Part III Exercise Physiology 1. The study of the body’s immediate and long- term responses to exercise Useful for... See table on p. 120 Generally, evaluating

Part III

Exercise Physiology

1

Exercise Physiology The study of the body’s immediate and long-

term responses to exercise Useful for...

•See table on p. 120•Generally, evaluating fitness programs, designing

effective fitness regimes, and assessing individual fitness in a vast array of applications

• It’s purpose is simply to understand everything there is to know about exercise

2

Chapter 10

Basic concepts of exercise metabolism

3

Objective from syllabus To summarize basic concepts of exercise

metabolism• The idea here is that, in order to understand

how we can exercise, we must understand the body’s capacity to do work (i.e. produce energy)

4

Exercise metabolism Production of energy for exercise

•What do you know about energy limits for exercise?

•Could you sprint a mile with the right kind of training?

5


•Production of ATP•Energy supply

• Muscles do work• Work requires energy• How does work done (energy cost) differ across different

exercises? • How does sprinting 100 yards differ from walking it?

From jogging it?• Our job is to understand the basic properties and

capabilities of energy supply

6


• Production of ATP (adenosine triphosphate)• ATP is the basic worker of the body• It is the source of energy that allows muscles to contract

(without muscle contraction you have no movement)• It provides the energy by breaking down into ADP and

phosphate• While exercising, continued work is possible provided ADP

and phosphate is reconstituted fast enough to provide enough ATP for the work done

• This reconstitution of ATP itself requires chemical energy, supplied by one of three different systems

7


•Production of ATP (adenosine triphosphate)•3 systems:

(Differ according to the intensity of work they support – that is, the units of ATP per second they can reconstitute)

• The immediate energy system• The anaerobic glycolytic system• The oxidative system

• See table on p. 124 (good summary)

8


• The immediate energy system• Relies on stores of phosphocreatine (PCr) to resynthesize

ADP & phosphate into ATP• Resynthesizes more ATP per unit time than any other system,

but has a finite capacity – PCr runs out• Used at the start of all exercise, and for high intensity brief

bursts of work• Doesn’t get replenished until you’ve been at rest for about 6

minutes• Creatine supplements – useful for repeated bouts of high

intensity work (health cost?)

9


• The anaerobic glycolytic system• Relies on glucose to resynthesize ADP & phosphate into ATP• Is the major source of ATP for exercise lasting between 20s

and 3min • In a 30s sprint, this system provides 60-65% of the ATP• Glucose comes mostly from muscle stores, some from blood• Lactic acid is the byproduct of glycolysis• ATP is produced via the Krebs cycle• Glycogen boosting/loading – see later

10


• The oxidative system• Relies on oxygen to resynthesize ADP & phosphate into ATP• Is the major source of ATP for exercise lasting more than

3min • Oxygen, of course, comes from breathing, hence when you

use this system, you breath heavily, or you get into oxygen debt

• This is the system where VO2 max becomes important – anyone heard of that? (see later)

• ATP resynthesis by this system is slow relative to the others

11


•The 3 energy systems as a continuum•All systems always function – it’s the extent to which

each is relied upon that changes with the kind of work done

•Think about a marathon...when would each system be used?

12

Production of energy for exercise•The 3 energy systems as a continuum

13

Exercise metabolism

The energy system continuum: the relative contribution of each system to ATP resynthesis depends on exercise duration and intensity


•The fueling of ATP by fats, proteins, and carbohydrates•Carbohydrate (glucose) – can be used to supply energy

aerobically or anaerobically•Fats (fatty acids) & proteins (amino acids) – can only be used

to supply energy via oxidative system •Relative use of fat (fatty acids) and carbohydrates (glucose):

• Rest, low intensity – each used equally• Higher intensity – relies more on glucose• (proteins - amino acids –used more only when glucose is in very

short supply – e.g. sustained endurance exercise)

14

15

fats

proteins

carbohydrates

Carbon dioxide

Lactic acid

The un-reconstituted ADP &Pi

The reconstituted ATP, & water


• Lactic acid – friend or foe?• Lactic acid accumulates as a consequence of glycolysis

• Concentration in muscles and blood can increase up to 15 x during max exercise (rowing example)

