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Medicine & Science in Sports & Exercise: Volume 28(12) December 1996 pp 1492-1497
Optimal pedaling rate estimated from
neuromuscular fatigue for cyclists
TAKAISHI TETSUO1, YASUDA YOSHIFUMI2; ONO TAKASHI3, MORITANI TOSHIO4
1. College of General Education, Nagoya City University, Mizuho-cho, Mizuho-ku, Nagoya 467, JAPAN;
2. Toyohashi University of Technology, Tempaku-cho, Toyohashi 441, JAPAN;
3. Graduate School, Aichi University of Education, Kariya 448, JAPAN;
4. Laboratory of Applied Physiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606, JAPAN
Submitted for publication February 1995.
Accepted for publication December 1995.
Address for correspondence: Tetsuo Takaishi, College of General Education, Nagoya City University, Nhzuho-cho,
Mizuho-ku, Nagoya 467 JAPAN. E-mail:takaishi@nsc.nagoya-cu.ac.jp
ABSTRACT
This study was designed to examine the optimal pedaling rate for pedaling exercise at a given work intensity
for cyclists. Six college-aged cyclists each performed six sessions of heavy pedaling exercise at individually
selected work rates based on their aerobic capacity. The optimal pedaling rate was evaluated on the basis of
minimal neuromuscular fatigue as evidenced by the integrated electromyogram (iEMG) slope defined by the
changes in iEMG as a function of time. The means of the iEMG slope demonstrated a quadratic curve versus
pedaling rate. The mean values at 80 rpm (0.53 (SD 0.20)μV·min-1) and 90 rpm (0.67 (SD 0.23)μV·min-1)
were significantly smaller than those values at any other pedaling rate. On the other hand, the mean value of
oxygen uptake(˙VO2) expressed as a percent of the subject's maximal˙VO2 (% ˙VO2max) at each pedaling rate
also showed a quadratic curve with minimal values at about 60 or 70 rpm. ˙VO2 at 70 rpm (84.0 (SD 5.0)%
˙VO2max) was significantly smaller than those values at 80 rpm (86.3 (SD 3.5)% ˙VO2max), 90 rpm (87.4 (SD
3.8)% ˙VO2max), and 100 rpm (90.1 (SD 3.8)% ˙VO2max).
These data strongly suggest that the optimal pedaling rate estimated from neuromuscular fatigue in working
muscles is not coincident with the pedaling rate at which the smallest ˙VO2 was obtained, but with the
preferred pedaling rate of the subjects. Our findings also suggest that the reason that cyclists prefer a higher
pedaling rate is closely related to the development of neuromuscular fatigue in the working muscles.
For endurance cyclists, it is interesting and advantageous to know the optimal combination of pedaling rate
and pedaling force to maintain a certain velocity. At the same time, many investigators are interested in
clarifying how the combination is decided in individuals. Generally, experienced cyclists prefer a
comparatively higher pedaling rate of approximately 90 rpm or more (14,18). Previous studies that attempted
to determine the optimal pedaling rate from the standpoint of energy expenditure confirmed that a higher
pedaling rate leads to poor mechanical efficiency because oxygen consumption (˙VO2) during exercise
increases linearly or exponentially according to the increase in pedaling rate (3,5,11,30) owing to the increase
in internal work for repetitive limb movements(36). Studies adopting the rate of perceived exertion(RPE) as a
measure of the optimal pedaling rate suggest that the most economical pedaling rate relative ˙VO2 is not
necessarily coincident with the pedaling rate at which the lowest RPE is obtained(18,24).
On the other hand, when a certain force output is maintained either isometrically (20,27) or
dynamically(23,26), the electrical discharge from working muscles gradually increases. In our previous
investigation performed with noncyclists (34), the increase in the integrated electromyogram (iEMG) as a
function of time, i.e., the iEMG slope (8,22,23), was applied as a criterion to compare the degree of
neuromuscular fatigue during cycling exercises with different pedaling rates versus a given power output. We
found that a pedaling rate at which the minimal neuromuscular fatigue could be obtained exists and that the
rate (70 rpm) is coincident to the preferred pedaling rate of the subjects.
We hypothesized that neuromuscular fatigue in the working muscles rather than the economy of metabolism
is closely related to the preferred pedaling rate of the subject. Because experienced cyclists generally prefer
and use higher pedaling rates in daily training, it is expected that the pedaling rate of the minimal
neuromuscular fatigue for cyclists is different from that for non-cyclists. Accordingly, the purpose of this
study was to investigate the pedaling rate at which the minimal neuromuscular fatigue takes place for cyclists
and to compare this rate with the rate-dependent energy expenditure.
