other contributing stressors

include frequent competition, monotonous training, psychosocial stressors and heavy

travel schedules (2)

The overtraining continuum appears to correspond closely with Hans Selye’s

theories. Selye proposed the notion that firstly the body’s stress response is triphasic

in nature and secondly that the body’s ability to resist stress is finite. Continual

exposure to a given stressor or stressors according to Selye, results initially in a

decline in general resistance (alarm reaction stage). As adaptation is acquired, the

body’s resistance to the stressor rises above normal (Stage of Resistance). However

under continual exposure to the stressor resistance drops to below normal levels and

a Stage of Exhaustion ensues (126). Selye observed this pattern of behaviour using

a variety of stimuli that included forced muscular work.


15

It is often suggested that the overtraining syndrome is the result of an accumulation

of stressors that exceed an athlete’s finite capacity, similar to that which Selye

observed (123). Selye stated that ‘stress shows itself as a specific syndrome, yet it is

non-specifically induced’, thus environmental, physical and/or emotional stressors

may result in a variety of responses (126). Some of the many symptoms and/or signs

of the overtraining syndrome that have been documented in the literature are

included below in Table 1.

___________________________________________________________________

Symptoms of overtraining and overreaching

Physiological/Physical:

Decreased performance

Inability to meet previously attained performance standards or criteria

Recovery prolonged

Reduced toleration of loading

Lack of supercompensation

Decreased muscular strength

Decreased maximum work capacity

Decreased maximal power output

Decreased maximal plasma lactate levels during exercise

Loss of coordination

Decreased efficiency or decreased amplitude of movement

Reappearance of mistakes already corrected

Reduced capacity of differentiation and correcting technical faults

Increased difference between lying and standing heart rate

Abnormal T wave pattern in ECG

Heart discomfort on slight exertion


16

Changes in blood pressure

Postural hypotension

Retarded return of blood pressure to basal levels after exercise

Changes in heart rate at rest, exercise and recovery

Increased frequency of respiration

Perfuse respiration

Decreased body fat

Increased oxygen consumption at submaximal workloads

Increased ventilation and heart rate at submaximal workloads

Suppressed heart rate-exercise profile

Suppressed glucose-exercise profile

Suppressed glucose-lactate profile

Suppressed neuromuscular excitability

Shift of the lactate curve towards the x axis

Decreased evening postworkout weight

Elevated basal metabolic rate

Chronic fatigue

Insomnia with and without night sweats

Feels thirsty

Anorexia nervosa

Loss of appetite

Bulimia

Amenorrhea and oligomenorrhea

Nausea

Increased aches and pains

Gastrointestinal disturbances

Muscle soreness or tenderness


17

Tendonostic complaints

Periosteal complaints

Muscle damage

Elevated C-reactive protein

Rhabdomyolysis

Organs zone complaints

Disturbed digestion

Headaches

Disturbed feeling around the heart

Sleep disturbance-difficulty getting to sleep, waking in the night, nightmares and

waking unrefreshed

Drawn appearance

Psychological/ Information processing:

Depression

Anxiety

General apathy

Decreased self-esteem or worsening feelings of self

Emotional instability

Difficulty in concentrating at work and training

Sensitive to environmental and emotional stress

Fear of competition

Changes in personality

Decreased ability to narrow concentration

Increased internal and external distractibility

Decreased capacity to deal with large amounts of information

Gives up when the going gets tough


18

Feelings of loss of purpose, energy and competitive drive

Feelings of helplessness, incompetence and being trapped in a routine

Emotional lability

Loss of libido

Restlessness and irritability

Immunological:

Increased susceptibility to and severity of illnesses, colds and allergies

Flu-like illnesses

Unconfirmed glandular fever

Minor scratches heal slowly

Swelling of the lymph glands

One-day colds

Decreased functional activity of neutrophils

Decreased total lymphocyte counts

Reduced response to mitogens

Increased blood eosinophil count

Decreased proportion of null (non-T, non-B) lymphocytes

Bacterial infection

Reactivation of herpes viral infection

Significant variations in CD4:CD8 lymphocytes

Frequent minor infections, particularly of the upper respiratory tract

Biochemical/ Hormonal:

Negative nitrogen balance

Hypothalamic dysfunction

Flat glucose tolerance curves


19

Depressed muscle glycogen concentration

Decreased bone mineral content

Delayed menarche

Decreased haemoglobin

Decreased serum iron

Decreased serum ferritin

Lowered TIBC

Mineral depletion (Zn, Co, Al, Mn, Se, Cu)

Increased urea concentrations

Elevated cortisol levels

Elevated ketosteroids in urine

Low free testosterone

Increased serum hormone binding globulin

Decreased ratio of free testosterone to cortisol ratio of more than 30%

Increased uric acid production

Decreased blood glucose

Decreased intrinsic sympathetic activity

Decreased β-adrenoreceptor density

Altered plasma noradrenaline levels

Suppressed catecholamine sensitivity

Altered hypothalamic/pituitary, adrenal/gonadal function

Hypoglycaemia during exercise

Abnormal resting hormonal profiles

___________________________________________________________________

Table 1: Signs and symptoms associated with overreaching and overtraining

documented in the literature (24, 26, 56, 81, 84, 85, 107)


20

Incidence of overtraining and overreaching

The balance between training and overtraining is a delicate one. It is for this reason

that the incidence of the overtraining syndrome among a variety of athletes appears

to be relatively high. Over a one-year period Morgan et al (102) reported that of 400

swimmers who trained up to 14 000metres/day, 5-10% were ‘stale’. Both O’Connor et

al (102, 106) and Hooper et al (61) reported a similar incidence of overtraining in

swimmers over a six-month period. Hooper et al (61) reported three of 14 swimmers

as ‘stale’, while O’Connor et al (106) classified three of eleven swimmers as ‘stale’. In

a study of 170 college swimmers over a four-year period, Raglin & Morgan (116)

classified 6.8% of swimmers as stale each season. However, on average 32.1% of

the swimmers studied showed signs of training ‘distress’ each season and 45.9%

were ‘distressed’ in more than one training session.

Koutedakis & Sharp (79) examined 257 elite athletes who were members of British

National Teams and/or Olympic squads in a variety of sports over a twelve-month

training season. Thirty-eight cases (15%) of athletes were classified as overtrained

and in 50% of these cases the state of overtraining developed in the three-month

competition phase. The incidence rate was slightly higher in males (17%) as opposed

for female athletes (11%). Interestingly, when sports were divided into predominantly

aerobic and anaerobic events, there was no significant difference in incidence of

overtraining over the study period.

Finally, Morgan et al (102) in an examination of elite distance runners reported that

64% of female and 66% of male runners would experience ‘staleness’ in their

competitive career.


21

Changes in variables that occur with overreaching / overtraining

Performance

The operational definition of overtraining indicates clearly that a decrement in

performance capacity is the defining characteristic. As there is currently no

universally accepted diagnostic tool to identify the presence of a state of overtraining,

a decrement in performance is one of the only indicators that has significant

diagnostic power. Despite this there are only a limited number of studies in the total

pool of overtraining literature that report performance data. Other papers report a

range of physiological, biochemical, psychological and/or hormonal responses to

overtraining yet fail to either report or measure changes in performance.

Jeukendrup et al (70) examined the effects of two weeks of intensified training

followed by a period of reduced training. On average, cycling time trial performance

decreased, with times increasing from 830 ± 14 seconds to 871 ± 19 seconds. In

swimmers who had previously been identified as ‘stale’, performance times at the

Australian National Swimming Trials were 2.4% lower than previous personal bests.

This is in contrast to the swimmers who were considered well trained (94) who

showed a 1.1% improvement in swimming times.

A reduction in total running distance during an incremental treadmill test (4719 ±

912m to 4361 ± 788m) following a 28-day period of increased volume training has

been reported (83). This was in comparison to an increase in total running distance

reported after the same period of increased intensity training.

Urhausen et al (146), in a prospective longitudinal study, examined 17 male

endurance trained athletes prior to and following a period of intensified training.

Using a cycling test (110% of individual anaerobic threshold) the authors reported a


22

27% decrease in time to exhaustion (1362s vs 996s) following the increase in training

load. Similarly, Fry et al (50) reported a 29% decrease in performance following

twice-daily interval training in elite soldiers. On completion of the 10 days of

increased training, run time to exhaustion decreased from 369s to 261s.

Physiological Measures

Oxygen Uptake

A number of studies have measured physiological variables that are related to

performance. An 8% decrease in peak oxygen uptake (VO2peak) (4.8 vs. 4.4 l.min-1)

was reported after 14 days of intensified training (70). A decrease in VO2peak was also

reported by Snyder et al (136) after 15 days of increased high intensity training (4.94

vs. 4.65 l.min-1).

Maximal and submaximal heart rate

Jeukendrup et al (70), Lehmann et al (83) and Urhausen at al (146) all reported

reduced maximal heart rates (HRmax) after increased training. This may possibly be

the result of a reduced exercise duration observed during maximal exercise due to an

inability to achieve a maximal effort. However, it is not clear whether the decreased

maximal heart rate and possibly a decreased cardiac output is the cause or the

consequence of premature fatigue. There have been suggestions that disturbances

in the autonomic nervous system are responsible for the altered heart rate during

overtraining (84). Decreasing sympathetic influence and/or increasing

parasympathetic influence, decreased ß-adrenergic receptor number or density,

increased stroke volume and plasma volume expansion are all possible mechanisms

for the reduction in maximal heart rate (160). However, strong evidence for any of

these mechanisms is lacking.


23

Lehmann et al (83) reported a tendency toward increased stroke volume after an

increase in training volume in middle- and long-distance runners. This was in

conjunction with a decreased maximal heart rate. A recent study by Hedelin et al (58)

reported increased plasma volume and reduced maximal heart rates following a 50%

increase in training volume in elite canoeists. While performance was not assessed

following recovery and therefore it could not be determined if the athletes were

fatigued or overreached, there was no relationship between the changes in HRmax

and changes in blood volume.

Decreases in HRmax may also be the result of a down-regulation of the sympathetic

nervous system or changes in parasympathic/sympathetic tone. A number of

investigations have examined changes in plasma and urinary catecholamine

production during periods of intensified training that resulted in overreaching or

overtraining (58, 83, 147). Lehmann et al (83) reported decreased nocturnal urinary

noradrenaline and adrenaline excretion and increased submaximal plasma

noradrenaline concentration following an increase in training volume. Submaximal

and maximal heart rates significantly declined alongside the changes in

catecholamines. However, the findings of unchanged catecholamine concentrations

and significantly decreased maximal heart rates have also been reported (58, 146).

Unchanged resting, submaximal and maximal free adrenaline and noradrenaline

concentrations were described by Urhausen et al (146) in underperforming cyclists

and triathletes over a 15-month period. While catecholamine concentration remained

stable, maximal heart rate was significantly reduced. Finally, Hedelin et al (58) also

reported decreased maximal heart rates yet no change in resting catecholamine

production was observed. Thus, there does not appear to be a consistent relationship

between changes in heart rate and changes in catecholamine concentration.

However, down-regulation of ß-adrenoreceptors, or a decrease in receptor number,


24

may occur as a result of the prolonged exposure to catecholamines that can occur as

a result of intensified training and/or psychological stress (160). This may be one

unexplored alteration that could explain the reduction in maximal heart rate observed

in overtrained athletes.

When viewed as a whole the above studies suggest that periods of intensified

training that result in overreaching or overtraining are coincident with a diminished

exercise capacity and results in alterations in physiological responses to standard

exercise challenges. However, this data may also suggest that the subjects were

unable to produce a maximal effort. The mechanism/s for the reduced maximal

performance may be related to the generation of fatigue prior to the maximal

engagement of the cardiorespiratory and/or metabolic systems (70). These

seemingly submaximal efforts may be due to a variety of reasons, including fatigue

bought about by centrally mediated mechanisms.

To elucidate some of the physiological responses a number of investigations have

examined various aspects related to the subject’s anaerobic threshold (AT).

Lehmann et al (87) reported an increase in running speed at 2 mmol lactate

concentrations in both groups of athletes who completed a period of increased

intensity training and those who completed a period of increased volume training.

However in the group of athletes who experienced a decline in performance due to

the increased training, i.e., increased volume group, running speed at 4 mmol.l-1

lactate concentration stagnated. This was in comparison to the increased intensity

training group who showed a significant increase in this variable (87). An increase in

power output at 4 mmol.l-1 lactate concentration (234 vs. 267W) has also been

reported (70). Finally, Urhausen et al (146) reported a slight, but non-significant


25

increase in individual AT in the overtrained state, even though performance declined

by approximately 27%.

Many of these changes related to individual anaerobic threshold should be

considered in the presence of any changes in submaximal blood lactate

concentration. When viewed in isolation some of the reported increases in AT would

appear to indicate an enhanced performance and should only be viewed in

conjunction with appropriate performance based assessment.

Cycling efficiency and economy

Gross efficiency is defined as the ratio of power output to power input and is most

commonly expressed as a percentage (111). Horowitz et al (64) demonstrated that

gross efficiency could affect performance by comparing cyclists with similar oxygen

uptakes, but significantly different gross efficiencies. Subjects with a higher gross

efficiency demonstrated higher average power outputs during a 1-hour cycling

performance test (342 vs 315 W) (64). Given that gross efficiency has been shown to

be reduced following moderate intensity endurance cycling (111), and this reduction

in efficiency affects cycling performance, it may be possible that intensified training

could alter cycling, or indeed running, efficiency to such an extent that this may

explain the underperformance evident in overreached and overtrained athletes. To

date there has been no research investigating this possibility.

Biochemistry

In the search for a reliable and valid indicator of a state of overtraining, a variety of

responses to an increased training load have been explored. Lowered submaximal

and maximal blood lactate concentrations have been observed in a number of

investigations (50, 70, 87, 136, 146). Jeukendrup et al (70) noted a shift to the right in


26

lactate curves in cyclists who underwent two weeks of intensified training. Lehmann

et al (87) reported a decrease in submaximal lactate values (2.87 vs. 2.42 mmol.l-1)

as well as maximal values (11.31 vs. 9.47 mmol.l-1). A number of other studies have

however not reported significant changes in lactate concentrations (50, 83, 135, 146).

It appears somewhat paradoxical that lowered submaximal and maximal blood

lactate concentrations are generally indicative of improved endurance performance,

yet performance is markedly diminished in the overtraining syndrome. A possible

explanation for the lowered lactate values is the depletion of glycogen due to

repeated and intense periods of training with little or inadequate recovery. However,

when glycogen content was maintained, Snyder et al (136) successfully induced

‘short-term overtraining’ in cyclists. Similarly, reduced muscle glycogen content has

been noted during increases in training load in the absence of a state of overtraining

(35).

Other biochemical markers such as concentrations of creatine kinase (CK), urea and

iron levels have all been considered as possible indicators of overtraining. However,

inconsistent findings and the inability to distinguish intensive training from

overreaching or overtraining does not support the use of the majority of biochemical

markers as a diagnostic tool.

The role of biochemical markers in the diagnosis of the overtraining syndrome is not

conclusive. Lowered maximal lactate concentrations in combination with a reduction

in performance capacity may be a useful indicator of overreaching and overtraining. It

is apparent that further research in this domain is needed.


27

Glycogen depletion

It has long been known that muscle glycogen depletion results in fatigue and a

reduction in performance (72). The effects of repeated bouts of high intensity

exercise on muscle glycogen stores are also well established (34). The effect of high

carbohydrate (CHO) diets during periods of normal and intense training has been

less well established (66). Jacobs and Sherman in a review on the efficacy of CHO

supplementation and chronic high CHO diets for improving endurance performance,

suggest that a high CHO diet may be necessary for optimal adaptations to training

(66). Sherman et al (131) examined the effects of either a moderate- (5g CHO.kg-

1.day-1) or high-CHO (10g CHO.kg-1.day-1) diet for a 7-day period on performance

following normal training. Athletes who consumed the high-CHO diet were able to

maintain basal muscle glycogen levels (122 and 140 mmol glucose.kg ww-1 for

runners and cyclists, respectively). However, athletes on the moderate CHO diet had

a 30-36% reduction in muscle glycogen concentration after 5 days of training.

Despite this reduction in basal glycogen concentration, all training sessions were

completed and performance was not significantly different after the 7 days of training.

However, when the difference in basal muscle glycogen concentration is much

greater (40-50 mmol glucose.kg ww-1 vs. ~220 mmol glucose.kg ww-1, high fat/

protein diet vs. high CHO diet, respectively) the effect on performance can be

significant (14). In this study subjects who consumed a high fat/ protein diet exhibited

a three-fold decrease in time to exhaustion when compared to the high CHO diet

(14).

Both of the above studies involved altering the diet without changing the subjects

training volume. However, the amount of CHO in the diet may play a more critical

role in performance ability when training intensity is increased and thus the reliance


28

on CHO as fuel during exercise is also increased. Simonsen et al (132) intensely

trained rowers for a period of 4 weeks and examined the effects of consuming either

a 5g CHO.kg-1.day-1 diet or a 10g CHO.kg-1.day-1 diet. The athletes on the moderate

CHO diet maintained muscle glycogen content, while those on the high CHO diet

increased muscle glycogen content by 65% (132). Both groups showed an increase

in performance following the increased training, however the group consuming the

moderate CHO diet had a 2% improvement in average power output during a rowing

time trial and the high CHO diet group had an average 11% performance

improvement. This study indicates that while CHO intake may not affect an athlete’s

ability to increase training and complete the more difficult training sessions, it does

however, highlight the importance of CHO in the optimal adaptation to training and

the resultant enhancement of performance. Athletes in this study did not demonstrate

a reduction in performance and although the intensity of training was increased, the

athletes cannot be considered overtrained or overreached and thus extrapolation to

the effects of a high diet during overtraining is not possible.

As overtraining is commonly brought about by high intensity training with limited

recovery, it is conceivable that the fatigue and underperformance associated with

overtraining is at least partly attributable to a decrease in muscle glycogen levels.

Costill et al (35) investigated this possibility by examining the effects of 10 days of

increased training volume on performance and muscle glycogen levels. Of the 12

swimmers participating in the investigation, 4 were unable to tolerate the increase

from 4000 metres per day to 9000 metres per day and were consequently classified

as non-responders. The group of non-responders consumed approximately 1000

kcal per day less than their estimated energy requirement and consumed less

carbohydrate than the responders (5.3 g.kg-1.d-1 vs. 8.2 g.kg-1.d-1). However,

importantly, muscular power, sprint swimming ability and swimming endurance ability


29

were not affected in either the responders, or the non-responders. Costill et al (35)

concluded that the glycogen levels of the non-responders were sufficient to maintain

performance, but inadequate for the energy required during training and thus fatigue

resulted. As overreaching and overtraining are primarily defined by a reduction in

performance, the ability to ascertain whether the non-responders were indeed

overreached or overtrained is limited.

These findings directed Snyder et al (136) to examine performance responses to

intensified training with the addition of sufficient dietary carbohydrate, in a bid to

determine whether overreaching could still occur in the presence of normal muscle

glycogen levels. To ensure sufficient carbohydrate intake, subjects consumed a

liquid of 160g of carbohydrate in the two hours following exercise. Subjects

completed 7 days of normal training (N), 15 days of intensified training (OVER) and 6

days of minimal or recovery training (REC). Resting muscle glycogen was not

significantly different when compared between N (530.9 µmol.g-1 DW) and OVER

(571.2 µmol.g-1 DW). Maximal work performed during an incremental cycle test was

unchanged from N to OVER, however seven of the eight subjects had an average

decrease in Wmax of 3%. The symptoms of overtraining were reported to have

occurred despite normal resting muscle glycogen levels.

Mood disturbance

An objective physiological marker to indicate negative adaptation to training stress is

clearly lacking in the research literature. However, there is general agreement that

the overtraining syndrome is characterised by psychological disturbances and

negative affective states (61).


30

In several studies in which subjects were identified as overreached, clear signs of

psychological distress were observed (48, 50, 70, 146). After a period of increased

intensive training that resulted in a 27% decline in performance time, male endurance

trained athletes complained of intense daily fatigue or lack of mental concentration

(146). Similar symptoms were reported by Fry et al (49) where subjects indicated

they were emotionally unstable, failed to remember things, had no interest in

everyday tasks, had difficulty in focussing/ holding concentration and ordinary tasks

were an effort. Competitive cyclists who underwent two weeks of intensified training

reported that it was harder to complete training during the intensified training period

and during this period they were more likely to omit a training session (70).

The Profile of Mood States (POMS) questionnaire has been used by a number of

researchers to quantify athletes’ mood states during periods of overtraining. The

questionnaire yields measures of tension, depression, anger, vigour, fatigue,

confusion as well as a global measure of mood. Members of Special Air Services

(SAS) Regiment of the Australian Army who showed a decline in performance

following ten days of increased intensive interval training, reported significant

elevations in fatigue, decreases in vigour and an increase in total mood disturbance

(49). Similarly, Flynn et al (48) documented an increase in global POMS scores from

159 ± 12 during normal training to 189 ± 14 following a two week training camp that

resulted in a decline in swimming performance.

However, increases in global POMS scores have also been reported in periods of

increased training that have not resulted in a state of overtraining (103, 105).

Increased global POMS scores were noted in swimmers after three days of

increased training (105) as well as after ten days of increased training (103). In both

of these studies alterations in mood state occurred in the absence of changes in


31

performance. Over a four-year period, the POMS questionnaire was able to correctly

identify ‘stale’ athletes on an average of 81.45% of occasions in collegiate swimmers

(103, 106). However, performance data was not recorded and the team coach using

some objective and subjective measures completed the classification of stale

athletes.

In recognising that athletes go through normal cycles of fatigue and recovery, Rushall

(123) developed a questionnaire to assess stress tolerance in athletes. A training

‘window’ is created, which documents normal responses to training and can be used

for baseline comparison. During this time responses may fluctuate as a result of

fatigue from acute training bouts. Consistently elevated responses above the

predetermined window, however, can indicate a state of overreaching and the need

for increased regeneration. Despite the possible usefulness and practicality of this

questionnaire, research utilising this questionnaire to aid in the identification of

overtraining is lacking.

Rating of Perceived Exertion

An alternative perceptual and subjective method of identifying stress during exercise

is the athlete’s rating of perceived exertion (RPE) (21). The estimation of effort during

exercise is based on a combination of physiological sensations that is integrated into

a numerical value (95). Morgan (101) describes perception of exertion as a

configuration of sensory input in combination with physiological and psychological

traits as well as the previous experience of the subject. In essence, the perception of

exertion is suggested to be principally governed by the intensity of exercise with the

addition of certain physiological factors. Such factors include heart rate, power

output, catecholamines, lactate production, blood glucose levels and muscle

glycogen levels (101). Gender, personality and training status are other possible


32

influences. Recent research in trained cyclists suggests that perception of exertion

during cycling is based on a combination of leg muscle pain and feelings of

breathlessness (69).

Significantly higher RPE values as measured on the Borg scale, were reported by

athletes in a state of overreaching when compared to normal training (146). At the

tenth minute of a cycling test at 100% of AT till exhaustion, RPE scores were 14.6 ±

0.3 during normal training and 16.3 ± 0.3 during overreaching.

Snyder et al (135, 136) however, did not report changes in RPE following increased

training. As blood lactate concentration is expected to decrease during an

overtrained state, the ratio between lactate and RPE scores has been proposed as

an indicator of overreaching. The La:RPE ratio multiplied by 100 should not fall below

100 in well trained athletes. Snyder et al (135) reported that athletes who were

classified as overreached based on performance times, all had ratios below 100 at

workloads above AT. The ratio also returned to near normal values following the

recovery period (135). The use of this ratio is practical and relatively inexpensive,

however its ability to accurately diagnose the overtraining syndrome should be

further investigated.

Immune system

The response of the immune system to exercise is typically dependent upon the

nature of the stress that the exercise induces. Pederson et al (112) suggests that

moderate exercise may enhance the immune system and result in an exercise-

related reduction in illness. However, intense exercise of a long duration may result

in immunodepression. The occurrence of the “open window” or period of

immunodepression flowing exercise, is dependent upon the intensity and duration of


33

exercise. During this period, infections may occur due to an invasion of

microbacterial agents and a decrease in the concentration of lymphocytes, natural

killer cells and secretory IgA in mucosa, which provide defence against common

infections, especially viruses (112).

Given the many anecdotal reports of increased illness rates and upper respiratory

tract infections (URTI) in overreached and overtrained athletes (134), the role of

exercise-induced immunodepression has been explored. It seems possible that the

prolonged and/or intense exercise usually required to induce a state of overtraining,

may increase both the duration of this “open window” and the degree of the resultant

immunodepression. While this alteration in immune function is indeed possible and

there are numerous anecdotal reports of increased susceptibility to illness in athletes

diagnosed as overtrained, there is little scientific information to substantiate this

inference.

Mackinnon and Hooper (93) increased the intensity of training of a group of 24

swimmers. Of those swimmers that were identified as overreached, one in eight

(12.5%) reported symptoms of URTI. Surprisingly, in the group of 16 athletes who

responded positively to the intensified training, nine (56%) exhibited self-reported

symptoms of URTI. Thus, increased URTI incidence is likely to reflect the increase in

training, regardless of the response of the athlete to the increased physical stress.

Whilst a plethora of literature exists on the effects of single exercise bouts and

periods of increased training on URTI incidence, the above mentioned study is the

only investigation that has examined increased URTI incidence with a decline in

performance indicative of a state of overreaching or overtraining. Similarly, a limited


34

number of investigations have been performed which explore the relationship

between immune suppression and overtraining (49, 63, 89, 94, 120).

As leukocytosis is typically the immediate response to intensive exercise (130),

resting peripheral blood leukocyte number has been determined during both periods

of training that has resulted in overreaching (63, 89, 94, 120). With the exception of

Lehmann et al (89) all previous studies have not demonstrated changes in leukocyte

number in overtrained or overreached subjects. Interestingly, Lehmann et al (89)

reported a significant decline in leukocyte number when the training volume was

increased. No changes were observed following an increase in training intensity and

during this condition a state of overreaching did not develop. The clinical

consequence of a reduction in leukocyte number is not presently clear and changes

may simply reflect cell redistribution or increased cell turnover (91).

Similarly, resting peripheral blood lymphocyte numbers also appear not to be

influenced by overreaching (63, 94, 120). However, while cell numbers may remain

constant, activation of lymphocytes may be increased. Fry et al (49) reported a

significant increase in the activation level of peripheral blood lymphocytes (CD25+,

HLA-DR+, CD3+: CD25+ ratio). Following intensified training that resulted in

overreaching, Gabriel et al (51) also reported slight increases in HLA-DR+ T-cells and

higher cell-surface expression of CD45RO. However, an immunosuppressive effect

was not observed and it was concluded that overreaching does not lead to clinically

relevant alterations of immunophenotypes in peripheral blood cell counts due to a

lack of change of neutrophils, T, B, and natural killer cells.

Neutrophil numbers have been reported to be unchanged (49, 51, 94) and increased

(63) in overreached and overtrained athletes. Importantly, neutrophil function has not


35

been assessed in overtrained athletes and thus the relative contribution of neutrophil

cells to possible immune dysfunction in overtrained athletes is unknown.

Natural killer cell numbers appear to be unaltered in athletes showing symptoms of

overtraining (49, 51). Currently, there are no existing reports in the literature that

document natural killer cell function.

The mucosal immune system response has been examined in overtrained athletes

using salivary IgA as a marker (91). IgA is an important factor in host defence and

has been observed in relation to increased upper respiratory tract infection (URTI)

incidence in endurance-trained athletes (90). To date, there is limited data on

changes in mucosal IgA as a result of overreaching. Mackinnon et al (92) reported

18-32% lower salivary IgA concentrations in athletes showing symptoms of

overtraining compared to those who were well trained. Salivary IgA may prove to be

a useful indictor of immune depression in athletes and may therefore be beneficial in

the early diagnosis of URTI and perhaps overtraining.

Taken together, the current information regarding the immune system and

overtraining seems to only confirm the role of intensified training in immune

depression. Whilst many cell numbers do not appear to change during overreaching

or overtraining, those cells that do alter appear to simply reflect the nature of the

training performed. Thus, immune parameters may change in response to intensified

training independent of whether the training results in overreaching or overtraining.

Hence, the role of immunodepression in the aetiology of overtraining appears

unlikely.


36

Cytokine hypothesis of overtraining

Recently, Smith (134) proposed the cytokine hypothesis of overtraining endeavouring

to explain the mechanism/s behind the variety of changes that accompany the

overtraining syndrome. The author suggested that excessive musculoskeletal stress

in combination with limited recovery induces a local inflammatory response that

evolves into systemic inflammation. This leads to the production of pro-inflammatory

cytokines, IL-1β, IL-6 and TNF-α, which act on the central nervous system. This

induces ‘sickness’ behaviour (fatigue, appetite suppression, depression), activation of

the sympathetic nervous system and the hypothalamic-pituitary-adrenal-axis,

suppression of the hypothalamic-pituitary-gonadal-axis, up-regulation of liver function

and possibly immunosuppression (134). However, there is presently very little

documentation of changes in plasma cytokines in response to overreaching or

overtraining.

Glutamine

Glutamine is a neutral amino acid found in high levels in a number of human tissues

(121). It is the most abundant amino acid in human muscle tissue and plasma (155)

and under normal conditions glutamine levels are maintained by a balance between

the release and utilisation of glutamine by various organs (121). The brain, lungs,

liver, skeletal muscle and possibly adipose tissue release glutamine, while cells of

the immune system, the liver, kidneys and gastrointestinal tract are the primary

utilisers (121). Depending on the net release of glutamine from such organs and

tissues, the typical normal plasma level of glutamine after an overnight fast is

between 500 and 750 µmol.l-1 (155). Muscle is thought to be the most important

releaser in terms of quantity (28) and is also the body’s largest store of glutamine

(20mmol.l-1 of intracellular water) (121).


37

The determination of whether a cell is a net producer or consumer of glutamine is

based on the direction of a single reversible reaction (121, 155). Glutamine is

synthesised from ammonia and glutamate by glutamine synthetase. Glutaminase

catalyses the reverse reaction to form ammonia and glutamate from glutamine (121).

According to Rowbottom et al (121) glutamine may be the most versatile of the amino

acids. This is evidenced by the differing roles that glutamine has in a number of

tissues and organs. These include: the transfer of nitrogen between organs and

detoxification of ammonia, maintenance of acid-base balance during acidosis, as a

nitrogen precursor for the synthesis of nucleotides, a fuel for gut mucosal cells, a fuel

for cells of the immune system and as a possible direct regulator of protein synthesis

and degradation (121).

Due to the significant role of skeletal muscle tissue in both the release and storage of

glutamine, a number of studies have investigated the effect of exercise on plasma

and muscle concentrations of glutamine. During prolonged exercise several studies

have reported an increase in plasma glutamine concentrations during exercise (6, 46,

97, 124). Some research has suggested that this increase during exercise is a result

of increased release from skeletal muscle, evidenced by a decline in levels of

glutamine in skeletal muscle (118, 124). However, other studies have shown a

decline in plasma glutamine concentrations during exercise (110, 119). From this

information it appears that short-term exercise increases the plasma concentration of

glutamine in athletes, while prolonged exercise results in a decline during exercise

(28).

When investigating changes in skeletal muscle, other studies have reported

unchanged (120) or increased skeletal muscle glutamine content (13). Importantly,

there is limited knowledge regarding changes in glutamine content in other human


38

organs and tissues. However, rat studies have shown decreases in muscle (43) and

liver (32, 43) and due to the similarities between human and rat plasma and muscle

changes, rat liver glutamine alterations may be representative for the human model.

Numerous studies have reported a postexercise fall in plasma glutamine following

prolonged exercise (22, 60, 74, 119, 127). While the data concerning changes in

glutamine concentration during exercise is contradictory, the majority of research

investigating changes following exercise suggests that plasma concentrations

significantly decline.

Explanations for the increase in plasma glutamine during exercise have been

proposed by Walsh et al (155) and include: changes in haemoconcentration,

increased ammoniagenesis from adenine nucleotide breakdown and the effects of

cortisol on muscle Na+-dependent glutamine transport. The decline in plasma

glutamine concentration during recovery from exercise suggests that there is either

an increased demand for glutamine by tissues that require glutamine as a fuel and/or

a decreased production or altered transport kinetics of this amino acid (155). A recent

hypothesis suggests that increased hepatic and gastrointestinal uptake of glutamine

for gluconeogenesis is occurring at a time when muscle release of glutamine remains

constant or is decreasing (155), thereby explaining the fall in postexercise plasma

glutamine.

Glutamine is an important substrate for cells of the immune system, especially

lymphocytes, macrophages and possibly natural killer cells (121) and may be

important in wound healing (27). Glutamine is both an energy source for immune

cells and an important component to cell replication as a precursor for purines and

pyrimidines (121). Plasma glutamine levels may also be reduced in the presence of

systemic inflammation. During prolonged exercise appropriate blood glucose levels


39

are maintained by increasing liver gluconeogenesis for which glutamine is an

important precursor (134). Glutamine is also essential for the de novo synthesis of

large quantities of inflammatory-related proteins by the liver, such as C-reactive

protein and haptoglobin, which are vital in the immune/inflammatory response (134).

Therefore, during periods of immunological challenge, glutamine production is

increased. Thus, it may be expected that low plasma glutamine levels commonly

observed after prolonged exercise may result in reductions in immune function.

