.,/4/ 6./ 47 0

CIRCULATORY AND RESPIRATORY RESPONSES

TO CYCLE ERGOMETRY AT DIFFERENT

PEDAL RATES.

THESIS

Presented to the Graduate Council of the

University of North Texas in Partial

Fulfillment of the Requirements

For the Degree of

MASTER OF SCIENCE

By

Raymundo Hernandez, B.S.

Denton, Texas

May, 1991

Hernandez, Raymundo. Circulatory and respiratory responses to cycle

ergometry at different pedal rates. Master of Science (Biology), May, 1991, 63

pp., 21 tables, 24 illustrations, reference, 107 titles.

The effects of moderate workload exercise at different pedal rates on

circulatory and respiratory parameters were studied. Five subjects performed

seven discontinuous constant-load cycle ergometer tests of 30 minutes duration at

pedal rates of 40, 50, 60, 70, 80, 90 and 100 rpm. Oxygen uptake and carbon

dioxide production were determined by standard open circuit spirometry, while

heart rate was recorded by electrocardiograph. The CO2 rebreathing procedure

was administered during the exercise bout in order to determine cardiac output.

Blood pressure was determined for each test, and total peripheral resistance was

calculated. The findings indicate that progressive increases in pedal frequency

during discontinuous constant-load cycle ergometry produce progressive increases

in cardiovascular, respiratory and metabolic responses and a decrease in gross

exercise mechanical efficiency. The results indicate that oxygen uptake, cardiac

output, heart rate, ventilation and arterial-venous oxygen difference increases

curvilinearly as pedal rate increases, possibly as a result of increases in

recruitment of muscle fibers and/or muscle groups. These findings suggest that

circulatory and respiratory responses are due to "central command" which sets

the basic efferent response pattern. However, this effector pattern is modulated

by afferent input originating from the legs during progressive increases in pedal

rate.

INTRODUCTION AND OVERVIEW

The relationship between exercise efficiency and pedalling frequency

during cycle ergometry has been investigated for over 80 years. While numerous

studies 4,6,8,13,16,17,23,24,31,32,35,40,41,45,47,68,79,85,87-91,101,102 have examined the effect of

workload and pedal rate on energy expenditure and efficiency, the findings are

inconsistent. Some studies4,42 suggested that an optimal pedal rate exists for all

workloads, while others 9,16,25,31,84 suggested that the optimal pedal rate increases

as workload increases. Astrand and Rodahl4 and Hermansen42 reported that a

pedal rate of 60 rpm produced the highest maximal oxygen uptake capacity,

while Israel et al.Y recommended that 60 rpm be used for studies of ergometric

performance. However, Dickinson23 reported that energy expenditure and

mechanical efficiency varied with the speed of pedalling, with the highest

efficiency occurring at 33 rpm. Seabury et al.85 and Coast and Welch16 reported

that the most optimal pedal rate progressively increases with increases in power

output, while Hagberg et a139 reported that for trained cyclists the optimal pedal

rate occurred at 91 rpm.

A number of studies8 ,24 ,27,60,77 have failed to observe an optimal pedal rate

for various workloads. In early studies, Benedict and Cathcart8 studied an elite

cyclist pedalling from 70 to 120 rpm, while Duffield and McDonald24 studied

pedal rates of 40 and 85 rpm. The findings from these studies suggest that

1

2energy expenditure increases progressively with increases in pedal rate. Loligen

et al. 6 reported that increases in pedal rates at constant power output lead to

progressive increases in oxygen uptake. Faria et al.27 reported for high power

outputs that gross efficiency is unchanged for pedal rates from 65 to 130 rpm,

while at low power output efficiency decreases with increases in pedal rate.

Patterson and Pearson7 reported that oxygen uptake increased slightly but did

not change significantly with pedal rates from 40 to 90 rpm. Despite these

differences, most studies6,8,2 7 ,47 ,59,72,75, 77,78,4 have shown that increases in pedal rate

lead to progressive increases in oxygen uptake and decreases in efficiency.

While the effect of pedal frequency and workload on oxygen uptake and

energy expenditure has been the subject of many investigations, no study has

sought to examine the circulatory and respiratory responses associated with

changes in exercise efficiency as a result of changes in pedal rate. Thus, there are

two fundamental questions concerning the effect of pedal frequency on exercise

efficiency during constant-load exercise: 1) What is the effect of pedal rate on

cardiac output, stroke volume, heart rate, blood pressure and total peripheral

resistance?; and 2) What is the effect of pedal frequency on ventilation, tidal

volume, breath frequency, inspiratory and expiratory durations, and mean

inspiratory flow and inspiratory duty cycle?

A further examination of these questions will provide fundamental

information leading to a better understanding of how leg cycling rates affect the

cardiovascular and respiratory responses to muscular exercise.

3

REVIEW OF THE LITERATURE

Circulatory and respiratory responses to workload during exercise.

The circulatory and respiratory responses to exercise has been studied

extensively over the last 100 years. The findings from these studies show that

oxygen uptake, cardiac output, heart rate, and arterial-venous oxygen difference

increase linearly in relation to increases in workload, while carbon dioxide

production and pulmonary ventilation increase exponentially with increases in

workload 4,16,17,31,39,87. Stroke volume increases and reaches a plateau during

progressive increases in workload, while total peripheral resistance decreases

progressively with increasing workloads4,39,90.

Increases in ventilation (VE) occur as a result of increases in tidal volume

and breathing rate . Increases in ventilation also are accompanied by increases

in mean inspiratory flow and the respiratory duty cycle58 due to decreases in both

inspiration and expiration time. Tidal volume increases as ventilation rises, but

eventually reaches a plateau forcing further increases in ventilation due to a rise

in breathing rate.

The relationships among oxygen uptake, cardiac output and workload are

not affected by the level of exercise training. However, training decreases heart

rate and increases stroke volume at submaximal workloads. In the trained

individual, the larger stroke volume is due to a larger left ventricular

end-diastolic volume. This leads to greater maximal cardiac output at maximal

oxygen uptake. Trained individuals have a higher maximal ventilation and breath

frequency, but a similar tidal volume to untrained individuals.

4Efficiency and muscular responses to pedal frequency.

The concept that efficiency is related to an optimal speed of muscle

contraction is based on the classic studies of Hartree and Hill. In this study,

isolated frog sartorius muscle was stimulated maximally against different

resistances. The amount of work and power produced were calculated, and

myothermic heat production was recorded. These investigators defined efficiency

as work output divided by energy expenditure. Work output equalled: W =

WO(1-k/t) where; (WO)= theoretical maximum work done, (k)= viscosity of the

muscle, and (t)= duration of the stimulus. Energy expenditure equalled: H =

Wa(1+bt) where; (a)= energy required to set up a contraction of unit strength,

and (b)= energy required to do one unit of work per second of stimulus. Thus,

efficiency equalled the ratio of work output to energy expenditure: E = W/H

=(1-k/t)/a(1+bt).

Hartree and HillI also showed that power output and mechanical

efficiency are greatest at an optimal velocity of contraction. The maximal power

output was obtained at approximately 30% of maximal speed of contraction of a

muscle, whereas maximal efficiency was obtained at approximately 20% of

maximal speed of contraction. At very fast and very slow speeds of muscle

contraction, power output and mechanical efficiency approached zero. Thus, the

speed of contraction of a muscle is dependent upon the work required and that

maintaining a speed of contraction close to the maximal power output would

result in the highest efficiency.

AV. Hill45 4 suggested that this efficiency equation could be applied to a

non-isolated human muscle at work. This concept is supported by the work of

5Sargeant et al. on maximum leg force and power outputs during cycle

ergometer, anaerobic work. They reported that maximal power output occurred

at a pedal rate of 110 rpm, and that power decreases at pedal rates below and

above 110 rpm. These findings imply that mechanical efficiency also decreases at

pedal rates below and above 110 rpm.

Hartree and Hill" defined efficiency as the ratio of work performed to

energy expended. However, over the years, four definitions of efficiency

applicable to the human performing work have been used. These are gross, net,work and delta efficiency.

Gross efficiency, as originally defined by Hartree and Hill, is total amount

of energy expended (E) to accomplish a given amount of external work (W), i.e.

gross efficiency = (W/E) X 100%. In this definition, no subtraction is made for

energy expenditures associated with rest or zero-load work. Net efficiency is

defined as the ratio of external work (W) performed to energy expended (E)

above that at rest (R). This definition subtracts the resting basal energy

expenditure from the total energy expended to perform work, i.e. net efficiency

= (W/E-R) X 100%. Work efficiency is defined as the ratio of work performed

(W) to energy expended (E) above that in cycling during unloaded pedalling

(UL), i.e. work efficiency = (W/E-UL) X 100%. This definition subtracts the

energy expended by the legs performing "zero-load" work on a cycle ergometer.