METHODS
Subjects. Six healthy male members of a college cycling team volunteered for this study. Mean height, body
mass, and age were 172.8 (SD 3.2) cm, 62.5 (SD 3.1) kg, 20.7 (SD 1.5) yr, respectively. The study was
approved by the Institutional Review Board for Use of Human Subjects at Toyohashi University of
Technology. All experimental procedures were explained in detail to each subject who then signed a statement
of informed consent in accordance with the policy statement of the American College of Sports Medicine.
Protocol. A ramp exercise test and six sessions of the criterion exercise were performed during four separate
laboratory visits. However, two subjects had an additional experiment, bringing their total to five visits. On
the first visit, they performed a ramp exercise test to the point of exhaustion on an electromagnetically braked
ergometer. Following the warm-up exercise, the ramp test was started with 2 min of unloaded exercise at 60
rpm, then the intensity was increased by 20 W·min-1. Six sessions of the criterion exercise, composed of
warm-up exercise and main exercise on the ergometer, were performed on the second, third, and fourth visits.
The warm-up exercise consisted of 2 min of unloaded pedaling and 5 min of pedaling at 100 W. The main
exercise consisted of 15 min of pedaling at individually decided power output. The two exercises were
performed consecutively without a break. The intensity (power output) of each individual for the main
exercise was decided as that at which approximately 85% maximal oxygen uptake(˙VO2max) was elicited while
pedaling at 60 rpm. Six sessions of exercise were performed in random order at the pedaling rates of 50, 60,
70, 80, 90, and 100 rpm, respectively. The subjects exercised twice on each experimental day but had at least
3 h of rest between the sessions. After performing all sessions of the criterion exercise, each subject was asked
which pedaling rate they preferred.
To gain further knowledge of the difference in pedaling skill estimated by the electromyogram (EMG)
between cyclists and noncyclists, two cyclists from this study and two noncyclists from the previous study(34)
took part in an additional experimental program. They performed seven sessions of a nonfatiguing pedaling
exercise for a short period (less than 2 min) in random order at 40, 50, 60, 70, 80, 90, and 100 rpm,
respectively. The individual power output for pedaling was different among subjects; however, it was the
same as that for the main exercise of the criterion exercise. Each session was preceded by the warm-up
exercise consisting of 1 min of unloaded pedaling and 2 min of 60-W (for noncyclists) or 100-W (for cyclists)
pedaling. A rest of at least 15 min or more was taken between the sessions. During the exercises, a metronome
was used as a pacemaker.
Measurement of EMG. Myoelectric signals during the six sessions of criterion exercise and the short period
exercise were recorded by the surface EMG technique. The EMG instrumentation used here was fully
described in our previous study (34). Briefly, two miniature electrodes (Ag-AgCl, 6-mm contact diameter,
4-cm inter-electrode distance) were placed over the belly of the vastus lateralis muscle and a reference
electrode was placed over the anterior superior spine of the iliac crest. All electrode placements were preceded
by abrasion of the skin to reduce the source impedance to less than 2 k ω. Myoelectric signals were
amplified(AM-601G, Nihon Koden, Japan) with band pass filtering (5-500 Hz) and recorded digitally
(RD-101T, TEAC, Japan). The recorded data were digitized at a sampling rate of 1 kHz, and the iEMG was
calculated at 20-s intervals for a period of 15 min with a Hewlett-Packard 98580C desktop computer. The
iEMG for the short period exercise was calculated using the stable 30-s period after the beginning of a
nonfatiguing exercise performed at the same power output as the main exercise of the criterion exercise. The
pedaling rate was estimated by using the electric signals from a goniometer attached to a leg and judged to be
stable when the difference from a given pedaling rate was less than± 1 rpm.
Measurement of oxygen uptake. Measurements of oxygen uptake(˙VO2) were made in all subjects for the
ramp test and the criterion exercise. During the ramp test and six sessions of criterion exercise, respiratory
measurements were obtained by our on-line computer system, which consisted of a mass spectrometer
(WSMR-1400, Westron, Japan) and pneumotachograph connected to a respiratory flow transducer. The
analog signals of fractional concentration of O2, CO2, and N2 from the mass spectrometer and those from the
flow transducer were continuously digitized at 100 Hz by the computer system (PC-9801 FIII, NEC, Japan).