Parry-Billings et al (110) reported lower plasma glutamine concentrations (503

µmol.l-1) in 40 athletes diagnosed as overtrained when compared to controls (550

µmol.l-1). Rowbottom et al (120) reported similar findings with reduced glutamine

concentrations in overtrained athletes, in comparison to age-matched sedentary and

athlete controls. While Mackinnon and Hooper (93) found no relationship between

incidence of URTI and glutamine, they observed 23% lower glutamine concentrations

in swimmers who were reported to be overtrained than in well-trained swimmers.

Similarly, fatigued British athletes prior to the 1992 Olympic Games presented with

significantly lower plasma glutamine levels than non-fatigued athletes (74).

However, a recent study by Smith and Norris (133) reported statistically similar

plasma glutamine levels in five athletes who were diagnosed as overtrained to

athletes who responded normally to training and competition. At present the role of

glutamine in overreaching and overtraining is not clear. While plasma glutamine

concentration may or may not decrease following periods of intensified training, there

is still no evidence to link low glutamine levels with impaired immune function and

increased susceptibility to illness or infection. However, the use of glutamine

concentrations as a marker to indicate impending or current overtraining warrants

further attention.


40

Glutamate

Glutamate is an important intermediate in nitrogen elimination as well as in anabolic

pathways (10) and as described earlier is implicated in both the synthesis and

breakdown of glutamine. Two studies have reported elevated plasma glutamate in

overtrained athletes (110, 133). Parry-Billings et al (110) reported significantly

elevated plasma glutamate in overtrained athletes in comparison to control athletes

(160 ± 10 vs. 125 ± 8 µmol.L-1). A recent study also reported elevated plasma

glutamate in athletes who were diagnosed as overtrained (133). In this particular

study, the authors suggested that the ratio of glutamine divided by glutamate could

represent global training status (Gln/Glu). A ratio of less than 3.58 was proposed as

an indicator of overreaching. Athletes could be further classified as overreached or

overtrained depending on the time taken for this ratio to increase above 3.58 (133).

The mechanism for the increase in plasma glutamate in athletes with the OTS is

presently not known. Elevated plasma glutamate has previously been reported in

patients with cancer, human immunodeficiency virus infection (HIV) and sepsis (55,

75). Elevated plasma glutamate levels were reported in pre-catabolic cancer patients

and this finding was suggested to indicate decreased capacity of peripheral muscle

tissue to take up glutamate (55). The significance of elevated plasma glutamate in

the mechanism/s of overtraining is unknown. An alteration in the ratio of glutamine to

glutamate may be of assistance in monitoring training load and thus, overreaching

and/or overtraining.

Neuroendocrine function

Homeostasis, or the maintenance of a constant internal environment is necessary for

the normal functioning of various cellular components of tissues and organs of the

body (57). Stimuli, of extrinsic (environmental) and intrinsic (within the body) origin


41

affect physiological processes and given the variety of physiological responses that

occur during and after exercise, the role of the neuroendocrine system during

exercise is sizeable (57). During exercise the neuroendocrine system is involved in

regulation of fuel metabolism, circulatory responses, fluid and electrolyte balance,

body temperature control, gastrointestinal regulation, pain sensation and other

neurobehavioral effects (57). The hypothalamic-pituitary (HP) axes, particularly the

hypothalamic-pituitary-adrenal (HPA) axis, in combination with the sympathetic

adrenal medullary (ANS) axis contribute to the majority of the regulatory responses to

stress, being either from physical or emotional stressors (73).

Hypothalamic-Pituitary Function

Coordination of the neuroendocrine system is under the major control of the

hypothalamus (126). In response to stressful stimuli hypothalamic releasing and

inhibiting hormones are released from hypophyseal veins that transport the

hormones to the pituitary lobe (99). From the pituitary lobe, hormones can stimulate

or inhibit the release of other hormones from the pituitary lobe. These hormones can

then act directly on body tissues or act on target organs, which in turn release

hormones that act on various body tissues (99). Examples of the latter hormones

include adrenocorticotropin (ACTH), prolactin (PRL) and growth hormone (GH) (98).

The hypothalamic-pituitary (HP) axis functions to maintain basal and stress-related

homeostasis (45). Exercise can profoundly alter numerous hormonal and metabolic

systems (114) and during exercise there is an increase in plasma stress hormone

concentrations (73). During normal training, in combination with adequate recovery,

the stability of the hypothalamic-pituitary axes are maintained (134). Appropriate

recovery allows an adaptation to the stress, which occurs during a termination of the

stress response (73). When the training load is high and recovery is minimal, as in


42

the case of overreaching and overtraining, the excessive physiological and

psychological stress may lead to a sustained alteration in the regulation of the HP

axes. Recent research has suggested that altered HP axis function may predispose

individuals to a variety of illnesses including depressive illness and inflammatory

disease (113). From this information it may be postulated that a number of the

symptoms of overreaching and overtraining may be the result of dysfunction of the

HP axis.

During acute exercise the increase in whole body energy metabolism and oxygen

uptake necessitates changes in fuel utilisation and cardiovascular adjustments and

hence a subsequent need to maintain internal homeostasis (77). Thus, generally

speaking, there is an increase in hormone release during acute exercise, which has

been well documented (77). As mentioned earlier, an adaptation to a given amount of

stress can occur if the athlete is given the appropriate amount of recovery and this

corresponds closely to Selye’s General Adaptation Syndrome (126). Hence, plasma

hormone levels at a given absolute workload decrease after periods of physical

training (158). The finding that trained athletes also have lower hormonal responses

than untrained individuals at identical workloads, indicates that hormonal responses

are dependent on relative (percentage of maximal oxygen uptake) rather then

absolute workload (76).

However, the role of the HP axis in the aetiology of overtraining has not been

thoroughly investigated. Barron et al (11) administered an insulin-induced

hypoglycaemic challenge to assess HP axis function in overtrained athletes. This

challenge alters the secretion of the hypothalamic factors that stimulate the release

of adrenocorticotropin (ACTH), growth hormone (GH) and prolactin (PRL). Athletes

were also intravenously administered luteinizing-hormone releasing hormone (LHRH)


43

and thyrotropin-releasing hormone (TRH), which act at the level of the pituitary.

Overtrained athletes had significant decreases in GH, ACTH and consequently

cortisol responses as a result of insulin administration, which returned to levels

similar to that of asymptomatic runners following four weeks of rest. This suggests

that there was impairment at the hypothalamic level. Responses of hormones

released as a result of LHRH and TRH (i.e. thyroid-stimulating hormone (TSH), PRL,

luteinizing hormone (LH) and follicle-stimulating hormone (FSH)) were unchanged.

This demonstrated that there was no evidence of pituitary dysfunction and hence the

impairment was at the level of the hypothalamus (11). Following the results of this

investigation a number of researchers have focussed on alterations in hormone

levels in overtrained athletes, however further work on pituitary sensitivity has not

been performed.

Cortisol

The glucocorticoid, cortisol, is necessary to maintain critical processes during periods

of prolonged stress and to contain inflammatory reactions (71). The effects of cortisol

are considered permissive, as they are not directly responsible for the initiation of

metabolic or circulatory processes, however it is necessary for their complete

expression (71). Specifically, the main actions of cortisol are (44, 71):

• To maintain life

• Carbohydrate metabolism (raise blood glucose through gluconeogenesis and

to stimulate glycogenolysis)

• Fat metabolism (reduces the utilisation of amino acids for the formation of

protein, except in the liver)

• Protein metabolism (increased breakdown with overall negative nitrogen

balance)


44

• Suppression of the inflammatory response

• Stimulate red blood cell production and decrease phagocytosis

• Minor effect on sodium retention and potassium excretion

• Suppression of ACTH secretion

• Necessary for the normal excretion of water

• Modulation of perception and emotion in the CNS

This list documents the importance of cortisol in the regulation of bodily processes,

but also highlights its critical involvement during exercise and recovery.

Barron et al (11) reported lower cortisol responses to insulin-induced hypoglycaemia

in overtrained athletes compared to asymptomatic runners, yet basal cortisol levels

were elevated. Lehmann et al (83) reported decreased 24-hour urinary cortisol

excretion after 21 days of intensified training that resulted in underperformance.

In a study examining the pituitary hormonal response in overreached endurance

athletes, Urhausen et al (146) reported no significant changes in resting cortisol

(baseline: 254 ± 19 nmol.l-1; OT: 264 ± 28 nmol.l-1) when subjects were examined

prior to and during intensified training. Rowbottom et al reported unchanged resting

cortisol levels in athletes suffering from the overtraining syndrome (120) and

similarly, no changes in resting serum cortisol concentrations were observed by

Flynn et al (48), Mackinnon et al (94) or Hooper at al (63).

Maximal cortisol responses appear to be reduced during overreaching. Snyder et al

(136) reported a decrease in plasma cortisol concentration from 514.8 ± 56.8 nmol.l-1

to 381.8 ± 52 nmol.l-1 following a period of intensified training that resulted in a state


45

of overtraining. Urhausen et al (145) also reported similar reductions in maximal

cortisol levels.

Adrenocorticotropin (ACTH)

Adrenocorticotropin (ACTH) controls the function of the adrenal cortex. Corticotropin-

releasing hormone (CRH), as it name suggests, is the principal regulator of ACTH,

which in turn, increases cortisol secretion by increasing its synthesis (73). Despite

the relationship between ACTH and cortisol production, little research has been

conducted to identify changes in ACTH as a result of overtraining.

As mentioned earlier, Barron et al (11) reported a reduced increase in ACTH

responses to insulin-induced hypoglycaemia. Lower resting ACTH levels and lower

exercise-induced ACTH release was also observed by Urhausen et al (145) in

overreached athletes. From this limited information, it may be possible that there is a

reduced adrenal responsiveness to ACTH in overtraining.

Testosterone

Testosterone is a gonadal hormone that exerts a number of actions on the body (73),

and depending on the intensity and duration of previous exercise can have anabolic

effects (144). This response can be reversed during periods of recovery and

therefore there has been interest in controlling periodisation by monitoring

testosterone levels in the blood (144). Testosterone may be important during

recovery due to its role in protein synthesis, but also possibly for the ability to

enhance glycogen storage through increased muscle glycogen synthetase activity

(144).


46

The documented response of both total and free testosterone concentrations in

overtrained athletes is contradictory. Flynn et al (48) observed decreased serum total

and free testosterone levels coincident with a decrease in performance following

intensive training. Vervoorn et al (153) also reported lower testosterone levels in

rowers following an increase in intensive training, however there were no significant

changes in performance and hence the presence of a state of overreaching or

overtraining cannot be confirmed. In endurance athletes identified as overreached by

a significant reduction in performance there were no significant differences in resting

testosterone levels during normal training and during a state of overtraining (145).

Growth hormone – Somatotropic hormone (GH)

Growth hormone, or somatotropic hormone is influenced by a number of hormones,

neuropeptides and neurotransmitters or by altering growth hormone-releasing factor

(GHRF) or somatotropin release inhibiting factor (SRIH) (73). GH is an important

hormone in relation to exercise due to its role in stimulating protein anabolism and

lipolysis and also has insulin-like effects (73). GH is under the control of the HP axis

and is partly responsible for the anabolic effects of exercise. During endurance

exercise GH peaks in the plasma before the end of exercise and will return to normal

values within 1-2 hours.

From the limited research that has examined GH responses during overtraining, it

appears that GH responds in a similar manner to other hormones under HP axis

control. Barron et al (11) reported decreased GH release in response to insulin-

induced hypoglycaemia and Urhausen et al (145) also demonstrated a reduced

maximal plasma GH concentration following overreaching.


47

Prolactin

The main function of prolactin is to induce mammary gland growth and milk secretion

(98). However, prolactin may be of interest during exercise as it is considered a

stress hormone, it is released from the anterior pituitary gland and is closely

associated with serotonin and dopamine (42). While most hormones are regulated by

releasing hormones, prolactin is unique in that is regulated by tonic inhibition by the

hypothalamus itself (42). This effect is mediated by one or more prolactin-inhibiting

factors (PIF) and it is believed that dopamine is a primary PIF (42). Prolactin-

releasing factors (PRF) are thought to include serotonin, opioid peptides, vasoactive

intestinal peptide and neurotensin (42).

Physical exercise is a potent stimulator of prolactin release and the rise in prolactin

has been suggested to correspond to anaerobic threshold (41). It is not known

whether lactic acid accumulation is the stimulus for the prolactin release or whether

the rise in lactic acid reflects the level of exercise intensity required to stimulate the

HP axes (41).

The role of prolactin in overreaching and overtraining has not been extensively

investigated. Barron et al (11) in their examination of the hypothalamic-pituitary axis

in overtrained athletes reported a decreased prolactin response to hypoglycaemia.

However, Lehmann et al reported unchanged resting and maximal prolactin

responses in overreached athletes (86).

Testosterone: Cortisol Ratio

The ratio of testosterone: cortisol is suggested to indicate the balance between

androgenic-anabolic activity (testosterone) and catabolic (cortisol) activity (138).

Cortisol, a steroid and primary stress hormone, and testosterone, a primary


48

androgenic-anabolic hormone, are both released in response to high intensity

(>60%VO2max) aerobic and anaerobic exercise (138). The testosterone: cortisol ratio

is believed to be an indicator of the positive and negative effects of training due to the

opposing effects that the hormones have on growth, protein synthesis and muscle

metabolism (94).

A decrease in the testosterone: cortisol ratio of approximately 30% or a fall below

0.35 X 10-3 has been offered as an indicator of a state of overtraining (5). The

usefulness of this ratio as a diagnostic tool has not been supported in the literature.

The ratio has been shown to remain unchanged in overtrained athletes who are

underperforming (145), yet a decreased ratio has been reported in athletes who

show no performance decrements after intensive training (153). Thus, the ratio of

testosterone: cortisol has not been proven to discriminate overtrained athletes from

well-trained athletes.

Autonomic nervous system

The autonomic nervous system (ANS), particularly the (sympathetic adrenal

medullary (SAM) axis, in conjunction with the HP axes maintains homeostasis and as

such is activated during physical exercise. The ANS regulates the function of all

innervated tissues and organs of the body with the exception of skeletal muscle and

thus forms the major efferent component of the peripheral nervous system (45). The

ANS consists of three components: (1) the sympathetic (noradrenergic) system, (2)

the parasympathetic (cholinergic) system and (3) the enteric system, which lies in the

walls of the gastrointestinal tract (45).

The parasympathetic nervous system processes are related to digestion, movement

of metabolic substrates and the conservation and storage of these substrates (57).


49

The sympathetic system plays a particularly important role during periods of stress as

it increases heart rate and blood flow to the brain and muscle and decreases blood

flow to the skin, digestive tract and kidneys (57). Impulses received through

preganglionic sympathetic nerves stimulate the release catecholamines: dopamine

(DA), adrenaline (AD) and noradrenaline (NA) from the adrenal medulla (44).

Adrenaline and Noradrenaline

Circulating catecholamines have their main effects in the cardiovascular system, the

central nervous system and in carbohydrate and lipid metabolism (57). The effects of

AD and NA are mediated through the four sympathetic receptors: α1, α2, β1, β2. Both

AD and NA can interact with α-and β- adrenergic receptors and therefore the

response of a given system to adrenergic stimulation is largely determined by the

type of receptors that populate the system (71).

Under conditions of stress, blood glucose is elevated through the stimulatory effects

of catecholamines on hepatic glycogenolysis and insulin secretion inhibition (57).

Catecholamine-induced cAMP production activates a triglyceride lipase, which

metabolises fats into free fatty acids and glycerol and also decreases the release of

amino acids from skeletal muscle (57). AD also increases the force and rate of the

heartbeat, by increasing cardiac contractility and cardiac conduction velocity. Finally,

relaxation of gastrointestinal, urinary and bronchial muscle occurs (71).

Arterial concentrations of AD and NA increase linearly with exercise duration and

exponentially with exercise intensity (77). Measurement of catecholamines can

provide an indication of the activation of the sympathetic nervous system, which is

predominantly activated during physical exercise.


50

Israel (65) has previously attempted to distinguish between a parasympathetic or

vagal form of overtraining and a sympathetic form. The parasympathetic form is

characterised by increased fatigue, apathy and altered mood state, immune and

reproductive function (65). Lehmann et al (84) suggests that this form of overtraining

is more frequently observed and may be referred to as the modern form of

overtraining. This form of overtraining is said to be the consequence of an imbalance

between high duration, high intensity endurance training and little regeneration,

possibly in combination with other non-training stress factors (84).

Catecholamine levels in urine and plasma can reflect the activity of the sympathetic

nervous system and can therefore examine the possibility of a parasympathetic-

sympathetic imbalance or autonomic imbalance (144). Basal urinary catecholamine

excretion was has been reported to be significantly reduced in overtrained athletes

(84). Catecholamine excretion was negatively correlated to fatigue ratings and

following a period of recovery, catecholamine excretion returned to baseline levels

(84). Increased resting plasma NA levels were observed by Hooper et al (62) in

overtrained athletes. Lehmann et al (88) also observed increased resting NA levels

following a period of increased training volume that resulted in performance

incompetence. However, Urhausen et al (145) could not replicate the above findings

and reported no significant differences in submaximal and maximal plasma

catecholamine concentrations in overreached athletes. The differences in the above

findings may be related to methodological differences and high inter-individual

differences in catecholamine responses to exercise. Additionally, this may a different

form of overtraining (parasympathetic vs. sympathetic) or a different stage of the

overtraining / overreaching continuum.


51

Dopamine

Recent research suggests that the ANS profile in exercise consists in enhanced

dopaminergic (DA) relative to noradrenergic (NA) activity and increased vagal tone

(54). DA is the principal catecholamine of the brain and is directly involved in motor

control in the striatum the regulation of cardiovascular and renal function, muscle

tone and visual processing (54). Hypothalamic DA is considered to have a role in the

control of body temperature and underlies a portion of the functional component of

the heat loss system (82).

In the context of overtraining, the role of changes in DA has not been thoroughly

investigated. This is despite the additional role of dopamine as the major prolactin-

inhibiting factor. At present there is only one study that has examined changes in DA

as a result of overtraining (88). In this experiment, DA remain unchanged as a result

of intensified training, however, this was attributed to high inter- and intra-assay

variability (up to 30%), reflecting both high methodological variation and high inter-

subject variation (88).

Heart Rate Variability

The circulation of blood throughout the body is the result of cyclic activity of the heart,

for which the unit of measurement is one heart cycle (1). The length of this cycle is

referred to as the heart period and is inversely proportional to heart rate (HR) (3). On

occasion HR is unchanged from cycle to cycle and this negative clinical sign is

referred to as embriocardia or pendulum-like rhythm (3). Embriocardia is rarely

observed due to perturbations of cardiovascular function (1). This variability of the

periodic processes in the circulation is a function of integrative neurohumoral

influences (3).


52

Heart Rate Variability (HRV) is the term used to describe the oscillation in the interval

between consecutive heart beats (1). HRV is commonly assessed by examining the

intervals between successive R waves, which is determined from the detection of

each QRS complex (1). See Chapter 4: Methodology for additional details.

The occurrence of resting bradycardia in endurance-trained athletes is well

established and according to Uusitalo et al (148) may be attributable to four possible

factors (1) decreased cardiac sympathetic modulation, (2) increased cardiac

parasympathetic modulation, (3) decreased intrinsic heart rate and (4) a combination

of the afore mentioned factors. As mentioned previously, alterations in resting,

submaximal and maximal heart rates have been reported following intensified

training that has resulted in overreaching or overtraining. Assessment of HRV may

allow the detection of an imbalance in autonomic activity on the heart, which may

contribute to the alterations in heart rate and other fatigue symptoms, commonly

observed in overreached and overtrained athletes.

To date, four studies have investigated heart rate variability in overreached or

overtrained athletes, with studies showing no change (58, 148), inconsistent changes

(149) or increased parasympathetic modulation (59). The lack of uniformity in

findings is most likely related to different techniques and methods of presenting HRV

analysis, differing methods of identifying overreaching, different stages in the

overreaching/overtraining continuum and individual variation in both HRV and

responses to training.

Hedelin et al (58) increased the training load of nine canoeists by 50% over a 6-day

training camp. Running time to fatigue, VO2max, submaximal and maximal heart

rates and maximal blood lactate production all decreased in response to the

intensified training, however all indices of HRV remained unchanged. On average,


53

there were no significant changes in low frequency power, high frequency power,

total power or the ratio of low to high frequency power, both in the lying position and

after head-up tilt. Similarly, Uusitalo et al (148) reported no change in intrinsic heart

rate and autonomic balance in female athletes following 6-9 weeks of intensified

training. This involved the investigation of autonomic balance was assessed through

pharmacological vagal blockade. In addition, both the time domain and power

spectral analysis in the frequency domain were calculated during supine rest and in

response to head-up tilt (149). Results suggest that heart rate variability in the

standing position had a tendency to decrease in response to intensified training in the

subjects who were identified as overtrained (149). This may indicate vagal withdrawal

and/or decreased sympathetic excitability. However, between-subject variability was

high in this investigation.

Finally, Hedelin et al (59) reported increased heart rate variability and decreased

resting heart rate in a single overtrained athlete. In comparison to normally

responding subjects examined during the same period, the overtrained subject

exhibited an increase in high frequency and total power in the lying position during

intensified training, which decreased after recovery. The increase in high frequency

power was suggested to be most likely the result of increased parasympathetic

activity (59).

From the information available on HRV and overtraining, it is clear that further

investigations are warranted and systematically controlled and monitored studies are

needed.


54

Central and peripheral fatigue:

The role of peripheral mechanisms in the aetiology of muscular fatigue is well

documented in the literature. Such peripheral mechanisms include (23, 104):

• Depletion of the phosphocreatine concentration in muscle.

• A decrease in blood glucose.

• A depletion of glycogen stores within the muscle.

• An accumulation of by-products such as hydrogen ions, inorganic phosphate,

creatine, free AMP, free ADP and IMP.

• A loss of potassium from the cell.

• Dysfunction within the sarcoplasmic reticulum, including calcium release and

uptake.

• Impairments in neuromuscular transmission and propagation.

• Disruption of internal structures such as myofibrillar disorientation and

damage to the cytoskeletal framework.

• An increase in the plasma ratio of free tryptophan (f-TRP): branched chain

amino acids (BCAA) (f-TRP:BCAA).

Many or all of these impairments or disruptions to the differing elements of the

periphery leads to fatigue and this is unquestioned and unchallenged. What is

disputable is the proportionate role that peripheral fatigue plays during exercise and

how fatigue is explained in the absence of peripheral alterations.

Central Fatigue

Central fatigue is generally considered to be fatigue originating proximal to the

neuromuscular junction and is associated with factors residing in the central nervous

system (37). Like the term fatigue itself, central fatigue may be termed differently in


55

different contexts. Central fatigue is often referred to as impaired firing rate

modulation or reduced motor unit recruitment during fatiguing exercise (53). In this

case, a decrease in muscular activation that is proximal to the point of stimulation of

the motor nerve is used to differentiate central from peripheral fatigue mechanisms

(53). Insufficiency in central neural drive (52), although not the recipient of rigorous

scientific investigation, is generally regarded to be a significant contributor to fatigue

processes.

Central fatigue can also be viewed in a more integrated biological and neurological

context that involves both peripheral and central mechanisms. As such, central

fatigue may have its origins in the periphery as the result of biological or metabolic

activity during exercise, yet manifest itself neurologically through alterations in

specific elements of the central nervous system. This slightly different theory of

central fatigue, labelled the central fatigue hypothesis (CFH), was first proposed by

Newsholme in 1987 (104). Fundamental to this hypothesis are several biological

issues:

1. Activity of the neurotransmitter 5-hydroxytryptamine (5-HT) or serotonin is linked

to a variety of psychological responses such as lethargy, arousal, mood, appetite,

pain, motor neurone excitation and thermoregulation.

2. The precursor to 5-HT is the aromatic essential amino acid tryptophan (TRP).

3. TRP is the only amino acid that binds to plasma albumin and therefore exists in

both a bound and a biologically active free form, which are in equilibrium. An

increase in free fatty acids separates the bound TRP from albumin and thus

increases free tryptophan (f-TRP)


56

4. Branched-chain amino acids (BCAA’s) (leucine, isoleucine and valine) are not

take up by the liver, but by muscle. The rate of uptake by the muscle is increased

during exercise.

5. A competition for entry to the brain of blood-borne BCAA’s and f-TRP exists as

they both share the same amino acid carrier (a large neutral amino acid- LNAA).

6. There is no flux-generating step in the conversion of TRP to 5-HT as none of the

enzymes involved in the series of reactions are saturated with substrate. Thus,

the conversion of TRP to 5-HT can be influenced by substrate availability.

7. It is therefore suggested that an increase in TRP will increase the rate of

formation of 5-HT in the brain and lead to an increased firing of 5-HT neurons.

In essence, the CFH suggests that an increase in the activity of the serotonergic

system via an increased rate of 5-HT formation from TRP can lead to an increased

perception of fatigue. The rate of conversion of plasma f-TRP to brain 5-HT is

controlled by the ratio of f-TRP:BCAA’s. Thus, either an increase in f-TRP or a

decrease in plasma BCAA concentration can lead to an increase in TRP transport

across the blood-brain barrier. Such an increase in the f-TRP: BCAA ratio has been

hypothesised to be influenced during prolonged exercise by two concurrent events.

Firstly, during sustained exercise plasma leucine and part of isoleucine are taken up

by skeletal muscles, oxidised and converted to acetyl-Co A (154). TCA-cycle

intermediates and glutamine are synthesised from the other carbon skeletons (108,

154). Secondly, free fatty acids increase in the blood during prolonged exercise

which displaces TRP from albumin and results in increased plasma f-TRP (37) (See

Figure 2).


57

Figure 2: Central Fatigue Hypothesis. BCAA: branched chain amino acids; ALB:

albumin; TRP: tryptophan; f-TRP: free tryptophan; FFA: free fatty acids; 5-HT: 5-

hydroxytrypamine; PRL: prolactin.

Once f-TRP has entered the brain it is synthesised to 5-hydroxytryptophan (5-HTP)

by the enzyme tryptophan hydroxylase. 5-HTP is then converted to 5-HT by the

enzyme aromatic L-amino decarboxylase. Degradation of 5-HT to 5-hydoxyindole

acetaldehyde is achieved via monoamine and finally by aldehyde dehydrogenase to

form the primary metabolite of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), which is

excreted in the urine (117). 5-HT receptors are found in the dorsal raphe and median

raphe nucleus, which sends projections to the hypothalamus. Stimulation of 5-HT

receptors results in the release of the single polypeptide chain stress hormone

prolactin from the anterior pituitary gland (108).

Muscle

Blood

Brain

FFAFFA

ALB TT

TRP

ALB TT

TRP

fTRPfTRP

BCAABCAA

BCAABCAA

TRPTRP

5-HT5-HT

5-HT Receptor5-HT Receptor

PRLPRL

PRLPRL f-TRP:BCAAf-TRP:BCAA


58

Since the CFH was first proposed, investigations have begun to scientifically

examine its validity. Fundamental questions relating to various aspects of the

hypothesis have been and are currently being addressed. This research is briefly

described in the following section and has included: determining the influence of

exercise on plasma levels of BCAA’s and/or TRP and changes in the f-TRP:BCAA

ratio, determining the effect of an altered ratio on endurance performance,

determining whether dietary manipulation of the ratio enhances performance. Finally

recent research has focussed on whether pharmacological manipulation of 5-HT

receptor activity affects performance and finally, what the role of receptor sensitivity

plays in the exercise capacity of highly trained endurance athletes and patients with

chronic fatigue syndrome.

Experimental evidence for the central fatigue hypothesis

In its simplest terms the CFH centres on the conversion of blood-borne tryptophan to

firstly TRP in the brain and then to 5-HT, also in the brain. First support for the

hypothesis was observed when a link was shown between an increase in intravenous

TRP and an increase in brain TRP in rats (29). Further, evidence for an increase in

TRP in both rats and humans, as a consequence of physical exercise has been

provided (16, 18, 20, 30, 31, 40, 47, 67, 139).

Subsequent research has also examined the effect of exercise on plasma BCAA

concentration. Levels of BCAA’s after exercise in both animal and human studies

have been reported to increase (20), remain unchanged (31) and decrease (4, 15-17,

139, 151). Unchanged plasma and brain concentrations of leucine, isoleucine and

valine after two hours of exercise have also been shown (31). Thus the proposal that

plasma BCAA concentration is decreased after prolonged exercise is generally

considered valid and has provided positive scientific support for the CFH.


59

Additionally, many of the above mentioned studies have also indicated that exercise

has a stimulatory effect on the ratio of f-TRP: BCAA’s (4, 15, 16, 31, 139, 151). The

resultant increase in the ratio of these amino acids is suggested to confirm the belief

that TRP entry to the brain is heightened after endurance exercise. However, the

implications of the change in ratio may be questioned. Does the increase in the ratio

result in increased TRP transport to the brain and does this stimulate fatigue

sensations? Additionally, the effect that dietary manipulations of f-TRP and/or

BCAA’s have on endurance performance is also of interest.

The theoretical possibility of altering the influx of TRP into the brain and hence

delaying fatigue has recently gained research interest. Investigations have focussed

on nutritional strategies involving supplementation of BCAA’s, CHO and f-TRP (15,

17, 19, 139, 140, 151). The proposed ergogenic benefit of BCAA supplementation is

centred on delaying the reduction of BCAA’s as a consequence of oxidisation by the

skeletal muscles during exercise. In theory this is thought to prolong fatigue by

delaying the conversion of f-TRP to 5-HT in the brain as a result of changes in the

ratio of f-TRP: BCAA’s. Similarly, CHO has a suppressive effect on the mobilisation

of free fatty acids (36). Consequently, this may reduce the unbinding effect that free

fatty acids has on TRP and albumin and delay the increase in f-TRP in the blood

during exercise. Some researchers have proposed a benefit of TRP supplementation

during exercise (125). It is postulated that increased TRP leading to increased 5-HT

may actually prolong fatigue due to possible effects of 5-HT on nociception (125).

This was suggested to have an effect on the encephalin-endorphin system and

hence reduce the sense of discomfort and pain during exercise (125).

BCAA supplementation has been shown to increase endurance performance during

a 42.2 km marathon (17), and during submaximal cycling (15). However


60

supplementation with BCAA’s did not prove performance during a graded

incremental exercise to exhaustion (152) and submaximal cycling (140, 151).

Further efforts to provide scientific validation of the CFH has resulted in a series of

investigations into the effects of TRP supplementation on exercise performance (125,

141, 151). L-tryptophan (L-TRP) supplementation was shown to improve submaximal

treadmill running (125), however further research could not replicate these findings

(137, 141, 150).

The lack of consistent support for altered exercise performance after nutritional

supplementation lead researchers to examine the effects of specific drugs that either

increase (agonists) or decrease (antagonists) 5-HT activity on fatigue during

exercise. Research involving administration of pharmacological agents aims to

investigate the possibility that alterations in receptor sensitivity may be a possible

cause of fatigue. This is hypothesised as alterations in BCAA and or TRP do not

appear to influence performance, yet the serotonergic or 5-HT system is still thought

to influence fatigue and performance.

Run time to exhaustion is reported to be decreased in a dose-response manner after

administration of a 5-HT agonist in rats (7, 8). In an attempt to replicate the findings

of the rat models, Wilson & Maughan (157) examined the effect of a 5-HT agonist on

fatigue in human subjects. Subjects were either administered a placebo or 20mg

Paroxetine (5-HT re-uptake inhibitor). Subjects cycled to exhaustion at a power

output corresponding to 70%VO2max, and those who received the placebo exercised

for 116 minutes as compared to the Paroxetine group who exercised for 94 minutes

only (p=0.036). There were no significant differences in the other measured

variables- relative workload, carbohydrate oxidisation, blood glucose levels, peak


61

blood lactate, plasma ammonia and water consumption. Thus, the increased fatigue

experienced by the Paroxetine group was not due to the metabolic effects measured.

The authors conclude that the difference between the fatigue experienced by the two

groups was primarily due to altered 5-HT activity. Davis et al (39) conducted a

methodologically similar study to that of Wilson & Maughan and reported very similar

results.

Marvin et al (96) administered Buspirone, a partial 5-HT1A agonist at postsynaptic 5-

HT1A receptors, to thirteen ‘active males’ 45 minutes prior to exercise at 80%VO2max.

Time to volitional fatigue fell from 26 minutes (range: 24-30) after the placebo to 16

(range: 11-19) following Buspirone ingestion. There were no significant differences in

VO2 values as a percentage of maximum after 5 minutes of exercise, blood lactate or

blood glucose levels. RPE scores were significantly higher after Buspirone during

early stages of exercise and prolactin levels were increased throughout exercise and

at fatigue despite the fact that subjects receiving Buspirone exercised for only two-

thirds the time of the placebo group. The higher RPE scores and thus heightened

perception of fatigue as a result of Buspirone, in conjunction with a reduced exercise

time, supports the theory that 5-HT activity affects endurance performance. Similar

results were found by Struder et al (140) who showed a significant reduction in

exercise time after administration of Paroxetine (157 ± 53 vs. 131 ± 36 min).

The subsequent opposing research approach has been used to investigate the

effects a 5-HT receptor antagonist on exercise performance and fatigability in human

subjects. Pannier et al (109) and Meeusen et al (100) however, found no differences

in exercise time to fatigue after ingestion of a 5HT antagonist.


62

Thus, the data on human subjects are somewhat inconclusive. The effects of 5-HT

agonists are relatively well documented and appear relatively consistent. Less

research attention has been focussed on 5-HT antagonists and exercise and thus its

specific role in central fatigue mechanisms remains unclear. In general, manipulation

of 5-HT release can have significant effects on fatigue and exercise performance,

thereby establishing a role for 5-HT pathways in fatigue during exercise.