A fourth definition of efficiency, delta efficiency, is defined as the ratio of the

change in work accomplished (dW) to the change in energy expended (dE), i.e.

delta efficiency = (dW/dE) X 100%. Delta efficiency is also referred to as

apparent efficiency and is the inverse of the slope of energy expenditure topower output during a progressive incremental-load exercise test.

6Early study of Exercise efficiency and pedal rate

Many studies6 ,8,23,24 ,27,38,39,60,77,78,8O,8s,91 have utilized Hill's efficiency equation

to examine the relationship between exercise efficiency and energy expenditure.

Benedict and Cathcart reported that gross efficiency decreased from 70 to 120

rpm due to an increase in heat production by the working muscles. These

investigators further reported that the highest gross efficiency was reached at a

pedal rate of 70 rpm which was the slowest pedal rate consented to by their

cyclist. Although their study did not examine efficiency at slower pedal rates,

their data suggested that gross efficiency would be higher at slower pedal rates.

Duffield and McDonald 2 4 extended the work of Benedict and Cathcart8 to

include responses to work at 40 to 85 rpm and found that gross efficiency

increased as pedal rate decreased. They suggested that the rate of movement

and workload were the main components contributing to heat production during

cycling and that this relationship was a linear equation: Q= aK + bV, where;

(Q)= heat production, (V)=rate of movement, (K)= resistance load, and (a) and

(b) are constants. These investigators suggested that the total energy cost of

work is due in part to work done at a relatively constant efficiency and partly to

the cost of producing that movement at a specific speed. Therefore, as speed

and workload increase, efficiency decreases due to higher heat production.

Dickinson23, using Hartree and Hills' formula, reported the optimum time

of one foot movement (half a pedal revolution) to be 0.9 seconds or a pedal rate

of 33 rpm. Dickinson found also that efficiency was not significantly affected by

changes in workload. Thus, the highest efficiency occurred at an optimum speed

of contraction, and for all pedal speeds above or below the optimal pedal

7

frequency more energy is expended.

Garry and Wishart32 reviewed the equation and findings of Hartree and

Hill" and those of Dickinson and reported that Hartree and Hills' equation was

only useful in estimating the efficiency of a isolated human muscle. They stated

that the energy expended to maintain the body in a working position was not

included in the equation. Also, the Hill equation did not account for the energy

cost of the respiratory and circulatory systems during work. Although these

investigators reported efficiency values in accordance with Hartree and Hills'

formula, they also reported that "the only efficiencies obtainable from metabolic

experiments on the human subject, that are of any practical value, are gross

efficiencies." Therefore, it was suggested that applying Hartree and Hills' formula

to a human subject performing steady state leg cycling exercise made it

impossible to calculate the actual metabolic energy required for the individual

muscles involved in the cycling motion.

EXERCISE EFFICIENCY AND CYCLE PEDAL RATES

Instantaneous power output and cycling ergometry.

Previous descriptions of the force-velocity relationship of human muscle in

vivo are based on single, isolated muscular contractions. However, a few studies

have examined the effect of pedal rate on maximal anaerobic work. Sargeant et

al.8 studied the effect of pedal rate on maximal anaerobic power. These

investigators reported that for cycle ergometry during a 20-second maximal

dynamic exercise, the force-velocity relationship was linear and that peak force

was exerted at 900 past top dead center in each pedal revolution. Furthermore,

their power-velocity relationship plots showed that this relationship was parabolic

8and that maximal power output occurred at 110 rpm. The maximum mean

power output at this pedal rate was approximately three times the maximum

mean power output available from aerobic sources.

McCartney et al.63 ,' also studied short term instantaneous power output,

leg muscle volume and fiber types during maximal cycling exercise. These

investigators found that the power-velocity relationship was parabolic and that

maximal peak power output and mean peak power output occurred at 140 rpm.

They also reported that the subject with the highest maximal peak power output

had 72% of type II (fast-twitch) fibers, whereas, the subject with the lowest

maximal peak power output had 53% type II fibers. This supports the concept

that a larger proportion of type II fibers are present in athletes required to

perform mostly short term maximal exercise. They also found a positive

relationship between thigh muscle volume and peak power output, which may

have significantly contributed to the exertion of force especially at slow rates ofmuscle contraction. McCartney et al.65 later supported their previous findings by

describing the power-velocity relationship as indeed parabolic and that the range

at which individuals can produce maximal peak power is between 120 to 160

rpm.

Maximal V02 and pedal rate

Since a number of studies have suggested the existence of an optimal

pedal rate for cycle ergometer work at different power outputs, it has been

suggested that VO2 is also related to the pedal rate of the maximal exercise

test. However, the findings from these studies are inconclusive. Hermansen42

studied the effects of variation in pedal frequency on maximal oxygen uptake and

9reported that for cycle ergometer tests performed at 50, 60 and 70 rpm, themean value for oxygen uptake increased as pedal rates increased from 50 to 60

rpm. However, no significant increase in oxygen uptake was seen when thepedal rate was increased to 70 rpm. Therefore, he suggested that 60 rpm is

better suited for calculating maximal oxygen uptake in cycle ergometry.

The findings of Buchanan and Weltmanl 0 based on maximal tests

conducted at 60, 90 and 120 rpm supports Hermansens' findings. In the study,

maximum values for both V02 and work output were higher at 60 rpm than at

90 or 120 rpm. Therefore, they concluded that 60 rpm should be used for

laboratory assessment of V02 and work output. Israel et al.4 studied the effects

of varying pedal frequencies from 30 to 90 rpm on oxygen uptake, heart rate andblood pressure. They reported that the lower pedal frequencies produce the

highest efficiency of movement, whereas, the high pedal frequencies are less

efficient. Therefore, they recommended that 60 rpm should be used for bicycle

ergometer testing in order to accurately determine maximal oxygen uptake.

Coast and Welch'16 17 found that during prolonged bouts of exercise with varyingpedal rates and power outputs that work at 80 rpm produced the highest VO2.and power output. McKay and Banister67 compared bicycle and treadmill

maximum oxygen uptake determinations at various speeds and reported that asimilar VO2. was achieved at 80 and 100 rpm. However, Lollgen et al.5 9'

found no statistically significant differences in VO2 for work done at 40, 60, 80and 100 rpm, and Pivarnik78 studied maximal oxygen uptake at 50 and 90 rpmand found that there was no significant difference between the mean peak

oxygen uptake (V0 2) values at either pedal rate. Jessup et al.49 studied the

10validity of the Astrand-Rhyming submaximal exercise test used to predict VO

capacity and found that predicted VO to be equivalent for both the 50 and

80 rpm tests. Michielli and Stricevic6 7 reported that for varying pedal rates from

40 to 80 rpm at a constant power output of 100 W, significantly higher heart

rates were seen at 70 and 80 rpm than at 40 to 60 rpm. Therefore, they

suggested that untrained and high risk individuals should work on a cycle

ergometer at low power outputs (<100 W) and pedal rates of 40 to 60 rpm.

Submaximal exercise and pedal rate

Numerous studies have examined the relationship between cycle pedaling

rate and exercise efficiency. However, the findings from these studies are

inconsistent and controversial regarding the postulated mechanisms underlying

exercise efficiency. Pugh"" studied the relationship between submaximal exercise

efficiency and pedal rate and reported that, for work rates from 145 to 300 W,

the efficiency value was 25%. At 88 rpm and work rates from 145 to 300 W,

efficiency declined to 22%. He further showed that, at work rates less than 145

W, mechanical efficiency decreased progressively and significantly at the higher

pedal rates, but did not decrease significantly at the lowest pedal rate. These

findings are supported by the study of Bannister and Jackson6 who reported that

mechanical efficiency remained significantly constant over a wide range of work

rates. However, Knuttgen et al.56 reported that, during concentric work at 130

W, gross efficiency was higher for 100 rpm than for the same work at 20 rpm

and concluded that efficiency increases with increases in pedal rate and work

rate.