• Increases acidity of muscles & blood (LA La+ H-, & H-lowers pH of muscle/blood) [lower pH acidity]

• Increased acidity slows anaerobic pathway• This inhibits ATP production• ...= fatigue• Protective, as excess acidity kills cells…self-regulation

16


• Lactic acid – friend or foe?• Lactic acid is circulated to various body parts (heart, liver,

other muscles) & oxidized (removed) both during and after exercise

• In muscle, its breakdown can be used to reconstitute ATP (providing further fuel for exercise) via oxidative pathway

• In the liver, after exercise, it can be used to form glucose, which is used to resynthesize glycogen lost during exercise

• 20-40 minutes to remove LA after exercise• Removal is faster if still gently exercising (LA used as fuel to

reconstitute ATP) • Recovery exercise should be gentle – don’t want to create more

LA

17

Exercise metabolism Oxygen supply during sustained exercise

• Aerobic system provides >50% ATP for exercise > 3 minutes, & 20-30% when exercise lasts 30-60s

• Whatever ATP cannot be supplied by aerobic system must be supplied anaerobically

18


• VO2 measures energy expenditure• First few minutes – oxygen debt (energy supplied

anaerobically – discomfort) • then O2 system kicks in (“second wind”)• Constant exercise can result in plateau of VO2 (steady state)

– could go on forever…• If intensity keeps rising, so does VO2

• ...until it reaches “VO2 max”• After exercise, oxygen continues to be used, to remove

lactate, and resynthesize the various energy stores (called excess post exercise oxygen consumption - EPOC)

19


• Summary of previous slide:

20


•VO2 max (aerobic power) as an indicator of endurance exercise capacity•VO2 max is...the maximum amount of oxygen that can

be used to synthesize ATP – hence a measure of the highest intensity work you can manage without relying in addition on the finite energy supplies of the other two energy systems (to increase total possible energy supply)

21


•VO2 max (aerobic power) as an indicator of endurance exercise capacity•VO2 max responds to training, but is also partially

genetically determined •Be careful of simplistic statements here – the extent of

genetic determination is a complex matter (c. 40%...used to be thought to be 90%!)

•Also, many other factors combine to determine who succeeds at high intensity aerobic events (Lance Armstrong did not succeed just because he has a huge VO2 max...though he does)

22

Exercise metabolism Measurement of exercise capacity

•Aerobic or endurance exercise capacity•VO2 max measures aerobic power, but endurance

exercise capacity measures capacity to perform prolonged aerobic exercise (not the maximum intensity)

•Specificity of exercise (running, bicycling, arm ergometers, rowing machines, etc...)

•VO2 max – highest volume of O2 (p/unit time) consumed during exercise – but the person will continue exercising for a while after reaching this – why?

23

Exercise metabolism Measurement of exercise capacity

• Anaerobic exercise capacity

•Anaerobic power (2-3s)• E.g. Margaria-Kalamen step test

•Anaerobic capacity (30-60s)• E.g. Wingate bike test (30s in my experience)

• Why measure exercise capacity?• Measures training effectiveness• Talent identification• Exercise prescription (VO2 max, heart rate, perceived exertion –

see next slide)• Different levels of VO2 appropriate for different types of

athlete (see ch. 11)

24

25

Exercise metabolism The cardiorespiratory system and oxygen supply

during exercise• Cardiorespiratory system:

• Lungs, breathing tubes (trachea, bronchii, other tubes), heart & blood vessels

• Oxygen passed from air sacs in lungs (alveoli) to blood in capillaries surrounding these sacs

• Transfer v. rapid• Blood goes from pulmonary veins to heart, then to arteries, then to

capillaries• It is this later stage of distribution and gas exchange that limits

endurance performance

26


during exercise• Cardiovascular response to exercise

• HR & respiration increase prior to exercise in the trained person

• HR increases with work intensity (oxygen supply)• Max HR estimate = 220 – age

• (very variable about this estimate (I can still get to 200 – shouldn’t be able to according to this)

27


during exercise• Cardiovascular response to exercise

•Stroke volume (amount of blood pumped per contraction of heart): increases with work intensity

• With training, SV continues to increase•Cardiac output: Blood pumped p/minute

• Function of both SV and HR, naturally• Increases linearly with increased work rate