Effect of training on the serotonergic system

Jakeman (67) suggested that trained individuals should demonstrate a lower f-

TRP:BCAA ratio due to a decrease in non-esterified fatty acids due to the decrease

in fat oxidisation that occurs following endurance training. Thus, there would be

expected to be a reduction in the unbinding of TRP from albumin and hence

decrease f-TRP levels and its conversion to 5-HT. However, Jakeman (67) has

reported no differences in the f-TRP:BCAA both at rest and post exercise in trained

and non-trained subjects. Thus an altered ratio cannot explain the lower perception

of effort commonly reported by endurance athletes.

Further work by Jakeman et al (68) involved administration of a serotonergic

challenge test to endurance trained and non-endurance trained subjects. This test

involves subjects ingesting a 5-HT receptor agonist at rest, in this particular study

Buspirone, and the amount of prolactin secreted into the blood from the anterior

pituitary gland is measured. Prolactin secretion following a given stimulation of the 5-

HT receptor with a standardised dose of a serotonergic agent is considered an

indicator of the sensitivity of the 5-HT receptor. Jakeman et al (68) performed this

test on five endurance trained and five untrained matched controls and found that the

total prolactin release was significantly lower in trained subjects (p=0.042) and peak

prolactin production occurred later in trained individuals (60 vs. 120 min). Further,


63

sixteen weeks of endurance training in previously untrained subjects resulted in a

reduced response of approximately 30% to a serotonergic agonist (67). Combined

these data suggest that serotonergic pathways are involved in fatigue mechanisms

during exercise and that these pathways may be adaptable following endurance

training (67).

Chronic fatigue disorders and the serotonergic system

Bakheit et al (9) examined the role of 5-HT receptor sensitivity in patients with the

postviral fatigue syndrome (PVFS) using a buspirone challenge test. The results of

this study indicated no significant differences between baseline prolactin levels in

postviral fatigue patients and controls. However, significant percentage differences

were found between peak and baseline values in these two groups. The patients with

PVFS showed increased prolactin responses to the buspirone challenge when

compared to the control group which consisted of both normal healthy subjects and

subjects with primary depression. A similar increased prolactin response to buspirone

in chronic fatigue syndrome (CFS) patients was shown by Sharpe et al (128) (peak

prolactin 438 ± 75 vs. 246 ± 54). Further investigations into this area by Sharpe et al

(129) supported this previous study and found that men with the CFS showed

increased brain serotonin function. In this study a significant rise in prolactin

responses to dl-fenfluramine was found. Alternatively, two further studies both

investigating the effect of fenfluramine on prolactin release did not show any

significant difference between patients and controls (12, 159). From these studies it

has been hypothesised that patients with CFS have an upregulation or increased

sensitivity of 5-HT receptors. Thus an increase in receptor sensitivity to 5-HT may

play a functional role in CFS.


64

5-Hydroxytryptamine (5-HT) / Serotonin

The serotonergic system is the largest modulator of behaviour in the brain and has

influences on fatigue and mood state (142). Increased activation of the serotonergic

system can have effects on arousal, lethargy, the sleep-wake cycle and mood (38).

This may be caused through an inhibition of dopamine or by reducing arousal and

elevating perception of effort (38). As mentioned previously, 5-HT increases during

exercise and drugs that manipulate 5-HT activity can have effects on physical

performance. The role of the central fatigue hypothesis in overtraining has achieved

little research attention. Very few studies have attempted to investigate the

unexplained fatigue characteristic of overtraining by exploring the role of the

serotonergic system.

A non-significant change in the f-TRP: BCAA ratio has been reported after a 40%

increase in training volume (143). However, performance remained relatively stable,

with no signs of decrements that would indicate a state of overreaching or

overtraining. Lehmann et al (87) subjected experienced runners firstly to an increase

in training mileage/ volume (ITV) followed twelve months later by an increase in

training intensity (ITI). The ITV study resulted in a decrease in maximal exercise

capacity, while the ITI study improved maximal exercise capacity. However, in both

studies similar increases in the f-TRP: BCAA ratios were noted. Thus, well trained

and overreached runners could not be discerned on the basis of this ratio.

Recently, Weicker and Struder (156) examined the effects of 4 weeks of increased

duration training on 5-HT transporters (5-HTT) and 5-HT2A receptors (5-HT2AR) on

isolated blood platelets as well as basal prolactin levels. While no measures of

performance were made and a recovery period was not examined, subjects reported

increased self-perceived fatigue following the training period. Results of this study


65

showed a reduction in maximal binding of 5-HT2AR and no changes in 5-HTT. It was

suggested that ‘overstrain’ disturbs central 5-HT neurotransmission and exercise of

a chronic form amplifies the 5-HT system to attenuate the central neuromodular

disturbance (156).

The role of 5-HT receptors during exercise in ‘normal’ exercising subjects has been

mentioned previously and it appears that the 5-HT receptor may play a role in fatigue

during exercise. As was eluded to earlier, evidence suggests that the 5-HT receptor

may be adaptable, that is, the receptor sensitivity may be decreased following

endurance training. As the f-TRP: BCAA ratio does not appear to change during

overtraining, perhaps it is not the availability of 5-HT that is more important in fatigue

during overtraining, rather than an altered sensitivity of 5-HT receptors. Altered

sensitivity of 5-HT receptors, while theoretically possible, is yet to be conclusively

proven.

Neuropeptides and immune function interaction

The two neuroendocrine systems mentioned above, the hypothalamic-pituitary axes

and the autonomic nervous system, both link the brain and the immune system

through humoral outflow and direct neural influences (45). The adrenal corticoids,

which are the end result of HP-adrenal axis activation, have reasonably well-

established immunosuppressive and anti-inflammatory effects (45). Lymphocytes

have receptors for products of the immune system and also receptors for various

hormones and as such, glucocorticoids can modulate lymphocyte viability and

function (77). The ANS innervates lymphoid organs and AD and NA cause both

quantitative and qualitative alterations in peripheral blood lymphocytes, which may be

positive or negative effects (115). Additionally, cytokines, which are released from

lymphocytes, have autocrine, endocrine and paracrine functions and can cross the


66

blood-brain barrier to bind to receptors in the brain (115). According to Smith (134),

cytokines, particularly IL-1β, IL-6 and TNF-α can activate the CNS and result in

‘vegetative’ or ‘sickness’ behaviours’. Thus, a complex bi-directional communication

may exist between the immune system and the central nervous system.

The possibility of altered ANS function and the reported changes in a number of

hormones as the result of overtraining could provide a link to the changes in immune

function, metabolism and mood state which commonly occur as a result of

overtraining.

The role of hormonal imbalances in both the aetiology and diagnosis of the

overtraining syndrome remains unclear. It is critical to examine levels of hormones at

standardised time points to determine if changes are a function of overreaching or

overtraining, or the result of decreased exercise duration or intensity as a result of

accumulated fatigue. Determination of blood hormonal levels is often laborious and

expensive and high subject intra- and inter-assay variability of current laboratory

methods make the regular assessment of hormones challenging. However recent

information relating to both physiological and psychological stress should be

encouraged to continue and plasma hormone levels can provide us with one of the

only possible measures of neuroendocrine function in humans.

Problems associated with overtraining and overreaching research

It is evident that research in the area of overtraining is lacking in a number of

aspects. Generally, there is a lack of well-controlled investigations that include

appropriate measures of performance as well as baseline and recovery periods of

assessment. There are also issues inherent to the lack of diagnostic tools to indicate


67

a state of overreaching or overtraining as well as a variety of definitions in use to

define the conditions.

Specifically, some of the major concerns associated with investigations in this area

include:

• Different terminology and definitions, which hinder the ability to compare

similar research.

• No single definitive diagnostic tool, which leads to the diagnosis of

overreaching and overtraining in differing ways and can only be achieved by

exclusion of other possible contributors, such as illness and injury.

• Numerous studies do not report or measure performance. As a reduction in

performance is one of the only methods to definitively diagnose overreaching

and overtraining, and hence to determine if an athlete has positively or

negatively adapted to the training, it is essential that investigations report and

measure performance appropriately.

• The nature and details of the intensified training is often not reported or

measured. Therefore, the duration and intensity of training required to induce

a state of overreaching is unknown.

• A lack of performance measures during intensified training periods means we

know little about the time course of changes in performance and related

markers used to identify overreaching.

• Responses to intensified training are likely to be individual and differences

may exist between different sporting activities.

• As it is not possible to intentionally overtrain an athlete, it is necessary to

perform overreaching studies. Therefore, there is a lack of investigations on

overtrained as opposed to overreached athletes.


68

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Chapter 3- Time course of performance changes and fatigue

markers during intensified training in trained cyclists

2002, Journal of Applied Physiology, 93 (3), 947-56

Chapter 3 Changes in performance and fatigue markers

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Statement of Joint Authorship Shona L. Halson (candidate)

• Assisted in study design and development • Recruitment of subjects • Conducted all exercise testing sessions • Collection of blood and assaying of samples • Statistical analysis • Interpretation of data • Preparation of manuscript

Matthew W. Bridge

• Assisted in several exercise testing sessions • Assistance in assaying of samples

Romain Meeusen • Assistance in assaying of catecholamines

Bart Busschaert • Assistance in assaying of catecholamines

Michael Gleeson • Assistance in assaying of samples • Assistance in revision and editing of manuscript

David A. Jones

• Assistance in revision and editing of manuscript • Assistance with funding acquisition

Asker E. Jeukendrup • Supervision of progress • Assistance in study design and development • Assistance in data collection • Assistance in data interpretation • Assistance in revision and editing of manuscript


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ABSTRACT

To study the cumulative effects of exercise stress and subsequent recovery on

performance changes and fatigue indicators, the training of eight endurance cyclists

was systematically controlled and monitored for a six-week period. Subjects

completed 2 weeks of normal (N), intensified (ITP) and recovery training (R),

respectively. A significant decline in maximal power output (N=338±17W,

ITP=319±17W) and a significant increase in time to complete a simulated time trial

(N= 59.4±1.9min, ITP= 65.3±2.6min) occurred after ITP in conjunction with a 29%

increase in global mood disturbance. The decline in performance was associated

with a 9.3% reduction in maximal heart rate, a 5% reduction in maximal oxygen

uptake and an 8.6% increase in perception of effort. Despite the large reductions in

performance no changes were observed in substrate utilisation, cycling efficiency,

lactate concentration, plasma urea, ammonia and catecholamine concentration.

These findings indicate that a state of overreaching can already be induced after 7

days of intensified training with limited recovery.

Deleted: ¶

Inserted: ¶


103

INTRODUCTION

The balance between training and overtraining is often a very delicate one. Many

athletes incorporate high training volumes and limited recovery periods into their

training regimes. This may disrupt the fragile balance and the accumulation of

exercise stress may exceed an athlete’s finite capacity of internal resistance. Often

this can result in overreaching, defined as an accumulation of training and/or non-

training stress resulting in a short-term decrement in performance capacity, in which

restoration of performance capacity may take from several days to several weeks

(OR) (17). It is generally believed that if the imbalance between training and recovery

persists this may result in an accumulation of training and/or non-training stress

resulting in a long-term decrement in performance capacity, in which restoration of

performance capacity may take several weeks or months. This condition is termed

overtraining (OT) (17).

Increased exercise stress is manifested in physiological and biochemical changes

and is often in conjunction with psychological alterations, all of which result from an

imbalance in homeostasis (10). However, the quantity of training stimuli that results

in either performance enhancement or a chronic fatigue state is presently unknown.

Of the current information regarding training regimes and protocols, most is derived

from conjectural or experiential sources and has little research support. As it is

difficult to ascertain the volume of training that will result in overreaching or

overtraining, it is necessary to identify markers that distinguish between acute

training-related fatigue and overtraining.

Similarly, much of our knowledge about overtraining is derived from cross sectional

studies and anecdotal information (2, 14). Whilst a number of studies have used a

longitudinal approach (8, 19, 22, 24, 27), in many cases failure to adequately monitor


104

performance means we know little about the time course of changes of potential

indicators of overreaching and early phases of the overtraining syndrome.

The aim of this investigation was to identify the time course of changes in selected

physiological, biochemical and psychological parameters during two weeks of

intensified training and two weeks of recovery in trained cyclists. In order to ascertain

the time course and fluctuations of these changes, repeated performance tests were

conducted. To our knowledge, this is one of the first attempts to systematically

induce a state of overreaching while monitoring training stress and performance in a

supervised and highly controlled environment. We hypothesise that the intensified

training program employed will result in a state of overreaching, identified by a

reduction in performance and an increase in global mood disturbance. In addition, we

hypothesise that the intensified training will result in a decrement in performance

during the initial period of training; however, consistent elevations in mood

disturbance will not occur until later during the intensified training period. It is

hypothesised that laboratory assessed performance will continue to decline

throughout the intensified training period and will return to baseline or above baseline

levels upon completion of a recovery period. Changes in performance will occur

alongside changes in maximal physiological parameters (i.e. heart rate, oxygen

consumption), however substrate utilisation, cycling efficiency and other biochemical

indicators will remain unchanged.


105

METHODS

Subjects:

Eight endurance-trained male cyclists volunteered for this study. All subjects had

competed for at least two years and were training a minimum of three days per week.

The study was approved by the South Birmingham Local Research Ethics

Committee. Prior to participation, and after both comprehensive verbal and written

explanations of the study, all subjects gave written informed consent. Subject

characteristics are presented in Table 1.

_____________________________________________________________ Age Height Body mass Body Fat VO2max (yrs) (cm) (kg) (%) (ml.kg-1.min-1) _____________________________________________________________ Mean 27.1 179.7 73.7 14.6 58.0 SE 3.0 1.9 2.5 1.1 1.7 _____________________________________________________________

Table 1- Selected characteristics of the subjects at Week 1.

Experimental Protocol:

Subjects were familiarised to the test procedures by completing both a maximal cycle

ergometer test and a time trial in the week preceding the study commencement. No

subjects exhibited signs or symptoms of OR or OT based on the previously

mentioned definitions (18), i.e. during the two weeks of baseline training maximum

power output was unchanged and mood state was within normal ranges for athlete

populations.

The training of each subject was then controlled and monitored for a period of six (6)

weeks in total, which was divided into 3 distinct phases each of two weeks duration

(Figure 1). The first phase consisted of moderate training with a small number


106

exercise testing sessions. Subjects completed their normal or usual amount and type

of training (Figure 1).

The second phase consisted of an increase in training volume and intensity (Figure

1) as well as the number of exercise tests performed. Subjects trained 7 days per

week for these two weeks in addition to the laboratory tests. A similar protocol has

previously been shown to induce a state of OR in the time frame specified (16). The

third phase of the study was one of reduced training (Figure 1) and aimed to provide

subjects with a period of recovery.

Week 1

MT

IT

Week 2

MT

TT

IT

Week 3

TT

IT

MT

TT

IT

Week 4

TT

IT

MT

TT

IT

Week 5

MT

IT

Week 6

MT

TT

IT


107

Figure 1- Study Design

MT- Maximal Oxygen Uptake

TT- Time Trial

IT- Intermittent Test

Moderate to High Intensity Training

To describe the time course of the changes in performance and potential indicators

of overreaching, subjects performed three different exercise tests at regular intervals

during the examination period (Figure 2). Each individual test was performed at the

same time of day. A total of 20 exercise tests were performed per subject, 10 of

which were in the OT phase. In total, subjects underwent six maximal cycle

ergometer tests (MT), six Time Trial tests (TT) and eight Intermittent Tests (IT).

Training Quantification

Each subject received a Polar NV Vantage heart rate monitor (Polar Electro Oy,

Kempele, Finland) for the duration of the study. Each subject was given a training

diary to record duration of training, distance covered, average heart rate, maximal

heart rate and weather conditions. Subjects recorded all training sessions, which

were downloaded to a computer using the Polar Interface (Polar Electro Oy,

Kempele, Finland). From this information average heart rate, maximum heart rate

and time spent in each of the heart rate zones could be calculated and verified

against the training diary.

The majority of subjects performed their training outdoors, however on occasion

subjects trained inside the laboratory if weather conditions prevented them from

training outdoors. Subjects were encouraged to consume a carbohydrate rich diet

and to remain euhydrated during the entire experimental period.


108

After each Maximal Test subjects’ training zones were calculated from their individual

lactate and heart rate curves. Lactate threshold was determined using the Dmax

method as described elsewhere (4). Five training zones were calculated and

expressed as percentages of individual maximum heart rate. The training zones for

the 8 subjects prior to the intensified training period were, on average as follows:

• Zone 1 <69% HRmax

• Zone 2 69% - 81% HRmax

• Zone 3 82% - 87% HRmax

• Zone 4 88% - 94% HRmax

• Zone 5 >94% HRmax

Subjects training programs for the intensive training weeks were based on their

current amount of training in the two baseline weeks. In the two intensive training

weeks the researchers aimed to increase the amount of time the subjects trained in

zones 3, 4 and 5. This was achieved by designing individual training programs that

doubled normal training volumes. The majority of the increase in training volume was

in the form of high intensity training, i.e. above the lactate threshold (Figure 2).


109

Figure 2- Changes in Time Spent in Heart Rate Zones during normal training (N),

intensified training (ITP) and recovery (R).

Maximal Cycle Ergometer Test

Subjects attended the laboratory after an overnight fast and a teflon catheter (Becton

Dickinson, Quickcath) was inserted into an antecubital vein. Following this, the

subjects performed an incremental test to exhaustion on an electrically braked cycle

ergometer (Lode Excalibur Sport, Groningen, The Netherlands) to determine

maximal power output (Wmax), submaximal and maximal oxygen consumption and

heart rate throughout the test.

Resting data was collected before subjects began cycling at 95 Watts for three

minutes. The load was increased by 35 Watts every 3 minutes until volitional

Training

Tim

e (h

h:m

m)

Zone 1Zone 2Zone 3Zone 4Zone 5

7:12 7:21

14:3313:51

03:0204:15

15:00

7:30

0:00

Normal Intensified Recovery


110

exhaustion. Expiratory gases were collected and averaged over a 10 second period,

using a computerised on-line system (Oxycon Alpha, Jaeger, Bunnik, The

Netherlands). Wmax was determined using the equation:

Wmax = Wfinal + (t/ T)*W (1)

Where Wfinal (W) is the final stage completed, t (s) is the amount of time reached in

the final uncompleted stage, T (s) is the duration of each stage and W (W) is the

workload increment.

Heart rate was recorded throughout the exercise test using a heart rate monitor (NV

Vantage, Polar, Finland). Rating of Perceived Exertion (RPE) was recorded at the

end of each stage, using the Modified Borg Scale (3).

Blood samples were collected at rest, in the last 30 seconds of each stage and

immediately following the cessation of the test for the determination of blood lactate,

plasma urea, plasma ammonia and catecholamine concentration. Blood samples

were immediately analysed for lactate (YSI 2300 STAT Plus, Ohio, USA).

Heparinized blood samples were centrifuged for 10 minutes at 1500-x g. Plasma was

stored at –20 °C and analysed for ammonia (Sigma, Poole, UK, 171-UV) and urea

(Sigma, Poole, UK, 640).

Plasma adrenaline, noradrenaline and dopamine were measured by high

performance liquid chromatography (HPLC) with electrical detection (BioRad,

Nazareth, Belgium). Inter-assay CV’s for adrenaline and noradrenaline were 7.8%

and 4.2%, respectively.


111

From carbon dioxide (VCO2) and oxygen production (VO2), rates of carbohydrate and

fat oxidation were calculated using stoichiometric equations (6).

Gross efficiency was calculated using the formula (11):

GE = (Power / EE)* 100% (2)

Where EE= Energy Expenditure (VO2 at given workload)

Cycling economy was calculated using the formula (28)

Economy (J.L-1) = Power / VO2 (3)

Time Trial

After a five minute warm-up at 50% Wmax, subjects performed a simulated time trial

in which a target amount of work was to be completed in as short a time as possible.

The amount of work to be performed was calculated by assuming that subjects could

cycle at 75% of their Wmax for ~60 minutes and thus these time trials lasted

approximately 60 min for all subjects. The formula for this is described elsewhere

(15) and is as follows:

Total amount of work = 0.75 * Wmax * 3600 s (4)

For each of the time trials the ergometer was set in the pedalling dependent mode so

as to replicate as accurately as possible a time trial in a field setting. Thus, power

varies with cadence (RPM) and is represented by the following formula:

W = L * (RPM)2 (5)


112

Hence, the work rate (W) measured in watts is equal to the cadence squared (RPM)2

multiplied by the linear factor (L). The linear factor was based on each subjects

Wmax and calculated so that 75% Wmax was produced at a pedalling rate of 90

RPM. Using the above equation L could be calculated by W/ (RPM)2.

A computer was connected to the ergometer and work, power and time were

recorded. However, subjects received little information other than the amount of work

performed and the present amount of work relative to the total to be completed.

Subjects received no feedback on time, work rate, cadence or heart rate. Any

changes in time trial performance in response to the intensified training were

determined by examining changes in time taken to complete the set amount of work

for each subject.

Subjects were required to fast for at least 3 hours prior to each test. Blood samples

were taken prior to and immediately following each test and were analysed for

lactate. Heart rate was monitored continuously throughout the test (Vantage NV,

Polar Electro Oy, Kempele, Finland).

Intermittent Test

Unlike the TT tests, the Intermittent Test was of a set duration and a change in work

production was assessed. Subjects completed a 5 minute warm-up at 50% Wmax

followed by two ten minute bouts of maximal exercise. Each subject was given 5

minutes rest between bouts.

Subjects were asked to cycle as ‘hard’ as possible for each of the ten-minute bouts.

Similar to the TT protocol, the ergometer was set in the pedalling dependent rate

mode. However, in this case the work rate (W) was set as 90% Wmax. The


113

ergometer was again connected to a computer as in the time trial tests, however

subjects only received information on time and power indicated graphically. Heart

rate was recorded continuously throughout the test (Vantage NV, Polar, Kempele,

Finland).

Any changes in IT performance over time were analysed by examining both work and

power for each of the bouts. Additionally, any alterations in heart rate responses to

the IT were examined by observing changes in maximum heart rates and minimum

heart rates for both bouts and the 5 min of recovery after each bout. Subjects were

again fasted for at least 3 hours prior to testing. Blood samples were taken prior to

the test and upon completion of the second exercise bout and were assayed for

lactate concentration.

Questionnaires

Every day for the duration of the study, subjects completed both the Daily Analysis of

Life Demands of Athletes (DALDA) (29) and Profile of Mood States Short Form

Questionnaire (POMS-22) (25). The DALDA is divided into parts A and B, which

represent the sources of stress and the manifestation of this stress in the form of

symptoms, respectively. Subjects were asked to complete these questionnaires at

the same time of each day prior to training. Subjects also completed the 65-question

version of the POMS (25) once a week on the morning of the MT. Global mood state

was determined using the method described by Morgan et al (26).

Additional Measurements

Once per week a number of additional measurements were taken. Skinfold

measurements were made to estimate percent body fat and body weight was also

measured. Subjects also recorded their morning resting heart rate (RHR) every day


114

for the duration of the study using the heart rate monitor (Vantage NV, Polar,

Kempele, Finland). Subjects recorded their resting heart rate in the supine position

for a period of three minutes, immediately after waking.

Statistical Analysis

One-way Analysis of Variance with Repeated Measures was used with Least

Significance Difference comparison performed to identify significant differences

between the individual means. The level of significance was set at 0.05.

RESULTS

Subjects completed two weeks of normal training (N, 7±2hrs per week), 2 weeks of

intensified training (ITP, 14±5hrs per week) and a final 2 weeks of recovery training

(R, 3.5±2.5hrs per week) (Figure 2). The laboratory tests were included during the

calculation of total hours of training completed in each period. The intensified training

period predominantly consisted of high intensity interval training, with significant

increases in training in zones 3, 4 and 5 (450%, 200% and 147%, respectively). The

previous criteria for the detection of overreaching set by Jeukendrup et al (16) were

used to determine if the training protocol resulted in overreaching. The criteria to be

met were (1) a reduction in performance in the laboratory tests and (2) increased

affirmative responses to questionnaires that assessed impaired general health

status, negative mood, psychological status and feelings of fatigue.

All eight subjects completed the intensified training period and met the criteria for

overreaching at the conclusion of the two-week intensified training phase. Some of

the observed responses to intensified training included: reduced performance in the

form of reduced maximal power output during the MT, increased time taken to

complete the TT and a reduction in average work produced during the IT. Maximal


115

heart rate was reduced in all three tests and responses to all questionnaires

completed were altered.

Maximal Test

Following the two weeks of intensified training Wmax significantly declined (Figure

3a) and at completion of the recovery phase was unchanged from baseline values.

After one week of intensified training, Wmax during the MT had declined in 6 of the 8

subjects. In the other 2 subjects Wmax remained unchanged. On average Wmax

declined 3.3% during week one of ITP and 5.4% during week 2 of intensified training

(Table 2). Maximal oxygen uptake (L.min-1) significantly declined (4.5%) after ITP;

however it was unchanged after week 1 of intensified training. There were no

changes in submaximal oxygen uptake at 200W (Table 2).


116

80

90

100

110

120

130

Training

POM

S-65

Tot

al

3,4 3,4

1,2 1,2,5,6

44


175

180

185

190

195

200

Max

imum

Hea

rt R

ate

(bpm

)

2,3,4,5

1,4,6

1,6

1,2,5,6

1,4,6

2,3,4,5

310

320

330

340

350

360

370

Max

imum

Pow

er (W

) 3,4 3,4

1,2,6

1,2,5,6

4,6

3,4,5


117

Figure 3a- Changes in maximum power output during MT, during normal training (N),

intensified training (ITP) and recovery (R). 1 indicates significantly different from Test

1, 2 indicates significantly different from Test 2, 3 indicates significantly different from

Test 3, 4 indicates significantly different from Test 4, 5 indicates significantly different

from Test 5, 6 indicates significantly different from Test 6.

Figure 3b- Changes in maximum heart rate during MT, during normal training (N),





Figure 3c- Changes in Total POMS-65 Scores during MT, during normal training (N),





There was a 15 bpm decline in maximal heart rate during the MT as a result of the

intensified training (Figure 3b), however submaximal heart rate (at 200W) remained

unchanged (Table 2). Maximal lactate concentrations from the MT were lower in ITP

however this did not reach statistical significance (Table 2). There were also no

significant changes in resting or submaximal concentrations of plasma lactate (Table

2). Rating of Perceived Exertion scores reported at 200W were significantly


118

increased during ITP and following two weeks recovery were significantly lower than

baseline scores (Table 2).

N ITP

Week

1

2

3

4

Maximal Test: Maximal Responses

VO2max (ml.min-1) 4271 ± 187 4372 ± 197 4391 ± 196 4078 ± 198*a 4110 ±

VO2max (ml.kg-1.min-1) 58.0 ± 1.73 59.0 ± 1.49 60.0 ± 1.88* 55.5 ± 1.50a 56.5 ±

La max (mmol.L-1) 7.2 ± 0.6 7.8 ± 0.7 7.2 ± 0.7 6.7 ± 0.6 7.7

Submaximal Responses

VO2@200W (ml.min-1) 2852 ± 72 2766 ± 46 2873 ± 39 2821 ± 75 2834

HR@200W (bpm) 152 ± 7 146 ± 8 147 ± 7 145 ± 6 148

La@200W (mmol.L-1) 1.2 ± 0.2 1.3 ± 0.3 1.1 ± 0.3 1.3 ± 0.2 1.3

RPE @200W 9.4 ± 0.8a 9.2 ± 0.9 10.0 ± 1.3 10.9 ± 1.2* 9.4

Table 2- Selected changes in Maximal Test variables over the course of the study period. ‘*’ indicates sig

training (N). ‘a’ indicates significantly different from recovery (R).


120

Time Trial

Time taken to perform the time trial test significantly increased by 9.8% from 59.4

minutes during N to 65.3 minutes at the end of the first week of ITP (Figure 4).

Subjects on average took 4 minutes and 30 seconds longer to complete the given

amount of work. Correspondingly, average power declined during ITP and slightly but

non-significantly increased after R (Table 3). A decline in maximal heart rate and

average heart rate were noted in the TT after intensified training (Table 3). Resting

and maximal blood lactate concentrations from the TT did not change significantly

over the training period.

Figure 4- Changes in time taken to complete TT during normal training (N),





55

58

61

64

67

70

Training

Tim

e (m

in)

2,3

1,6 1,6

6

2,3,4


Table 3- Selected changes in Time Trial and Intermittent Test variables over the course of the study peri

different from N. ‘a’ indicates significantly different from R.

N ITP

Week

1

2

3

4

Time Trial HR max (bpm) 179 ± 3

173 ± 3*a 168 ± 2*a 173 ± 4*a 171 ± 4

HR average (bpm) 162 ± 3 161 ± 3a 156 ± 2a 156 ± 2a 156 ± 4

Average Power (W) 261.7 ± 18.5 240.0 ± 16.2*a 239.5 ± 17.1*a 247.9 ± 19.0a 241.6 ± 1

Resting La (mmol.L-1) 1.32 ± 0.23 1.29 ± 0.24 0.93 ± 0.12 1.29 ± 0.27 1.09 ± 0

Maximal La (mmol.L-1) 8.06 ± 0.83 5.87 ± .24 5.87 ± 1.39 7.87 ± 0.92 6.82 ± 0

Intermittent Test Average Work (kJ) 181.3 ± 10.1 171.2 ± 10.3 169.8 ± 10.6* 164.4 ± 8.8* 169.1 ± 8.9* 166.6 ± 1

Average HR (bpm) 168 ± 5 166 ± 4 160 ± 6* 157 ± 3* 163 ± 3* 162 ±

Resting La (mmol.L-1) 1.33 ± 0.25 1.22 ± 0.16 1.30 ± 0.30 1.30 ± 0.20 1.22 ± 0.22 0.94 ± 0

Maximal La (mmol.L-1) 10.39 ± 1.25 8.62 ± 1.45 8.35 ± 1.26*a 8.45 ± 1.35*a 8.38 ± 0.92a 8.54 ± 1.


122

Intermittent Test

Average work over the complete IT was significantly reduced during ITP and returned

almost to baseline upon completion of R (Table 3). Average heart rate also declined

(Table 3). Resting IT blood lactate concentrations were unchanged, however

maximal lactate concentrations were significantly reduced (Table 3).

Time course of changes

The changes in performance of the three exercise tests, expressed as a percentage

of initial values, all show a similar time course of change over the study period

(Figure 5). For both the TT and IT the greatest reduction in performance occurs

around the middle of the intensified training period. While the decrease in

performance towards the end of the intensified training period is still large,

performance does not continually decrease. In all tests there is a gradual decrease in

performance until approximately mid way through ITP.


123

Figure 5- Time course of changes of the three exercise tests, expressed as a

percentage of baseline, during normal training (N), intensified training (ITP) and

recovery (R).

Maximal Test

Time Trial

Intermittent Test

Perc

ent c

hang

e in

per

form

ance

Training

-12

-10

-8

-6

-4

-2

0

2

4



124

Biochemical and Hormonal Variables

Resting plasma ammonia and urea concentrations were unchanged throughout the

testing period (Table 4). Resting and maximal plasma adrenaline, noradrenaline and

dopamine concentrations were also not different during the six-week training period

(Table 4).

Substrate Oxidation and Cycling Efficiency

Carbohydrate and fat oxidation were unchanged over the 6-week period. Fat

oxidation had a tendency to be increased during ITP, however this was not

statistically significant (Table 4). Submaximal efficiency, submaximal economy and

maximal economy were unaffected by the intensified training (Table 4).

N ITP

Week 1 2 3 4 5

Additional Measures Maximal Plasma Adrenaline (nmol.L-1) 4.61 ± 3.36 2.71 ± 2.20 4.67 ± 1.74 1.45 ± 0.70 5.57 ± 3

Maximal Plasma Noradrenaline (nmol.L-1) 24.82 ± 16.37 18.72 ±

12.71 34.15 ± 15.70 20.48 ± 11.52 33.44 ±

Maximal Plasma Dopamine (nmol.L-1) 12.18 ± 6.69 13.79± 6.76 14.91± 1.14 17.11± 1.23 14.99±

Economy (Max) (J/L) 4.7 ± 0.1 4.7 ± 0.1 4.6 ± 0.1 4.7 ± 0.1 4.7 ± 0

Economy (200W) 4.2 ± 0.1 4.3 ± 0.1 4.2 ± 0.1 4.3 ± 0.1 4.2 ± 0GE @ 200W 18.0 ± 0.4 19.1 ± 0.3 18.5 ± 0.4 19.1 ± 0.5 18.1 ±

CHO Oxidation @ 200W (g.min-1) 3.12 ± 0.09 2.75 ± 0.21 2.6 ± 0.22 2.6 ± 0.21 2.84 ± 0

FAT Oxidation (g.min-1) 0.34 ± 0.04 0.35 ± 0.09 0.46 ± 0.07 0.44 ± 0.07 0.34 ± 0

Resting HR (bpm) 52 ± 1 47 ± 1 54 ± 1a 53 ± 1a 51 ± POMS-22 -0.3 ± 0.7 0.3 ± 0.7 2.0 ± 0.8 2.8 ± 1.3*a -0.2 ± 0Plasma Urea (mmol.L-1) 2.2 ± 0.2 2.3 ± 0.1 2.6 ± 0.2 2.8 ± 0.2 2.4 ± 0Plasma Ammonia (µM) 38.6 ± 7.5 60.2 ± 14.4 45.1 ± 15.3 60.8 ± 14.4 40.5 ± 1Body Weight (Kg) 73.7 ± 2.5a 74.0 ± 2.5a 73.2 ± 2.4*a 73.3 ± 2.3 72.7 ± 2

Body Fat (%) 14.6 ± 1.1a 14.3 ± 1.1a 13.8 ± 1.2* 13.2 ± 1.0* 13.1 ± 1Table 4- Selected changes in Additional Measures over the course of the study period. ‘*’ indicates signi

indicates significantly different from R.