11Based on the concept of an optimal pedal rate, several studies have

attempted to model the relationship between pedal rate and efficiency utilizing

parabolic equations. Eckermann and Millahn reported that for workloads of

600 and 900 kgm/min conducted at 30, 40, 60, and 90 rpm oxygen uptake was

best predicted utilizing a parabolic equation of the form: y = a + bx + c/x2

(where x=rpm). Utilizing this equation, it was reported that a pedal rate of 45

rpm produced the highest efficiency. Seabury et al. also reported on the effects

of pedal frequency on energy expenditure utilizing the parabolic equation

developed by Eckermann and Millahn. In their study, workloads from 250 to

2000 kgm/min were associated with the most optimal pedal rates which varied

from 42 to 62 rpm. It was found that each workload had its own most optimal

pedal rate and that as workload increases so did the most optimal pedal rate.

Other investigators"'9 1 7 have sought to model the relationship between

energy expenditure and pedal rate utilizing a parabolic equation of the form: y

= a + bx + cx2 (where x=rpm). Boning et al.9 reported that the lowest V02

and highest efficiency shifted to higher pedal frequencies as the workload

increased. They suggested that these responses were due to the selective

recruitment of different muscle fiber types. Coast and Welch 6 also used the

parabolic equation model of y = a + bx + cx2 (where x=rpm) and reported that

progressive increases in workload were associated with progressive increases in

the most optimal pedal rate and hence the highest efficiency. These findings

imply that efficiency is related to both the amount of force being generated by

the muscle and the velocity of the muscle contraction. The work of Suzuki9o

showing fast twitch fibers to be more mechanically efficient at fast pedal rates

12supports this concept. In a later study, Coast et al.17 found that prolonged bouts

of cycle ergometry are most efficient when the pedal rate is 60 - 80 rpm. These

investigators reported that, at 60 - 80 rpm, heart rate, gross efficiency and rating

of perceived exertion was statistically lower than at 40, 100 and 120 rpm.

However, several studies47 ,77 ,05 have failed to find a parabolic relationship

between pedal frequency and energy expenditure. Israel et al.47 reported on the

effect of incremental-load work conducted at varying pedal frequencies. They

reported that the highest efficiency occurred at low pedal frequencies when

muscle forces were highest. In contrast, at high pedal rates, efficiency decrease

significantly. These investigators suggested that the relationship between pedal

frequency and oxygen uptake was linear. In order to make full use of this

relationship, a pedal rate of 60 rpm was recommended. The authors suggested

that this pedal rate would optimize oxygen uptake and muscle loading in order to

produce the highest efficiency possible. They suggested that parabolic equations

do not accurately describe the effect of pedal rate on energy expenditure.

Banister and Jackson 6 studied the effect of speed and load changes on

oxygen uptake while bicycling from 50 to 120 rpm at each workload of 360 to

2100 kgm/min. They reported a constant efficiency over all workloads and pedal

frequencies. It was suggested that a proper combination of pedal rate and

workload could be used to optimize oxygen uptake, and therefore, muscular

performance. In addition, Patterson and Pearson" failed to show any statistically

significant differences in oxygen uptake, heart rate or rating of perceived exertion

during varying pedalling rates of 40 to 90 rpm and constant power outputs.

13Wise 1s studied oxygen uptake, heart rate, and energy expenditure during

varying pedal rates and constant work rate and found a gradually increasing,

curvilinear relationship between oxygen uptake, heart rate, and energy

expenditure with increases in pedal frequency. Faria et al.? investigated the

oxygen cost during different pedalling speed and constant power output. They

reported that oxygen cost progressively increased with increased pedal rate at low

power outputs, but decreased with increased pedal rate at high power outputs.

In addition, they found that the highest gross efficiency value occurred at a slow

pedal rate (60 rpm) and low power output (800 kgm/min). While no significant

difference in efficiency was observed for all three pedal rates at a high power

output (1800 kgm/min), the lowest efficiency value was observed at a high pedal

rate and low power output.

Nag7 4 reported on the physiological responses to submaximal exercise. He

found that ventilation (VE) remained constant throughout various pedal rates,

except at 50 and 150 W at 75 rpm, which was significantly higher. Also, he found

that oxygen uptake (V02) and heart rate increased directly with increases in

pedal rate. He concluded that as pedal rate increased from 45 to 75 rpm and

work rate increased from 50 to 150 W, net mechanical efficiency decreases due

to a lower power output per liter of oxygen uptake.

Lollgen et al.59 reported that constant power output conducted at low

pedal rates had little affect on oxygen uptake. However, oxygen uptake

increased as pedal rate increased. In addition, increases in pedal rate had a

greater affect on oxygen uptake at low workloads. However, as workload

increased, the potentiating affect of increases in pedal rate on oxygen uptake

14

occurred at progressively higher pedal rates. Lollgen et al. supported their

previous findings by reporting that during submaximal exercise the rate of

perceived exertion is more closely related to workload rather than heart rate.

Therefore, they suggest that an individual perceives mechanical stress easier than

physiological strain, which may increase certain physiological factors (i.e. heart

rate and oxygen uptake).

Gaesser and Brooks31 studied delta efficiency during steady rate exercise

workloads from 0 to 800 Kgm/min and for pedalling rates from 40 to 100 rpm.

They suggested that efficiency progressively decreases as workload increases in a

curvilinear manner. In addition, these investigators reported that efficiency

decreased with progressive increases in pedal rate. They also evaluated the

various types of exercise efficiencies and concluded that delta efficiency best

represented the concept of exercise. In a related study, Henderson et al.4 1

studied the effects of circular and elliptical chainwheels on steady rate work

efficiency and found that the relationship between energy expenditure to work

rate appeared to increase linearly regardless of the type of chainwheel used.

Also, they found that delta efficiency decreased with increases in work rate for

all chainwheels. However, Stainsby et al.87 countered that the use of baseline

subtractions (i.e. subtracting rest, zero load, and previous workload energy

expenditure) did not reveal the mechanisms underlying exercise efficiency, and

thus, obviated delta efficiency as a more accurate definition of efficiency

compared to gross, net and work efficiency.

While the use of baseline subtractions from exercise expenditure has been

debated, the addition of "internal work" to the total workload has also been

15

performed. Morrissey et al.73 found that if internal work performed by the legs

were added to the external work rate, the total resulting power output would

significantly increase for concentric work and decrease for eccentric work. This

effect can best be observed at high pedal frequencies (90 rpm) and low power

outputs. They conclude that the difference in overall work performed may

account for the very large variation in physiologic responses reported throughout

the literature. Wells et al.95 supported these findings by reporting that when

comparing concentric and eccentric work, if internal work is not accounted for,

this may lead to errors in calculating total power output by as much as 12% to

97%.

Few investigators have examined pulmonary ventilatory responses to

changes in pedal rate. Gueli and Shepardm investigated the effects of pedal

frequency at 50, 60, 70, 85 and 100 rpm on breathing patterns and metabolic

responses. While breathing rate and ventilation slightly increased with increasing

pedal frequency these changes were statistically insignificant. However, heart

rate and oxygen uptake increased significantly as pedal frequency increased. They

reported an optimum efficiency at rates of 60 to 85 rpm. These investigators

suggested that changes in metabolic rates during exercise contributed to changes

in ventilation. In contrast, Bechbache and Duffin7 studied the entrainment of

breathing frequency by exercise rhythm during moderate steady state exercise at

50 rpm. They showed that using an external rhythm source influenced some

subjects to entrain their breathing patterns with that of the rhythmic device. Kay

et al.51 reported that breathing rate and inspiration and expiration times were

similar for work at 50 and 70 rpm.

16

Mechanisms of Exercise Efficiency

While many studies have described the affect of alterations in pedal rate

on oxygen uptake and exercise efficiency, few studies have attempted to describe

the mechanisms underlying the decrease in efficiency with increases in pedal rate.

Knuttgen et al. 56 reported that the high oxygen costs associated with high pedal

rates (100 rpm) was a result of the increased oxygen cost of accelerating the

contraction rate of the legs and an increase in tissue resistance due to internal

friction. They suggested that mechanoreceptor activity and/or central nervous

system motor activity influences on the circulatory and respiratory centers altered

the rate of oxygen uptake.

Gaesser and Brooks31, based upon the respiratory exchange ratio,

hypothesized that progressive increases in pedal frequency are accompanied by

the progressive recruitment of less efficient fast-twitch muscle fibers, and Gueli

and Shepherd8 suggested that decreased efficiency was due to recruitment of

inefficient fast twitch muscle fibers or by increasing the number of muscular

contractions to accomplish the work. Suzuki91 studied subjects with low and high

percentages of fast twitch fibers, and reported an increased efficiency in subjects

with a high percentage of fast twitch fibers performing incremental-load work at

100 rpm. He also found no difference between subjects with fast and slow twitch

fibers. Therefore, he suggested that the improper recruitment of slow twitch

fibers during rapid movements would require an increased energy expenditure,

and therefore, would significantly decrease efficiency. This is supported by

Miyashita et al. (72) who found that a subject with a high ratio of fast twitch

muscles was more efficient at high speed pedalling throughout five workloads

17(175 to 900 kgm/min.) and pedal rates of 40 and 100 rpm.