• Minute ventilation (air brought into lungs): number of breaths, and their depth

• Blood flowing though lungs is full of oxygen, even when working maximally – so that’s not a cause of exhaustion (nasal strips not necessary)

• Though respiratory muscles may fatigue

28

Viscera

Skin

Brain

Heart

Skeletal Muscle

Maximal

Viscera

Skin

Brain

Heart

Skeletal Muscle

Sub-maximal

Exercise metabolism The cardiorespiratory system and oxygen

supply during exercise•Distribution of blood flow during exercise

Viscera

Skin

Brain

Heart

Skeletal Muscle

At rest

29

Exercise metabolism Human skeletal muscle cells

Human Skeletal Muscle Fiber Types

CharacteristicSlow-twitch

(ST)Fast twitch

(FTa)Fast twitch

(FTb)

Fiber size Small Large Large

Contraction Speed

Slow Fast Fast

Force Low High High

Glycolytic capacity

Low High High

Oxidative capacity

High Moderately high Low

Capillary supply High Moderately high Low

Fatigue resistance

High Moderate Low

30


• Muscle fiber type and exercise capacity• Activation of fiber types during exercise• Fig 10.12

100

80

60

40

20

0

Light Moderate Maximal

% M

uscl

e fib

ers

used

Muscular force

ST fibers

FTa fibers

FTb fibers

Note – this is not a

diagram of the

amount of force

produced

Use this idea in the design of

training programs –

which type of fiber do you

need?

31


• Skeletal muscle “fiber typing” – muscle biopsy

32


• Importance of muscle fiber type to sport performance

0

10

20

30

40

50

60

70

80

90

Non

-ath

lete

Dis

tanc

e

runn

er

Swim

mer

Spri

nter

Wei

ghtl

ifte

r

Ty

pe

I o

r II

fib

ers

(%

)

Type I

Type II

Many other sports activities do not rely

exclusively on a particular fiber type

33

Exercise metabolism Energy cost of activity

•Factors implicated:•Intensity•Efficiency of technique•Body mass (depending on whether activity is supported

– for example, swimming and running differ greatly)•Has implications for:

•the amount you need to eat to support training•The number of calories you’ll burn performing an

activity

34

Exercise metabolism Importance of diet to energy metabolism and exercise

performance• Why athletes need a high carbohydrate diet

200

150

100

50

0

50 150 250

Low

Moderate

High

Exerc

ise t

ime

to e

xhaust

ion

Glycogen in muscle

Energy released per liter of O2 consumed

SubstrateEnergy p/l of O2 (kcal)

Carbohydrate 5.05

Fat 4.70

Protein 4.82So, if you have more

glycogen, you can exercise longer before exhaustion

35

So you get more energy p/l

of O2 with carbs

Exercise metabolism Importance of diet to energy metabolism and exercise

performance• Do athletes need extra protein?

• No, provided they have a healthy diet (see table 10.5, p. 141)• Having too much can be bad – excess is excreted through kidneys or

laid down as fat – it does not get used to produce extra muscle• Importance of replacing water lost during exercise

• 70-80% of work done is lost as heat• Can sweat 1 and 6.3 pints p/hr!• See recommendations on p.141• Note that for exercise of up to 1hr, recommendation is for plain

water• 1 hr+ of intense exercise brings a recommendation for sport drinks

(w/glucose, electrolytes)

36

Michael Phelps’ Breakfast http://www.guardian.co.uk/lifeandstyle/

wordofmouth/2008/aug/15/myattemptatmichaelphelpsb

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Chapter 11

Physiological adaptations to training

38

Objective from syllabus To summarize how training can affect the

capacity to perform work

39


Overall training goals:•Outcomes are dependent on the program – must

bear in mind the different energy systems•Always need to work on muscular strength, power

and endurance

40


Training-induced metabolic adaptations•Start by estimating needs of activity to be trained

for (in terms of energy system•Examples

•Endurance training increases muscle glycogen stores•Muscle PCr stores increase with power training and

short sprint training•Sweating increases in the trained person (starts earlier

and increases in total volume – e.g.Craig Sharp, Seb Coe)