126

Additional Measures

Body weight and percent body fat significantly declined throughout the testing period

and were lowest following R (Table 4). During ITP resting heart rate was not different

to N, however was slightly, but significantly lower during R (Table 4).

Questionnaire Responses

Global Mood State scores on the POMS-65 were significantly increased from 90.4

during N to 116.4 during ITP (Figure 3c). Upon completion of R, scores returned to

91.5. From this questionnaire the subscales of tension, fatigue and confusion were

also significantly elevated, while vigour significantly declined. No changes were

evident in the depression or anger subscales. Altered mood states were also

identified by the short version of the POMS questionnaire, with significantly elevated

total scores.

Sections A and B of the DALDA were both increased during ITP, however only

section B was significantly higher than N (Figure 6). The most common changes in

sources of stress, as identified by Part A of the DALDA, were related to sport training,

sleep and health. Part B of the DALDA showed the greatest changes during the ITP

period, with the majority of subjects showing changes on many of the items. The

most common alterations in responses were increased problems associated with the

following areas: need for a rest, recovery, irritability, between session recovery,

general weakness and training effort.


127

Figure 6- Changes in DALDA Part B ‘a’ scores, indicating symptoms are ‘worse than

normal’ during normal training (N), intensified training (ITP) and recovery (R).

DISCUSSION

It is generally assumed that overtraining results from chronic exercise stress in the

presence of an inadequate regeneration period. However, there are non-distinct

phases in the development of overtraining, which has been termed the overtraining

continuum (9). The first phase along this continuum relates to the fatigue

experienced following an isolated training session. Further intense training with

insufficient recovery can lead to overreaching and increased complexity and severity

of symptoms (9). Finally, if high training loads are continued with insufficient recovery

from the overreached state, the overtraining syndrome may develop. Currently, there

is no literature or information available to discriminate between the early and late

phases of this continuum (9). To our knowledge this is the first study to attempt to

identify the changes that occur in the transition from acute fatigue to overreaching.

Normal Intensified Recovery0

2

4

6

8

10

Training

DA

LDA

"b"

sco

res


128

A number of examinations have measured performance prior to and upon completion

of increased volume and/or intensity training (5, 24, 33), while few have examined

changes in performance during increased training (16, 23). Lehmann et al (23)

reported a number of performance changes prior to, during and upon completion of 4

weeks of increased volume training in runners. Subjects showed a decline in total

running distance during incremental ergometric exercise after 2 weeks of training,

however performance was not significantly reduced until after 4 weeks of training

was completed. This may, in part, be explained by the graded increase in volume

throughout the 4-week period. Jeukendrup et al (16) included examinations of time

trial performance pre, mid-way, and following a 2-week period of intensified training

in cyclists. Similar to the present investigation, time trial performance had declined

significantly following one week of training although declined further after an

additional week.

The present study incorporated an increased number of performance assessments,

including 4 time trials and 4 intermittent tests during the increased training period, in

addition to initial and recovery assessments. From the information on the time course

of performance changes it appears that overreaching may be induced after a period

of 7 days. Although time trial performance was decreased during the first several

days of increased training, subjects could not be considered overreached as mood

state was unaltered. On the first day of the intensified training period subjects

completed a long-duration, high intensity ride, and thus the initial decline in

performance most likely reflected fatigue from the previous training session.

Therefore, while performance was significantly lower than baseline, subjects were

acutely fatigued as opposed to overreached. It is likely that complete recovery would

have occurred within a few days. However the continual exercise stress, without

regeneration, results in failing adaptation and altered biochemical, physiological and


129

psychological states (10) which identify the athletes as reaching a chronic as

opposed to acute fatigue state.

To determine whether a reduction in performance is the result of acute fatigue from

previous exercise, or from overreaching, the DALDA questionnaire may be effective

and practical. As described by Rushall et al (29) a period of baseline assessment

should occur, with the recognition that scores may oscillate due to fatigue from

isolated training sessions. However, if scores remain elevated for greater than four

consecutive days, a period of rest should occur. As can be seen from Figure 6,

scores from the questionnaire oscillate during normal training. However, scores are

continually and consistently elevated above baseline for the minimum of 4

consecutive days, approximately midway through the intensified training period.

Thus, with the use of psychological questionnaires, it is possible to discriminate acute

from chronic or excessive fatigue in the presence of uniform performance

decrements. Figure 6 suggests that in this particular investigation it took 3-7 days of

intensified training before overreaching developed.

Continual intensive training after 7 days does not result in further performance

decrements, however performance is still significantly below that of baseline values.

It appears subjects become somewhat tolerant to the increased training and this was

expressed by a number of the subjects. A number of subjects stated that they had

reached a level of maximal fatigue and lethargy after the first week of training.

Continued training therefore did not result in a decline in performance due the

already high levels of fatigue. Interestingly, mood state continued to decline in the

final week of intensified training. All exercise tests employed in this study showed a

similar time course of change (Figure 5), however, the two performance tests (TT

and IT) showed a similar magnitude of decline in performance when expressed as


130

change from baseline. It is important to consider the training status of the individuals

who participated in this study and to appreciate possible differences in responses

between these cyclists and elite or world-class athletes. It is possible that the

physiological, biochemical and psychological responses observed in the present

group of moderately trained cyclists may be similar to those of more highly trained

cyclists. However, it is impossible to speculate upon the time course of changes and

the volume of training necessary to induce similar alterations in performance in elite

cyclists.

At the end of the first week of ITP it took the subjects 9.8% longer to complete the

simulated time trial. Given the daily variation of this test is less than 3% (15), the

major decline in performance can be attributed to the effects of the intensified training

protocol. Similarly, Jeukendrup et al (16) reported a 5% increase in time taken to

complete a time trial. This increase in time taken to complete an 8.5 km time trial (16)

is somewhat lower than the 9.8% found in this investigation. The time trial performed

by the subjects in the current study was of longer duration (to approximate a 40 km

time trial), which may explain the differences to the previous study.

Lehmann et al (19) reported an 8% decline in total running distance during

incremental ergometric exercise in 8 middle- and long distance runners who

performed three weeks of increased volume training, from 85 to 174 km/week. A 29%

reduction in time to fatigue was found in a group of 5 elite soldiers after 10 days of

increased intensity running training (8). A similar decline in time to fatigue on a cycle

ergometer (27%) was reported by Urhausen et al (33) after an undefined individual

increase in intensive training. From the information derived from the present study

and those mentioned above, it appears that the longer the duration of the exercise

bout the larger the impact of overreaching on performance.


131

Changes in mood state as assessed by the DALDA and POMS occurred alongside

the performance reductions. Continued elevated ‘a’ scores, indicating symptoms are

‘worse than normal’ can be a useful tool in determining early overreaching. The

subscales of the POMS may be useful to identify psychological aspects that may be

disturbed in individual athletes. Changes in mood state are highlighted in the

overtraining literature, and the POMS has been found to show significant changes

during OR and OT in other studies as well as the present examination (7, 13, 27).

At present the mechanisms behind the reduction in performance are relatively

unknown. Glycogen depletion has been previously suggested as a cause of the

underperformance characteristic of overtraining (5). Intensive training may result in a

decline in glycogen stores and an increased reliance of fat metabolism. However, the

results of this study suggest that substrate metabolism was unchanged after

intensified training. Other evidence to suggest that subjects in the present study were

not glycogen depleted includes unchanged resting, submaximal and maximal blood

lactate concentrations.

It has also been suggested that some of the performance changes that occur with

overtraining and overreaching may be due to reduced efficiency (1). Inadequate

recovery of cellular homeostasis can lead to fatigue of motor units and thus

additional, less efficient motor units may need to be recruited in a bid to maintain

performance (9). To our knowledge, this is the first study to systematically investigate

either gross efficiency or economy after a period of intensified training. No changes in

either of these variables were noted in this investigation and thus there is presently

no evidence to suggest that changes in gross efficiency or economy can explain the

performance deterioration that occurs with overreaching or overtraining. Other


132

suggested mechanisms have included changes in metabolic enzyme concentrations

and chronic dehydration (31). However, it would be expected that chronic

dehydration would result in an increase in submaximal heart rate to maintain cardiac

output. This was not evident in this study or other overtraining investigations (16, 19,

30, 33).

The mechanism(s) for the reduced maximal performance appears to be related to the

generation of fatigue prior to the maximal engagement of the cardiorespiratory and/or

metabolic systems. The underlying cause(s), of fatigue is not clear. However, from

this study it appears that subjects demonstrate an increased perception of exertion,

identified by significantly higher submaximal RPE scores.

During ITP maximal heart rate was decreased in all three performance tests.

Jeukendrup et al (16), Lehmann et al (19) and Urhausen at al (33) all reported

reduced maximal heart rates after increased training. This may possibly be the result

of a reduced power output observed during maximal exercise. At this stage, however,

it is not clear whether the decreased maximal heart rate and possibly a decreased

cardiac output is the cause or the consequence of premature fatigue. There have

been suggestions that disturbances in the autonomic nervous system are responsible

for the altered heart rate during overtraining (20). Decreasing sympathetic influence

and/or increasing parasympathetic influence, decreased ß-adrenergic receptor

number or density, increased stroke volume and plasma volume expansion are all

possible mechanisms for the reduction in maximal heart rate (34). However, strong

evidence for any of these mechanisms is lacking.

Lehmann et al (19) reported a tendency towards increased stroke volume after an

increase in training volume in middle-and long-distance runners. This was in


133

conjunction with a decreased maximal heart rate. A recent study by Hedelin et al (12)

reported increased plasma volume and reduced maximal heart rates following a 50%

increase in training volume in elite canoeists. While performance was not assessed

following recovery and therefore it could not be determined if the athletes were

fatigued or overreached, there was no relationship between the changes in HRmax

and changes in blood volume.

Decreases in maximal heart rate may also be the result of a down-regulation of the

sympathetic nervous system or changes in parasympathic/sympathetic tone. A

number of investigations have examined changes in plasma and urinary

catecholamine production during periods of intensified training that resulted in

overreaching or overtraining (12, 19, 33). Lehmann et al (19) reported decreased

nocturnal urinary noradrenaline and adrenaline excretion and increased submaximal

plasma noradrenaline concentration following an increase in training volume.

Submaximal and maximal heart rates significantly declined alongside the changes in

catecholamines. However, the findings of unchanged catecholamine concentrations

and significantly decreased maximal heart rates as evidenced during the present

study have also been reported (12, 32). Unchanged resting, submaximal and

maximal free adrenaline and noradrenaline concentrations were described by

Urhausen et al (32) in underperforming cyclists and triathletes over a 15-month

period. While catecholamine concentration remained stable, maximal heart rate was

significantly reduced. Finally, Hedelin et al (12) also reported decreased maximal

heart rates yet no changes in resting catecholamine production were observed. Thus,

there does not appear to be a consistent relationship between changes in heart rate

and changes in catecholamine concentration. However, down-regulation of ß-

adrenoreceptors, or a decrease in receptor number, may occur as a result of the

prolonged exposure to catecholamines that can occur as a result of intensified

Comment: Thought about adding a sentence here about the reduced HR yet maintained performance you mentioned in the Rabobank riders during the Tour. This would lead into other possible reasons for the decline in max HR other than an inability to fully engage the cardiorespiratory system.


134

training and/or psychological stress (20, 34). This may be one unexplored alteration

that could explain the reduction in maximal heart rate observed in overtrained

athletes.

The lack of change in maximal lactate concentration at the end of MT is in contrast to

other investigations (16, 19, 21). Although maximal lactate concentrations fell from

7.2 to 6.7 mmol.L-1, this was not statistically significant. The reduction in maximal

lactate concentration observed in the overtraining literature has previously been

suggested to result from reduced glycogen stores (5). However, both carbohydrate

and fat oxidation were unchanged during ITP and resting lactate concentration was

also unaltered.

Changes in morning heart rate, body weight and percentage body fat have previously

been suggested as markers of overtraining. However, many studies have failed to

show changes in these variables as a result of intensified training (8, 16, 19, 33).

Individual variation may partly explain the lack of changes in resting heart rate from

baseline.

CONCLUSION

Decreased performance was observed almost immediately after the onset of

increased training, which is likely the result of acute fatigue from the initial training

sessions. Successive training stimuli resulted in further fatigue, reductions in

performance and increased mood disturbance in the group of subjects studied. After

7 days of intensified training a state of overreaching developed. Maximum heart rate

was dramatically reduced and perception of exertion was increased. Changes in

substrate utilisation, cycling efficiency and economy were unrelated to performance


135

changes associated with overreaching and thus cannot explain the increased fatigue

and decreased performance.


136

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_____________________________________________________

Chapter 4: Mood disturbance, immunological responses and

changes in prolactin responses to exercise and pharmacological challenge during overreaching in cyclists

_____________________________________________________ A section of this manuscript is published:. “Immunological responses to overreaching”. Medicine and Science in Sports and Exercise, 2003; 35 (5), p 854-861 .

Chapter 4 Mood, immune system and serotonergic responses

141


• Assisted in study design and development • Recruitment of subjects • Conducted all exercise testing sessions • Collection of blood and assaying of samples • Analysis of questionnaire responses • Statistical analysis • Interpretation of data • Preparation of manuscript

Graeme I. Lancaster • Assistance in assaying of cytokines • Assistance in revision and editing of manuscript

Matthew W. Bridge

• Assisted in several exercise testing sessions • Assistance in conducting buspirone challenge tests • Assistance in assaying of samples

David A. Jones • Assistance in revision and editing of manuscript • Assistance with funding acquisition

Michael Gleeson

• Assistance in assaying of samples • Assistance in revision and editing of manuscript

Asker E. Jeukendrup • Supervision of progress • Assistance in study design and development • Assistance in data interpretation • Assistance in revision and editing of manuscript


142

ABSTRACT

Athletes often employ an increase in training intensity in a bid to improve

performance. However, if this is coincident with inadequate recovery, overreaching or

overtraining may result. Changes in mood state, the immune system and

serotonergic (5-HT) system have all been suggested as possible consequences of

intensified training that results in overreaching. However, few studies have examined

specific changes in mood, immunological responses or serotonergic responsiveness

as a result of intensified training. We investigated the effects of intensified training on

mood state, perceived stress, general health, plasma cytokines, glutamine,

glutamate, prolactin and serotonergic responsiveness in endurance-trained cyclists.

Eight male subjects (Age 27.0±3.0 years, VO2max 58.0±1.7 ml.kg-1.min-1, mass

73.7±2.1 kg) completed six weeks of training: two weeks each of normal training (N,

7±2 hr per week), intensified training (ITP, 14±5 hr per week) and recovery training

(R, 3.5±2.5 hr per week). During the study period subjects completed six graded

cycle ergometer tests to exhaustion (MT), six simulated time trial tests (TT) and eight

2X10 minute maximal effort bouts (IT) and three buspirone challenge tests (BCT).

Subjects also completed questionnaires to assess mood state. Plasma

concentrations of tumor necrosis factor-(TNF-α) and interleukin-6 (IL-6), salivary IgA,

plasma glutamine, glutamate, ammonia, urea, creatine kinase activity and routine

haematological measures were determined once per week. To examine the

sensitivity of hypothalamic 5-HT pathways, the plasma prolactin (PRL) response to

an oral dose (0.5 mg.kgbw-1) of the partial 5-HT1A agonist buspirone was measured

at the end of each training phase. PRL was also measured before and after a

simulated 40km time trial (TT). A reduction in time trial performance was observed

(9.8%) in Study 1 and significant increases in global mood disturbance as measured

by the POMS-65 (28.7%) Responses to the POMS-22 and Part B of the DALDA also

increased and significant elevations in PSS scores and subscales of the GHQ-28


143

were evident during ITP. Significant increases during the ITP were observed in

creatine kinase activity and glutamate, while the glutamine/glutamate ratio (Gln/Glu

ratio), red blood cell numbers (RBC), haemoglobin concentration (Hb) and packed

cell volume (PCV) declined following ITP. No significant changes were observed in

TNF-(, IL-6, salivary IgA, glutamine, ammonia, urea and various routine

haematological measures. Baseline corrected plasma PRL levels in response to

pharmacological challenge were significantly higher at 15, 105 and 120 minutes after

buspirone administration in R compared with N (p<0.05), while the total area under

the release curve doubled (p=0.05). This increase in 5-HT sensitivity to buspirone in

R was also reflected by an increased PRL response to exercise. PRL responses to

the TT were significantly greater at the end of R compared with N and ITP (p=0.001).

Large increases in mood disturbance, perceived stress, anxiety, insomnia and social

dysfunction occur after two weeks of intensified training without recovery. Alterations

in plasma cytokines do not appear to be related to the decline in performance and

increased mood state characteristic of overreaching, however the Gln/Glu ratio may

be of use as a marker of overreaching and/or overtraining. Additionally, results

suggest that there is an alteration in serotonergic responsiveness after two weeks of

recovery from a period of intensified training.


144

INTRODUCTION

Overtraining may be best described as an imbalance between stress, involving

training as well as non-training sources, and recovery. As many athletes incorporate

high training volumes and limited recovery periods into their training regimen, they

risk the development of overreaching. Overreaching is defined as an accumulation of

training and/ or non-training stress resulting in a short-term decrement in

performance capacity, in which restoration of performance capacity may take from

several days to several weeks (OR) (27). It is generally believed that if the imbalance

between training and recovery persists this may result in a long-term decrement in

performance capacity, in which restoration of performance capacity may take several

weeks or months. This condition is termed overtraining (OT) (27).

An increase in mood disturbance, commonly measured by the Profile of Mood States

(POMS) (38) is frequently suggested as a marker of overreaching and/ or

overtraining. Overreaching has previously been shown to be associated with

changes in POMS scores (15, 20). However, some of the previous research using

the POMS to monitor training stress is difficult to interpret as performance has either

not been measured or not reported (43, 47, 48, 52).

The Daily Analysis of Life Demands of Athletes (DALDA) (54) was designed to

identify changes in the sources of stress to athletes and the symptoms presented as

a result of this stress. As described by Rushall (54), a period of baseline assessment

should occur, with the recognition that scores may oscillate due to fatigue from

isolated training sessions. However, if scores remain elevated for greater than four

consecutive days, a period of rest should occur. This questionnaire may be useful in

determining if the sources of stress and/or the symptoms of such stress are altered

during intensified training that results in overreaching. If so, the DALDA may be used


145

to monitor increases in training stress and thus could be used as a tool to prevent

overreaching and overtraining. There is presently no scientific information relating to

the use of this tool in experimental research.

In a recent review by Armstrong and VanHeest (1), similarities are described

between the signs and symptoms of major depression and those experienced by

athletes diagnosed with the overtraining syndrome. According to Hans Selye (55),

stress is the human response to a noxious event (stressor) and this response results

in the activation of the hypothalamic-pituitary-adrenal axis. Chronic stress responses

of high intensity or duration can result in a disturbance of mood as well as hormonal

dysfunction, which in turn may lead to psychosomatic disorders (55). Additionally,

this response may be exaggerated or attenuated depending on the perception of the

stressor and the ability to physiologically and psychologically cope with the demands

of the stressor/s (8). Presently, there is no information regarding the perception of

stress in athletes undergoing intensified training.

While there is no information on the perception of stress in athletes who are

overreached or overtrained, increases in mood disturbance are uniformly reported in

such athletes (15, 19, 20, 24, 29, 42). Variability in physiological and biochemical

responses to intensified training is often reported, however alterations in mood state

are consistently altered in overreached and overtrained athletes regardless of

amount and type of training. This may be related to the interrelationship between

physical and psychological function, with increases in physical and psychosocial

stressors seen to affect physical and psychological health (55).

Long duration, high intensity exercise has been associated with immunosuppression

(46, 50), including a reduction in the circulating lymphocyte concentration and


146

suppression of natural killer cell activity and secretory IgA in mucosal fluid (32, 50).

Given the high volume of training and limited recovery periods often associated with

overtraining, it has been suggested that immunosuppression may occur in athletes

suffering from overtraining.

As the underlying mechanisms of the performance decrements associated with

overtraining are unclear, a combination of a number of markers is needed for early

diagnosis. Changes in the plasma glutamine/glutamate ratio (Gln/Glu) have recently

been suggested as a predictor of overreaching or overtraining in athletes (59).

Elevated plasma glutamate and hence a reduced Gln/Glu ratio was observed in

athletes who were classified as overtrained (59) and Parry-Billings et al (49) reported

lower glutamine and increased glutamate levels in overtrained athletes. However, no

studies have investigated changes in glutamine, glutamate and reported concurrent

performance measures during a period of intensified training that has resulted in

overreaching.

Currently, there is no unifying hypothesis to adequately explain the mechanism(s)

behind the variety of changes that are associated with overtraining. Recently, in an

attempt to integrate the available information regarding overtraining, Smith (60)

proposed the cytokine hypothesis of overtraining. It is suggested that exercise-

induced microtrauma to the musculoskeletal system leading to a local inflammatory

response is the initiating event in the development of overtraining. Inadequate

recovery and a continuation of the athletes' training regimen compound this initial

local inflammation leading to chronic inflammation. This results in the release of

inflammatory mediators and the subsequent release of pro-inflammatory cytokines

from activated monocytes, which causes systemic inflammation. This induces

'sickness' behaviour (fatigue, appetite suppression, depression), activation of the


147

sympathetic nervous system and the hypothalamic-pituitary-adrenal-axis,

suppression of the hypothalamic-pituitary-gonadal-axis, up-regulation of liver function

and possibly immuno suppression (60). Only one investigation has examined

interleukin-6 (IL-6) in overtrained athletes (n=4) and found that levels were within

normal ranges and unaffected by overtraining (49). However, until now there has

been no assessment of the changes in plasma cytokines and performance levels in

response to overreaching, a state considered to be the precursor of the overtraining

syndrome.

Another possible influence on fatigue is changes in serotonergic responsiveness.

The neuroendocrine system functions to maintain basal and stress-related

homeostasis (14). Exercise can profoundly alter homeostasis and consequently

hormonal and metabolic activity is increased (51). During normal training with

adequate recovery, the stability of the hypothalamic-pituitary-adrenal axis is

maintained (60). When the training load is high and recovery is minimal, as in the

case during the development of overreaching and overtraining, the excessive

physiological and psychological stress may lead to alterations in the regulation of

neuroendocrine system. The neurotransmitter 5-hydroxytryptamine (5-HT; serotonin)

has multiple actions in the CNS and can influence sleep and pain processing,

decrease motor neuron excitability, suppress appetite and has links with autonomic

and endocrine functions (39). The 'central fatigue hypothesis' (45) assumes that the

development of a centrally mediated component of fatigue occurs through pathways

involving 5-HT.

The role of the serotonergic system has been investigated in patients with chronic

fatigue syndrome (CFS) (57, 58) and the related post-viral fatigue syndrome (2) and

in endurance trained athletes. Research suggests that there may be an increased


148

sensitivity of the hypothalamic brain 5-HT1A receptors (57) in fatigue-related

conditions and a decrease in sensitivity in trained athletes (23). However, a recent

study did not observe changes in 5-HT receptor sensitivity following 9 weeks of

endurance training (12).

The majority of these studies administered the partial 5-HT1A agonist, buspirone,

and the extent of the PRL response is taken as an indication of the functional activity

of the receptor (4). Buspirone is largely selective for the 5-HT1A receptor although it

has a slight affinity for other 5-HT receptors and acts primarily on post-synaptic

receptors (13). The prolactinotrophic effects of buspirone administration are slightly

complicated by its partial dopamine (DA) D2 receptor blocking action (4, 13, 36). The

combination of hypothalamic 5-HT1A stimulation and pituitary D2 receptor blockade

(41) are both responsible for the release of PRL. However, the buspirone challenge

test is accepted as a viable method of determining serotonergic responsiveness (4).

One means by which the serotonergic system could be altered through training is

through an increase in the number or activity of neuronal 5-HT transporters. Strachan

and Maughan (61) found a greater 5-HT transporter density in the platelets of red

blood cells in endurance trained males compared to sedentary controls. It therefore

seems that the function of the 5-HT system may be altered by training and disease.

Further support for this idea comes from a recent single case study of a patient

suffering from CFS who's recovery over an 18-month period resulted in increases in

exercise tolerance, a reduction in subjective measures of fatigue and decrease in the

PRL response to buspirone from very high levels to normal (56).

Acute endurance training (9 days) reduced 5-HT2A receptor density on platelets and

a smaller increase in PRL response to exercise was observed after training (62).


149

Recently, Weicker and Struder (67) examined the effects of 4 weeks of increased

duration training on 5-HT transporters (5-HTT) and 5-HT2A receptors (5-HT2AR) on

isolated blood platelets as well as basal prolactin levels. It was suggested that

'overstrain' disturbs central 5-HT neurotransmission and exercise of a chronic form

amplifies the 5-HT system to attenuate the central neuromodular disturbance (67).

Further, PRL responses to BCT were unchanged after training (p<0.076). However,

no measures of performance were made and recovery was not included in either of

these investigations and thus it is difficult to determine if the athletes were

overreached or overtrained and if changes corresponded to possible changes in

performance.

The aim of the present investigation was to investigate a number of changes

associated with intensified training, specifically mood state, various immune

parameters and serotonergic responsiveness.


150

METHODS

Study Design

Eight endurance-trained male cyclists volunteered for this study (Table 1). All

subjects had competed for at least two years and were training a minimum of three

days per week. The training of each subject was controlled and monitored for a

period of six weeks in total, which was divided into three distinct phases each of two

weeks duration (Figure 1). The first phase consisted of moderate training with a small

number of exercise testing sessions. Subjects completed their normal or usual

amount and type of training (N). The second phase consisted of an increase in

training volume and intensity as well as the number of exercise tests performed

(ITP). Subjects trained 7 days per week for these two weeks in addition to the

laboratory tests. The third phase of the study was one of reduced training and aimed

to provide subjects with a period of recovery (R).

___________________________________________________________________

Age Body mass Body Fat VO2max

(yrs) (kg) (%) (ml.kg-1.min-1)

___________________________________________________________________

Mean 27.1 73.7 14.6 58.0

SE 3.0 2.5 1.1 1.7

___________________________________________________________________

Table 1- Subject Characteristics- Study 1


151

Figure 1- Study Design

Training

Subjects completed six weeks of training, which consisted of two weeks of normal

training (N), two weeks of an intensified training period (ITP) and two weeks of

recovery (R). Subjects wore a heart rate monitor during all training sessions. This

was so the researchers could document training intensity and to ensure that all

subjects completed the prescribed training. Training during the ITP was based on

each individual's normal training, which was quantified by heart rate monitoring

Normal Training

Week 1

Week 2

*MT #IT *MT TT #IT

Intensified Training

Week 3

Week 4

TT #IT *MT TT #IT TT #IT *MT TT #IT

Recovery Training

Week 5

Week 6

*MT #IT *MT TT #IT


152

(Vantage NV, Polar, Kempele, Finland) during training during N as well as

questionnaire assessment of normal training volumes.

Training Program Design and Development





were downloaded to a computer using the Polar Interface (Polar Electro Oy,

Kempele, Finland). From this information average heart rate, maximum heart rate

and time spent in each of the heart rate zones could be calculated and verified

against the training diary. The majority of subjects performed their training outdoors,

however on occasion subjects trained inside the laboratory if weather conditions

prevented them from training outdoors.

After each Maximal Test subjects’ training zones were calculated from their individual

lactate curves. Anaerobic threshold was determined using the Dmax method. This

method consists of calculating the point that yields the maximal distance from the

lactate curve to the line formed by the two end points of the curve (6).


153

The five zones were calculated as follows and depicted in Figure 2:

• Zone 1 Prior to the initial rise in lactate, i.e. where the lactate curve remains

flat (baseline) to the point after which blood lactate concentration

begins to rise (OBLA; onset of blood lactate accumulation)

• Zone 2 From OBLA to 1mmol lactate above baseline.

• Zone 3 From 1mmol lactate to lactate threshold (identified by Dmax method;

• Zone 4 From lactate threshold to up to 10% of maximum heart rate (HRmax)

• Zone 5 From 10% of HRmax to HRmax

Figure 2: Diagram indicating how training zones were created based on lactate and

heart rate responses to an incremental cycling test. OBLA: onset of blood lactate

accumulation; AT Dmax: anaerobic threshold as determined by the Dmax method;

HRmax: maximum heart rate.

0

20

40

60

80

100

120

140

160

180

200

0 95 130 165 200 235 270 305 340 375 410 445 480

Power (W)

Hear

t Rat

e (b

pm)

0

1

2

3

4

5

6

7

8

9

Lact

ate

(mm

ol.l-

1)

Heart Rate Lactate

Zone 1: <110 bpm

Zone 5; >171 bpm

Zone 4: 146- 170 bpm

Zone 3: 138- 145 bpm

Zone 2: 110-137 bpm

ATDmax

OBLA

1 mmol

10% HRmax


154

The heart rates corresponding to each of these zones were calculated. The five

zones were then expressed as percentages of individual maximum heart rate. The

training zones for the 8 subjects are outline below. These values represent the

average and standard deviation of the each zone for the eight subjects.

• Zone 1 <69 (±9)%

• Zone 2 69 (±9)% - 81(±1)%

• Zone 3 82 (±10)% - 87 (±1)%

• Zone 4 88 (±11)% - 94 (±1)%

• Zone 5 >94 (±11)%

Subjects training programs for the intensive training weeks were based on their

current amount of training in the two baseline weeks. In the two intensive training

weeks the researchers aimed to increase the amount of time the subjects trained in

zones 3, 4 and 5. This was achieved by designing individual training programs that

doubled training volumes. The majority of the increase in training volume was in the

form of high intensity training, i.e. above anaerobic threshold.

Maximal Cycle Ergometer Test (MT)

Subjects attended the laboratory after an overnight fast and a teflon catheter (Becton

Dickinson, Quickcath) was inserted into an antecubital vein. Following this, the

subjects performed an incremental test to exhaustion on an electrically braked cycle

ergometer (Lode Excalibur Sport, Groningen, The Netherlands) to determine

maximal aerobic power output (Wmax), submaximal and maximal oxygen

consumption and heart rate. Work rate began at 95W and increased by 35W every 3

minutes until volitional exhaustion. Blood samples were collected at the end of each


155

stage and blood lactate concentration was immediately determined (YSI 2300 STAT

Plus, Ohio, USA).

Time Trial (TT)

After a 5 minute warm-up at 50% Wmax, subjects performed a simulated time trial in

which they were asked to complete a target amount of work as fast as possible. The

amount of work to be performed was calculated by assuming that subjects could

cycle at 75% of their Wmax for ~60 minutes at a cadence of 80 rpm and thus these

time trials lasted approximately 60 min for all subjects.

Intermittent Test (IT)

Unlike the TT, the Intermittent Test was of a set duration and the change in work

produced and mean power output was assessed. Subjects completed a 5-minute

warm-up at 50% Wmax followed by two ten minute bouts of maximal exercise. Each

subject was given 5 minutes rest between bouts. Subjects were asked to produce a

maximal effort for each of the 10-minute bouts, i.e. to produce the maximal amount of

work possible, which could be viewed on a computer screen in front of the subject.

Psychological Assessment

Every day for the duration of the study, subjects completed both the Daily Analysis of

Life Demands of Athletes (DALDA) (54) and the Profile of Mood States Short Form

Questionnaire (POMS-22) (38). The DALDA is divided into parts A and B, which

represent the sources of stress and the manifestation of this stress in the form of

symptoms, respectively. Subjects were asked to complete these questionnaires at

the same time of each day prior to training. Subjects also completed the 65-question

version of the POMS (38) once a week at the end of each training period. Global

mood state was determined using the method described by Morgan et al (42). The


156

POMS has moderate test-retest reliability with alpha coefficients ranging from 0.61 to

0.69. The moderate coefficients are expected as the POMS is a state measure,

specifically designed to identify subtle changes in mood (37).

Subjects also completed the General Health Questionnaire (GHQ-28) (16), which

includes 28 questions and may be subdivided into four subscales (A: somatic

symptoms; B: anxiety and insomnia; C: social dysfunction; D: severe depression) in

addition to a total score. The GHQ-28 was completed at the end of each week. This

questionnaire has been shown to have a high test-retest reliability (0.90) over a

period of 6 months (16). Also completed once per week for the 6 weeks of the study

was the Perceived Stress Scale (PSS) (10). The PSS measures the degree to which

situations in one's life are perceived as stressful and as such determines the extent

that respondents find their lives unpredictable, uncontrollable and overloaded (10).

The PSS has high internal consistency with an alpha of 0.91 (10).

Buspirone Challenge Test (BCT)

Three BCT's were completed by each subject during the course of the study. A

baseline test was performed at the end of the initial two week period followed by

another test on the day immediately following the intensified training period. The final

BCT test was performed the day following the completion of the recovery period

(Figure 1).

Prior to the initial BCT each subject was screened by a medical practitioner for

psychological and physiological disorders that would contraindicate the use of

buspirone. Subjects attended the laboratory at 08:30 after an overnight fast and a

cannula was inserted into a forearm vein. At 09:00 the first baseline sample was

taken and baseline samples were collected every 15 minutes for one hour thereafter.