Goldspink et al.? suggests that as work rate increases during exercise,

different muscle fiber groups (i.e. slow twitch then fast twitch) become involved

in the muscular activity to hold efficiency constant. Commenting on previous

studies using isolated muscle preparations, Goldspink et al. stated that all

muscle fibers are stimulated at once and therefore the maximum efficiency will

be attained at the optimum rate of contraction of the predominant fiber type.

Goto et al.35 studied the integrated EMG of leg muscles during cycle

ergometry and reported that oxygen consumption showed a large curvilinear

increase with increases in pedal rate up to 100 rpm. They suggested that this

curvilinear relationship between oxygen consumption and speed of movement was

due in part to an increase in the internal friction or viscosity of muscle. In

addition, they suggested that as pedal rate increases a larger amount of muscle

mass from other parts are recruited to perform the desired workload and/or

pedal rate, thereby causing an increase in oxygen consumption which contributes

to a lower exercise efficiency.

Citterio et al. 4 studied the selective activation of muscle fibers during

pedal rates of 30 to 70 rpm and resistance forces of 1 to 3 kilograms. These

investigators reported that fast twitch fibers provide a greater power per stimulus.

They suggest that the quicker activation and relaxation of fast twitch muscle

fibers in response to electrical activity, selectively recruits them over slow twitch

fibers during high speed constant power outputs. Therefore, these investigators

postulated that at high pedal rates fast twitch muscle fibers are better able to

work on the ascending side of the power velocity relationship than the slow

18

twitch fibers.

STATEMENT OF THE PROBLEM

The purpose of this investigation was to evaluate the effect of pedal

frequency on the circulatory and respiratory responses to constant-load cycle

ergometry exercise. The objectives of this study were: 1) to determine the effect

of pedal frequency on the cardiac output, stroke volume, heart rate, blood

pressure and total peripheral resistance; and 2) to determine the effect of pedal

frequency on ventilation, tidal volume, breath frequency, inspiratory and

expiratory durations, mean inspiratory flow rate, and inspiratory duty cycle.

METHODS

Subjects

Five healthy males served as subjects in this study. The physical

characteristics of the subject are presented in Table 1. Prior to his voluntary

participation in this study, each subject completed a medical history

questionnaire, signed a statement of informed consent, and was administered a

resting and exercise electrocardiograph to identify any contraindications to

sustained ergometric exercise. Any individual having coronary heart disease,

hypertension, diabetes or lung disease was excluded from the subject population.

MEASUREMENTS AND DESIGN

Preliminary Measures

Each subject was measured for height in centimeters, and weight was

measured in kilograms. Pulmonary function was assessed from measures of

forced vital capacity (FVC), forced expiratory volume in one second (FEV10 ),

and peak expiratory flow.

19Maximal Exercise Tests

Each subject performed an incremental-load exercise test on a Quinton

electrically braked ergometer (Model 845) to determine maximal aerobic power

as indicated by peak oxygen uptake (VO2 max). Oxygen uptake was measured

during 5 minutes of rest and continuously throughout the workbout until the

subject reached exhaustion. Heart rates were monitored during each minute of

rest and work by 12-lead electrocardiography. The maximal test began at a

workload of 200 kgm/min and increased by 100 kgm/min every minute until the

subject reached exhaustion. During the maximal test, the pedal frequency was 60

rpm. The accepted criterion of a plateau or decrease in V02 with an increase in

work rate was used to indicate that the maximal V02 value had been achieved.

The highest value of V02 achieved was recorded as the subject's V0 2 max.

Blood pressure was monitored continuously during all phases of rest and exercise.

Table 1. Physical Characteristics of Subjects

SUBJECTSVariable 1 2 3 4 5 Mean + S.D.

Age (yrs) 43 26 21 22 21 26.6 + 9.4

Height (cm) 176.5 182.2 184.8 185.7 175.3 180.9 + 4.8

Weight (Kg) 67.6 75.2 86.8 101.3 62.6 78.0 +15.8

FVC (L) 5.1 6.1 5.5 6.2 5.9 5.76 + 0.46

FEVW. (L) 3.7 4.4 4.3 4.6 4.8 4.36 + 0.42

Peak Expir. 8.6 8.9 9.4 9.1 8.2 8.84 + 0.42Flow (I4sec)

Submaximal Exercise Tests

20On separate days, each subject performed seven submaximal tests, 30

minutes in duration, at a workload which represented 50% V02 max, as

determined during the V02 max test conducted at 60 rpm. Three of the five

subjects (no.1, 2, and 3) also performed tests at a workload which corresponded

to 25% V02 max, as determined during the initial V02 max test. The average

workloads were 130 Watts for the five subjects, and 54 Watts for the three

subjects. The seven submaximal tests at both power outputs were administered

in a randomized order at pedal frequencies of 40, 50, 60, 70, 80, 90, and 100

rpm.

The protocol for the seven submaximal tests at each work load included

10 minutes of seated rest on the ergometer followed by 30 minutes of pedalling

at the previously selected cadence. The CO2 rebreathing procedure was

administered on four separate occasions; during rest at minute 7, and during

exercise at minutes 9, 19, and 29.

Measurements

Dry bulb temperature (DB), wet bulb temperature (WB), barometric

pressure (P.), and vapor pressure (Pvp) were all measured and recorded before

each test. All equipment used to measure cardiovascular responses was also

calibrated prior to testing. Five electrodes were placed at V5, right arm, right

leg, left arm, and left leg positions on the torso, thus allowing exercise leads of

II, avf, and V5, to be monitored continuously on a Quinton electrocardiograph

(Model 630A).

The subject sat on an electronically-braked Quinton Ergometer (Model

845) whose height was adjusted to allow a comfortable pedalling action. The

21

subject was then fitted with a noseclip, a mouth piece was inserted, and placed

on the open circuit system for determination of oxygen uptake (VO2) and carbon

dioxide (CO2 ) production. After gases in the mixing chamber equilibrated with

those in the subject's lungs, the test was begun. Heart rate was measured and

recorded at the end of each minute of rest and exercise. Three blood pressure

measurements were taken during each of the four 10-minute phases of the test.

22

OPEN CIRCUIT SYSTEM

MuM C I I I =CmLAN UNT-

PhoasPneumoscan

General E

vo 2 V 9"""

Mixing

C LOCIL Clamber

DUILAY

Medical Gas02 Vm

Analyzer ~~CURT

C02,

Equations:

X (Fp,- F,02)

YCO V,'"" X (FCO,- FCO)

RER m VCO, / VOV, - HALDANE TRANSFORMATION -- >V,

Vi

m

Standards:

Temperature - 0OCPressure = 760 mmHg

Dry n 0%

Figure 1 Schematic of the open spirometry system.

23

Oxygen uptake and carbon dioxide production were measured utilizing the

open circuit spirometry method. The open circuit system utilized is diagrammed

in Figure 1. Expired air was collected and mixed in a 10-liter mixing chamber.

A continuous air sample was drawn at a rate of 1 ml ' sec1 into a Perkin-Elmer

medical gas analyzer (Model 1100) and analyzed for oxygen and carbon dioxide

concentrations.

Pulmonary ventilation was determined from measurements of inspired air

utilizing a Pneumoscan flow meter (Model S-301). Analogue voltage output from

the mass spectrometer and flow meter was recorded on a Soltec chart recorder

and fed through an A-D converter into an IBM PC/XT computer from which

breathing frequency (fB), tidal volume (VT), ventilation (VE, Llmin), inspiration

time (Ti), expiration time (Te), oxygen uptake (VO2 , L/min) and carbon dioxide

production (VCO2 , L/min) were calculated. Ventilation was corrected to body

temperature, pressure, saturated (BTPS), whereas, V02 and CO2 were corrected

to standard temperature, pressure, dry (STPD).

Cardiac output was determined by the CO2 rebreathing procedure as

described by Defares' 9. This indirect method estimates mixed venous CO2

pressure (PvCO2) by using a closed lung-bag system as an aerotonometer'.