The ˙VO2 carbon dioxide production and expired ventilation were calculated every 20 s, and those data were
stored on a floppy disk for subsequent analysis. To determine ˙VO2 during the main exercise for each subject,
the mean ˙VO2 after the initial 3 min was obtained because it would have taken at least 2 min to reach a steady
state of˙VO2 at the given intensity.
Data analysis. The iEMG data for the main exercise during each session of the exercise was fitted
mathematically to a straight line by linear regression technique and the slope coefficient was defined as the
iEMG slope.
Statistics. Mean and standard deviation for ˙VO2 and the iEMG slope were calculated by the standard
methods. Statistical comparisons were applied using one-way analysis of variance (ANOVA). When a
significance of P < 0.05 was obtained in ANOVA,post-hoc multiple comparison tests were performed to
compare the means among the respective pedaling rate treatments. Differences were considered significant at
P < 0.05.
RESULTS
The mean value of ˙VO2max for our cyclists were 3.55
(SD 0.38) l·min-1 and 57.8 (SD 1.2) ml·min-1·kg-1. The
exercise intensity of the main exercise, equal to the
intensity corresponding to 85% of ˙VO2max, ranged from
200 to 240 W. Figure 1 shows a typical set of data
indicating the changes in iEMG as a function of time
(A) and the differences of the iEMG slope in each
pedaling rate treatment (B) in one subject. With each
period of exercise, the linear increase of the iEMG was
obtained. The iEMG slope itself showed a tendency of
decrease with the increase of pedaling rate from 50 to
80 rpm; however, it increased at 90 and 100 rpm.
Similar changes of the iEMG as a function of time and
similar changing pattern of the iEMG slopes versus
pedaling rate were obtained with each subject. As
shown in Figure 2A, the mean value and SD of the
iEMG slopes demonstrated a quadratic curve with a
bottom at about 80 rpm. The value at 80 rpm (0.53 (SD
0.20) μV·min-1) was significantly smaller than those
values at 50, 60, 70, and 100 rpm (1.09 (SD 0.20)
μV·min-1), and the value at 90 rpm (0.67 (SD
0.23)μV·min-1) was significantly smaller than that at
100 rpm. There was no statistically significant
difference in the mean values between 80 rpm and 90
rpm.
Figure 1-A typical set of data for the change in integrated
electromyogram (iEMG) as a function of time at 80 rpm for a s
subject. The line through the symbols shows the regression lin
e
mathematically. The slope of the regression line was defined a
s
iEMG slope (A). The difference in the iEMG slopes for six dif
f
pedaling rates for the same subject (B).
The ˙VO2 for the main exercises for each
subject is represented by the average for
minutes 3 to 15, which is equal to the duration
to obtain the iEMG slope. To normalize the
variance of˙VO2 derived from the different
power output among subjects,˙VO2 for the main
exercises were expressed as a percent of the
subject's ˙VO2max. Figure 2B shows the mean
value and SD of% ˙VO2max versus pedaling rate.
The mean value for 70 rpm (84.0 (SD 5.0)%
˙VO2max) was significantly smaller than the
values at 80 rpm (86.3 (SD 3.5)% ˙VO2max) and
90 rpm (87.4 (SD 3.8)% ˙VO2max). The mean
value for 100 rpm (90.1 (SD 3.8)%˙VO2max)
was significantly larger than the value at any
other pedaling rate. There was no statistically
significant difference among the mean values
between 80 and 90 rpm. The means for the
absolute ˙VO2 for 50, 60, 70, 80, 90, and 100
rpm were 3.13, 3.02, 3.01, 3.04, 3. 10, and 3.21
l·min-1, respectively. The most preferred
pedaling rates obtained from subjective fatigue
sensations were 80 or 90 rpm, which were
similar to the pedaling rate preferred by
cyclists(4,14).
To evaluate possible differences in the muscle activation levels at the same power output, noncyclists and
cyclists participated in the additional experiments. For comparisons, the iEMG obtained during a short,
nonfatiguing 30-s recording at 40 rpm was used to normalize all subsequent iEMG data obtained at different
pedaling rates. Figure 3 demonstrates such normalized iEMG recorded from two noncyclists in our previous
study (34) and two cyclists from this study. For noncyclists the normalized iEMG showed an increase with the
increase of pedaling rate; however, cyclists did not have a large difference in normalized iEMG among the
pedaling rate treatments. These data suggest that pedaling performed at a pedaling rate higher than 70 rpm
would result in higher muscle activation level for the noncyclists while no such effect could be seen for the
cyclists.