157

At 10:00 an oral dose of Buspirone Hydrochloride (Bristol Meyers Squibb, 5mg.kgbw-

1) was administered. Blood samples were collected every 15 minutes for the next

150 minutes and analysed for PRL concentration.

Subjects also completed a short assessment of side effects from the drug after

administration. Immediately after each collection of each blood sample, beginning at

time point 0, subjects rated possible side effects on a scale of 0-4, where a score of 0

represented absent and 4 denoted severe. Categories were light-headedness,

nausea, dizziness, hot, cold, sleepy, fatigued, clammy skin, sweatiness and aches.

Blood handling, storage and analysis

Measurements were performed on resting, overnight-fasted samples, which were

collected in the morning, once per week over the six weeks of the study. Samples

were collected immediately prior to the maximal cycle ergometer tests following

insertion of a teflon catheter (Becton Dickinson, Quickcath) into an antecubital vein.

Venous blood was collected into K3EDTA tubes and centrifuged at 1500g for 10

minutes at 4°C; plasma was stored at -20°C. All samples were measured in duplicate

with the exception of haematological variables. To avoid inter-assay variation, all

samples were analysed in one batch at the end of the study, with the exception of

haematological measures, which were performed on the day of collection. The intra-

assay coefficient of variation for the metabolites, creatine kinase and cytokines

measured were all less than 5%, with the exception of glutamine and glutamate

which was 7% and salivary IgA which was 10%.

Saliva samples were collected before and after the 8 Intermittent Tests (IT). Subjects

were fasted for at least 3 hours prior to testing and saliva samples were collected

immediately prior to the first bout and immediately following the second bout.


158

Subjects were instructed to swallow and then unstimulated whole saliva was

collected over a 3-min period into tubes before exercise and immediately post-

exercise. Subjects were instructed to allow saliva to dribble into the collecting tubes

unaided by spitting. All saliva collections were made with subjects seated, leaning

forwards with their heads down.

Plasma Urea

Plasma urea was measured using an enzymatic colorimetric endpoint method (Kit

No. 640-A, Sigma, Poole, UK).

Plasma Creatine Kinase activity

Plasma creatine kinase (CK) activity was determined at 30°C using an enzymatic kit

(No. 47-10, Sigma, Poole, UK).

Plasma Ammonia and Glutamine

Plasma glutamine was analysed enzymatically by first determining the plasma

ammonia concentration based on the reductive amination of 2-oxoglutarate, using

glutamate dehydrogenase (EC 1.4.1.3) and reduced nicotinamide adenine

dinucleotide (Sigma, Poole, UK). Plasma was then incubated for 60 minutes at 37°C

with glutaminase (EC 3.5.1.2), converting free glutamine to ammonia and glutamate

(30), and the ammonia concentration measured. Plasma glutamine levels were

calculated by subtracting the untreated plasma ammonia concentration from the

ammonia concentration in the sample treated with glutaminase.

Plasma Glutamate

Plasma glutamate was analysed enzymatically using glutamate dehydrogenase (EC

1.4.1.3) and nicotinamide adenine dinucleotide.


159

Haematology

Venous blood was used for haematological analysis of differential leukocyte counts

using a Technicon H-2 laser system (Bayer Diagnostics, Basingstoke, UK). This

included determination of the total leukocyte count and neutrophil, lymphocyte and

monocyte counts.

Plasma cytokines

Plasma concentrations of IL-6 and TNF-α were determined in aliquots of plasma with

the use of quantitative sandwich-type enzyme-linked immunosorbant (ELISA) kits

(R&D Systems, Abingdon, UK). A high-sensitivity kit was used for analysis of IL-6.

Salivary IgA

After thawing, stored saliva samples were analysed for IgA using a sandwich-ELISA

method (65). Briefly, flat-bottomed microtitration plates (Linbro EIA plates, Flow

Laboratories Inc., McLean, VA, USA) were coated with the primary antibody, rabbit

anti-human IgA (I-8760, Sigma, Poole, UK), at a dilution of 1 in 800 in carbonate

buffer, pH 9.6. After washing with phosphate buffered saline (PBS, pH 7.2) the plates

were coated with blocking protein solution (2% w/v casein in PBS). Sample analysis

was performed in duplicate using saliva samples diluted 1 in 1000 with deionised

water and a range of standards (Human colostrum IgA, I-2636, Sigma) up to 400 µg l-

1. A reference sample was incorporated into each micro-well plate, and all samples

from a single subject were analysed on a single plate. The plates were incubated for

60 minutes at 20oC. Following a washing step, peroxidase-conjugated goat anti-

human IgA (A-4165, Sigma) was added and the plate incubated for a further 60

minutes at 20°C. Following another washing step, the substrate, ABTS (Boehringer

Mannheim, Lewes, UK), was added and after 30 minutes the absorbance was

measured at 405nm.


160

Prolactin

Heparinized blood samples from BCT and TT tests were separated by centrifugation

for 10 mins at 3000rpm at 4°C and the plasma stored at -70°C and analysed for

plasma PRL using an immunoradiometric assay (Skybio Ltd., Wyboston,

Bedfordshire, UK). To avoid inter-assay variation, all samples were analysed in one

batch at the end of the study. The detection limit of the assay was 20 mIU/l and the

intra-assay coefficient of variation was 3.65%.

Criteria for the detection of a state of overreaching

A state of overreaching was diagnosed if a subject had a decline in performance in

the TT in combination with an altered mood state as identified by the POMS-65.

These criteria have previously been employed to detect a state of overreaching (19,

24). In addition, both performance and mood state should return to baseline values

following a two-week period of recovery.


Changes in all variables over time, with the exception of prolactin responses to BCT

was analysed using a repeated measures Analysis of Variance, with Least

Significance Difference comparison performed to identify significant differences

between the individual means. The level of statistical significance was set at p< 0.05.

All data is reported as mean ± SEM.

The plasma PRL concentrations at each time point during the BCT were compared

for the three conditions (N, ITP, R) using a repeated measures analysis of variance,

with Bonferroni corrections for multiple comparisons. The PRL response was

calculated as the area under the curve (AUC) using the trapezoid method with


161

subtraction of the baseline area. Significance was determined using a one-way

analysis of variance. The level of significance was set at p<0.05.

RESULTS

Training

Subjects completed two weeks of normal training (N, 7 ± 2hrs per week), 2 weeks of

intensified training (ITP, 14 ± 5hrs per week) and a final 2 weeks of recovery training

(R, 3.5 ± 2.5hrs per week). The laboratory tests were included during the calculation

of total hours of training completed in each period. The previously mentioned criteria

for the detection of overreaching were met.

Performance

Maximal power output during the VO2max test significantly declined during ITP

(Table 2). Time taken to perform the time trial test significantly increased by 9.8%

from 59.4 minutes during N to 65.3 minutes at the end of the first week of ITP.

Subjects on average took 4 minutes and 30 seconds longer to complete the given

amount of work. At the end of ITP maximal work produced during the IT was also

significantly reduced from 181 ± 10 kJ to 166 ± 12 kJ. For additional information on

performance changes see Halson et al (19).

Mood State

Rating of perceived exertion scores at 200W were significantly elevated during ITP

(Table 2). Global Mood State scores on the POMS-65 were significantly increased

from 90.4 during N to 116.4 during ITP (Figure 3). Upon completion of R, scores

returned to 91.5. From this questionnaire the subscales of tension, fatigue and

confusion were also significantly elevated, while vigour significantly declined. No

changes were evident in the depression or anger subscales (Figure 4). Altered mood


162

states were also identified by the short version of the POMS questionnaire, with

significantly elevated total scores (Figure 5a).

179

Study 1 N N ITP ITP R R P value Maximal power output (W) 338.1 ± 16.5 340.0 ± 17.9 327.2 ± 16.7*a 319.7 ± 15.1*a 328.9 ± 13.8 340.4 ± 16.7 <0.001

RPE @ 200W 9.4 ± 0.8a 9.2 ± 0.9 10.0 ± 1.3 10.9 ± 1.2* 9.4 ± 1.1 8.5 ± 0.8 0.011

GHQ-28 Total 12.6 ± 1.2 15.0 ± 1.9 21.3 ± 3.0 22.4 ± 3.6 15.3 ± 3.3 15.1 ± 3.5 0.09

Scale A

(somatic symptoms) 2.6 ± 0.6 3.6 ± 0.9 5.6 ± 0.9 6.5 ± 1.4 3.4 ± 1.3 4.0 ± 1.3 0.11

Scale B

(anxiety/ insomnia) 2.7 ± 0.9 3.1 ± 1.1 5.4 ± 1.3* a 6.0 ± 1.5* a 3.1 ± 1.0 3.2 ± 1.4 0.03

Scale C

(social dysfunction) 6.9 ± 0.3 8.0 ± 1.4 9.8 ± 0.7* 9.3 ± 0.9* 7.9 ± 0.9 7.1 ± 1.1 0.04

Scale D

(severe depression) 0.4 ± 0.2 0.3 ± 0.2 0.5 ± 0.3 0.6 ± 0.4 0.9 ± 0.7 0.7 ± 0.7 0.72

PSS 19.6 ± 2.0 19.0 ± 2.0 23.8 ± 2.4* 27.8 ± 3.0*a 22.1 ± 2.7 18.8 ± 2.2 0.04

Table 2- Performance and responses to GHQ and PSS at weekly intervals throughout the study period. '*' indicates significantly different

from normal training. 'a' indicates significantly different from recovery.

164

Figure 3- Changes in Total POMS-65 Scores during MT, during normal training,

intensified training and recovery. 1 indicates significantly different from Test 1, 2

indicates significantly different from Test 2, 3 indicates significantly different from



Figure 4- Changes in POMS subscale scores during normal training, intensified

training and recovery.

80

90

100

110

120

130

Training

Glo

bal P

OM

S Sc

ore

3,4 3,4

1,2 1,2,5,6

4 4


-5

0

5

10

15

20

25

Tension Depression Anger Vigour Fatigue Confusion

POM

S-65

N ITP R


165

Figure 5- Changes in POMS-22 (a), DALDA Part A (b) and DALDA Part B (c)

responses during normal training, intensified training and recovery.

0

2

4

6

8

10

Training

DA

LDA

Par

t B


0.00.51.01.52.02.53.0

DA

LDA

Par

t A

-4

-2

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2

4

6PO

MS-

22

a

b

c


166

Parts A (Figure 5b) and B (Figure 5c) of the DALDA were both increased during ITP,

however only Part B was significantly higher in ITP than N. The most common

changes in sources of stress, as identified by Part A of the DALDA, were related to

sport training, sleep and health. Part B of the DALDA showed the greatest changes

during the ITP period, with the majority of subjects showing sizeable changes on

many of the items. The most common alterations in responses were increased

problems associated with the following areas: need for a rest, recovery, irritability,

between session recovery, general weakness and training effort. Significant

increases in Part B of the DALDA occurred in all subjects between 3-7 days of

intensified training.

Total GHQ-28 scores were not significantly different at any time point during the

study. However, Scales B and C of the GHQ-28 were significantly elevated during

ITP (Table 2) and returned to baseline levels following recovery. Scales A and D

were also increased during ITP, however this was not statistically significant. Scores

on the PSS were significantly elevated during ITP and also returned to baseline after

recovery (Table 2).

Immunology

Saliva IgA concentration was 121 ± 14 mg/l during N and fell during ITP to 91 ± 14

mg/l, with some recovery by the end of R (110 ± 14 mg/l) (Table 4), however, these

changes were not statistically significant, even after statistical analysis was

performed on normalised data. No significant changes were observed in resting

plasma IL-6 or TNF-α concentrations throughout the duration of the study (Table 4).


167

Biochemistry

Plasma creatine kinase activity was significantly elevated during the ITP and returned

to baseline levels during R (Table 3). Plasma urea concentration tended to be

slightly elevated during the ITP (p=0.057) and also declined to pre-intensive training

levels following recovery (Table 3). However, this increase was not statistically

significant. Plasma ammonia also showed a trend for increased levels during ITP

(p=0.067) (Table 3).

There were no significant changes in plasma glutamine concentration over the six

week period, however values declined to 475 ± 40 µM after ITP (Figure 6a). Plasma

glutamate was significantly elevated during ITP and returned to baseline levels

during R (Figure 6b). Hence, the Gln/Glu ratio was significantly lower in the ITP

compared to N. Although the ratio had not returned to pre-training values after R,

there was no statistically significant difference between R and N (Figure 6c).

Haematology

During the ITP red blood cell count (RBC), haemoglobin (Hb), and packed cell

volume (PCV) significantly declined and following R had returned to initial levels

(Table 4). No changes were observed in mean red blood cell volume (MCV),

platelets, white blood cell count, neutrophils, lymphocytes, monocytes or

neutrophil/lymphocyte ratio (Table 4).

N ITP R

Week 1 2 3 4 5 6 P value

Resting Salivary IgA (mg.L-1) 121.4 ±1 4.4 112.5 ± 14.9 109.9 ± 13.1 113.5 ± 15.6 105.3 ± 13.2 91.0 ± 14.1 108.6 ± 18.2 109.5 ± 13.9 0.115

Maximal Salivary IgA (mg.L-1) 89.5 ± 11.2 100.6 ± 9.6 84.5 ± 13.5 100 ± 16.8 87.2 ± 16.2 95.6 ± 11.8 111.9 ± 11.6 101.2 ± 12.7 0.347

IL-6 (pg/ml) 0.5 ± 0.2 0.5 ± 0.2 0.8 ± 0.2 0.7 ± 0.2 0.8 ± 0.3 0.6 ± 0.2 0.336

TNF-α (pg/ml) 7.1 ± 1.4 8.3 ± 2.7 8.0 ± 1.8 7.4 ± 1.8 6.6 ± 2.1 6.3 ± 1.8 0.785

Glutamine (µM) 631 ± 21 521 ± 29 555 ± 31 475 ± 40 515 ± 40 555 ± 39 0.700

Glutamate (µM) 158 ± 18 164 ± 28 200 ± 14*a 235 ± 18*a 198 ± 15a 157 ± 6 0.005

Gln/Glu ratio 4.38 ± 0.49 3.97 ± 0.73 2.86 ± 0.24* 2.13 ± 0.26*a 2.76 ± 0.35* 3.61 ± 0.37 0.004

Plasma CK activity (U.l-1) 55.4 ± 21.4 58.3 ± 14.4 80.9 ± 15.6 92.9 ± 18.1*a 54.7 ± 11.5 60.6 ± 6.9 0.038

Plasma Urea (mmol.L-1) 2.2 ± 0.2 2.3 ± 0.1 2.6 ± 0.2 2.8 ± 0.2 2.4 ± 0.1 2.4 ± 0.2 0.057

Plasma Ammonia (µM) 38.6 ± 7.5 60.2 ± 14.4 45.1 ± 15.3 60.8 ± 14.4 40.5 ± 14.9 48.1 ± 12.9 0.067

Table 3- Selected immunological and biochemical variables during normal training (N), intensified training (ITP) and recovery (R). '*'

indicates significantly different from normal training (N). 'a' indicates significantly different from recovery (R).


169

1.5

2.5

3.5

4.5

5.5

Training

Gln

/Glu

Rat

io

3,4,5

1,4

1,2,3,6

1

4 4


0

100

200

300

400

500

600

700

Gln

(uM

)

a

0

50

100

150

200

250

300

Glu

(uM

)

3,41,6

1,5,6

4,63,4,5

b


170

Figure 6a- Changes in glutamine concentration during normal training, intensified

training and recovery.

Figure 6b- Changes in glutamate concentration during normal training, intensified

training and recovery. 1 indicates significantly different from Test 1, 2 indicates

significantly different from Test 2, 3 indicates significantly different from Test 3, 4


Test 5, 6 indicates significantly different from Test 6.

Figure 6c- Changes in glutamine/glutamate ratio (Gln/Glu) during normal training,

intensified training and recovery. 1 indicates significantly different from Test 1, 2




N ITP R

Week 1 2 3 4 5 6 P value

RBC (x109.l-1) 4.95 ± 0.06a 4.58 ± 0.08 4.40 ± 0.08*a 4.27 ± 0.07*a 4.57 ± 0.06* 4.55 ± 0.08* <0.001

Hb (g.dl-1) 14.7 ± 0.2a 13.7 ± 0.2 13.1 ± 0.3*a 12.8 ± 0.2*a 13.6 ± 0.2* 13.5 ± 0.3* <0.001

PCV (fl) 0.44 ± 0.01a 0.41 ± 0.01* 0.39 ± 0.01*a 0.39 ± 0.01*a 0.41 ± 0.01*a 0.41 ± 0.01* <0.001

MCV (fl) 89.7 ± 0.7 90.1 ± 0.9 90.0 ± 0.5 90.8 ± 0.5 91.1 ± 0.4 89.6 ± 0.7 0.120

Platelets (x109.l-1) 238 ± 13 232 ± 10 240 ± 11 258 ± 15* 275 ± 16* 238 ± 21 0.005

WBC (x109.l-1) 5.6 ± 0.4 5.1 ± 0.2 5.3 ± 0.4 5.7 ± 0.7 5.2 ± 0.4 5.2 ± 0.5 0.813

Neutrophils (x109.l-1) 2.9 ± 0.3 2.5 ± 0.2 2.6 ± 0.3 3.1 ± 0.7 2.8 ± 0.3 2.6 ± 0.3 0.790

Lymphocytes (x109.l-1) 2.0 ± 0.2 2.0 ± 0.2 1.9 ± 0.2 1.8 ± 0.2 1.7 ± 0.2 2.0 ± 0.2 0.807

Monocytes (x109.l-1) 0.4 ± 0.04 0.4 ± 0.03 0.5 ± 0.02 0.5 ± 0.06 0.5 ± 0.04 0.5 ± 0.03 0.054

Neut: Lymph 2.0 ± 0.2 1.3 ± 0.2 1.4 ± 0.1 2.0 ± 0.7 1.8 ± 0.3 1.2 ± 0.1 0.192

Table 4- Selected haematological variables during normal training (N), intensified training (ITP) and recovery (R). '*' indicates significantly

different from normal training (N). 'a' indicates significantly different from recovery (R).


172

Buspirone Challenge Test

Baseline corrected plasma PRL concentrations were significantly higher at time

points 15, 105 and 120 minutes of the BCT during R when compared to N. Total area

under the release curve was significantly greater at the end of R when compared to

N (R: 63035 ± 8084 mIU.min.l-1; N: 32770 ± 10635 mIU.min.l-1) and the total AUC

was approximately two times greater after recovery. While AUC was increased after

ITP (51231 ± 15932 mIU.min.l-1) when compared to N, it was not statistically

significant (Figure 7).

Figure 7- Changes in plasma prolactin concentration during BCT following normal

training (N), intensified training (ITP) and recovery (R). * indicates time point

significantly different in R when compared to N.

▲ indicates N

● indicates ITP

■ indicates R

0

200

400

600

800

1000

1200

-60 -45 -30 -15 0 15 30 45 60 75 90 105 120 135 150Time (min)

Plam

sa [P

RL]

(mIu

.l-1)

*

*

*


173

During the challenge tests performed after ITP and R, all but one subject reported

increased side effects when compared to N. Subjects also indicated that the side

effects of the challenge developed earlier during the BCT after ITP and R when

compared to N. The most common side effects to increase after ITP and R were

fatigue, nausea, dizziness and headaches.

Resting plasma PRL concentration prior to the TT remained unchanged throughout

the study period, however maximal PRL concentrations declined during ITP and were

significantly lower than values following R (Figure 7).

Figure 8- Changes in plasma prolactin concentration prior to the TT and immediately

post TT normal training (N), intensified training (ITP) and recovery (R). 1 indicates

significantly different from Test 1, 2 indicates significantly different from Test 2, 3



from Test 6.

0

200

400

600

800

1000

Training

Plas

ma

[PR

L] (m

Iu.l-1

)


6 66

2,3,5


174

DISCUSSION

A state of overreaching was diagnosed as determined by a reduction in performance

and an increase in mood disturbance in all subjects. Determined from the long and

short versions of the Profile of Mood States as well as the Daily Analysis of Life

Demands of Athletes, increases in global mood state, increases in fatigue, decreases

in vigour and increased negative responses to questions relating to sources and

symptoms of stress occurred after continual intensified training.

Mood State

It is widely recognized that regular physical exercise can aid in the reduction of

depression and can be a useful tool alongside pharmacological therapy in patients

with severe depressive illness (42). However, the positive relationship between

increased training load, increased performance and positive mental health exists only

to an unidentified point, after which mood state becomes altered to the detriment of

the athlete.

Our findings of increased mood disturbance in response to intensified training are in

support of previous research in this area (15, 20, 42). A series of investigations

performed by Morgan et al (42) suggests a dose-response relationship between

mood state and training stimulus. An increase in training load resulted in a

disturbance in mood state, with increases in fatigue and decreases in vigour. Mood

disturbance declined to baseline values with a reduction in training load.

Comparisons between this study and the present studies are difficult as performance

was not reported in the earlier studies.

Fry et al (15) administered an abbreviated version of the POMS on four occasions

during a 16-day training study involving 10 days of intensified training in elite soldiers.


175

A 29% reduction in running time to fatigue occurred alongside an increase in total, or

global, mood disturbance following 10 days of training. Similar to our findings, mood

state was significantly altered after 5 days, and continued to increase at Day 11.

Significant increases were observed in the fatigue subscale, while decreases were

observed in the vigour subscale. Hooper et al (20) administered the POMS-65 to 19

swimmers during a six-month training season. Three subjects were identified as

'stale' based on decreased performance and increased ratings of fatigue. Two of

three 'stale' swimmers had significantly elevated global mood state scores.

In this investigation, the authors have endeavoured to discern 'normal' or acute

fatigue from that of overreaching. To achieve this, questionnaires were administered

daily and consistent elevations in responses were explored. In general, a state of

overreaching was observed after 3-7 days of intensified training without recovery.

Performance was measured regularly and we noted a decline in time trial

performance following the first several days of intensified training. This may be

attributable to the intense nature of the training sessions completed before the

performance assessment. Although performance had declined, a state of

overreaching was not diagnosed as mood state was unaltered and the fatigue

experienced was of an acute nature and is considered a normal response to an

isolated training session. The DALDA may be a useful tool in identifying the point at

which intensified training results in overreaching.

The elevations in RPE scores found during exercise indicate that at a given workload

subjects perceive the exercise to be more difficult following intensified training. The

present results support the use of increases in RPE scores as an indicator of

overreaching. Additionally, a heightened perception of exertion may be indicative of a

centrally mediated fatigue mechanism, highlighting the relationship between

physiological and psychological factors.


176

The perception of stress during intensified training that results in overreaching

appears to be increased. The perception of a stressor and the perceived ability to

cope with the stressor determine the activation, intensity and duration of the stress

response (21, 28). Thus, an increase in the perception of stress may be associated

with the increase in tiredness and fatigue associated with the intensified training and

the increased time demands placed on the subjects. Assessment of changes in

stress perception and methods of coping with additional or heightened stressors

warrants further research.

The lack of change in total GHQ-28 scores during the intensified training period may

be related to a combination of a lack of applicability to athletes and subject inter-

individual variability in psychological responses to increased training. The increase in

Scale B of the GHQ-28 represents increases in anxiety and insomnia, including lack

of sleep, irritability and nervousness. Scale C (social dysfunction) also significantly

increased most likely reflecting the increased time devoted to training. Possible

changes in social functioning during intensified training have received little research

attention. However, it would appear obvious that the increased time spent both

training and endeavouring to recover from training is an additional stressor to the

athlete. Less time may be spent in enjoyable social activities and may also result in

other activities not being performed or completed to a satisfactory degree.

It would have been expected that responses to Scale A of the GHG-28 (somatic

symptoms) would have been significantly increased as negative somatic symptoms

were elevated in both the POMS and DALDA questionnaire responses. However, the

symptoms described in Scale A are perhaps not representative of those experienced

by overreached or overtrained athletes and more likely reflect somatic symptoms

experienced by individuals with psychiatric disorders. Depression is often reported in


177

overtrained athletes, however in both studies the subscales of the GHQ-28 and the

POMS-65 were unchanged. This is most likely related to the nature of the artificial

intensified training program and the relatively short duration of performance decline.

Competitive athletes with the overtraining syndrome may experience more severe

depression or depressive illness due to the major decline in performance that is

associated with this condition. Therefore, changes in depression may not be evident

in overreaching and thus may not be a viable indicator of impending overtraining

syndrome.

The changes in Scale B of the GHQ-28 supports previous research that suggests

increases in anxiety and episodes of insomnia during overreaching and overtraining.

While the GHQ-28 total score may not be a useful tool in monitoring overreaching

and overtraining, Scales B and C may provide valuable information on changes in

anxiety and insomnia and social dysfunction.

Both the POMS questionnaires (long and short versions) and the DALDA

questionnaire appear to be useful tools to monitor changes in mood state that

accompany overreaching. In terms of practicality, the shorter version of the POMS

may be favoured as the identified changes due to overreaching are similar to that of

the longer version. The DALDA questionnaire may provide additional information by

identifying the sources of stress to the athlete and the resulting symptoms. The

DALDA questionnaire can easily be used on a daily basis and a pattern of responses

can be created during normal training, intensified training and tapering. Additionally,

the DALDA is perhaps more specific to athletes than the POMS, which was designed

to identify changes in mood state particularly in people undergoing counselling or

psychotherapy (38).


178

Immune Function

The present investigation does not provide evidence for alterations in cytokines and

other immune system parameters during overreaching. However, a decline in the

Gln/Glu ratio was evident and this ratio may be useful as a diagnostic tool for

overreaching.

Although in the present study there were no statistically significant changes in resting

glutamine concentrations, during the second week of ITP, glutamine concentrations

were lower compared to N. This is similar to two previous investigations (25, 40, 53)

which both reported a decline in glutamine concentration in overreached athletes.

Glutamine concentration remained unchanged in swimmers who were classified as

overreached after 4 weeks of intensified training. However, the well-trained athletes

had 20% higher concentrations of plasma glutamine compared to those who were

overreached (33). A decline in glutamine may be the result of greater uptake of this

amino acid for gluconeogenesis (66). An increase in gluconeogenesis may be the

result of glycogen depletion to continued intensified training, however alterations in

glucose kinetics as a result of overreaching has not been examined. While plasma

glutamine concentration may or may not decrease following periods of intensified

training, there is still little evidence to link low glutamine levels with impaired immune

function and increased susceptibility to illness or infection (5). However, the use of

glutamine concentrations as a marker to indicate impending or current overtraining

warrants further attention.

The mechanism/s for the elevation in plasma glutamate with intensified training are

unknown. High plasma glutamate concentrations have been reported in catabolic

conditions such as cancer, human immunodeficiency virus (HIV) infection and sepsis

(17). Elevated plasma glutamate concentration in cancer patients was reported to


179

indicate decreased uptake of glutamate into the peripheral muscle tissue, possibly as

a consequence of reduced transport activity (17). Kinscherf et al (26) suggested that

high plasma glutamate in combination with insufficient baseline glutamine levels may

result in catabolism or a loss of body cell mass (cachexia) in healthy subjects

following very high intensity exercise. These authors suggested that glutamate

transport activity may be inhibited when there is a high rate of glycolytic activity in

skeletal muscle (26). The significance of the elevated glutamate levels is unknown,

however glutamate had no effect on the rate of T-lymphocyte proliferation in vitro

(49). Elevated plasma glutamate concentrations may be associated with

overreaching and overtraining, however the role of glutamate in the mechanisms of

overreaching and overtraining is questionable.

Smith & Norris (59) reported unchanged resting plasma glutamine concentrations in

athletes who were classified as overtrained, yet plasma glutamate concentration was

significantly elevated in this group. Thus, our observation of an elevated Gln/Glu ratio

after intensified training was also shown in this previous investigation. The glutamine

and glutamate values reported by Smith & Norris (59) are similar to those of the

present investigation. Our data supports their values suggested to indicate

overreaching, i.e. a ratio <3.58. As performance in the present study returned to

baseline after 2 weeks of recovery, it was concluded that the subjects were

overreached as opposed to overtrained. Following recovery the Gln/Glu ratio

returned to above 3.58 and therefore supports the classification of overreaching

based on the Gln/Glu ratio suggested by Smith & Norris (59).

The decrease in RBC, Hb and PCV during intensified training most likely reflects

plasma volume expansion. The unchanged resting blood leukocyte counts are

consistent with previous research in this area (34). However, declining leukocyte


180

counts after 4 weeks of training have been found alongside lower lymphocyte counts

in overreached athletes when compared to well-trained athletes after 2 weeks of

intensified training (34). This may suggest that leukocyte counts reflect the athletes

training status and/or may be associated with longer term intensified training, i.e.

greater then 2 weeks.

Our findings of unchanged resting plasma IL-6 and TNF-α concentrations during a 2-

week period of intensified training despite changes in performance, fatigue and mood

state, do not support the role of cytokines in overreaching. According to the cytokine

hypothesis of overtraining, the pro-inflammatory cytokine IL-1ß, in addition to plasma

IL-6 or TNF-α, is central to the development of overtraining. In the present study we

did not measure IL-1ß, and the possibility cannot be excluded that elevated systemic

levels of IL-1ß may have accounted for some of the changes we observed in our

group of overreached subjects. However, as IL-6 and TNF-α were unchanged it is

doubtful that IL-1ß would have demonstrated considerable changes.

The cytokine hypothesis of overtraining proposes that trauma to the musculoskeletal

system leading to a local inflammatory response is the initiating event in the

development of overtraining. Mechanical injury to the musculoskeletal system due to

high impact forces; and in particular injury to those muscles which contract

eccentrically to absorb foot strike impact forces (7) are the likely source of

microtrauma and local inflammation during running. However, during cycling muscle

contraction is almost entirely concentric and mechanical trauma to the

musculoskeletal system from ground impact forces does not occur. While similar CK

levels have been observed during concentric, eccentric and isometric arm flexion

exercise (9), it is recognised that eccentric muscular contractions results in greater

muscle fibre injury that concentric contractions. It is therefore proposed that


181

ischemia/reperfusion injury may be a possible source of the microtrauma leading to

local inflammation during activities such as cycling which are predominately

composed of concentric muscle contractions.

Exercise-induced muscle ischemia/reperfusion injury may occur as a result of fibres

within the contracting muscle experiencing hypoxia followed by reoxygenation upon

the cessation of exercise and the subsequent generation of reactive oxygen species

(68). However, the available scientific evidence does not support such a view (22,

35) and it has been suggested that during prolonged exercise, athletes are highly

unlikely to experience ischemic muscle injury (7). Without an initial source of

microtrauma the development of local and chronic inflammation will not occur.

Furthermore, circulating monocytes will not become activated and therefore elevated

resting systemic pro-inflammatory cytokine concentrations would not be expected.

A tendency toward elevated resting plasma CK was observed after the first week of

intensified training, and CK was significantly elevated at the end of the second

intensified training week. The current study employed cycling exercise, which

excludes eccentric muscle contractions, therefore the rise in resting plasma CK we

observed is unlikely to have been the result of muscle trauma. One possibility might

be that the cumulative effect of repeated bouts of prolonged exercise may induce

sufficient oxidative stress to impair the body's antioxidant defence systems, and

perhaps induce membrane peroxidation resulting in the leakage of CK from the

muscle into the circulation (64). Results of a previous study (63) do not support this

notion, however, the study employed only 3 consecutive days of prolonged cycling

exercise compared to 14 days in the present study. Although statistically significant,

the rise in resting plasma CK was quantitatively small and the ability of this marker to


182

discriminate between normal, intensified training and intensified training that results

in underperformance is doubtful.

Mucosal IgA is an important factor in host defence and has been examined in relation

to increased upper respiratory tract infection (URTI) incidence and immune

depression in endurance trained athletes (31). To date, there is limited data on

changes in mucosal IgA as a result of overreaching with only Mackinnon et al (32)

reporting 18-32% lower salivary IgA concentrations in athletes showing symptoms of

overreaching compared to those who were well trained. We found lower IgA

concentrations during ITP compared to N, however this was not statistically

significant.

The results of the present investigation do not provide clear evidence to either

definitively confirm or refute the recently proposed cytokine hypothesis of

overtraining. While the underlying causative mechanism(s) of overreaching and

overtraining still remain unclear, it does not appear that elevations in circulating

cytokines are primarily responsible for the fatigue and underperformance associated

with overreaching. It was possible to induce a state of overreaching, evident by

underperformance and changes in mood state, yet resting plasma cytokine

concentrations remained unchanged. However, it cannot be stated that changes in

cytokines will not occur in athletes suffering from the overtraining syndrome.

Although it is generally assumed that continued training whist in a state of

overreaching will lead to overtraining, it cannot be said that the symptoms and

characteristics of both states are identical. If the athlete continues to train whist

overreached and does not incorporate adequate recovery between exercise

sessions, this acute inflammatory response may develop into a chronic response,

ultimately resulting in the activation of circulating monocytes. Pro-inflammatory


183

cytokines released by these activated monocytes may result in systemic

inflammation, perhaps accounting for some of the multitude of symptoms observed in

overtrained athletes. Furthermore, it is possible that during running, where the

stimulus for the initial microtrauma to the musculoskeletal system is greater, a local

acute inflammatory response may occur. Finally, subjects in the present study were

trained endurance athletes with a moderately high fitness level and it is not known if

the results are applicable to athletes of differing fitness levels.

Serotonergic responsiveness

Results show that the training protocol adopted significantly reduced performance

and increased mood disturbance, and therefore a state of overreaching was

identified. The main purpose of the study was to determine whether intensified

training, followed by a period of recovery would affect the prolactin responses to

exercise and pharmacological challenge and whether possible changes

corresponded to changes in performance. In this respect the results of the buspirone

challenge test are intriguing, in that they show an increase in 5-HT responsiveness in

the recovery period following the intensified training. Not only was this seen in the

prolactin response to the buspirone, but also in the elevated prolactin response to

exercise at the same time point during the study.