Arterial PCO2 (PaCO2 ) was determined from end-tidal CO2 values. Once the

P,CO2 and PaCO2 estimates were obtained, they were converted to arterial and

venous CO2 contents (CVCO2 and CaCO2 ), respectively, utilizing the CO2

dissociation equation of Comroe1 6 . The Fick equation was then used to calculate

cardiac output:

24

Cardiac output, L/min = (Volume of expired CO2 (VCO 2) / (CCO2 -CaCO2 )

where; volume of expired CO2 (VCO 2) is the CO2 output determined by

standard open circuit spirometry, CvCO2 is the CO2 content of the mixed venous

blood, and CaCO2 is the content of the arterial blood.

In this study, the rebreathing bag contained 4% CO2 in 96% 02. During

the procedure the subject rebreathed in the bag for 10 breathing cycles

(approximately 10-15 seconds) in order to reach a PCO2 equilibrium between the

bag, lungs, and pulmonary artery. End-tidal CO2 (PETCO2) was measured and

through the use of a CO2 dissociation curve the CO2 content of the mixed

venous blood was calculated. In addition, through the utilization of heart rate

and arterial systolic blood pressure, stroke volume and total peripheral resistance

(systolic pressure/cardiac output), respectively, were also calculated.

Statistical Analysis

The effect of pedal frequency on the various cardiorespiratory measures

was analyzed utilizing repeated measures of one-way analysis of variance. In this

design the independent variable was pedal rate, with the dependent variable as

the various circulatory and respiratory measurements. Post-hoc comparisons

were made using the Student Newman-Keuls method. An alpha level of 0.05 was

accepted as significant (Table 2).

25

Table 2. Peak cardiorespiratory values attained during incremental-workSUBJElr

Variable

Workload(kgm/min)

Vo2(I/min)

VCo2(L/min)

Heart Rate(beats/min)

VE(BTPS)('/min)

VT(Ibreath)

RER

1

1400

3.26

4.07

180

152.3

3.24

1.2

2

1900

4.17

4.51

175

137.7

3.28

1.1

SUBJECTS3 4

1700 2100

3.87 4.76

4.42 5.18

173 183

107.3 151.8

3.16 3.79

1.1 1.1

5

1500

3.28

3.90

189

121.6

2.97

1.2

Mean +S.D.

1720 + 390

3.87 0.82

4.42 + 0.70

180+ 8

134.1 + 18.3

3.29 + 0.33

1.1 + 0.1

47 42 34 40 41fBr(breaths/min)

41 +4

mmmm

26

RESULTS

The data were analyzed utilizing repeated measures one-way analysis of

variance (ANOVA) indicating a statistically significant (F=13.89, P<0.001) effect

of pedal rate on gross mechanical efficiency. Post-hoc comparisons utilizing

Student Newman-Keuls (SNK) indicates similar values (P>0.05) for gross

mechanical efficiency occurred between pedal rates of 40 to 70 rpm, 40, 70, and

80 rpm, 80 and 90 rpm, and 100 rpm (Fig.2). Table 3 lists the mean values for

mechanical efficiency (ME) for each pedal rate.

TABLE 3. Mean values for gross mechanical efficiency during work at 130Watts for pedal rates from 40 to 100 rpm. Means with the same letter groupingare not significantly different.

RPM MEAN S.E.M SIGNIFICANT GROUPINGS

40 18.56 0.30 B A50 19.52 0.35 A60 19.13 0.35 A70 18.45 0.22 B A80 17.71 0.30 B C90 16.70 0.58 C100 15.44 0.55 D

The data were analyzed utilizing ANOVA indicating a statistically

significant (F=108.31, P<0.0001) effect of pedal rate on oxygen uptake. Post-

hoc comparisons utilizing Student Newman-Keuls indicates similar values

(P>0.05) for oxygen uptake occurred between pedal rates of 40 to 70 rpm, and

70 and 80 rpm (Fig.3). Table 4 lists the mean values for oxygen uptake (V02 )

for each pedal rate.

27

U

U

U

U

0

0 40 50 60 70 80 90 100 110

RPM (rev -min-')

Figure 2 Mean gross mechanical efficiency responses ( S.D.) to pedal rate.

3.00 r

T T.I

I I I I I Ip

40 50 60 70 80 90 100 110

RPM (rev - min')

Figure 3 Mean V0 2 (L min-) responses ( S.D.) to increasing pedal rate.

21

20-

19-

18k

17

IIIIIII

121-

15 -

143c )

2.50

2.00

I

0",1.50 F

1.00 '3C )

I

I

28

TABLE 4. Mean values for oxygen uptake (L - mi-i) for work at 130 Watts forpedal rates from 40 to 100 rpm. Means with the same letter grouping are notsignificantly different.

RPM MEAN S.E.M. SIGNIFICANT GROUPINGS

40 2.02 0.18 C A50 1.92 0.17 C60 1.96 0.19 C70 2.03 0.18 C A80 2.12 0.20 A90 2.23 0.16 B100 2.41 0.17 D

The carbon dioxide production data were analyzed utilizing ANOVA

indicating a statistically significant (F=93.85, P<0.0001) effect of pedal rate on

carbon dioxide production. Post-hoc comparisons utilizing Student Newman-

Keuls indicates similar carbon dioxide production values (P>0.05) were found for

pedal rates of 40 to 70 rpm, and 70 and 80 rpm (Fig.4). Table 5 lists the mean

values for carbon dioxide production (VCO2 ) for each pedal rate.

TABLE 5. Mean values for carbon dioxide production (L - mi- 1) for work at130 Watts for pedal rates from 40 to 100 rpm. Means with the same letterrou Ing are not sificantly different.

MEAN S.RMI SIGNIFICANT GROUPINGS

40 1.95 0.18 B A50 1.86 0.16 A60 1.91 0.19 A70 1.96 0.17 B A80 2.06 0.19 B90 2.19 0.15 C100 2.36 0.16 D

29

4

00

1

0

TrT

' I III

30 40 50 60 70 80 90 100 110

RPM (rev - min-')

Figure 4 Mean VCO2 (L - min-1) responses ( S.D.) to increasing pedal rate.

65

60 [

CA

A-

55

50

45

40

35

p

30 40 50 60 70 80 90 100 110

RPM (rev - min')

Figure 5 Mean Ventilation (BTPS) responses ( S.D.) to increasing pedal rate.

3

2

30

The ventilation data were analyzed utilizing ANOVA indicating a

statistically significant (F=24.28, P<0.0001) effect of pedal rate on ventilation.

Post-hoc comparisons utilizing Student Newman-Keuls indicates similar ventilation

values (P>0.05) were found for 40 to 80 rpm, 40 and 60 to 100 rpm (Fig.5).

Table 6 lists the mean values for ventilation (VE) for each pedal rate.

TABLE 6. Mean values for ventilation (BTPS) during work at 130 Watts forpedal rates from 40 to 100 rpm. Means with the same letter grouping are notsignificantly different.

RPM MEAN S.E.M. SIGNIFICANT GROUPINGS

40 56.64 3.93 B A50 53.95 3.89 A60 54.38 3.92 B A70 55.04 4.09 B A80 58.60 4.05 B A90 62.40 3.68 B100 68.98 3.69 C

ANOVA analysis indicated no statistically significant (P>0.05) effect of

pedal rate on respiratory exchange ratio data. Post-hoc analysis indicated no

statistically significant (P>0.05) difference in the respiratory exchange ratio across

all pedal rates (Fig. 6). Table 7 lists the mean values for respiratory exchange

ratio (RER) for each pedal rate.

TABLE 7. Mean values for respiratory exchange ratio during work at 130 Wattsfor pedal rates from 40 to 100 rpm. Means with the same letter grouping arenot sificantly different.

RPMMEAN S.EM. SIGNIFICANT GROUPINGS

40 0.96 0.01 A50 0.97 0.01 A60 0.97 0.00 A70 0.96 0.01 A80 0.97 0.01 A90 0.98 0.01 A100 0.98 0.01 A

31

Blood pressure data were analyzed utilizing ANOVA indicating no

statistically significant (P>0.05) difference in systolic, diastolic, or mean arterial

pressure across all pedal rates (Fig.7). Table 8 lists the mean values for systolic

(SBP), diastolic (DBP), and mean arterial blood pressure (MAP).

TABLE & Mean values for systolic (SYS), diastolic (DIA) blood pressure andmean arterial pressure (MAP) in (mmHg) during work at 130 Watts for pedalrates from 40 to 100 rpm.