Figure 2-The relationship between pedaling rate and the means of the
iEMG slope (A) and pedaling rate and the means of oxygen uptake
expressed as a percentage of the individual maximal oxygen uptake
(B).* P < 0.05. ** P < 0.01.
DISCUSSION
An increase of the iEMG as a function of time was obtained for each session of the pedaling rate treatment
in individuals in this study. These results are similar to those in our previous study (34). The increased iEMG
owing to a progressive recruitment of an additional motor unit(MU) and/or an increase of firing rates of an
already-recruited MU may take place to compensate for impaired force generation caused by some peripheral
factors such as the decrease of intramuscular pH owing to the increase in lactic acid (10,29); the disturbance
of the potassium homeostasis, i.e., the loss of K+ from the muscle cells(33); and the worsening of relaxation
of a muscle resulting from changes in the rate of calcium removal from the contractile material (16).
Comparisons of the iEMG slopes among different pedaling rates indicate that a pedaling rate exists at which
significantly smaller neuromuscular fatigue can be obtained (80 or 90 rpm for cyclists). The optimal pedaling
rate was higher than that for noncyclists (70 rpm) (see Fig. 2A in(34)).
It is assumed that the difference in the sensing of fatigue plays an important role in deciding the preferred
pedaling rate for a cycling exercise. To estimate the optimal pedaling rate from the standpoint of the
preference, the rate of perceived exertion (RPE) has often been used(4,19). Pandolf and Noble (24) pointed
out that the RPE was closely related to the feelings of strain in the working muscles and joints on the basis of
results that demonstrated that the RPE at 80 rpm was lower than those at 40 and 60 rpm despite ˙VO2 and HR
at 80 rpm being higher than those at 40 and 60 rpm. In addition, Ekblom and Goldberg (9) reported that the
RPE for running and swimming were lower than that for pedaling when compared at the same condition of
˙VO2, and they suggested that the RPE was strongly related to the feelings of strain to overcome resistance in
the working muscles rather than a central factor, i.e., perceived tachycardia and dyspnea.
In this study we did not use the RPE because we thought the RPE were not appropriate to compare the
differences in slight fatigue sensations among severe exercises performed at the same power output with
different pedaling rates. But the preferred pedaling rate of our subjects (80 or 90 rpm) was coincident to the
rate at which minimal neuromuscular fatigue took place(Fig. 2A) although ˙VO2 at these pedaling rates was
significantly higher than at 70 rpm and/or 60 rpm (Fig. 2B). When judged from the standpoint of the energy
Figure 3-The relationship between pedaling rate and
normalized iEMG for cyclists (CYC 1, CYC 2) and
noncyclists (NON 1, NON 2). Normalized iEMG at
each pedaling rate was obtained by a percentage to
the iEMG at 40 rpm for individuals.
expenditure, a higher pedaling rate does not lead to advantage because the internal work for repeated limb
movements gradually increases according to the increase in pedaling rate (34,36). However, it has been
pointed out that pedaling at a higher rate has the advantage of decreasing both the actual pedaling force to turn
the crank and the ratio of the maximal peak tension on the pedal to the maximal leg force for dynamic
contraction at a given pedaling rate (25,32), both of which are related not only to the feelings of strain in the
working muscles but also to the muscle fiber type recruited for the exercise (21).
According to previous studies on the relationship between exercise intensity and the type of muscle fibers
recruited for the exercise(12,35), the work intensity in our study, ranging from 85 to 90% ˙VO2max,
corresponds to the intensity at which fast-twitch (FT; Type 2) fibers should be recruited in addition to the
slow-twitch (ST; Type 1) fibers that are recruited. Then it is expected that changes in pedaling rate, which
reflect the speed of muscle contraction, would result in different recruitment of muscle fibers. Recently
Ahlquist et al.(1) reported that prolonged pedaling exercise at an intensity of 85% ˙VO2max at 50 rpm rather
than 100 rpm resulted in greater Type 2 fiber glycogen depletion. Their results indicate that the required force
output derived from changing the pedaling rate might change the recruitment of MUs and have a great effect
on subsequent metabolism. Furthermore, Hagan et al. (13) reported that the respiratory exchange ratio (R) for
90 rpm was significantly lower than that for 60 rpm. These results would seem to suggest that many ST fibers,
which are suitable for a prolonged exercise based on higher oxidative capacity(17) and higher mechanical
efficiency for contraction(7,37), are recruited at higher pedaling rates to maintain a given power output.