Buspirone Challenge Test

It was anticipated that the changes in performance that occurred with overreaching

and recovery would have been related to changes in PRL responses to the challenge

tests. Although total PRL release during the BCT after ITP was greater than baseline,

this was not statistically significant. However, when compared to N, the PRL

response to the BCT was significantly increased after the recovery period, at which

time performance had returned to baseline.


184

This is the first time that a buspirone challenge test has been performed in subjects

who were identified as overreached by a significant decline in performance and

which also incorporated a period of recovery. The increased prolactin response to

buspirone during recovery is similar to the previous research in chronic fatigue

syndrome patients, which showed a possible up-regulation of 5-HT receptors in this

group after buspirone administration (2, 57).

Research examining changes in receptor number and function following normal

training and/ or intensified training are limited. However, studies in rats have

indicated that either mild or chronic exercise stress resulted in sprouting of neurons

or degeneration of neurons, respectively (11, 44). It is uncertain whether the elevated

responsiveness observed during recovery are reflecting an up-regulation of receptors

as a result of decreased 5-HT activity caused by a reduction in training volume. This

decrease in 5-HT activity as a result of a lack of exercise may also explain the up-

regulation of receptor sensitivity in CFS patients. However, this is not supported by

the approximately 36% higher AUC after intensified training, suggesting that

intensified training resulted in elevated 5-HT responsiveness. While this increase was

not statistically significant a trend for increased responsiveness was observed

(p=0.1).

Prolactin Responses to Exercise

Upon completion of the recovery period PRL concentrations at the end of the TT

were significantly higher than at all other phases of training. Given that time taken to

complete the TT was not different from baseline and subjects had to complete a

given amount of work for each TT, the change in prolactin release from N to R cannot

be attributed to changes in exercise intensity and/ or duration.


185

The mechanism for the enhanced PRL release is unclear. Possibilities include a

reduction in short-loop PRL-dopamine feedback or a suppression of PRL-PRL

inhibition as a result of lower basal PRL levels (18). However, resting levels were not

significantly different throughout the study period. It is possible that an increase in 5-

HT1A receptor sensitivity was induced by the increase in training stress. This is

supported by the increase in total area under the release curve following buspirone

administration at the completion of the recovery period. Studies investigating the

involvement of 5-HT receptors in depression have suggested that post-synaptic

serotonergic transmission can be increased through an increase in post-synaptic 5-

HT1A receptor sensitivity or altering somatodendritic 5-HT1A (3).

The results of this investigation indicate that intensive training, which results in

overreaching may cause changes in 5-HT responsiveness. This is supported by the

increased PRL responses to both the BCT and exercise tests after recovery. Thus,

regardless of the nature of the challenge to the hypothalamus, i.e. either exercise or

pharmacological, a significant increase in prolactin responses, compared to that at

baseline occurred following the recovery period.

As mentioned previously, buspirone is a partial dopamine antagonist, which can also

result in the release of PRL from the anterior pituitary gland. As such it is not possible

to definitively state that the serotonergic system is entirely responsible for the

observed changes. However, the lack of change in basal PRL suggests that perhaps

DA did not change in these individuals as basal release is under mainly tonic DA

inhibition which accounts for around 90% of basal control (4).


186

CONCLUSION

In summary, questionnaires assessing mood state and tolerance to stress in athletes

were used to identify overreaching in cyclists. Furthermore, such questionnaires may

be useful in identifying the point at which overreaching develops. The results of the

study suggest that overreaching can be induced after 3-7 days of intensified training

without recovery in the group of subjects studied.

The current information regarding the immune system and overreaching seems only

to confirm the role of intensified training in immune depression. Many cell numbers

do not appear to change during overreaching and those cells that do alter appear to

simply reflect the nature of the training performed. Thus, immune parameters may

change in response to intensified training independent of whether the training results

in overreaching. Hence, the role of changes in the immune system in the aetiology of

overreaching is in doubt. This study supports the classification of training tolerance

and the categorisation of overreaching based on changes in the Gln/Glu ratio. A

lowering of the Gln/Glu ratio in conjunction with a decline in performance and altered

mood state may be a useful tool for the diagnosis of overreaching.

This is the first study to examine changes in central 5-HT responsiveness during a

period of intensified training and recovery, which also incorporated measures of

performance. Although it appears that the serotonergic system may be implicated in

overreaching, further research is needed. Future work should focus on distinguishing

the serotonergic system effects from those of the dopaminergic system. It is also

important that future studies investigate changes that may occur after recovery is

complete. This is especially critical when examining central changes as such

changes may persist after peripheral markers have returned to normal, leaving the

athlete susceptible to further fatigue symptoms.


187

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Chapter 5- Effects of intensified training on heart rate

variability and hormonal indices of neuroendocrine function

Chapter 5 Heart Rate Variability

196


• Assisted in study design and development • Recruitment of subjects • Conducted all exercise testing sessions • Recording and analysis of all heart rate variability data • Collection of blood and assaying of samples • Statistical analysis • Interpretation of data • Preparation of manuscript

Graeme I. Lancaster

• Assisted in exercise testing sessions and subject recruitment • Assistance in assaying of samples

Michael Gleeson • Assistance in assaying of samples • Assistance in revision and editing of manuscript

Asker E. Jeukendrup

• Supervision of progress • Assistance in study design and development • Assistance in data collection • Assistance in data interpretation • Assistance in revision and editing of manuscript


197

ABSTRACT

Alterations in the hypothalamic-pituitary-adrenal axis and autonomic balance have

been implicated in the fatigue and reduced performance experienced by overtrained

athletes. We examined the effect of 7 days of intensified training on performance,

mood state, heart rate variability (HRV) and hormone levels. Seven subjects

completed 1 week each of normal (N) and intensified (ITP) training and 2 weeks of

recovery training (R). Performance declined and mood disturbance increased

following ITP. Time and frequency domain measures of HRV increased from baseline

in both the supine and upright positions (Average RRI:upright:N: 904±67,

ITP:976±63ms; TP:supine:N: 7849±854, ITP: 18315±3898ms2; HFP:upright:N:

1012±307, ITP: 1401±340ms2). Following ITP there was a significant decline in both

adrenaline concentration from baseline (0.82±0.11 to 0.64±0.07nmol.l-1) and the

percentage increase in cortisol over 60 minutes of exercise (N: 44±15, ITP: 1±7%).

The increased HRV suggests a dominance of the parasympathetic system over the

sympathetic system. Autonomic imbalance in combination with decreased adrenaline

and cortisol responsiveness appears to be related to the decline in performance and

elevated fatigue apparent in overreached athletes.

Key words: Sympathetic and parasympathetic nervous system, adrenaline, cortisol,

fatigue


198

INTRODUCTION

The overtraining syndrome is the result of increased physiological and/or

psychological stress together with inadequate recovery. Increased stress disrupts the

body’s homeostatic balance and periods of regeneration are required to re-establish

homeostasis (22). Overtrained athletes are distinguished by reduced performance,

increased mood disturbance and feelings of excessive fatigue. Overreaching is often

considered short-term overtraining in which recovery occurs more rapidly and is a

common element in training programs of many elite athletes. While it appears clear

that the cause of overtraining and overreaching is related to prolonged exposure to

stressors, the underlying mechanisms for the decrease in performance and elevated

fatigue state are still unresolved. One possible explanation that was first proposed by

Israel (19) and further investigated by Lehmann et al (24) is that altered functioning of

the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system

adrenal medullary (SAM) axis may be responsible for the decreased performance in

overtrained athletes.

Two types of overtraining have been proposed (19): the parasympathetic (vagal) and

sympathetic form. In the parasympathetic form of overtraining there is said to be

strong inhibition of the sympathetic system, which results in a relative dominance of

the parasympathetic system at rest and during exercise (22). The sympathetic form

of overtraining is characterised by an increase in resting sympathetic nervous system

activity (22). It is often suggested that the sympathetic form of overtraining precedes

the parasympathetic form and thus the sympathetic form is associated with

overreaching while the parasympathic form is associated with the overtraining

syndrome (11). However, to date there is no scientific data to either prove or disprove

this theory and the sympathetic form is often associated with speed and power


199

athletes, whereas the parasympathetic form is mainly associated with endurance

athletes (11, 21).

A number of researchers have investigated changes in adrenaline and noradrenaline

as an indicator of an altered autonomic system (17, 23, 26, 29, 47, 48). Plasma

catecholamine concentrations are representative of SAM activation with respect to

exercise (45). Basal levels of circulating catecholamines have been shown to both

increase (17, 26) and decrease (24) after a period of intensified training. Urhausen et

al (46) reported no significant differences in submaximal and maximal plasma

catecholamine concentrations in overtrained athletes.

Endocrine responses to overreaching appear somewhat contradictory. Resting

cortisol has been shown to remain unchanged (10, 18, 29, 37, 47), to decline (15, 25,

42) and to increase (33) while maximal post-exercise concentrations appear reduced

(42, 46). Barron et al (5) administered an insulin-induced hypoglycaemic challenge to

assess hypothalamic-pituitary function in overtrained athletes. Overtrained athletes

had significant smaller increases in plasma growth hormone, adrenocorticotropin

(ACTH) and consequently lower cortisol concentrations in response to insulin

administration, which returned to levels similar to that of asymptomatic runners

following four weeks of rest. This suggests that there was impairment at the

hypothalamic level. Responses of hormones released as a result of pituitary

stimulation were unchanged. This demonstrated that there was no evidence of

pituitary dysfunction and hence the impairment was at the level of the hypothalamus.

However, there has been no further research to confirm or refute these results.

Heart rate variability (HRV) analysis has been used as a measure of cardiac

autonomic balance, with an increase in HRV indicating an increase in vagal

(parasympathetic) tone relative to sympathetic activity (50). Numerous studies have


200

examined the effects of training on indices of heart rate variability, with studies

showing unequivocal results (2, 3, 8, 27, 28, 31, 35, 39, 40, 43). To date, few studies

have investigated heart rate variability in overreached or overtrained athletes, with

studies showing either no change (15, 49), inconsistent changes (50) or changes in

parasympathetic modulation (16).

Hedelin et al (15) increased the training load of 9 canoeists by 50% over a 6-day

training camp. Running time to fatigue, VO2max, submaximal and maximal heart

rates and maximal blood lactate production all decreased in response to the

intensified training; however, all indices of HRV remained unchanged. On average,

there were no significant changes in low frequency power, high frequency power,

total power or the ratio of low to high frequency power, both in the supine position

and after head-up tilt. Similarly, Uusitalo et al (49) reported no change in intrinsic

heart rate and autonomic balance in female athletes following 6-9 weeks of

intensified training. This involved the investigation of autonomic balance assessed by

pharmacological vagal and ß-blockade. In addition, both the time domain and power

spectral analysis in the frequency domain were calculated during rest and in

response to head-up tilt (50). Results suggest that heart rate variability in the upright

position had a tendency to decrease in response to intensified training in the subjects

who were identified as overtrained (50). This may indicate vagal withdrawal and/or

decreased sympathetic activity. However, between-subject variability was high in this

investigation.

Finally, Hedelin et al (16) reported increased heart rate variability and decreased

resting heart rate in a single overtrained athlete when compared to baseline

measures. In comparison to normally responding subjects examined during the same

period, the overtrained subject exhibited an increase in high frequency and total


201

power in the supine position during intensified training, which decreased after

recovery. The increase in high frequency power was suggested to be most likely the

result of increased parasympathetic activity (16).

Highly controlled and monitored studies that examine possible changes in heart rate

variability following overreaching are lacking. The present study was undertaken to

determine whether intensified training that results in overreaching is accompanied by

changes in heart rate variability. In addition, submaximal heart rate, plasma cortisol

and adrenaline concentrations were determined to identify possible changes that

may reflect autonomic balance. As exercise duration and intensity plays an

important role in hormone release, constant load ride to exhaustion tests were

performed. This allows the determination of possible changes at a pre-determined

submaximal time point during fixed intensity exercise, which controls for changes in

total exercise duration due to fatigue following intensified training. It is hypothesized

that intensified training that results in overreaching will result in a decrease in time

and frequency domain measures of heart rate variability characteristic of the

sympathetic form of overtraining.


202

METHODS

Subjects

Seven male endurance trained cyclists (Age:29.7 ± 1.5 yr; Body Mass: 74.7 ± 3.3 kg;

VO2max: 61.9 ± 1.3 ml.kg-1.min-1) gave written consent to participate in the study,

which was approved by the South Birmingham Local Research Ethics Committee.

Study Design

Subjects completed 4 weeks of training consisting of one week of normal training (N),

one week of intensified training (ITP) and two weeks of recovery training (R).

Training





were downloaded to a computer using the Polar Interface. From this information

average heart rate (HR), maximum heart rate (HRmax) and time spent in each of the

predetermined heart rate zones could be calculated and verified against the training

diary.

Training zones, based on exercising heart rate were classified as follows:


• Zone 2 69% - 81% HRmax

• Zone 3 82% - 87% HRmax

• Zone 4 88% - 94% HRmax



203

Subjects’ training zones were calculated from their individual lactate and heart rate

curves derived from a maximal incremental cycle test, described elsewhere (14). Five

training zones were calculated and expressed as percentages of individual maximum

heart rate. Subject’s training programs for the intensive training week were based on

their current amount of training in the baseline period. In the intensified training

periods the researchers aimed to double the total training volume and to specifically

increase the amount of time the subjects trained in zones 3, 4 and 5. The majority of

the increase in training volume was designed to be in the form of high intensity

training.

Performance Assessment

On three occasions, during N, at the end of ITP and at the end of R, subjects

performed a ride at a constant power output until volitional exhaustion. During each

trial, subjects cycled at 62.5 ± 1.1% of peak power output (Wmax) determined from

an initial maximal incremental cycle test. Subjects performed with a 10 minute warm-

up consisting of 5 minutes at 35% Wmax and a further 5 minutes at 45% Wmax.

Mood state

Subjects completed the 65-question version of Profile of Mood States (POMS)

questionnaire at the end of each week. A global score was calculated by adding the 5

subscales representing negative mood state (tension, depression, anger, fatigue and

confusion) and subtracting the one positive mood state subscale (vigour). A constant

of 100 was added to avoid negative scores (32).

Blood Sampling

On the morning of the experimental trials, subjects arrived at the laboratory after an

overnight fast and an indwelling 21g Teflon catheter (Baxter, Norfolk, UK) was


204

inserted into an antecubital forearm vein. Subjects then rested quietly for a period of

20 minutes after which time the first blood sample was drawn. Blood samples were

collected every 10 minutes up to and including the 60 minute time point and at

volitional fatigue for the measurement of plasma lactate and glucose concentrations.

Resting, 60 minute and maximal (immediately post-exercise) blood samples were

additionally assayed for adrenaline and cortisol. Plasma adrenaline was determined

by an enzyme linked immunosorbant assay (ELISA) (IBL, Hamburg, Germany).

Plasma cortisol concentrations were also determined by an ELISA assay (DRG

Instruments, Germany).


Prior to the commencement of each ride to exhaustion, heart rate variability was

assessed using the Polar R-R Recorder (Polar Electro Oy, Kempele, Finland). Each

subject wore a chest belt wired to the R-R Recorder and QRS-signal wave-form (R-R

signal) was sampled at the resolution of 1 ms. Sampling was performed during 15

minutes of supine rest followed by 5 minutes of standing upright. From QRS-signal

waveform average of all normal RR intervals in ms, standard deviation of RR

intervals in ms (SDRRI), square root of the mean of the squared differences between

adjacent RR intervals in ms (RMSSD) and percentage of differences between

adjacent RR intervals greater than 50 ms (pNN50) were calculated.

From quantitative two-dimensional vector analysis, the standard deviation of the

continuous long-term RR interval variability (SD2; in ms) and the instantaneous beat-

to-beat RR interval variability (SD1; in ms) were determined. Essentially a

scattergram (Poincaré Plot) is created in which each R-R interval is plotted as a

function of the previous R-R interval (44). Instantaneous beat-to-beat variability is


205

mediated by vagal activity on the sinus node and thus is representative of

parasympathetic activity (44).

The spectral power density of 0.00-0.04 Hz (very low frequency -VLF), 0.04-0.15 Hz

(low frequency -LF), 0.15-0.4 Hz (high frequency –HF), 0.00-0.4 Hz (total power-TP)

and LF/HF ratio were also calculated using Fast Fourier transformation.


Data was analysed with the use of one-way analysis of variance with repeated

measures and least significant difference comparison was performed to identify

significant differences between the individual means. The levels of significance was

set at p<0.05. All data are presented as mean ± SEM.


206

RESULTS

Training

On average, subjects completed 10hr 12min (± 43min) during N, 16hr 45 (± 1hr

38min) during ITP and a total of 6hr 47min (± 21min) in the two recovery weeks. This

increase in total duration included a 55% increase in training at heart rates above

82% HRmax.

Exercise capacity significantly declined 13 ± 11% following ITP from 115 ± 7min to 85

± 9min at the end of intensified training. Following recovery, performance increased

above that of after ITP, but did not return to baseline levels (107 ± 11min) (Figure

1a).

Mood State

Global Mood State assessed by the POMS-65, significantly increased during ITP and

then decreased following R (Figure 1b). The subscales of the POMS-65 remained

unchanged with the exception of fatigue, which was significantly increased.


207

Figure 1- Percentage change in time to fatigue (a) and change in Profile of Mood

States (b) during normal, intensified and recovery training. ‘N’ signifies significantly

different to normal training. ‘R’ signifies significantly different to recovery training.

0

20

40

60

80

100

120

140

160

Training

Glo

bal P

OM

S Sc

ore


b

N, R

-30-25-20-15-10-505

101520

% C

hang

e

a

N, R


208


All time domain measures of HRV increased from baseline following ITP in both

supine and upright conditions (Table I), with the exception of pNN50, which was

unchanged in the supine position. Although almost all indices of HRV increased from

baseline (Tables I and II), due to the high between-subject variability, statistically

significant increases were observed only in average RRI (upright), SDRRI (supine),

SD1 (upright), SD2 (supine) RMSSD (upright) (Figure 2), TP (supine), VLF (supine)

and LF (supine) (Figure 3). Significant decreases in the percentage change of

frequency domain measures following ITP were observed. The change in TP, VLF

power and LF power in response to standing upright was significantly reduced after

ITP (Table III).

Adrenaline

Resting adrenaline concentrations were unaltered over the 4-week period (p= 0.256).

Plasma adrenaline concentrations after 60 minutes of exercise and immediately post-

exercise were significantly lower after ITP (Table IV).

N ITP R

Average RRI (ms)- supine 1185 ± 92 1216 ± 99 1174 ± 73

Average RRI (ms)- upright 904 ± 67 976 ± 63 *† 891 ± 58

SDRRI (ms)- supine 81 ± 5 127 ± 22 * 108 ± 11

SDRRI (ms)- upright 124 ± 14 144 ± 21 119 ± 13

Index SD1 (ms)- supine 47 ± 5 69 ± 15 54 ± 6

Index SD1 (ms)- upright 35 ± 5 47 ± 6 *† 35 ± 3

Index SD2 (ms)- supine 103 ± 7 159 ± 23 * 142 ± 15

Index SD2 (ms)- upright 171 ± 19 206 ± 28 159 ± 18

RMSSD (ms)- supine 67 ± 7 95 ± 19 76 ± 9

RMSSD (ms)- upright 50 ± 7 68 ± 8 *† 49 ± 4

pNN50 (%)- supine 20 ± 2 19 ± 2 21 ± 3

pNN50 (%)- upright 13 ± 2 15 ± 2 12 ± 2

Table 1- Time domain measures of heart rate variability during normal, intensified and recovery training. * indicates significantly different to

Normal training. † indicates significantly different from Recovery training.

N ITP R

TP (ms2)- supine 7849 ± 854 18315 ± 3898 * 16190 ± 3584

TP (ms2)- upright 28442 ± 5852 37152 ± 9630 26650 ± 6825

VLFP (ms2)- supine 4352 ± 663 11647 ± 2619 * 11446 ± 3307

VLFP (ms2)- upright 22952 ± 5165 30915 ± 8675 21755 ± 6551

LFP (ms2)- supine 1653 ± 299 3512 ± 802 * 2584 ± 518

LFP (ms2)- upright 4479 ± 532 4836 ± 884 4239 ± 431

HFP (ms2)- supine 1844 ± 283 3159 ± 1044 2160 ± 572

HFP (ms2)- upright 1012 ± 307 1401 ± 340 † 656 ± 123

LF/ HF - supine 112 ± 34 153 ± 31 176 ± 44

LF/ HF - upright 753 ± 191 405 ± 59 774 ± 137

Table 2- Frequency domain measures of heart rate variability during normal, intensified and recovery training. * indicates significantly

different to Normal training. † indicates significantly different from Recovery training.


N ITP R

% Change in TP (ms2)

from supine to upright 248 ± 70 86 ± 34 *† 75 ± 14

% Change in VLFP (ms2)

from supine to upright 44 ± 6 27 ± 6 *† 27 ± 7

% Change in LFP (ms2)

from supine to upright 192 ± 58 50 ± 35 * 99 ± 50

% Change in HFP (ms2)

from supine to upright -51 ± 17 -46 ± 14 -66 ± 10

% Change in LF/HF from

supine to upright 692 ± 177 261 ± 95 845 ± 442

Table 3- Percentage change in frequency domain measures of heart rate variability after movement from the supine position to upright,

during normal, intensified and recovery training. * indicates significantly different to Normal training. † indicates significantly different from

Recovery training.


212

Figure 2- Changes in average RRI (ms) during upright (a), SDRRI (ms) in the supine

position (b), SD1 (ms) during upright (c), SD2 (ms) in the supine position (d) and

RMSSD (standard deviation of RR intervals) during upright during normal, intensified

and recovery training . ‘N’ signifies significantly different to normal training. ‘R’

signifies significantly different to recovery training.

30

35

40

45

50

55

60

Training

SD

1- S

tand

ing

(ms)


N,R

c

40

45

50

55

60

65

70

75

80

Training

RM

SS

D- S

tand

ing

(ms)


N, R

e

50

75

100

125

150

175

200

SD

2- L

ying

(ms)

d

N

b

40

60

80

100

120

140

160

180

SD

RR

I- ly

ing

(ms)

N

800

850

900

950

1000

1050

1100A

v R

RI-

Sta

ndin

g (m

s)

N, R


213

Figure 3- Changes in total power (ms2), very low frequency power (ms2) and low

frequency power (ms2) in the supine condition during normal, intensified and

recovery training. ‘N’ signifies significantly different to normal training. ‘R’ signifies

significantly different to recovery training.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Training

LF P

ower

Lyi

ng (m

s2 )

c

N


50007000

900011000

1300015000

1700019000

2100023000

25000

Tota

l Pow

er L

ying

(ms2 )

a

N

2000

4000

6000

8000

10000

12000

14000

16000

VLF

Pow

er L

ying

(ms2 )

b

N


214

Heart rate, lactate, glucose and cortisol concentrations

There was a trend for a decrease in resting heart rate, however statistical

significance was not reached (p= 0.07). Resting heart rate decreased from 53 ± 4 at

N to 51 ± 5 after ITP and returned to 53 ± 4 bpm after R. Average HR throughout the

ride to exhaustion declined approximately 2% after IT (Table IV). Plasma lactate

concentration was lower at all time points after ITP in both trials, however this was

not statistically significant (Table IV). Plasma glucose concentration was not

significantly different after ITP; however, concentrations were lower than both

baseline and recovery measurements after 60 minutes of the ride to exhaustion

(Table IV). Resting plasma cortisol concentrations were unchanged over the training

period and were not different between trials. However, cortisol concentration was

significantly lower at all other time points during the ride to exhaustion after ITP (i.e.,

after 60 minutes of exercise, the end of exercise and 1 hour post exercise). The

percentage increase in cortisol over 60 minutes of exercise (i.e. from baseline to the

60 minute time point) was significantly reduced after ITP (Table IV).

N ITP R

Heart Rate- submaximal

(bpm) 157 ± 5 154 ± 4 *† 157 ± 6

Lactate- submaximal

(mmol.l-1) 2.36 ± 0.42 1.87 ± 0.25 2.14 ± 0.48

Glucose- submaximal

(mmol.l-1) 4.66 ± 0.06 4.28 ± 0.14 4.81 ± 0.02

Cortisol- % increase over 60

minutes of exercise 44 ± 15 1 ± 7 *† 12 ± 8

Adrenaline- resting

(nmol.L-1) 0.51 ± 0.04 0.52 ± 0.02 0.48 ± 0.03

Adrenaline- submaximal

(nmol.L-1) 0.82 ± 0.11 0.64 ± 0.04 *† 0.89 ± 0.09

Adrenaline- maximal

(nmol.L-1) 1.08 ± 0.18 0.68 ± 0.05 *† 1.36 ± 0.20

Table 4- Changes in submaximal (i.e. after 60 minutes of constant work) heart rate, lactate, glucose and cortisol concentrations and

resting, submaximal and maximal plasma adrenaline during normal, intensified and recovery training.† indicates significantly different from

Recovery training.


217

DISCUSSION

Reduced exercise capacity in combination with increased mood disturbance following

intensified training and a return to baseline or near baseline values after recovery,

support the classification of all athletes in this investigation as overreached.

Measures of heart rate variability including: average RRI (upright), SDRRI (supine),

SD1 (upright), SD2 (supine) RMSSD (upright), TP (supine), VLF (supine) and LF

(supine), were significantly elevated above normal values, during both supine and

upright conditions, after intensified training. This suggests an increase in the relative

contribution of parasympathetic to sympathetic activity.

Over 25 years ago Israel (19) suggested an increase in parasympathetic nervous

system activity relative to sympathetic activity in overtrained athletes. Research

examining this possibility has focused on alterations in urinary and plasma

catecholamine concentrations (18, 23, 26, 48). The parasympathetic form of

overtraining is also referred to as Addison type as the clinical pattern is similar to

adrenal insufficiency (Morbus Addison) (24). Lehmann et al (24) has reported the

effects of high volume endurance training on indices of sympathetic activity. A

decreased intrinsic sympathetic activity compared to baseline is suggested,

supported by reduced heart rates, increased or decreased submaximal plasma

noradrenaline concentrations, decreased adrenaline concentrations and decreased

metabolic responses (plasma lactate and glucose concentrations) (24, 45). Our

findings of reduced heart rates, reduced plasma lactate and plasma glucose

concentrations after 60 minutes of constant work, in combination with a reduction in

performance after intensified training, support the previous suggestion of decreased

sympathetic activity in overreached athletes. Additionally, the parasympathetic form

of overtraining is reported to be characterized by a reduction in cortisol responses to


218

exercise after intensified training, as observed in the present study, or following

insulin-induced hypoglycemia (5, 24).

Recently, Armstrong and Van Heest (4) provided insights into the mechanism of

overtraining by investigating the similarities between overtraining and major

depression. The mechanism by which intensified training causes decreased

performance, mood disturbance and fatigue is suggested to be related to the

exposure of the body to environmental or internal stressors (4). Such exposure

evokes the activation of the SAM axis and the HPA axis. The responses of these

axes are synergistic and are intricately involved in the regulation of fuel metabolism

and the cardiovascular system through their principal hormones- adrenaline,

noradrenaline and cortisol (4). The increases in heart rate variability measures and

decreases in adrenaline, cortisol, lactate and glucose concentrations provide indirect

evidence of changes in SAM and HPA axes.

Heart rate variability analysis is proposed to delineate parasympathetic and

sympathetic influences on autonomic tone (38) and is reported to be one of the most

practical and reliable tools for the measurement of sympathetic and vagal activity (1).

It is well documented that vagal activity is predominant contributor to the HF

component of heart rate variability, however physiological interpretation of LF and

VLF power is still uncertain (1) and caution is needed when interpreting such data.

Previous research investigating changes in heart rate variability following intensified

training have provided inconclusive results. Of major concern has been the accurate

determination of a state of overreaching, identified by a decline in performance

following intensified training. In the present investigation exercise capacity was

measured prior to intensified training, following intensified training and upon


219

completion of recovery. Additionally, all training was controlled and monitored and

mood state was assessed regularly. The decline in performance in combination with

an increase in mood disturbance allows the confirmation of a state of overreaching in

the athletes in the present study.

Previous investigations have reported no change in heart rate variability after

intensified training (15, 49), an increase in low frequency power in the supine position

(50) and cardiac autonomic imbalance with increased parasympathetic modulation

(16). The lack of change in heart rate variability reported by Hedelin et al (15) in

comparison to the present study, may be related to the relatively low degree of high

intensity training (25% of total training load) performed by subjects and additionally

the subjects were international standard canoeists who may have tolerated the

increased training load more successfully. No changes in intrinsic heart rate or

cardiac autonomic modulation were observed in female athletes (49); however,

comparisons to this study are limited as the authors utilized pharmacological

blockade (graded atropinisation followed by graded β- blockade) to determine

possible changes. However, when heart rate variability was assessed in the same

subjects (50) using traditional ECG methods, a slight increase in low frequency

power was observed, with no changes in other variables. Performance and mood

state was not reported in this study and thus it cannot be determined if the subjects

were indeed overreached. Finally, in an athlete diagnosed as overtrained, large

increases in high frequency power and decreases in low frequency power were

observed, which suggests parasympathetic dominance (16). Although this

investigation was based on a single athlete, large changes were observed in

parameters that suggest increased parasympathetic activity, which is similar to the

present results.


220

The increases in almost all measures of heart rate variability and the significant

decline in submaximal heart rate indicates an increased vagal modulation of heart

rate in overreaching. The increase in total and high frequency power following ITP is

indicative of increased vagal modulation of heart rate (1). Interpretation of changes in

LF power is difficult, as considerable controversy exists as to whether this index is

representative of sympathetic activity or a combination of both parasympathetic and

sympathetic influences (1). The increased LF power in the supine position observed

after ITP and the corresponding increases in TP and HF shows increased power in

all spectral components. An increase in all components most likely suggests an

increase in vagal activity, with the increase in LF power the result of increases in the

parasympathetic contribution to this measure. However, a decrease in sympathetic

activity alongside this increase in parasympathetic activity cannot be excluded as a

decrease in LF/HF ratio was observed in the upright position. This ratio has been

proposed to indicate sympathetic activity (1). As the physiological correlates of VLF

power are unknown and those of LF power are debatable, it is difficult to speculate

upon the significance of changes in these components of the power spectrum.

A greater influence of the parasympathetic system in heart rate responses after

intensified training is provided by the frequency spectrum changes that occurred

when position altered from the supine position to the upright position. The significant

reduction in TP, VLFP and LFP as a result of a shift in position that occurred after

ITP denotes a greater influence of the parasympathetic system.

Our finding of increased heart rate variability after intensified training appears to be in

opposition to the findings following acute exercise. Previous studies investigating the

changes in heart rate variability following acute exercise have shown persistent

sympathetic activation immediately following exercise, which returned to normal


221

following either 24 (6, 12) or 72 hours of rest (20). The increase in heart rate

variability after 7 days of intensified training is interesting as numerous studies have

reported an increase in heart rate variability in endurance-trained athletes compared

to sedentary controls (7, 9, 13, 30, 36, 38), suggesting that elevated heart rate

variability is a positive adaptation to training. This is supported by a large body of

research that suggests that elevated heart rate variability is cardioprotective (1).

Additionally, some training studies report increases in heart rate variability after

endurance training; however, this appears to be dependent on the duration of the

training program (2, 3, 8, 27, 28, 31, 35, 39, 40, 43). Generally, only training studies

longer than 12 weeks result in measurable increases in heart rate variability. The

large increases in many measures of heart rate variability in the present study may

be the result of the substantial amount of high intensity training completed and

therefore may be more related to the physiological demands of high intensity training

than to the duration of the training program per se.

Although the increased heart rate variability reported in the present investigation is in

agreement with the parasympathetic form of overtraining, this is generally thought to

only occur in athletes with the overtraining syndrome. The results of this study

suggest that perhaps the parasympathetic form of overtraining may be more related

to the type of training performed (i.e. intensive endurance training) than to either the

state of overreaching or overtraining. There have been no longitudinal studies

examining whether the sympathetic form of overtraining, suggested to be evident

during overreaching, progresses into the more serious state of overtraining which is

said to demonstrate characteristics typical of the parasympathetic form. Indeed,

symptoms associated with the parasympathetic form of overtraining have also been

reported in athletes suggested to demonstrate the sympathetic form. Thus, the


222

progression of the sympathetic to parasympathetic forms of overtraining may be an

oversimplification.

Like many other indicators of overreaching and overtraining (i.e. decreases in heart

rate and lactate), increased heart rate variability may only be used as a possible

indicator of overreaching if used in conjunction with a decrease in performance. High

inter-subject variability is also common in measures of heart rate variability and a

recent study reported that genetic factors contribute towards a large proportion of the

variation in heart rate variability (41). Therefore, comparing changes to the

individual’s own baseline data is necessary.

The findings of the study may be limited to a certain extent as we decided not to

control breathing rate during heart rate variability assessment. Respiratory rate

influences HF power (1) and some debate exists as to whether breathing rate should

be controlled in longitudinal studies or whether allowing the athlete to breath

spontaneously is more appropriate. Recent research however, has suggested that

metronome breathing and hence controlling breathing frequency may not be

necessary, as similar HF power has been reported under controlled and spontaneous

breathing conditions (34). Additionally, controlled breathing was reported to increase

mean heart rate and as such may be a form of mild stress to the subject (34).