RPM SYS S.E.M. DIA S.E.M. MAP S.E.M

40 159 3 74 2 102.4 1.250 157 3 74 2 101.6 1.360 159 3 74 2 102.3 1.070 161 4 74 2 102.6 1.280 161 4 74 2 102.7 1.590 161 5 74 2 102.9 1.7100 165 4 74 2 104.6 1.5

The cardiac output data were analyzed utilizing ANOVA indicating a

statistically significant (F=28.05, P<0.0001) effect of pedal rate on cardiac

output. Post-hoc comparisons utilizing Student Newman-Keuls indicates cardiac

output similar (P>0.05) between 40 to 80, 60 to 90, and 70 to 100 rpm (Fig.8).

Table 9 lists the mean values for cardiac output (Qr).

TABLE 9. Mean values for cardiac output (L - min1 ) during work at 130 Wattsfor pedal rates from 40 to 100 rpm. Means with the same letter grouping arenot significantly different.

RPM MEAN S.E.M. SIGNIFICANT GROUPINGS

40 13.92 1.10 A50 13.83 0.86 A60 14.52 1.02 B A70 14.95 0.92 B A C80 15.27 1.14 B A C90 15.72 1.01 B C100 16.18 1.03 C

0

'.4C

0.

U

1.05 F

1.02

1.00 -

0.97 F0.95

0.92

0.90 I Ip

30 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 6 Mean R.E.R. responses ( S.D.) to increasing pedal rate.

* Systolic 0 DiastoHc * M.A.P.

be

0164

0

14"

tm

0'C

180170 -160-150 -140-130-120-110-100-90-80-70 -60

30-Ip

40 50 60 70 80 90 100 110

RPM (rev - min')

Figure 7 Mean Blood Pressure (mmHg) responses ( S.D.) to pedal rate.

32

I I ITIT

a

AL AL AL 'AOLlow '4V

IT,

46 w6b GAm

I

a

33

A slight decrease in mean values of total peripheral resistance occurred as

pedal rate increased. However, ANOVA and post-hoc analysis indicated no

statistically significant (P>0.05) difference in total peripheral resistance values

throughout all pedal rates (Fig.9). Table 10 lists the mean values for total

peripheral resistance (TPR) for each pedal rate.

TABLE 10. Mean values for total peripheral resistance in (mmHg/L - min,QC)during work at 130 Wafts for pedalmrates from 40to 100 rpn. Means with thesame letter grouping are not significantly different.

RPM MEAN S.E.M. SIGNIFICANT GROUPINGS

40 7.6 0.6 A50 7.5 0.5 A60 7.2 0.5 A70 7.0 0.5 A80 6.9 0.6 A90 6.6 0.4 A100 6.6 0.4 A

34

18

17

16 -1

A 15 -

~13

12 -30 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 8 Mean Q, (L - min-) responses ( S.D.) to increasing pedal rate.

10

8

F4

30 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 9 Mean TPR (mmHg/L min) responses ( S.D.) to increasing pedalrate.

35A statistically significant (P<0.0001) linear relationship between cardiac

output and oxygen uptake exists: Q,= 5.004(VO2) + 4.4129, R2 = .833, (Fig. 10).Table 11 lists the linear regression analysis of the relationship between cardiac

output (Q,) and oxygen uptake (VO2) for all tests conducted.

TABLE 11. linear regression eqation relating cardiac output (Qc, L-min 1)with oxygen uptake (VO2 , L-nin ) for each rpm test during work at 130 Wattsfor pedal rates from 40 to 100 rpm.

tion#OBS SEE( ) C.V.(%) R2 P

40 Qc= 5.97 (V02) + 1.84 5 0.59 3.48 .971 0.00250 Qc= 4.61 (V02) + 4.97 5 1.33 7.21 .799 0.0460 Qc= 4.87 (V02) + 4.96 5 1.38 8.01 .806 0.03970 Qc= 4.59 (V02) + 5.60 5 1.25 6.79 .818 0.03580 Qc= 5.39 (V02) + 3.85 5 1.24 7.17 .863 0.02390 QC= 5.15 (V02) + 4.26 5 1.99 9.22 689 0.08100 QC= 5.17_(V02) + 3.73 5 1.71 8.14 .753 0.057

OVERALL Qr= 5.004 (VO2) + 4.4129 35 0.42 6.49 .833 0.0001

U

20

18

16

14

12

10

8

6

4

2

0

o 54W (nm3)

- @ l130W (n=S)

Qcm-5.004(Vo,+4.4129 R2=0.833

-

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Vo (L- min-9

Figure 10 Plot of Qc vs. V0 2 regression line.

36Heart rate data were analyzed, ANOVA indicated a statistically significant

(F=3.81, P<0.004) effect of pedal rate on heart rate. Post-hoc comparisons

utilizing Student Newman-Keuls indicates similar values (P>0.05) for heart rates

were found for 40 to 80 rpm and from 90 to 100 rpm (Fig.11). Table 12 lists

the mean values of heart rate for each pedal rate.

TABLE 12. Mean values for heart rate (bpm) during pedal work at 130 Wattsfor pedal rates from 40 to 100 rpm. Means with the same letter grouping arenot significantly different.

RPM MEAN &S..M. SIGNIFICANT GROUPINGS

40 117 3 A50 114 5 A60 121 5 A70 125 4 A80 126 5 A90 129 3 A B100 141 4 B

ANOVA and post-hoc analysis indicated no statistically significant

(P>0.05) difference in stroke volume values with increases in pedal rate (Fig.12).

Table 13 lists the mean values for stroke volume.

TABLE 13. Mean values for stroke volume (ml - bt) during work at 130 Wattsfor pedal rates from 40 to 100 rpm. Means with the same letter grouping arenot significantly different.

RPMMEAN S.E.M. SIGNIFICANT GROUPINGS

40 119.5 8.9 A50 121.7 6.3 A60 120.3 6.6 A70 120.3 6.9 A80 121.6 7.4 A90 122.4 9.1 A100 115.2 7.1 A

37

150

-- 140

130- T

9120 - T

a 110-

10030 40 50 60 70 80 90 100 110

RPM (rev - min')

Figure 11 Mean Heart rate (bpm) responses ( S.D.) to increasing pedal rate.

135 -

WA 130 -

125 -

120 -

10 01150

0 110

10530 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 12 Mean Stroke volume (ml - bt') responses ( S.D.) to increasing pedalrate.

38

ANOVA analysis indicated a statistically significant (F=10.67, P<0.0001)

effect of pedal frequency on the Qc/VO2 ratio. Post-hoc comparisons utilizing

Student Newman-Keuls indicates, QC/V0 2 ratio was similar (P>0.05) between 40

to 90 rpm, and between 40, 50, 80, 90, and 100 rpm (Fig.13). Table 14 lists the

mean values for the QC/VO2 ratio for each pedal rate.

TABLE 14. Mean values for Q(/VO2 ratio during work at 130 Watts for pedalrates from 40 to 100 rpm.

RPM_ MEAN S.E.M SIGNIFICANT GROUPINGS

40 6.91 0.14 B A50 7.29 0.34 B A60 7.50 0.35 A70 7.44 0.32 A80 7.28 0.25 B A90 7.10 0.27 B A100 6.74 0.22 B

ANOVA analysis indicated a statistically significant (F=11.65, P<0.0001)

effect of pedal rate on oxygen extraction. Post-hoc comparisons utilizing Student

Newman-Keuls indicates, a-v 02 difference was similar (P>0.05) between 40 to

90 rpm, and between 40, 50, 80, 90, and 100 rpm (Fig.14). Table 15 lists the

mean values for a-v 02 difference for each pedal rate.

TABLE 15. Mean values for a-v 02 difference (ml 14) during work at 130Watts for pedal rates from 40 to 100 rpm.

MEAN .E.M SIGNIFICANT GROUPINGS

40 14.5 0.3 B A50 13.8 0.6 B A60 13.5 0.6 A70 13.5 0.6 A80 13.8 0.5 B A90 14.2 0.5 B A100 14.9 0.5 B

39

8.50

0 8.00-

7.50

o 7.00

6.50

6.00,I30 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 13 Mean QC/VO2 ratio ( S.D.) in relation to increasing pedal rate.

* 16 -

% 15

0

(4 13-

0

40 1230 40 50 60 70 80 90 100 110

RPM (rev- min"')

Figure 14 Mean changes in a-v 02 difference ( S.D.) in relation to pedal rate.

40

ANOVA and post-hoc analysis indicated no statistically significant

(P>0.05) effect of pedal rate on breathing rate (Fig.15). Table 16 lists the mean

values of breath rate (Fb) for each pedal rate.

TABLE 16. Mean values for breath rate (breath - mi-i1 ) during work at 130Watts for pedal rates from 40 to 100 rpm. Means with the same letter groupingare not significantly different.