Higher pedaling rates may elicit another advantage. It has been reported that muscle blood flow, which is
closely related to capillary density in the working muscles (6), was occluded at the intensity of force output
corresponding to 15-20% of maximal voluntary contraction(15). This finding suggests that a slight decrease in
pedaling force and a shortened contraction time resulting from a higher pedaling rate would result in better
blood flow and venous return in the working muscles and would influence the type of muscle fibers to be
recruited for the work (2). Thus, it is clear that a higher pedaling rate leads to some improvements in blood
flow, recruited muscle fiber type, and required pedaling force. These findings may explain the reason that
neuromuscular fatigue estimated by the iEMG slope, which shows the largest value at 50 rpm, became
significantly smaller with the increase in the pedaling rate.
On the other hand, Patterson and Moreno (25) demonstrated that the average of resultant force, which was
determined as the vector sum of the shear and normal pedal forces, was lowest at 90 rpm for 100 W and 100
rpm for 200 W, despite the fact that the crank force, which acted perpendicularly to the crank arm, gradually
decreased when the pedaling rate was increased in the range of 40-120 rpm. The findings indicate that an
excessively high pedaling rate does not necessarily lead to an advantage of decreasing the pedaling force.
They have also confirmed that the resultant force for the same work varied widely among individuals and
showed that a difference in pedaling skill existed among subjects. Coyle et al.(6) demonstrated that a
difference in pedaling skill exists even between highly trained cyclists groups (elite-national class vs
good-state class) on the basis of the difference of the peak torque during the downstroke when a given work
output at the same pedaling rate was performed. Our EMG data (Fig. 3) seem to support the existence of such
skill differences, especially at high pedaling rates of over 80 rpm, i.e., higher iEMG for the noncyclists.
Assuming that the difference in the iEMG at higher pedaling rates in noncyclists results from the excessive
recruitment of FT fibers (11) to compensate for the lack of the leg force owing to the inefficient pedaling skill,
it is probable that noncyclists prefer to use a lower pedaling rate such as 65 rpm(19) to avoid earlier
neuromuscular fatigue and higher˙VO2.
In this study, ˙VO2 was expressed as the average value for the exercise duration (from 3 to 15 min) because
we wanted to compare the differences in energy expenditure for the same duration for the iEMG slopes among
the pedaling rates. However, it is well known that ˙VO2 increases linearly and slowly as a function of time
when physical exercise of more than 3 min is performed at a constant work rate of moderate intensity(38). In
addition, such an increase of ˙VO2, which is named a ˙VO2 slow component, has recently been explained by
the increase in activity of working muscles(28). Meanwhile, Shinohara and Moritani(31) demonstrated that a
close relationship exists between the increase in iEMG and a slow increase in ˙VO2 during heavy exercise.
Actually, our subjects showed a slow increase in˙VO2 during exercise, and some reached almost 95%
of˙VO2max at the end of 50- and/or 100-rpm sessions. If the relationship between the increase in ˙VO2 and
the iEMG slope is direct and close, it is reasonable to speculate that the cyclists may prefer the pedaling rate
that elicits the smallest increase of ˙VO2, which may be reflected in the smallest iEMG slope. This hypothesis
holds great potential. However, it is not clear at present because some of our subjects had no increase of ˙VO2
in spite of a significant increase of iEMG.
The pedaling rate of minimal neuromuscular fatigue, 80 or 90 rpm, was slightly lower than the pedaling rate
that we had predicted for cyclists. Our subjects were cyclists with 3-4 yr of experience in road races and
accustomed to pedaling at high rates. However, they were not in the same physical condition as national-class
or state-class cyclists(6,7). We assumed that the pedaling rate of minimal neuromuscular fatigue would be
higher if it was obtained from national-class cyclists with higher level of physical fitness.
In conclusion, our results suggest that the reason that cyclists prefer a higher pedaling rate is closely related
to the neuromuscular fatigue in working muscles rather than the economy for pedaling exercise. It was
speculated that the optimal pedaling rate estimated by neuromuscular fatigue would gradually shift to a higher
pedaling rate with acquisition of better pedaling skills during the course of training.
ACKNOWLEDGEMENTS
The authors would like to acknowledge Mr. Jeffrey L. Brown for his careful reading of the manuscript. We
are also indebted to the students who participated in this research project.
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