41

Physiological adaptations to training Training-induced metabolic

adaptations• Factors limiting exercise performance

• Power & Speed lasting a few seconds• Muscle fiber (FT) recruitment, balance &

coordination• Brief high intensity (can be maintained < 1

min)• ATP from PCr system primarily• PCr depletion, “highish” lactate levels,

chemical...• Elite sprinters (100m-200m) use PCr to

resynthesize ATP quicker than non-elite sprinters

42

Physiological adaptations to training Training-induced metabolic adaptations

• Factors limiting exercise performance• Longer high intensity (1-7 minutes)

• 30s to 2-3 min• PCr depletion, high lactate levels,

chemical...see last bullet pt.• ATP provided quickly, but limited by LA• Electrolyte (potassium, sodium,

calcium, etc…) distribution becomes an issue

• 3-10 min• LA accumulation, glycogen depletion,

electrolyte distribution

43

Physiological adaptations to training Training-induced metabolic

adaptations• Factors limiting exercise performance

• Prolonged moderate to high (10-40 min)• Some lactate, some glycogen loss,

dehydration, chemical...• Very prolonged

• Glycogen loss, dehydration, increased body temperature, low blood glucose, amino acid ratio in blood

• Latter 2 highly involved in sensation of fatigue

44


Training-induced metabolic adaptations•Factors limiting exercise performance

•Note that some (many) sports use combinations of all three systems, in different proportions, so training needs to reflect that

•Research attempts to specify what energy systems are used most in which sporting activities

45


Training-induced metabolic adaptations• Immediate and anaerobic system changes after

strength and sprint training• Increased stores of PCr, ATP & glycogen in muscle (esp. FT)• Increased ATP generated by anaerobic glycolysis (also higher

levels of lactic acid, but increased capacity to tolerate it balances this out)

• Muscle fiber size increases, increased # cross bridges, more muscle fibers are activated, and chemical balance is maintained (allowing for better maintenance of electrical conductance & excitation)

•All changes lead to more power, of course

See t

ab

le o

n p

ag

e

145

46


Training-induced metabolic adaptations•Changes in aerobic metabolism after endurance

training•6 weeks should increase VO2 max by 20% to 40%!•Activity of enzymes in Krebs cycle increases by 100% +…

See t

ab

le o

n p

ag

e

146

47


Training-induced metabolic adaptations•Activity of enzymes in Krebs cycle increases by 100% +…

See t

ab

le o

n p

ag

e

146

48


Training-induced metabolic adaptations•Changes in aerobic metabolism after endurance

training• Summary of important changes…

See t

ab

le o

n p

ag

e

146

49


Summary of important changes...Adaptation Consequence

VO2 max Duh...

Muscle glycogen work before fatigue

Kreb’s cycle Enyzmes

use of oxygen

Use of fats for fuel Don’t use so much glycogen

Lactic acid removal work before fatigue

Lactate threshold work before fatigue

# capillaries within muscle

Good stuff in, bad out

Muscle oxygen extraction

O2 for ATP

Muscle myoglobin O2 transport in muscle

50

Iron containing protein – enhances O2 transport for metabolism


Endurance training-induced changes in the cardiorespiratory system•Oxygen consumption

•Stays the same at rest or at moderate exercise•It’s the max that increases•Amount of adaptation with training depends on

amount of training and whether you’re already close to your max

51

Physiological adaptations to training Endurance training-induced changes in the

cardiorespiratory system•Heart rate

•Normal = 60-70 bpm•Endurance = 30-40 bpm (sometimes)•Amount of blood pumped maintained by bigger stroke

volume•Stroke volume

•Increases both at rest and at work•As intensity increases so stroke volume increases (in the

trained person)

52


Endurance training-induced changes in the cardiorespiratory system•Cardiac output

•Increases with alteration in stroke volume (only when exercising)

•Oxygen extraction•Increased (muscles are able to extract more oxygen

from blood during exercise)•There’s also more blood available (see above)

53


Endurance training-induced changes in the cardiorespiratory system•Blood composition

•Less viscous, more oxygen carrying capacity, better thermoregulation

•Endurance training-induced respiratory changes•More air breathed p/minute (adaptations in respiratory

muscles)•Better able to get rid of CO2, deplete lactic acid

54

Physiological adaptations to training Endurance training-induced changes in the

cardiorespiratory system• Endurance training induced changes in the lactate threshold