RPM MEAN SEM. SIGNIFICANT GROUPINGS

40 27 2 A50 25 1 A60 24 1 A70 25 1 A80 27 1 A90 27 1 A100 29 1 A

ANOVA and post-hoc analysis indicated no statistically significant

(P>0.05) effect of pedal rate on tidal volume (Fig.16). Table 17 lists the mean

values for tidal volume (VT) for each pedal rate.

TABLE 17. Mean Values for tidal volume (L - breath1 ) during work at 130Watts for pedal rates from 40 to 100 rpm. Means with the same letter groupingare not significantly different.

RPM MEAN S.E.M. SIGNIFICANT GROUPINGS

40 2.14 0.21 A50 2.18 0.16 A60 2.26 0.18 A70 2.19 0.15 A80 2.23 0.18 A90 2.34 0.14 A100 2.38 0.12 A

41

40

351-

830-

0-

25

06 20-

15

30 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 15 Mean Breath rate (breath - min-) responses ( S.D.) to increasingpedal rate.

3.00-

2.75 -

2.500T

2.00 -

1.75 -

1.5030 40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 16 Mean Tidal Volume (L breath-) responses ( S.D.) to increasingpedal rate.

42

Inspiratory duration data were analyzed utilizing ANOVA and SNK post-

hoc analysis indicating no statistically significant (P>0.05) effect of pedal rate

(Fig.17). Table 18 lists the mean values for inspiratory breath duration (Ti) for

each pedal rate.

TABLE 1& Mean values for inspiratory breath duration (sec - breath) duringwork at 130Watts for pedal rates from 40to 100 rpr. Means with the sameletter grouping are not significantly different

RPM MEAN S..M. SIGNIFICANT GROUPINGS

40 0.99 0.04 A50 1.02 0.02 A60 1.05 0.03 A70 1.03 0.05 A80 1.03 0.06 A90 1.02 0.05 A100 0.96 0.04 A

ANOVA and post-hoc analysis indicated no statistically significant

(P>0.05) difference in the expiratory duration values with increasing pedal rates

(Fig.18). Table 19 lists the mean values for expiratory breath duration (Te) for

each pedal rate.

TABLE 19. Mean values for expiratory breath duration (sec - breath-1) duringwork at 130Watts for pedal rates from 40oto100rpn. Means with the sameletter grouping are not significantly different.

MEAN SE.M. SIGNIFICANT GROUPINGS

40 1.27 0.10 A50 1.43 0.12 A60 1.46 0.08 A70 1.38 0.10 A80 1.27 0.10 A90 1.26 0.11 A100 1.12 0.09 A

43

4..a0I-'C

U0

120

1.10

1.00

0.90

0.8o

0.70 '3(D

T L 1 T j

I

40 50 60 70 80 90 100 110

RPM (rev - min0')

Figure 17 Mean TI (sec breath-1) responses ( S.D.) to increasing pedal rate.

1.70 -

1.60-

1.50 -T

1.40 TaF

130 -

120 -

1.10

1.00

0.90-

o.8030

I Ia - aIII

40 50 60 70 80 90 100 110

RPM (rev min-')

Figure 18 Mean TE (sec breath-1) responses ( S.D.) to increasing pedal rate.

EM4

ANOVA and post-hoc analysis indicated no statistically significant

(P>0.05) difference in mean inspiratory flow for all pedal rates (Fig.19). Table

20 lists the mean values for mean inspiratory flow (V-fJ74) for each pedal rate.

TABLE 20. Mean values for mean inspiratory flow (L - sec1 ) during work at130 Watts for pedal rates from 40 to 100 rpm. Means with the same lettergrouping are not significantly different.

MEAN S.E.M. SIGNIFICANT GROUPINGS

40 2.15 0.18 A50 2.13 0.15 A60 2.16 0.17 A70 2.14 0.17 A80 2.19 0.17 A90 2.31 0.13 A100 2.47 0.13 A

ANOVA and post-hoc analysis indicated no statistically significant

(P>0.05) difference in values throughout all pedal rates (Fig. 20). Table 21

shows the mean values for the inspiratory duty cycle (T/Jrt) for each pedal rate.

Table 21. Mean values for inspiratory duty cycle (L - min) during work at 130Watts for pedal rates from 40 to 100 rpm. Means with the same letter groupingare not significantly different.

RPM_ MEAN S.EM. SIGNIFICANT GROUPINGS

40 0.44 0.03 A50 0.42 0.04 A60 0.42 0.03 A70 0.43 0.03 A80 0.45 0.04 A90 0.45 0.04 A100 0.47 0.04 A

44

T

~ I I I

2.80

2.69

2.58

2.47

236F

2.24

2.13 -

2.02

1.91 -

1.8oL30

90 100 110

Figure 19 Mean MIF (L sec-) responses ( S.D.) to increasing pedal rate.

40 50 60 70 80

RPM (rev min')

90 100 110

Figure 20 Mean IDC (L sec~1) responses ( S.D.) to increasing pedal rate.

45

U

0

0.

U

40 50 60 70 80

RPM (rev - min')

0.70

0.60

0.50 -

EoNwe

0

1 06

bo

0.40-

0.30

020)

___I _ ___ _ I I-I

46

DISCUSSION

The findings from the present investigation show that progressive increases

in pedal frequency during discontinuous constant-load cycle ergometer exercise

produce progressive increases in cardiovascular, respiratory and metabolic

responses and a decrease in exercise efficiency. These findings are similar to

those of other studies reporting a linear relationship between V02 and increasing

rpm8 ,1 0,22. However, the findings are in contrast to those studies showing that

energy expenditure and exercise efficiency follow a parabolic response pattern as

pedal rate progressively increases. Several studies9 ,16, 17 ,2, 8 5 ,8 9 have suggested a

parabolic relationship between pedal frequency and energy expenditure. This

model indicates that exercise efficiency is diminished at low and high pedal

frequencies, and thus optimal at some intermediate pedal rate. Many

investigators have attributed this response pattern to the use of different muscle

fiber types as pedal rate increases, with a most optimal pedal rate due to the use

of a mixture of fiber types. However, my findings and a review of previous

studies77'78 suggest that this concept is incorrect. The parabolic relationship is

intuitively incorrect because it predicts that slow pedalling at zero or light

workload produces an elevation in oxygen uptake above that of some

hypothetical optimal rate. The problem appears to be an inappropriate use of

quadratic equations to describe responses which are only curvilinear at elevated

pedal rates. My data suggest that oxygen uptake increases in a curvilinear

manner as pedal rate increases. This is supported by previous

studies 27,31,47 ,59 ,77,78 ,105 which also show a curvilinear increase in oxygen uptake as

pedal rate increases. The same relation is evident for cardiac output, heart rate,

47

ventilation and a-v 02 difference which suggest an increase in the recruitment of

more muscle groups and/or muscle mass.

Many previous studies were performed at various workloads and pedal

rates. Therefore, a concurrent study was performed at 54 Watts to study

response patterns to low workloads at varying pedal rates. The findings from

this study, the concurrent study and a previous study 05 which was conducted as a

continuous incremental-load exercise protocol are very similar. The overall

comparison of these three studies shows a consistency of results describing the

effects of progressive increases in pedal frequency on the cardiovascular,

respiratory and metabolic responses (Figures 21 and 22). The findings suggest

that the rate of increase for V02 is affected more by increasing rpm than by

increasing workloads. In addition, the findings and those of previous

studies 4' 59"' 0 5 indicate that the effect of increases in pedal rate is more

pronounced at low workload, while at the higher workloads the effect of pedal

rate is less. In our studies, gross mechanical efficiency progressively decreased as

pedal rate progressively increased. The increased QC and a-v 02 difference

indicates that peripheral blood flow and oxygen extraction are increased. The

increase in cardiac output and a-v 02 difference suggests an increase in blood

flow in order to supply an increased number of muscle fibers and/or muscle

groups. These muscle fibers are probably primarily slow-twitch fibers; fewer

slow-twitch muscle fibers are preferentially recruited over fast-twitch until all

slow-twitch fibers have been recruited.

Numerous investigators have described the relation between cardiac

output and oxygen uptake. An averaging of published equations by

4.00

3.50

3.00

2.50

2.00

1.50

1.00

0.50

0.000 50

100

00706 0 40 (130W)

100

490

500.50 40 (54W)

I - II mp p I

100 150 200 250

F/V Ratio (N - m -sec')

300

Figure 21 V02 vs. F/V ratio response for 54 and 130 Watts.

