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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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