• Lactic acid production increases rapidly at a certain work intensity (= the LA threshold)

• Somewhere between 50% (untrained low) to 85% (trained high) of VO2 max

• Here’s the difference between trained/untrained• It’s the max intensity that the aerobic system can manage without

the anaerobic system contributing a large dose of the energy• Actually a better measurement of max aerobic performance than VO2

max (important to measure in elite athletes)• The intensity that can be maintained without fatigue (theoretically)

55


Muscular system changes after strength training• Muscular fitness

• Strength, power, endurance

• Muscular strength• Can increase for a variety of causes (neural, structural,

metabolic)• Contribution may vary across individuals (20% to 100% over

several months)• Training specificity is still relevant (if you want maximum

strength gains, must train the 1-3 rep max occasionally (largest FTb fibers only recruited at 70% of max or greater)

56

Physiological adaptations to training Muscular system changes after strength training

• Muscular strength• Muscle hypertrophy

• Starts after 6-8 weeks training• Major cause of strength gain after this muscle fiber size, connective tissue between fibers

• Fiber size because of # of contractile filaments (more cross bridges that generate force)

• Protein synthesis , exceeds protein degradation (more protein in muscle)

• Hypertrophy will be specific to the muscle fibers trained (if you want hypertrophy in all fibers, vary resistance and increase training time...but that means longer sessions, more problems with fatigue...wait, I’ll take some supplements...you can see how it goes)

• Largest fibers are FTb, and they are also the strongest, so they are the ones to target for big muscles (big loads - grunt)

57


• Muscular strength• Metabolic adaptations

• ATP, PCr & glycogen content of muscle • Enzyme activity ( PCr brkdown, ATP production)• Increases capacity for brief powerful contractions

• Neural adaptations• 1-8 weeks• Better synchronicity of motor unit recruitment, less neural

inhibition…real neural level adaptations• Reduced antagonist muscle activation, increased synergist

muscle activation, and of course better coordination

58


• Muscular power and endurance• Power = strength (greater force) with speed• Faster contractions have less potential force, and vice versa (at any

one point – clearly to move a 10lb weight quicker requires more force)

• Max power occurs at something like 30-50% max force• How you train (speed/strength) is directly linked to the training

effect...specificity of training• Endurance increases with strength – the stronger you are, the less

%MVC you need to use for any given contraction, so you can maintain it for longer (same total submax force can be achieved w/fewer motor units)

59


•Training and muscle fiber number or type•Fiber type largely genetically determined in # fibers possible, but unlikely to contribute

much to strength change compared to hypertrophy and neural adaptation

•Alteration from FTb to FTa also possible (though very difficult) – but can be reversed when training stops oxidative capacity, capillary #...endurance

•No evidence of alteration from ST to FT

60

Now questioned (see for example Ericsson 2004)

Now questioned (see for example Ericsson 2004)

Physiological adaptations to training Basic principles of training

• Specificity• Match the speed, force, and timing of the target activity

• Training variables• Mode, duration, intensity and frequency...all can be varied• Training for health will differ greatly from training for sport

• Overload• Manipulate training variables across workouts to ensure

muscles worked to capacity

61

e.g. Steve Cram

e.g. Surgeon general’s recommendation, ACSM

Physiological adaptations to training Basic principles of training

• Individualization• Tailor training to suit your own needs...we’re all a little different

• Reversibility• Unless you keep exercising you will lose the adaptations caused by

becoming fit (detraining is rapid)• Training to maintain fitness does not have to be as rigorous as that

required to cause it (50% reduction in training ok for 2-3 weeks…little loss of fitness)

• Periodization• Little peaks, followed by plateaus, followed by changes in intensity

or other training variables, followed by increased peaks, and so on...• Microcycles (1-2 weeks) and macrocycles (2 weeks – 2 months)• Training is planned around peaking at the right time

62


Basic principles of training•Overtraining

•Too much of a good thing...can have serious consequences

• Fatigue, illness, injury• Requires prolonged rest and less training – sometimes

for several months

•Correct training requires both understanding the scientific principles, and observing the individual athlete to see whether it’s working for them.