21

20

19

18

17

16

15

14

13

12

11

10

- ,, so

- .704 (1 30W)

-so-

- 90 s 40 (S4W)

. 60

-70

-so

-o

too

0 50 100 150

F/V Ratio (N-

200 250

m-' . sec-')

300

Figure 22 Gross Mechanical efficiency vs. F/VWatts.

ratio response for 55 and 130

48

U

0

0

. _

0

I

49

Faulkner et al.2 produced the following equation Qc (Lmin) = 5.5(VO2 , Lmin-

1) + 5.0. My study found the cardiac output to oxygen uptake relation to be:

Qc (L-min-1) = 5.004(VO2, L min-') + 4.4129, R2 = .833, P=0.0001. This is very

similar to the equation compiled by Faulkner et al. The cardiovascular

response during cycle ergometry is closely matched to the intensity of the

exercise. During this type of exercise, the increases in oxygen uptake are

matched by proportional increases in cardiac output. Our findings show that

during constant-load work, or at any given intensity, increases in pedal rate

increase both oxygen uptake and cardiac output proportionately in accordance to

the classic cardiac output-oxygen uptake relationship (Figure 10). Therefore, this

suggests that more muscle mass is involved with the use of faster pedal rates, not

merely the use of fast-twitch muscle fibers.

Pedal rate had an additive effect on most measures of respiratory

function. Animal studies23 suggest that increases in f and VE associated with

rhythmic exercise are related to the amount of neurogenic feedback originating

from contracting muscle. Ablation studies" of the brain stem indicate that the

pneumotaxic center is responsible for controlling respiratory rate, while the

apneustic center controls tidal volume. In the human subject, respiration can be

examined utilizing the mean inspiratory flow (V.I') as an expression of

inspiratoryy drive", and inspiratory duty cycle (T/I',) as an index of "respiratory

timing"57. The progressive increases in VT/Ti and T/I, suggest that respiration

is related to the speed and pattern of muscle contraction, possibly due to an

increased neurogenic drive originating from the legs. It could be that the higher

pedal rate and/or lower force per cycle stroke initiates muscle afferent signals

50

which input to the brain stem increasing Fb and VT, and subsequently VE.

A comparison of findings from the present study with that of Wise105

demonstrates the similarity of results in oxygen uptake to pedal rate while

utilizing different exercise protocols. The present study utilized a randomized

discontinuous constant-load, constant-rate protocol, while Wise 05 utilized

continuous incremental-pedal rate protocols. Figures 21 and 22 show the

similarity of oxygen uptake and heart rate between the discontinuous (present

study) exercise protocols conducted at 54 W and 130 W, and continuous105

incremental-rate exercise protocols conducted at similar workloads. This

indicates that continuous or discontinuous incremental-pedal rate protocols for

low and moderate level work can be used to evaluate the effect of pedal rate on

cardiorespiratory responses.

The concept of dynamic exercise efficiency defined by Hill suggests that

efficiency was influenced by both the force of contraction and speed of

contraction. In both cases efficiency decreased when the force of contraction or

speed of contraction was elevated. However, our data suggest that decreases in

exercise efficiency are primarily related to increases in the velocity of contraction,

with increases in the force of contraction having a minimal effect from 40 to 70

rpm. This is shown in the relationship between oxygen uptake and the leg

force-velocity ratio (Figures 23 and 24). These findings show that oxygen uptake

in relation to leg force-velocity ratio remains nearly constant from 40 to 80 rpm,

while from 80 to 100 rpm the oxygen uptake response greatly increases. This

suggests that a constant force-velocity ratio is an underlying factor in exercise

51

DIS 130W *CON 130W A

3.00-DIS 54W 0

CON 54W A2.50 -

2.00-

1.50 -

1.00-

0.50 -

0.00130 40 50 60 70 80 90 100 110

RPM (rev -min-')

Figure 23 V02 vs. rpm comparison of a continuous and a discontinuousprotocol at 54 and 130 Watts.

DIS 130W *CON 130W A

160- DIS 54W 015S - CON 54W A

140 -

* 130

V 120 -

110 -

100 -

80 -

70

30 40 50 60 70 80 90 100 110

RPM (rev - min-')

Figure 24 Heart rate comparison of a'continuous and discontinuous protocolat 54 and 130 Watts.

52efficiency. That is, when the force-velocity ratio is approximately

75 N m-1 sec-1 or greater, oxygen uptake and gross mechanical efficiency are

unaffected by pedal frequency. However, when the force-velocity ratio is less

than 75 N nm-1- sec-1 there is a marked increase in oxygen uptake and decrease

in exercise efficiency.

In this study, pedal rate had an additive effect on the mean

cardiorespiratory response pattern, i.e., the greater the pedal rate the higher the

HR, VE, and V02 responses. This finding is in agreement with the findings of

others9,16 3 1,8 5 . However, the explanation for the higher responses during faster

pedal rates is controversial. Most investigators 9 ,16 ,31',8 have postulated that the

greater cardiorespiratory response to faster pedal rates is related to the use of

fast-twitch or inefficient muscle fibers. However, experimental studies have

shown that both cortical and neurally mediated muscle reflex mechanisms are

important regulators of cardiorespiratory function',92-94 .

The cortical mechanism, also termed "central command", is responsible for

the level of efferent sympathetic and parasympathetic activity to the heart and

vascular system and recruitment of neuromuscular motor units. In situ studies

show a general relation between the number of motor unit impulses used to

produce a contraction and the amount of oxygen used for that contraction. The

muscle mechano- and chemo-reflex mechanism, also called the "exercise pressor

reflex" is related to both the mechanical and metabolic activity of the contracting

muscle through the activation of Group III and IV muscle afferent fibers,

respectively71 . Thus, the progressively higher cardiorespiratory response to

progressive increases in pedal rate may reflect a greater activation of both

53cortical and muscle metabo- and mechano-reflex mechanisms due to muscle

contractions of low force and high velocity of shortening for the purpose of

matching blood flow to the metabolic needs of the active muscle.

Central command and muscle metabo- and mechano-reflexes also provide

information concerning the amount of skeletal muscle involved in the exercise .

Animal studies have suggested that muscle reflexes during dynamic work are

the main contributors to the total cardiovascular and respiratory response to

exercise. Studies in the human subject indicate that cardiovascular and metabolic

responses to dynamic exercise progressively increase with the addition of muscle

mass57. Additional support for this concept comes from Ericson26 who reported

that elevations in pedal rate lead to recruitment of additional muscle groups and

muscle fibers within a given muscle. Thus, the higher cardiovascular, respiratory

and metabolic responses associated with the faster pedal rates are likely due to

the utilization of a greater amount of active muscle mass.

In situ studies suggest a general relationship between the number of

impulses used to produce a contraction and the amount of oxygen used for that

contraction. The concept is that the major determinant of force and velocity in a

voluntary contraction is the total number of motor units that are activated to

produce the contraction. The number of motor units times the frequency of

stimulation yields the number of impulses delivered to the muscle for the

contraction. The number of impulses delivered to the muscle determines the

oxygen uptake for the contraction. Thus, the central nervous system activates

enough motor units to move the point of applied force at the velocity necessary

to perform the desired motions in the time required. The more motor units that

54

are used, the greater the oxygen uptake for the movement. If one equates the

number of motor units required with effort, then the greater the effort, the

greater the oxygen uptake for the contraction or movement. Finally, the more a

contraction or movement is repeated the more the oxygen that will be consumed.

CONCLUSIONS

The findings from this study show that constant-load cycle ergometry

exercise conducted at progressively faster pedal rates produces progressively

higher HR, V, VO2 and Q responses. The progressive increase in Qc, decrease

in total peripheral resistance, and widening of the arterial-venous oxygen

difference suggests that more muscle mass and/or muscle groups are recruited in

order to maintain constant power output. These findings also suggest that

decreases in exercise efficiency occur as a result of increases in leg movement

speed, due to oxygen uptake and gross exercise efficiency remaining constant

with progressive increases in the leg force-velocity of shortening ratio. However,

the general pattern of responses observed for the ratio of Qc -to- VO2 and for

arterial-venous oxygen difference, suggest that a range of pedal frequencies from

50 to 70 rpm may produce optimal oxygen delivery and extraction. In addition,

the slight decrease in total peripheral resistance during moderate work for pedal

rates from 40 to 100 rpm, suggests that local vasodilation is counteracted by

vasoconstriction occurring in the active muscle. This occurs in order to maintain

mean arterial pressure and peripheral blood flow. The responses seen in this

study are likely due to "central command", which sets the basic efferent response

pattern. However, these findings suggest modulation of "central command" by

afferent input originating from stimulation of skeletal muscle mechano-receptors.

55

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