The parasympathetic form of overtraining is suggested to relate to strong inhibition or

exhaustion of the sympathetic nervous system (22). Our finding of a decreased

submaximal heart rate provides additional evidence to suggest a reduction in

sympathetic nervous system activation during exercise. The smaller increase in

plasma cortisol during exercise after intensified training may be explained as

negative feedback regulation in response to hypersecretion of cortisol during


223

prolonged, intense exercise (22). The reduction in hormonal release may be viewed

as a protective mechanism against exhaustion of the endocrine system. Reductions

in growth hormone and cortisol in response to insulin-induced hypoglycemia have

previously been reported in overtrained athletes (5); however, it is not clear whether

the decreased cortisol release found in some overreached and overtrained athletes

(25, 42, 46) is the result of hypothalamic dysfunction (i.e. ACTH release) or of the

target organ itself (i.e. adrenal responsiveness). Exposure to exercise stress leads to

increases in cortisol and catecholamine release during exercise and continual

exposure without adequate recovery may lead to a decrease in adrenal

responsiveness and a decrease in tissue sensitivity via a fall in the density of

adrenoreceptors (45). These adaptations may occur to counteract the negative

effects of prolonged exposure to exercise-induced increases in cortisol and

catecholamine release and most likely serves as a protective mechanism against

fatal exhaustion (22).

In summary, our data demonstrate that intensified training with inadequate recovery

over a 7-day period results in overreaching, identified by decreased performance and

increased mood disturbance. Alongside these changes, increased heart rate

variability, decreased submaximal adrenaline and decreased submaximal heart rate

after intensified training may suggest a decrease in sympathetic nervous system

activity and changes in autonomic tone. The reductions in cortisol concentration also

after intensified training suggest alterations in the hypothalamic-pituitary-adrenal axis.

Overreaching and overtraining may be characterized by autonomic imbalance and

disturbance of the sympathetic-adrenal medullary and the hypothalamic-pituitary-

adrenocortical axes.


224

Acknowledgements We are extremely grateful for the enthusiasm and cooperation of the subjects who

completed this study. We also acknowledge Martin Whitham and Meg McLellan for

assistance in data collection.

This study was funded by a research grant from GlaxoSmithKline Consumer

Healthcare, UK.


225

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Chapter 6- Effects of carbohydrate supplementation on

performance and substrate utilization following intensified

training

Chapter 6 Carbohydrate supplementation during overreaching

231


• Assisted in study design and development • Recruitment of subjects • Conducted all exercise testing sessions • Collection of blood and assaying of samples • Statistical analysis • Interpretation of data • Preparation of manuscript

Graeme I. Lancaster

• Assisted in study design and development • Recruitment of subjects • Conducted all exercise testing sessions • Collection of blood

Michael Gleeson

• Assistance in assaying of samples • Assistance in revision and editing of manuscript

Asker E. Jeukendrup

• Supervision of progress • Assistance in study design and development • Assistance in data collection • Assistance in data interpretation • Assistance in revision and editing of manuscript


232

ABSTRACT

To study the effects of carbohydrate (CHO) supplementation on performance

changes and symptoms of overreaching, six endurance cyclists completed one week

of normal (N), one week of intensified (ITP) and two weeks of recovery training (R)

on two separate occasions in a randomized cross-over design, separated by a wash-

out period. Subjects completed one trial with a 6% CHO solution provided before

and during training and a 20% solution in the one hour post exercise (H-CHO trial).

On the other occasion subjects consumed a 2% CHO solution at the same time

points. A significant decline in endurance capacity (H-CHO:17±3%; L-CHO: 26±7%)

and a significant increase in mood disturbance (H-CHO:11±5%; L-CHO: 31%±14)

occurred in both trials after ITP. The decline in performance was significantly greater

in the L-CHO trial. After ITP a significant decrease in CHO oxidation (H-CHO: N:

166±8g: ITP: 129±9g; L-CHO: N: 163±8g: ITP: 129±13g) and increase in fat

oxidation (H-CHO: N: 20±3g: ITP: 32±3g; L-CHO: N: 20±3g: ITP: 31±5g) occurred

alongside significant increases in glycerol and free fatty acids and decreases in free

triglycerides in both trials. A trial X diet effect was observed for submaximal plasma

concentrations of cortisol, prolactin and adrenaline, with significantly greater

reductions in these stress hormones in the L-CHO trial when compared to H-CHO

after ITP. These findings indicate that carbohydrate supplementation can reduce

many of the symptoms of overreaching, but cannot prevent the development of

overreaching in cyclists. Decreased cortisol responsiveness to exercise may be

implicated in the decreased performance and increased mood disturbance

characteristic of overreaching.


233

INTRODUCTION

Intensified training in combination with inadequate recovery can result in a decrement

in performance that may be short-term (overreaching) or long-term (overtraining).

Whilst training stress and a disturbance in homeostasis is generally accepted to be

the precipitating factor leading to overreaching and overtraining, the underlying

mechanism remains unknown. A number of hypotheses have been suggested

including autonomic imbalance (18), neuroendocrine disturbances (1), influence of

plasma cytokines (25) and glycogen depletion (26). The glycogen depletion

hypothesis proposes that the high intensity training with limited recovery periods may

result in reduced muscle glycogen levels, which may impair performance (26).

It has long been known that muscle glycogen depletion results in fatigue and a

reduction in performance (15). The effects of repeated bouts of high intensity

exercise on muscle glycogen stores are also well established (5). The effect of high

carbohydrate (CHO) diets during periods of normal and intensive training on

performance has been less well established (13). Jacobs and Sherman in a review

on the efficacy of CHO supplementation and chronic high CHO diets for improving

endurance performance, suggest that a high CHO diet may be necessary for optimal

adaptations to training (13).

The impact of periods of training in which CHO intake was manipulated are

conflicting, with no changes in performance reported by Sherman et al (23) and

dramatic changes found by Bergstrom et al (2). Both of the above studies involved

altering the diet without changing the subjects training volume. However, the amount

of CHO in the diet may play a more critical role in performance ability when training

volume is increased and thus the reliance on CHO as fuel during exercise is also

increased. Simonsen et al (24) intensely trained rowers for a period of 4 weeks and


234

examined the effects of consuming either a 5g CHO.kg-1.day-1 diet or a 10g CHO.kg-

1.day-1 diet. The athletes on the moderate CHO diet maintained muscle glycogen

content, while those on the high CHO diet increased muscle glycogen content by

65% (24). Both groups showed an increase in performance following the increased

training, however the group consuming the moderate CHO diet had a 2%

improvement in average power output during a rowing time trial and the high CHO

diet group had an average 11% performance improvement. This study indicates the

importance of CHO in the optimal adaptation to training and the resultant

enhancement of performance. Athletes in this study did not demonstrate a reduction

in performance and although the intensity of training was increased, the athletes

cannot be considered overtrained or overreached and thus extrapolation to the

effects of a high diet during overtraining is not possible.

As overreaching and/ or overtraining is commonly brought about by high intensity

training with limited recovery, it is perceivable that the fatigue and underperformance

associated with overtraining is at least partly attributable to a decrease in muscle

glycogen levels. Previous research has reported reduced submaximal lactate

concentrations (14, 17, 27), reduced blood glucose concentrations (8) and reduced

maximal respiratory exchange ratios (27, 28).

Costill et al (6) investigated the effects of 10 days of increased training volume on

performance and muscle glycogen levels. Of the 12 swimmers participating in the

investigation, 4 were unable to tolerate the increase from 4000 metres per day to

9000 metres per day and were consequently classified as non-responders. The

group of non-responders consumed approximately 1000 kcal per day less than their

estimated energy requirement and consumed less carbohydrate than the responders.

However, importantly, muscular power, sprint swimming ability and swimming

endurance ability were not affected in either the responders, or the non-responders.


235

Costill et al (6) concluded that the glycogen levels of the non-responders were

sufficient to maintain performance, but inadequate for the energy required during

training and thus fatigue resulted. As overreaching and overtraining are primarily

defined by a reduction in performance, the ability to ascertain whether the non-

responders were indeed overreached or overtrained is limited.

These findings directed Snyder et al (27) to examine performance responses to

intensified training with the addition of sufficient dietary carbohydrate, in a bid to

determine whether overreaching could still occur in the presence of normal muscle

glycogen levels. To ensure sufficient carbohydrate intake, subjects consumed 160g

of liquid carbohydrate in the two hours following exercise. Subjects completed 7 days

of normal training, 15 days of intensified training and 6 days of minimal training.

Resting muscle glycogen was not significantly different from baseline after intensified

training. Subjects were reported to be overreached, however maximal power output

during an incremental cycle test was not statistically different after intensified training.

Additionally, a control group with normal or lower dietary CHO was not incorporated

and thus the comparative role of CHO and diet in changes in performance during

overreaching is unknown.

It is hypothesised that CHO supplementation before, during and following training

during a 7 day intensified training period will not prevent a decline in performance

characteristic of overreaching. However, when compared to a low CHO trial, high

CHO supplementation will result in a relatively smaller decrease in performance.

Additionally, the change in variables associated with overreaching, such as mood

state, heart rate and hormone concentrations will be attenuated with a high CHO

intake. The present study examined the metabolic effects of carbohydrate

supplementation and the impact of carbohydrate availability on cycling performance

before a period of overreaching, immediately following overreaching and following a


236

period of recovery. The study was a randomised, double blind, placebo-controlled

design.

METHODS

Subjects:

Six endurance-trained cyclists (age 29.7 ± 1.5 yr, VO2max 61.9 ± 1.3 ml.kg-1.min-1,

weight 74.7 ± 3.3 kg) participated in this study. The nature and risks of the

experimental procedures were explained and written informed consent was obtained.

The study was approved by the South Birmingham Local Research Ethics

Committee.

Experimental Design:

All subjects completed two, four-week training periods. Each training period

consisted of one week of normal training (N), eight days of intensified training (ITP)

and two weeks of recovery (R). A washout period of at least two weeks was provided

between training periods. During each training period subjects were provided with

carbohydrate in liquid form to be consumed prior to, during and immediately following

all training sessions during ITP. Different concentrations of CHO solutions were

provided during each training period, with subjects receiving either high (H-CHO) or

low (L-CHO) concentration solutions. During H-CHO trials subjects received 500 ml

of a 6.4% solution prior to each training session and consumed an additional 500 ml

of this solution for each hour of training performed. During the first hour immediately

following each training session a more concentrated carbohydrate beverage (20%)

was supplied. Subjects consumed 1000 ml of this solution and were prohibited from

consuming other fluids or food during this one hour immediately following training. In

the L-CHO condition subjects consumed a 2% CHO solution in the same volumes

and at the same time points before, during and following training sessions. Subjects


237

completed trials in random order and both subjects and researchers were blinded to

CHO treatment.

Training Procedures:

Subjects were asked to complete and record a typical training week during N. Each

athlete was provided with a Polar Vantage NV heart rate monitor (Polar Electro Oy,

Kempele, Finland) and a training diary to monitor and record all training sessions.

Subjects were required to train on all eight days of ITP. And were given a training

program consisting of high intensity interval sessions, lasting approximately 3-4

hours per session. Intensity of training was set at percentages of individual maximum

heart rates achieved during an incremental cycling test to volitional fatigue. These

training zones (1-4) were based on previous work in our laboratory (11) and equated

to:


• Zone 2 69% - 81% HRmax

• Zone 3 82% - 87% HRmax


Experimental Trials:

During each four-week training period subjects completed three maximal cycle

ergometer tests to volitional fatigue (MT) and three ride to exhaustion tests (RE). The

three RE occurred immediately prior to and immediately following ITP and upon

completion of the recovery period. Each RE was performed on the day immediately

following the MT. All subjects completed a habituation MT and RE prior to the

commencement of the study.


238

Maximal Cycle Ergometer Test

Subjects attended the laboratory after an overnight fast and a Teflon catheter

(Becton Dickinson, Quickcath) was inserted into an antecubital vein. Following this,

the subjects performed an incremental test to exhaustion on an electrically braked

cycle ergometer (Lode Excalibur Sport, Groningen, The Netherlands) to determine

maximal power output (Wmax), submaximal and maximal oxygen consumption and

heart rate throughout the test.

Resting data was collected before subjects began cycling at 95 Watts for three

minutes. The load was increased by 35 Watts every 3 minutes until volitional

exhaustion. Expiratory gases were collected and averaged over a 10 second period,

using a computerised on-line system (Oxycon Alpha, Jaeger, Bunnik, The

Netherlands). Heart rate was recorded throughout the exercise test using a heart rate

monitor (Vantage NV, Polar, Finland). Rating of Perceived Exertion (RPE) was

recorded at the end of each stage, using the Modified Borg Scale (4). Blood samples

were collected at rest, in the last 30 seconds of each stage and immediately following

the cessation of the test for the determination of blood lactate.

Exercise Capacity (EC) Test

Subjects again reported to the laboratory after an overnight fast and a Tethlon

catheter was inserted into an antecubital vein and following 30 minutes rest a 30 ml

blood sample was taken. During each trial, subjects cycled at 62.5 ± 1.1% Wmax

determined from the initial MT, which equated to 74.0 ± 1.9% VO2max. Subjects were

provided with a 10 minute warm-up consisting of 5 minutes at 35% Wmax and a

further 5 minutes at 45% Wmax. During each test subjects received no feedback

regarding duration or heart rate.


239

Oxygen (VO2) and carbon dioxide (VCO2) production and respiratory exchange ratio

(RER) were measured during the final 5 minutes of each 10-minute period during the

first hour of exercise. Heart rate and RPE were recorded at the end of each 10-

minute period during the first hour of exercise. Blood samples were also collected at

these time points for the measurement of plasma lactate, glucose, glycerol, free fatty

acids and free triglycerides. At the 60-minute time point and upon volitional

exhaustion samples were also collected for the determination of catecholamines,

prolactin and cortisol. Subjects were required to remain in the laboratory in the first

hour following cessation of the RE, during which only water was consumed. A final

blood sample one-hour post exercise was taken for the measurement of cortisol and

prolactin.

All subjects were given instructions on measuring, weighing and recording food

intake and were asked to document food intake on a number of occasions. Firstly,

subjects were asked to complete a three-day record during N, consisting of two

weekdays and one weekend day. This was used to determine habitual dietary intake.

Secondly, food intake was recorded on the day prior to each RE and finally, during

the eight days of ITP. Subjects were requested to consume their usual diet during the

periods when dietary intake was assessed and were instructed to consume a diet as

similar as possible before each testing session. Caloric and micronutrient intake was

determined using the CompEat Version 5.6 (Nutrition Systems, UK).

During each day of the study subjects completed the short version of the Profile of

Mood States (POMS) (10) and the Daily Analysis of Life Demands of Athletes

(DALDA) (21) questionnaires. In addition, subjects completed the 65-question

version of the POMS (19) prior to ITP, immediately following ITP and upon

completion of R.


240

Analytic techniques:

Ten ml of blood was collected into K3EDTA tubes and centrifuged at 1500g for 10

minutes at 4°C; plasma was immediately frozen in liquid nitrogen and stored at -80°C

for analysis of glucose (Sigma Diagnostics, Dorset, UK), lactate (Sigma Diagnostics,

Dorset, UK), free fatty acids (Wako chemicals, Richmond, USA) and glycerol (Sigma

Diagnostics, Dorset, UK) which was performed on a semi automatic analyser

(COBAS BIO, Roche, Switzerland). To determine the triglycerides concentration in

plasma, lipoprotein lipase (LL) was added to the plasma samples to hydrolyse the

triglycerides. By subtracting the free glycerol concentration from total glycerol

concentration, true triglyceride concentration was determined.

Aliquots of plasma were frozen at -20°C until analysis of cortisol, adrenaline, prolactin

and growth hormone. Plasma adrenaline was determined by an enzyme linked

immunosorbant assay (ELISA) (IBL, Hamburg, Germany). Plasma cortisol

concentrations were also determined by an ELISA assay (DRG Instruments,

Germany). To examine the cortisol response to exercise, the cortisol concentration at

rest was subtracted from the concentrations at exhaustion and at 60 min and these

values were compared between N, ITP and R and also across trials. Prolactin and

growth hormone were measured using an immunoradiometric assay (Skybio Ltd.,

Wyboston, Bedfordshire, UK). From carbon dioxide (VCO2) and oxygen production

(VO2), rates of carbohydrate and fat oxidation were calculated using stoichiometric

equations (7).

Statistical analyses

The metabolic and hormonal data were analysed using a three-factor analysis of

variance, where the factors were diet, trial number and time, with Tukey’s HSD


241

performed to identify significant differences between the individual means. Possible

differences in dietary intake between the H-CHO trial and the L-CHO trial were

assessed using a dependent t-test. The levels of significance was set at p<0.05. All

data are expressed as mean ± SE.

RESULTS

During the H-CHO trial, subjects completed slightly, but non-significantly, greater

training hours during ITP (17hr 33min vs. 16hr 45min per week) than during L-CHO

(Figure 1). In both trials there was an increase in training performed from baseline,

both in total hours and in each of the training zones.

During the H-CHO trial, subjects had a greater energy intake than during the L-CHO

trial (16.49 ± 0.93 vs. 12.97 ± 1.03 MJ.day-1). Subjects consumed significantly more

CHO during the CHO trial (9.4 ± 0.94 vs. 6.43 ± 0.47 g.kgbw-1) and received 70.1 ±

2.3% of total energy intake from CHO, compared to 62.1 ± 3.1% in the L-CHO trial.

Subjects consumed significantly more CHO from dietary sources during L-CHO.

During the H-CHO trial 33.9 % of CHO came from the supplied CHO drinks, in

comparison to 8.3% during the L-CHO trial. Subjects consumed similar total amounts

of fat and protein in both trials (Table 1).


242

Figure 1- Changes in Time Spent in Heart Rate Zones during normal training,

intensified training and recovery during H-CHO and L-CHO trials.

0:00

3:00

6:00

9:00

12:00

15:00

18:00

Normal Intensified Recovery Recovery

Training

Tim

e (h

h:m

m) Zone 1

Zone 2Zone 3Zone 4

H-CHO

0:00

3:00

6:00

9:00

12:00

15:00

18:00

Normal Intensified Recovery Recovery

Training

Tim

e (h

h:m

m) Zone 1

Zone 2Zone 3Zone 4

L-CHO


243

Intensified Training

(mean daily intake during ITP)

Energy CHO Fat Protein

MJ MJ/kg g g/kg %E % diet %

drinks

g %E g %E

H-CHO 16.49

*

0.22

*

686.8

*

9.40

*

70.1

*

36.3

*

33.9

*

85.5 20.3 96.0 10.0

0.93 0.02 55.0 0.95 2.3 3.8 2.1 7.4 2.2 10.0 1.4

L-CHO 12.97 0.18 473.7 6.43 62.1 53.8 8.3 85.7 24.8 103.7 13.5

1.03 0.02 30.2 0.47 3.1 2.7 0.6 13.0 2.2 13.3 1.0

Table 1- Energy intake and nutrient composition of diets during intensified training

during H-HCO and L-CHO trials. % diet, percentage of energy intake from dietary

carbohydrate; % drinks, percentage of energy intake from carbohydrate drinks

supplied. * indicates significant difference between trials.

Endurance capacity significantly declined following ITP in both trials. However, upon

completion of ITP, the L-CHO trial had a greater decrease in time to fatigue than the

H-CHO trial (Figure 2). Additionally, a supercompensation effect was seen in the H-

CHO trial, with a 10.5 ± 6.4% improvement in time to fatigue upon completion of the

2-week recovery period. During the LCHO trial performance remained 13.1 ± 11.1%

below baseline at the completion of R. Absolute performance times were: H-CHO N:

96.6 ± 4.6, ITP: 80.6 ±5.0, R: 107 ± 8.3; L-CHO R: 112.2 ± 7.3, ITP: 83.2 ± 10.4, R:

97.5 ± 15.2 min)


244

Figure 2- Percentage change in time to fatigue following intensified training and

recovery. N= significantly different from normal training (H-CHO), n= significantly

different from normal training (LCHO), *= significantly different from corresponding

time point during L-CHO trial.

Average HR throughout EC declined approximately 6% after ITP in the H-CHO trial

and 2% in the L-CHO trial (Figure 3). However, statistical significance was only

attained during the H-CHO trial.

-30

-25

-20

-15

-10

-5

0

5

10

15

20

Training

% C

hang

e in

Tim

e to

Fat

igue

H-CHOL-CHO


N, *

n

N, *

n


245

Figure 3- Percent change in heart rate throughout the EC. N= significantly different

from normal training during H-CHO trial.

Rating of perceived exertion was elevated in both trials (L-CHO trial ~10%; H-CHO

trial ~2%, however, this was only statistically significant in the L-CHO trial. Following

the two week recovery period, RPE was significantly lower than baseline values in

the H-CHO trial, yet remained significantly elevated after recovery in the L-CHO trial

and an effect of diet was evident at this time point (Figure 4). Body mass and % body

fat did not change significantly from baseline throughout the study in either trial.

-7-6-5-4-3-2-10123


Training

% C

hang

e in

Hea

rt R

ate

HCHOLCHO

N


246

Figure 4- Percentage change in rating of perceived exertion following intensified

training and recovery. N= significantly different from normal training (H-CHO), *=

significantly different from corresponding time point during L-CHO trial.

RER was not statistically different after ITP during the initial 5-10 minutes of the

fatigue ride in the H-CHO trial, however RER was significantly lower at this time point

during the L-CHO trial. At all other time points during EC, RER was significantly lower

after ITP than at baseline and following recovery in both trials. Similar results for

CHO oxidation were found, with a significant reduction in CHO oxidation in both trials

after ITP. Correspondingly, fat oxidation increased in both trials with significant

differences from baseline found at the 25-30, 45-50 and 55-60 minute time points.

There was no diet X trial X time effect for RER, CHO oxidation or fat oxidation. Figure

5 summarizes the RER (a), CHO oxidation (b) and fat oxidation (c) for the first 60

minutes of the exercise capacity test during N, ITP and R.

-15

-10

-5

0

5

10

15

20


Training

% C

hang

e in

RPE

afte

r 60

min

HCHOLCHO

n

n,*


247

Figure 5- RER (a), CHO oxidation (b) and fat oxidation (c) for the first 60 minutes of

the exercise capacity test during N, ITP and R during H-CHO trial (left) and L-CHO

trial (right). N= significantly different from normal training, R= significantly different

from recovery.

0.84

0.87

0.90

0.93

0.96

0.99

0 10 20 30 40 50 60

RER

N, R

L-CHO Trial

2.0

2.4

2.8

3.2

3.6

4.0

0 10 20 30 40 50 60

CHO

Oxi

datio

n (g

.min

-1)

2.0

2.4

2.8

3.2

3.6

4.0

0 10 20 30 40 50 60

CH

O O

xida

tion

(g.m

in-1

)

b

N, R N, R

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60

Time

Fat O

xida

tion

(g.m

in-1

)

N ITP R

c

N, R

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60

Time

Fat O

xida

tion

(g.m

in-1

)

N ITP R

N, R

0.84

0.87

0.90

0.93

0.96

0.99

0 10 20 30 40 50 60

RER

N, R

a

H-CHO Trial


248

Whole-body fat and carbohydrate oxidation derived from gaseous exchange is

summarized in Figure 6. Fat oxidation increased (p= 0.011) with a concomitant

decrease in carbohydrate oxidation decreased (p=0.010) in both trials with no

significant effect of diet.

Figure 6- Estimated contribution of fat and carbohydrate oxidation to substrate

oxidation during the first 60 minutes of EC during H-CHO (left) and L-CHO (right)

during normal (N), intensified (ITP) and recovery (R) training. N= significantly

different from normal training (H-CHO), n= significantly different from normal training

(L-CHO). R= significantly different from recovery training (H-CHO), r= significantly

different from recovery training (L-CHO). Values are mean ± SE for the 6 subjects.

15±5g31±5g

20±3g17±4g32±3g

20±3g

163±8g166±8g129±9g

170±10g129±13g

168±13g

0

100200

300

400500

600

700800

900

N ITP R N ITP R

Subs

trate

oxi

datio

n (k

cal/6

0 m

in)

CHOFAT

N,R

N,R

n,r

n,r

H-CHO L-HCO


249

Plasma glucose, lactate, glycerol, free triglycerides and free fatty acid concentrations

are summarized in Figures 7 and 8. Plasma lactate concentration was lower when

compared to baseline at all time points after ITP in both trials, with the exception of

resting values, which were not different and maximal concentrations at the end of EC

in the H-CHO trial. The decline in plasma lactate concentration was greater in the L-

CHO trial, however this was only statistically significant at the end of the EC (i.e.

max). Plasma glucose concentration was lower after ITP than both baseline and

recovery measurements in both trials at all time points with the exception of resting

values during the L-CHO trial and maximal values during H-CHO. Plasma glycerol

concentrations after ITP were significantly greater than normal training and recovery

in the H-CHO after the 30 minute time point and significantly higher than normal

training and recovery at all time points during the L-CHO trial. Plasma triglycerides

were significantly lower than normal training after ITP in both trials at all time points,

with the exception of maximal concentrations during the L-CHO trial. Plasma free

fatty acid (FFA) concentrations were significantly higher after ITP during H-CHO at

rest and after the 40 minute time point. During the L-CHO trial, plasma FFA

concentration was significantly higher than during normal training and recovery after

ITP at all time points and there was a significant effect of diet on plasma FFA

concentrations.


250

Figure 7- Plasma lactate (a) and plasma glucose (b) concentrations during H-CHO

(left) and L-CHO (right) after normal (N), intensified (ITP) and recovery (R) training.

N= significantly different from normal training. *= significantly different from

corresponding time point during L-CHO trial.

0.5

1.5

2.5

3.5

4.5

5.5

Rest 10 20 30 40 50 60 Max

Time

Plas

ma

lact

ate

(mm

ol.L

-1)

N

3.84.04.24.44.64.85.05.25.45.6

Rest 10 20 30 40 50 60 MaxTime

Plas

ma

gluc

ose

(mm

ol.L

-1)

N ITP R

N

3.84.04.24.44.64.85.05.25.45.6

Rest 10 20 30 40 50 60 MaxTime

Plas

ma

gluc

ose

(mm

ol.L

-1)

N ITP R

N

0.5

1.5

2.5

3.5

4.5

5.5

Rest 10 20 30 40 50 60 Max

Time

Plas

ma

lact

ate

(mm

ol.L

-1)

N

a

b

*


251

Figure 8- Plasma glycerol (a), plasma triglycerides (b) and plasma free fatty acid (c)

concentrations during H-CHO (left) and L-CHO (right) after normal (N), intensified

(ITP) and recovery (R) training. N= significantly different from normal training.

0200400600800

1000120014001600

Rest 10 20 30 40 50 60 MAX

Time

FFA

(µm

ol.l-1

)

N ITP R

0200400600800

1000120014001600

Rest 10 20 30 40 50 60 MAX

Time

FFA

(µm

ol.l-1

)

N ITP R

N, R

c

NN

R

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Rest 10 20 30 40 50 60 Max

Time

f-TG

(mm

ol.L

-1)

N, R

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Rest 10 20 30 40 50 60 Max

Time

f-TG

(mm

ol.L

-1)

N

0

0.1

0.2

0.3

0.4

0.5

0.6

Rest 10 20 30 40 50 60 Max

Time

Gly

cero

l (m

mol

.L-1

)

0

0.1

0.2

0.3

0.4

0.5

0.6

Rest 10 20 30 40 50 60 Max

Time

Gly

cero

l (m

mol

.L-1

)

L-CHOH-CHO

N, R

a

b

R


252

Resting plasma cortisol concentrations were unchanged over the training period and

were not different between trials. However, in both trials cortisol concentration was

significantly lower at all other time points (i.e., 60 minutes, maximum and 1 hour post

exercise. Plasma cortisol concentrations returned to baseline levels following

recovery in the H-CHO trial, yet remained significantly suppressed after 60 minutes

of exercise in the L-CHO trial. There was a significant diet X exercise time

interaction, with lower cortisol concentrations during L-CHO after ITP.

To assess the sensitivity of the HPA axis to stress, the difference between resting

cortisol concentrations and the concentration at both 60 minutes (Figure 9a) and

maximal exercise were calculated (Figure 9b). There was a significant decline in the

cortisol response to exercise after ITP in L-CHO group but not the H-CHO group.

This was for both the difference in concentrations between rest and 60 minutes

(p=0.02) of exercise and the difference between rest and maximal exercise

concentrations (p=0.001).

Plasma prolactin concentration was significantly reduced at all time points following

ITP in both trials, with the exception of resting values which were unchanged over the

study period. There was a significant trial X time interaction for plasma prolactin, with

lower concentrations after 60 minutes during the L-CHO trial after ITP (H-CHO N=

297 ± 41, ITP= 231 ± 16; R= 277 ± 34: L-CHO N= 365 ± 76, ITP= 202 ± 21, R= 284 ±

65 mIu.l-1). Resting plasma adrenaline concentrations were unchanged however

concentrations were significantly lower at both the 60-minute (H-CHO N= 0.83 ±

0.05, ITP= 0.79 ± 0.07, R= 0.81 ± 0.07; L-CHO N= 0.82 ± 0.11, ITP= 0.64 ± 0.07, R=

0.89 ± 0.09 mmol.l-1) and maximum (H-CHO N= 0.95 ± 0.02, ITP= 0.78 ± 0.11, R=

1.39 ± 0.04; L-CHO N= 1.08 ± 0.18, ITP= 0.68 ± 0.05, R= 1.36 ± 0.02 mmol.l-1) time

points after ITP in both H-CHO and L-CHO trials.


253

Figure 9- Changes in plasma cortisol concentrations during H-CHO and L-CHO after

normal, intensified and recovery training. (a) Changes in plasma cortisol

concentrations from rest to 60 minutes of exercise (b) Changes in plasma cortisol

concentrations from rest to maximal exercise. n= significantly different from normal

training (L-CHO).

0

50

100

150

200

250


Training

Chan

ge in

[Cor

tisol

]

H-CHO L-HCO

n

0

50

100

150

200

250

300


Training

Chan

ge in

[Cor

tisol

]

H-CHO L-HCO

n

a

b


254

Global Mood State assessed by the POMS-65, significantly increased during ITP and

then decreased following R in both trials (Figure 10). However, mood disturbance

increased to greater extent in the L-CHO trial and remained significantly higher after

R in this trial. The subscales of the POMS-65 remained unchanged with the

exception of fatigue, which was significantly increased.

Figure 10- Global Mood Scores during H-CHO and L-CHO trials during normal,

intensified and recovery training. N= significantly different from normal training during

H-CHO, n= significantly different from normal training during L-CHO. * = significantly

different from corresponding dietary trial.

60.0

70.0

80.0

90.0

100.0

110.0

120.0

130.0

140.0

150.0

160.0


Training

Glo

bal P

OM

S Sc

ore

HCHOLCHO

N, R

n,r

*

*


255

The short version of the POMS (POMS-22), showed similar changes to that of the

longer version, with increased total scores during ITP and higher scores during L-

CHO than H-CHO. Altered mood state was also reflected in the responses to the

DALDA questionnaire. The DALDA Part A ‘a’ scores (indicating ‘worse than normal’

response) were not significantly increased, although there was quite a large increase

in the number of these responses. DALDA Part B ‘a’ scores were significantly

elevated during ITP. While there was no significant diet X trial interaction, there was

a trend for increased ‘a’ scores during the L-CHO trial in both Part A and Part B of

the DALDA. Both Parts A and B of the DALDA were significantly elevated above

baseline after 5 days of intensified training (Figure 11).


256

Figure 11- Changes in POMS-22 (a), DALDA Part A (b) and DALDA Part B (c)

responses during normal training, intensified training and recovery during H-CHO

and L-CHO.

0.00.51.01.52.02.53.0

DA

LDA

Par

t A

HCHOLCHO

0

2

4

6

8

10

12

Training

DA

LDA

Par

t B

HCHOLCHO


-2

0

2

4

6

8PO

MS-

22

HCHOLCHO

a

b

c


257

DISCUSSION

The primary aim of the preset investigation was to determine if dietary

supplementation with carbohydrate would prevent the development of overreaching

during a period of intensified training. All subjects demonstrated a reduction in

performance and an increase in mood disturbance, indicating that all subjects in both

trials were overreached. However, the symptoms experienced by the subjects were

attenuated with the consumption of a high carbohydrate and high energy intake diet.

Performance and mood disturbance, the two primary indicators of overreaching, were

altered by increased energy and carbohydrate intake. Subjects had a significantly

higher energy and carbohydrate intake during the H-CHO trial than during the L-CHO

trial. Although performance declined in both trials, the reduction in performance was

greater in the L-CHO trial. Additionally, performance remained below that of baseline

values after recovery in the L-CHO trial, whereas a supercompensation effect

occurred after recovery in the H-CHO trial. The slower rate of return to baseline

performance in the L-CHO trial after recovery highlights the importance of

carbohydrate and total energy intake in maximising recovery from intense exercise.

Whole-body rates of carbohydrate oxidation were significantly lower and rates of fat

oxidation were significantly higher after intensified training in both trials. This

reduction in carbohydrate oxidation may be the result of lowered muscle glycogen

concentrations as a result of the increased training volume and insufficient CHO

intake. Muscle glycogen concentration has been shown to be reduced after similar

durations of intensified training in combination with low carbohydrate intakes (16, 23).