63


Basic principles of training•Continuous and interval training

64



•Continuous training• Benefits vary (see table previous slide)• Low intensity: 50-60% for non-athletes, 70-80% for

athletes• High intensity: 60% + for non-athlete, 85% + for athlete• Can vary pace to avoid monotony, spread training

benefits

65



•Interval training• Often more beneficial than continuous (can work at

greater intensity, causing greater adaptations – e.g. synchronous motor unit recruitment)

66


Training for cardiovascular endurance•Healthy, young individual: To improve VO2

max, exercise for at least 15min at 60% of VO2 max or better, 3 x p/week or more

•Older, unfit, infirm: can still improve with less intensity (low as 30-40% VO2 max)

67


Training for cardiovascular endurance•Reliably improving fitness: 50-85% VO2 max for

20-60m, 3-5 x p/wk•Elite athlete: several hours a day at 85% or

more of max (!)•It’s a continuum – the fitter you are, the

harder it is to gain further improvements

68


Methods of strength training•Health stuff:

•strength training improves:• glucose tolerance• blood lipid levels• body composition

•Strength training helps with:• Back pain• Osteoporosis• Mobility• Muscle tone

69


Methods of strength training• Types of muscle contractions

• Static (isometric) & dynamic (concentric, eccentric) contractions can be used in training (static are rare)

• Types of strength training• Isometric not good (gains specific to joint angle trained)• Iso-inertial (isotonic – fixed resistance) & isokinetic (fixed

speed, you maximize force [machine measures how much force you can produce moving at a given speed])

• Remember training specificity• Isotonic training most realistic and so gives most gains• Isokinetic machines mostly used therapeutically

70


Methods of strength training• Training to improve muscular strength and endurance and

to induce hypertrophy• # reps; # sets; # sets x # reps (total volume); resistance• Express intensity as either an absolute (10RM) or relative

weight (% 1RM)• Power: hypertrophy first, then strength, then speed work

To develop

Reps Sets Intensity Rest between sets

Max strength 2-6 3—6 High > 3 min

Hypertrophy 8-12 3-6 Moderate > 3 min

Endurance 15-25 1-4 Moderate < 1 min

Power 2-6 3-5 Fast moving > 3 min

HR fitness 8-20 1-2 Moderate < 1 min71


Methods of strength training• The role of eccentric muscle actions in strength training

• These are most problematic for injury/soreness, but seem to confer benefits in training effects too (why would this be a surprise?)

• Most normal exercises incorporate both concentric and eccentric contractions

72

Physiological adaptations to training Causes of muscle soreness

• Weakens muscle (sore muscle is weak muscle)• Can be immediate...

• “Burning” in the muscle caused by LA build up – temporary (gone after a few hours)

• Or delayed...• DOMS can last for several days (it’s the one that greets you

when you wake up the next day, even two days later)• Likely after eccentric work • Once you’ve had it once, it becomes less likely to occur again

(in that training regime)• It does not seem to be a necessary part of training…though

tissue damage is involved in strength gain

73


Exercise for health-related fitness• ACSM and USSG exercise guideline summaries

• www.acsm.org/physicalactivity

• What should I do to stave off illness/CVD/stay healthy?• Answer varies greatly from one individual to another• See tables on p. 161 for summary

• Explaining the summaries• Types of recommended exercise

• “large muscle groups” – walking, cycling, jogging – impact CVD risk factors, and less likely to be risky in terms of inflated blood pressure (as opposed to weight training)

74

Physiological adaptations to training Exercise for health-related fitness

• Explaining the summaries• Intensity of exercise

• “moderate” – you get the training benefits but at less injury risk• 50-70% for fat burn & health, 70-85% for fitness gain

• Duration of exercise• 15+ min for health, less than 60 min to avoid injury• Long duration low intensity for fat burn vice versa for…

• Frequency of exercise• Less than 3 x per week – little gain in fitness, more than 5, greater

risk of injury• Low intensity exercise can be done every day (low injury risk)

75

Physiological adaptations to training Exercise for health-related fitness

• Resistance exercise•Good for reduced risk of heart disease, osteoporosis,

and increased functional capacity

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Documents

Part III Exercise Physiology 1. The study of the body’s immediate and long- term responses to exercise Useful for... See table on p. 120 Generally, evaluating