The significantly lower plasma lactate and glucose concentrations and lowered

respiratory exchange ratio after intensified training in both trials support the

suggestion that muscle glycogen concentrations were reduced. The decrease in


258

carbohydrate oxidation occurred in both trials and thus carbohydrate intake may have

been insufficient even with additional carbohydrate supplementation. It should be

noted that during H-CHO subjects consume less dietary carbohydrate than during L-

CHO which may be related to a suppression of appetite. A reduction in appetite has

been anecdotally reported in overreached and overtrained athletes.

Plasma concentrations of glycerol and FFA were also significantly higher after

intensified training, alongside increased fat oxidation. The altered substrate utilization

during submaximal exercise suggests lower muscle glycogen concentrations.

However, it is also possible that a down-regulation of β-adrenergic receptor

sensitivity occurred, as a consequence of continually elevated catecholamine levels

during training. A down-regulation of β-adrenergic receptor sensitivity has been

demonstrated in moderately trained subjects after increased volume training (22).

After 10 weeks of increased training, the exercise-induced increase in ß-adrenergic

receptor number, measured on mononuclear lymphocytes (MNL), was attenuated.

Additionally, the responsiveness of the receptor was measured by examining the

basal production of cAMP by MNL as well as production after stimulation by

isoproterenol. In athletes who experienced increased incidence of illness and

increased mood disturbance, the decrease in receptor number was combined with an

upregulation of the sensitivity of the postreceptor. However, performance was

unchanged in this investigation. The blunted ß-adrenoreceptor upregulation after

training was suggested to be a consequence of the enhanced catecholamine

concentrations during training sessions (22). The importance of changes in receptor

function and/ or sensitivity warrants attention in further overreaching and overtraining

investigations.


259

The endocrine system is intricately involved in responding to both physical and

psychological stress, alterations in the hypothalamic-pituitary-adrenal (HPA) axis and

sympathetic-adrenal medullary (SAM) axis have been indicated in the etiology of

overreaching and overtraining (1). It has also been suggested that high volume

training causes a reduction in circulating hormone concentrations as a result of

sustained elevations in hormones due to excessive exercise (1). The findings of this

study support this suggestion, with significantly lower cortisol, prolactin and

adrenaline concentrations after intensified training. Further, hypocortisolism has been

implicated in numerous stress-related bodily disorders (i.e. autoimmune diseases,

chronic pain and inflammation) (12). The decline in cortisol after intensified training in

the L-CHO trial may be the result of reduced adrenocortical secretion, reduced

adrenocortical reactivity, enhanced negative feedback inhibition of the HPA axis or a

reduced sensitivity/density of target cells (12).

Previous research that has examined the effect of diet on plasma cortisol

concentrations during exercise has demonstrated that diets low in carbohydrate

result in significantly greater increases in cortisol during exercise (3, 9, 20). These

studies suggest that carbohydrate availability may influence the magnitude of change

in the cortisol response to exercise. The lower cortisol responsiveness to exercise

observed in the L-CHO trial in the present study may be the consequence of negative

feedback inhibition on the HPA axis or reduced sensitivity of receptors resulting from

high levels of cortisol produced during training.

CONCLUSION

In summary, the results of this investigation suggest that a high energy and

carbohydrate intake can attenuate the negative effects of intensified training on

symptoms of overreaching. Tolerance of increased training volume was enhanced


260

and a supercompensation effect occurred during the trial where carbohydrate was

given before, during and after exercise in higher doses. Carbohydrate oxidation

decreased and fat oxidation increased after intensified training in both trials

suggesting a decrease in muscle glycogen content. Although carbohydrate

supplementation minimized many of the negative symptoms associated with

overreaching, it could not prevent a decline in performance and an increase in mood

disturbance after intensified training. A decrease in cortisol responses to

standardized exercise suggests that the HPA axis may be desensitized during

overreaching, which is attenuated by a high carbohydrate diet.


261

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5. Costill, D. L., R. Bowers, G. Branam, and K. Sparks. Muscle glycogen

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9. Gleeson, M., A. K. Blannin, N. P. Walsh, N. C. Bishop, and A. M. Clark.

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264



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_____________________________________________________

Chapter 7- General Discussion

_____________________________________________________

Chapter 7 General Discussion

266

At the onset of the investigations performed in this thesis, it was the intention to

increase the understanding of overreaching and overtraining in athletes through

several avenues of research investigation. These were broadly identified as the

effects of exercise stress on various markers that may be useful in early diagnosis of

overtraining, the role of carbohydrate supplementation in minimising exercise stress

and examining the possible changes in neuroendocrine function as a result of

overreaching. To achieve this, investigations were performed in a highly controlled

and monitored manner, incorporating several methodological techniques that have

not previously been utilised in overreaching and overtraining research. After

examining the results of the investigations, a hypothesis relating to the mechanisms

of overreaching and overtraining is proposed.

Research problem revisited

Experimental examinations of both the nature and causes of overreaching and

overtraining are lacking. While there is relatively large amount of anecdotal evidence

relating to markers or indicators of overtraining, there are surprisingly few well-

controlled and monitored investigations. Hence, the mechanism(s) are presently

unclear.

There are no widely acknowledged and accepted markers of overreaching and

overtraining beside decreases in performance and changes in mood state. The time

course of performance changes occurring during intensified training resulting in

overreaching is also unknown. Several biochemical and immunological changes

have been reported such as glutamine and salivary IgA, however once again, this is

yet to be fully substantiated. Finally, numerous hypotheses have been outlined in a

bid to explain the generation of unexplained fatigue resulting from intensified training.

The cytokine hypothesis of overtraining has recently been proposed to explain the


267

fatigue generated as a result of intensified training (22). An alteration in the

serotonergic system has also previously been suggested in the development of

fatigue as well as associated changes in autonomic balance and neuroendocrine

function (1, 14). Finally, carbohydrate intake and the glycogen depletion hypothesis

have been suggested as possible mechanisms of overreaching and overtraining,

however the exact role of carbohydrate remains unclear (23). The collective aim of

the work presented in this thesis was to investigate such hypotheses in a controlled

manner, utilising novel techniques to this area.

Performance Changes

One of the major areas of uncertainty in training and overtraining research is the

quantity of training that will result in overreaching and/or overtraining. As

demonstrated by the Overtraining Continuum, fatigue and a decline in performance

are often experienced as the result of a single intense training session. Given that

definitions of overreaching and overtraining use a decline in performance as the

single diagnostic indicator, it is necessary to discriminate between the acute fatigue

experienced after a single training session and the more prolonged fatigue of

overreaching. As both conditions are characterised by a decline in performance

results from Study 1 indicated that the use of psychological monitoring can be useful

in delineating acute fatigue from overreaching in the presence of a consistent

decrease in performance. Through the use of the Daily Analysis of Life Demand of

Athletes questionnaire, a point at which negative psychological alterations occur can

be identified. As mood state oscillates with training and recovery, the point at which

mood disturbance is consistently elevated for 4 days can be used to identify a state

of overreaching. This point identifies when fatigue has become persistent and

recovery has not occurred, thereby elevating mood disturbance to an abnormal level.


268

In Study 1, the elevation in DALDA scores began at approximately Day 3 of training.

From this point it was consistently elevated for the required 4-day period and thus a

state of overreaching was identified after 7 days of continual high-intensity training

without adequate recovery. From this information it can be suggested that athletes

wishing to avoid a state of overreaching should include appropriate rest and recovery

within 7 days of intensive training.

The time course of performance changes investigated in Study 1 also revealed that

continued training after 7 days did not result in further performance decline, although

performance was still significantly below that of baseline values. While it was clear

that the training was not tolerated after 7 days of training, as performance was still

lower than baseline, it appeared that subjects had attained a maximal level of fatigue

as performance no longer declined after 7 days of training.

The incorporation of three different laboratory based exercise tests revealed the

importance of the type of test chosen to demonstrate performance changes. Smaller

percentage changes were observed in the incremental cycle test to exhaustion than

during the time trial and intermittent tests. The latter two performance-based tests

may be superior tests to indicate changes in performance, as they are more

representative of actual cycling performance. From these results and the results of

previous research examining overreaching, it appears that the greater the duration of

the exercise test, the greater the performance changes as a result of overreaching.

This was demonstrated in Study 2 where a constant load fatigue ride was used to

assess exercise capacity. A 26% reduction in time to fatigue occurred after

intensified training, while in Study 1 a 10% reduction occurred in time trial

performance and a 5% reduction occurred in maximal power produced during the

incremental test. Future investigations in overreaching and overtraining in cyclists


269

should ensure an exercise test of sufficient duration is incorporated in the study

design. Additionally, previous research that has only reported changes in maximal

power from incremental tests should be interpreted with caution, especially when the

tests are of short duration (i.e. 10-12 minutes).

Mood Disturbance

A positive relationship exists between increased training load, increased

performance and positive mental health. However, this association subsists only to

an unidentified point, after which mood state becomes disturbed. In both Study 1 and

2, mood disturbance was significantly increased after intensified training. This

increase was evident when examined by both the long and short versions of the

Profile of Mood States and the DALDA.

The changes observed in mood state are consistent with previous investigations in

this area using the POMS (4, 6, 17). The present work is the first occasion that the

DALDA has been incorporated in overreaching research. Results from both studies

indicate that this questionnaire may be beneficial in identifying the development of a

state of overreaching. Changes in questionnaire responses can discern the ‘normal’

or acute fatigue from training from that of the more serious fatigue during

overreaching. This can be achieved by identifying consistent elevations in mood

scores that occurs during periods of intensified training that results in overreaching.

Typical alterations observed in mood state as a result of intensified training in both

Study 1 and 2 include increases in fatigue and reductions in vigour, which results in

changes in the ‘iceberg profile’, increases in negative responses to Parts A and B of

the DALDA (sources and symptoms of stress, respectively) and increases in tension,


270

anxiety and unhappiness and decreases in feelings of relaxation, identified by the

POMS.

Increased incidence and severity of physical symptoms of exercise stress identified

from Part B of the DALDA included increases in muscle pains, unexplained aches,

between session recovery and general weakness. Alterations in these responses

may be used as markers of overreaching and can also be employed to identify the

point at which overreaching occurs.

The elevated perception of stress and the increased negative responses relating to

anxiety/insomnia and social dysfunction, highlight the increased negative effects that

increased training and fatigue has on mood state and social functioning. Social

dysfunction appeared the result of the decreased time spent in enjoyable social

activities as a result of the increased amount of time spent training and the recovery

from the subsequent fatigue.

Physiological and Biochemical Markers

Maximal and Submaximal Oxygen Uptake: Overtrained athletes have been

suggested to demonstrate a decreased working capacity (12). Support for this

inference was evident in Study 1, where VO2max declined 4.5% following intensified

training. This decline is similar in magnitude to previous research (9, 25) and

suggests that overreached athletes may have an inability to achieve a maximal effort

during an incremental exercise test to exhaustion. Therefore, the decrease in

working capacity demonstrated after intensified training may not be related to

physiological abnormalities per se, but appears to be related to the generation of

fatigue prior to the maximal engagement of the cardiorespiratory and/or metabolic


271

systems. However, one previous investigation did not report changes in VO2max

(27).

To examine this possibility in greater detail, a constant load fatigue ride was used to

assess performance in Study 2. This test allowed the determination of possible

changes at a pre-determined submaximal time point during fixed intensity exercise,

which accounts for changes in total exercise duration due to fatigue following

intensified training. This test revealed no changes in submaximal VO2 after

intensified training, suggesting that the significant decline in performance observed

in this study could not be explained by alterations in oxygen uptake.

Heart Rate: A reduction in exercising heart rate was observed after intensified

training in both studies and in all exercise tests performed and is in support of

previous research showing a reduction in maximal heart rate in overreached athletes

(9, 13, 27). Again this finding may have been the result of the reduced power output

observed during maximal exercise and/or the changes in exercise duration or

intensity that occur following the intensified training necessary to induce

overreaching.

There was a trend for a reduction in submaximal heart rates during the incremental

test in Study 1. Heart rate during the constant load test in Study 2 declined an

average of 4% suggesting that a reduction in heart rate occurs after intensified

training and that this is unexplained by changes in exercise duration or intensity. In

addition, a slight reduction in resting heart rate was also observed.

At this stage, however, it is not clear whether the decreased exercising heart rate is

the cause or the consequence of premature fatigue. There have been suggestions


272

that disturbances in the autonomic nervous system are responsible for the altered

heart rate during overtraining (14). Decreasing sympathetic influence and/or

increasing parasympathetic influence, decreased ß-adrenergic receptor number or

density, increased stroke volume and plasma volume expansion are all possible

mechanisms for the reduction in maximal heart rate (28). The role of alterations in

autonomic balance will be discussed in a later section.

Plasma Lactate and Glucose Concentrations: Reductions in submaximal and

maximal lactate production has been previously reported (9, 24) and a shift to the

right in the lactate curve has been reported (8). The results of studies performed in

this thesis indicate that there may be slight reductions in maximal lactate production

and additionally reductions in submaximal lactate production. Study 2 demonstrated

that at a submaximal workload plasma lactate is reduced and that this reduction is

greater when subjects are consuming a lower energy intake. Resting lactate

concentrations were unchanged in both studies, which may be the consequence of

the low values of lactate at rest.

Submaximal plasma glucose was also reduced during in Study 2 after intensified

training and resting glucose concentrations were also significantly reduced. Maximal

glucose concentrations were unchanged, which may be a reflection of the changes

in exercise duration that occurred after intensified training. The changes in lactate

and glucose concentration provide some support for the glycogen depletion

hypothesis, which will be discussed in detail in a later section.

Urea, Ammonia and Creatine Kinase: Biochemical indices such as urea, ammonia

and creatine kinase have been suggested to be marker of overreaching and

overtraining, however this has not been supported by the present research and


273

previous research in this area (5, 13, 27). Creatine kinase was significantly elevated

above baseline value after intensified training. Although statistically significant, the

rise in resting plasma CK was quantitatively small. The ability of this marker to

discriminate between normal, intensified training and intensified training that results

in underperformance is extremely doubtful.

Urea and ammonia remained constant in the presence of large changes in

performance and fatigue and therefore are not appropriate indicators of

overreaching. Additionally, the fatigue and decreased performance experienced by

overreached athletes is most likely not the result of abnormalities in these biological

processes.

Haematological Measures: Following intensified training, red blood cell count (RBC),

haemoglobin (Hb), and packed cell volume (PCV) significantly declined and following

recovery had returned to initial levels. No changes were observed in mean red blood

cell volume (MCV), platelets, white blood cell count, neutrophils, lymphocytes,

monocytes or neutrophil/lymphocyte ratio. The changes that were observed in RBC,

Hb and PCV most likely reflect plasma volume changes and do not appear to be

related to the causal mechanism(s) of overreaching and overtraining.

Rating of Perceived Exertion: Following periods of intensified training that resulted in

overreaching, increases in RPE scores have been documented (3, 17, 27). This

increase in RPE was also observed in the two overreaching studies performed for

this thesis. The elevations in RPE scores found during exercise indicate that at a

given workload subjects perceive the exercise to be more difficult following

intensified training. The present results support the use of increases in RPE scores

as indicators of overreaching. Additionally, a heightened perception of exertion may


274

be indicative of a centrally mediated fatigue mechanism. This is supported by the

finding of an increased perception of exertion and reduced performance capacity

after administration of centrally acting pharmacological agents during exercise (16).

Gross Efficiency and Economy: The examination of gross efficiency and economy is

the first examination of such changes in overreached athletes. It has been

speculated that the reduction in performance experienced by overreached and

overtrained athletes may be the result of decreases in cycling efficiency or economy.

Results of the present work suggest that neither of these variables change in

response to intensified training and thus cannot explain the decreases in

performance demonstrated by the subjects following intensified training.

Body weight and Percent Body Fat: The use of changes in body weight as a marker

of overreaching and overtraining could not be confirmed by the results of the present

studies. While small decreases in body weight and percent body fat were observed

in Study 1, this was not replicated in Study 2. This may be partially explained by the

duration of each of the investigations. However, as large changes in performance

were observed in both studies changes in body weight and percent body fat are most

likely not useful indicators of overreaching under all conditions.

Immune Function

Recently in an attempt to integrate the available information regarding mechanisms

of overtraining, Smith (22) proposed the cytokine hypothesis of overtraining. It is

suggested that exercise-induced microtrauma to the musculoskeletal system leading

to a local inflammatory response is the initiating event in the development of

overtraining. Inadequate recovery and a continuation of the athletes’ training regimen

compound this initial local inflammation leading to chronic inflammation, the release

of inflammatory mediators and the subsequent release of pro-inflammatory cytokines


275

from activated monocytes resulting in systemic inflammation. This induces ‘sickness’

behaviour (fatigue, appetite suppression, depression), activation of the sympathetic

nervous system and the hypothalamic-pituitary-adrenal-axis, suppression of the

hypothalamic-pituitary-gonadal-axis, up-regulation of liver function and possibly

immuno suppression (22). However, until now there has been no assessment of the

changes in plasma cytokine concentrations in response to overreaching or

overtraining. Results of Study 1 did not appear to support the cytokine hypothesis of

overtraining, with no changes observed TNF-α, IL-6 or salivary IgA. Thus, it does not

appear that elevations in circulating cytokines are primarily responsible for the

fatigue and underperformance associated with overtraining. It was possible to induce

a state of overreaching, evident by underperformance and changes in mood state,

yet resting plasma cytokine concentrations remained unchanged. However, in the

present studies athletes were overreached as opposed to overtrained and thus it

cannot be ruled out that significant elevations in cytokines do not occur in

overtrained athletes. Additionally, athletes involved in sports with a higher degree of

muscle damage (i.e. running), may experience greater elevations in plasma

cytokines.

As the mechanism(s) behind the underperformance associated with overtraining is

unclear, a combination of a number of markers is needed for early diagnosis.

Changes in the plasma glutamine/glutamate ratio (Gln/Glu) have recently been

suggested as a predictor of overreaching or overtraining in athletes (21). Elevated

plasma glutamate and hence a reduced Gln/Glu ratio was observed in athletes who

were classified as overtrained. Results of Study 1 support the suggested

classification of overreaching with of a ratio above 3.58.


276

As glutamine is an important fuel for cells of the immune system, reductions in

glutamine has been suggested as possible marker of overtraining (20). However, we

could not support this contention as although significant increases in the Gln/Glu

ratio was observed, the increase occurred through an increase in glutamate rather

than a decrease in glutamine. A lowering of the Gln/Glu ratio in conjunction with a

decline in performance and altered mood state may be a useful tool for the diagnosis

of overreaching and overtraining. However, further investigations into this area are

needed to confirm the above results.

At present, immunological parameters do not appear to be useful indicators of

overreaching and overtraining, with perhaps the exception of the Gln/Glu ratio. It also

does not appear that immunological changes underlie the effects and symptoms

associated with overreaching. This may be related to the small magnitude of

changes in the immune system in response to overreaching, analysis and

methodological limitations and individual responses to training and fatigue. Thus, it

appears that the clinical symptoms of overreaching and overtraining cannot be

explained by changes in the immune system or plasma cytokines. It is most likely

that mechanism(s) that cause overreaching is more complex than muscle damage

caused by intensified training resulting in an altered immunological response.

Substrate Utilisation and Dietary Intake

The results of Study 1 demonstrated no significant changes in substrate utilisation

following intensified training when measured during an incremental cycle test.

However, there was a trend (p=0.081) for elevated fat oxidation after intensified

training. When substrate utilization was measured using the same stoichiometric

equations during submaximal cycling (Study 2) large changes in substrate utilisation

were observed. There was a significant alteration in both carbohydrate and fat


277

oxidation, indicating a glycogen sparing effect. This was most likely the result of a

depletion of muscle glycogen despite supplementation.

However, while changes in substrate utilisation occurred after intensified training,

this decrease in carbohydrate oxidation and corresponding increase in fat oxidation,

was not different between trials. This was despite significant differences between

dietary trials in performance, mood state, perception of exertion, adrenaline and

cortisol. This may suggest that changes in substrate oxidation may not directly be

related to the underlying causes of the symptoms of overreaching.

Supplementation with carbohydrate and an increased total energy intake resulted in

an attenuation of the symptoms of overreaching, including a smaller decrease in

performance, a smaller increase in mood disturbance and smaller decreases in

submaximal plasma hormone concentrations. This was combined with a

supercompensation effect after recovery in the H-CHO trial compared to the L-CHO

trial where performance remained below that of baseline values.

The results of this section of Study 2 suggest that supplementation with

carbohydrate and an increased energy intake diminish, but do not prevent,

symptoms of overreaching. It also highlights the importance of carbohydrate and

energy intake during periods of intensified training in minimising training stress and

maximising recovery from such training.

Neuroendocrine Function

The hypothalamic-pituitary-adrenal (HPA) axis in combination with the autonomic

nervous system is the most important stress system in the body (10). This stress

system is activated once physical and/or psychological stressors exceed an


278

unknown threshold (10). The numerous and multifaceted signs and symptoms

exhibited by athletes who are diagnosed as overreached or overtrained suggests the

involvement of higher brain centres. Changes in mood state, fatigue and

performance may all be the resultant consequences of maladaptation of the

neuroendocrine system.

Blood Hormones

Endogenous hormones are intricately involved in adaptation to exercise training as

well as regeneration and recovery following exercise (26). It is also apparent that

alterations in hormones may play a significant role in the pathogenesis of

overreaching and overtraining (26). Results from both Study 1 and 2 support

previous research that has demonstrated alterations in blood hormones as a result of

overreaching.

The plasma concentration of catecholamines is indicative of sympatho-adrenergic

activation during exercise (26). The significant reduction in adrenaline observed in

Study 2 at the 60-minute time point during the exercise capacity test after intensified

training, is indicative of the parasympathetic form of overtraining described by Israel

(7). It is possible that the high levels of catecholamine release, which occurs as a

consequence of intensified training, may lead to a decrease in the sensitivity and

density of adrenoreceptors. This decrease in sensitivity and/ or density may play a

role in disturbing energy mobilization and result in the reduction in blood lactate

levels previously reported in overtraining literature as well as in the present work.

The lack of change in catecholamines in Study 1 may be due to the relatively short

duration of the exercise test employed. As such intramuscular glycogen availability,

which is known to affect catecholamine levels, becomes more critical during longer

duration exercise.


279

To date, there is only limited research investigating plasma prolactin (PRL) levels in

overreached and overtrained athletes (2, 15). In Study 1 a decline in PRL

concentrations as a result of overreaching was observed, followed by an increase in

release following recovery. In Study 2 a significant decline in PRL occurred after

intensified training and a significant effect of diet on PRL responses was observed.

The meaning of these changes remains unclear, however, it appears that alterations

in serotonergic responsiveness occurred as the result of the intensified training and

limited recovery. The implications of changes in the serotonergic system are

discussed in the subsequent section.

From the limited research available, it appears that growth hormone (GH) release

following overreaching is reduced (27). A significant decline in GH was evident at the

60-minute time point of exercise following intensified training. The reduction in GH

may be the result of a suppression of the hypothalamic-pituitary-growth hormone

(HPGH) axis. This may be caused by a negative feedback mechanism whereby high

levels of GH reduce GH secretion or by the suppressive effect of cortisol on GH

release (10). This decline in GH may be important during overreaching and

overtraining as GH has an important role in metabolic pathways and stimulates

protein anabolism and lipolysis. Additionally, low levels of GH affect cognitive

function and causes mood disturbance (10), both of which are common in

overreached and overtrained athletes.

One of the more striking and consistent findings of the research performed in this

thesis was the significant decline in cortisol concentrations following intensified

training. Like catecholamines, cortisol mobilises and redistributes metabolic fuels

and enhances the responsiveness of the cardiovascular system (1). The decline in


280

cortisol concentration as a result of intensified training that resulted in overreaching

may have resulted in metabolic changes sufficient to induce performance changes.

In addition, cortisol has been shown to have significant effects on emotion and mood

state (11).

Serotonergic System

It appears that changes are occurring at the level of the hypothalamus and/or

pituitary gland during overreaching, evidenced by the increased PRL responses to

both the BCT and exercise tests after recovery. Thus, regardless of the nature of the

challenge to the hypothalamus, i.e. either exercise or pharmacological, a significant

increase in prolactin responses, compared to that at baseline occurred following the

recovery period.

5-HT has multiple actions in the CNS and can influence sleep and pain processing,

decrease motor neuron excitability, suppress appetite and has links with autonomic

and endocrine functions (19). The ‘central fatigue hypothesis’ (18) assumes that the

development of a centrally mediated component of fatigue occurs through pathways

involving 5-HT. It appears that there are alterations in 5-HT responsiveness as a

result of intensified training and recovery, which may have some relation to the

symptoms associated with overreaching. While the mechanisms appear unclear and

the exact relationship to performance changes is vague, the large changes in

responses to buspirone administration observed in Study 1 suggest that future

research into both serotonin and dopamine during overreaching are warranted.


The results of Study 2 suggest that overreaching and subsequent recovery is

associated with an increase and then decrease, respectively of heart rate variability.


281

This increase in HRV after intensified training corresponds to Israel’s

‘parasympathetic form’ of overtraining (7) and suggests that the relative balance

between sympathetic and parasympathetic nervous system activity is altered. In the

case of increased HRV there is a dominance of parasympathetic activity over

sympathetic activity. This may be a result of increased parasympathetic nervous

system activity and/or a decrease in sympathetic nervous system activity.

The adaptation in autonomic balance may be a protective mechanism against

exhaustion and against consistent elevations in catecholamines, which occur during

high intensity training. Additionally, elevated heart rate variability may prove a useful

tool to diagnose overreaching.


282

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23. Snyder, A. C. Overtraining and Glycogen Depletion Hypothesis. Med. Sci.

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_____________________________________________________

Chapter 8- Summary

_____________________________________________________

Chapter 8 Summary

287

Mechanisms of Overreaching: Hypothesis

As a result of the findings reported in this thesis, a hypothesis outlining a possible

mechanism of overreaching is described below. This hypothesis aims to create a

unifying concept relating to the causes and manifestations of overreaching.

Adrenal cortex

Autonomic imbalance

Hypothalamus

↓ Prolactin

ACTH

Sympathetic spinal nerves

NA

↓ Blood lactate↓ Blood glucose↓ RER↑ Free fatty acids↑ Glycerol

Recovery

Training and / ornon-training stress

Imbalance

↑ stress

Anteriorpituitary

↓ Cortisol

Adrenal medulla

↓ Adrenaline

↓ Heart rate ↓ CHO oxidation↑ Fat oxidation

↑ Mooddisturbance

↑ Perceptionof stress

↑ Heart ratevariability

↑ DALDA↑ POMS scores

SAM axis HPA axis

Adrenal cortex

Autonomic imbalance

Hypothalamus

↓ Prolactin

ACTH

Sympathetic spinal nerves

NA

↓ Blood lactate↓ Blood glucose↓ RER↑ Free fatty acids↑ Glycerol

Recovery

Training and / ornon-training stress

Imbalance

↑ stress

Anteriorpituitary

↓ Cortisol

Adrenal medulla

↓ Adrenaline

↓ Heart rate ↓ CHO oxidation↑ Fat oxidation

↑ Mooddisturbance

↑ Perceptionof stress

↑ Heart ratevariability

↑ DALDA↑ POMS scores

SAM axis HPA axis

Chapter 8 Summary

288

This diagram illustrates the importance of the sympathetic-adrenal medullary (SAM)

and hypothalamic-pituitary-adrenal (HPA) axes in the response to increased exercise

stress without adequate recovery. When stress is prolonged or excessive, plasma

concentrations of stress hormones associated with these axes decrease, possibly as

a protective mechanism. This reduction in hormone concentration may be the result

of reduced secretion of the hormone, reduced reactivity associated with the hormone,

enhanced negative feedback inhibition and/ or a reduced sensitivity/density of target

cells. As a result of SAM and HPA axes alterations physiological, psychological and

biochemical variables become altered which may affect performance.

Such alterations include: increased heart rate variability, decreased heart rate,

changes in fuel utilisation, reduced responsiveness of cortisol to exercise and

increased mood disturbance. It is important to note that while markers may be useful

to identify the development of overreaching and they provide some information on

the underlying mechanisms, markers cannot be used solely to indicate the specific

mechanisms involved. Therefore, while the above-mentioned hypothesis is based on

the results of controlled studies, it remains speculative until further research is

conducted.

Markers of Overreaching

As a result of the investigations performed in this thesis a number of markers or

indictors of overreaching can be suggested. However, a number of important

practical aspects must be considered and applied when using such markers. Firstly,

as a number of the markers of overreaching are usually indicative of a positive

adaptation to training, it is necessary that an assessment of performance occur

alongside measurement of possible markers. Additionally, the assessment of

performance should replicate as closely as possible the demands of competition and

Chapter 8 Summary

289

have relatively low intra-subject variability. Finally, it is preferential that measures are

made at a fixed, submaximal time point to avoid alterations that may be the result of

a decrease in duration or intensity due to enhanced fatigue.

Markers of overreaching

• Decreased submaximal and maximal heart rate

• Decreased submaximal and maximal lactate concentrations

• Decreased submaximal and maximal plasma cortisol and adrenaline

concentrations

• Increased heart rate variability at rest

• Increased submaximal RPE

• Increased mood disturbance identified by the POMS and DALDA

From study 1 it was noted that performance declines rapidly after several days of

intensified training. If the subjects in this study were provided with a short period of

recovery in the first week, it would be expected that performance would have

returned to baseline relatively quickly. Thus, while a decline in performance is

necessary to diagnose a state of overreaching, this should be combined with an

assessment of mood state in order to accurately diagnose the decrease in

performance as overreaching.

Limitations

Previously, the major limitation of both overreaching and overtraining research has

been the lack of adequate performance assessments, insufficient information

regarding training volume and the omission of a period of recovery. While several

advances have been made in terms of the understanding of markers and

mechanisms of overreaching, there remain limitations to the interpretation of these

Chapter 8 Summary

290

studies. Primarily, this research is limited to the examination of overreaching and as it

unclear as to whether the symptoms of overreaching are similar to those of

overtraining, caution be used when comparing results to overtraining literature.

Overreaching is often utilised by athletes during a typical training cycle to enhance

performance. Intensified training can result in a decline in performance, however

when appropriate periods of recovery are provided, a supercompensation effect may

occur with the athlete exhibiting an enhanced performance when compared to

baseline levels. As it is possible to recover from a state of overreaching within a two-

week period, it may be argued that this condition is a relatively normal and non-

harmful stage of the training process. However, the effects of overreaching are

clearly disparate from those of a normal training phenomenon. By definition

overreaching is defined by a decline in performance, indicating a negative adaptation

to the training. Thus, while some of the markers of overreaching are similar to those

observed after a positive training adaptation (reduced submaximal lactate and heart

rate), a state of overreaching is considered abnormal as this is combined with a

decrease in performance whereas a positive adaptation is associated with an

increase in performance.

A further limitation to this research and to other research involving human subjects is

that access is limited to hormone concentrations in the peripheral circulation.

Additionally, as it is not possible to take direct measures of hypothalamic receptor

density and function, the response to pharmacological agents are taken as an

indicator of receptor sensitivity.

The small number of subjects examined in the investigations limits statistical power.

Subject recruitment and participation in intensive training studies is often limited due

Chapter 8 Summary

291

to time restrictions, the length of the research study and the increase in training

requirements. Confounding this problem is the range of individual responses to

intensified training. This variation highlights the importance of comparing individual

responses to baseline data rather than comparing to standard or mean values.

Finally, athletes studied in these investigations were well-trained endurance athletes,

however they were not elite athletes. Therefore, interpretation of data is limited to

athletes of a similar standard. Additionally, findings may not apply to athletes who are

primarily involved in strength or power disciplines.

Future Research

Given that the findings of the present studies indicate that both the HPA axis and the

sympatho-adrenal medullary system are altered as a result of intensified training that

resulted in overreaching, future research should continue to investigate such

alterations in the aetiology of overreaching and possibly overtraining. The use of

pharmacological agents that block ACTH/ cortisol may provide information on the

role of cortisol in overreaching. Similarly, changes in ß-adrenoreceptor density and/

sensitivity may provide information regarding a role of these receptors in the reduced

carbohydrate oxidation reported in Study 2. As changes were observed in 5-HT

responsiveness following recovery, the use of agents that alter 5-HT activity, such as

anti-depressant medication, may be investigated as a treatment for overtrained

athletes. Also, the relative contribution of the dopaminergic system to the PRL

release during buspirone challenge should also be elucidated.

As the perception of stress was elevated during intensified training, the usefulness of

cognitive behaviour therapy and stress management techniques to reduce the

stressful effects of training should be examined.

Chapter 8 Summary

292

Summary

The major findings of this thesis are, firstly, that overreaching can be induced after a

period of 7 days of intensified training without recovery. Secondly, markers of

overreaching have been described which are based on controlled and monitored

periods of training. Thirdly, it appears that the neuroendocrine system is altered after

intensified training and recovery. This results in decreases in submaximal plasma

concentrations of cortisol, adrenaline and prolactin. Additionally, a dominance of the

parasympathetic nervous system over the sympathetic nervous system was

observed after intensified training, which was associated with a reduction in

submaximal heart rates. Fourthly, substrate utilisation was also altered after

intensified training, possibly as a result of reduced glycogen concentrations. Finally,

carbohydrate supplementation and increased energy intake attenuated symptoms of

overreaching, however this could not prevent the development of a state

overreaching. From the results of the studies performed in this thesis, it appears

most likely that chronic exercise stress without recovery leads to a down-regulation of

the neuroendocrine system, which in turn decreases plasma hormone concentrations

which affects performance, mood state and physiological and biochemical responses

to exercise. This decrease in neuroendocrine function most likes serves as protection

against prolonged exposure to activation of the neuroendocrine system and

subsequent stress hormone release.

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