ArticlePDF Available

Differences in leg muscle activity during running and cycling in humans

Authors:

Abstract and Figures

Delta (delta) efficiency is defined as the ratio of an increment in the external mechanical power output to the increase in metabolic power required to produce it. The purpose of the present study was to investigate whether differences in leg muscle activity between running and cycling can explain the observed difference in delta efficiency between the two activities. A group of 11 subjects performed incremental submaximal running and cycling tests on successive days. The delta efficiencies during running and cycling were based on five exercise stages. Electromyograph (EMG) measurements were made of three leg muscles (gastrocnemius, vastus lateralis and biceps femoris). Kendall's correlation coefficients between the mean EMG activity and the load applied were calculated for each muscle, for both running and cycling. As expected, the mean delta efficiency during running (42%) was significantly greater than that during cycling (25%). For cycling, all muscles showed a significant correlation between mean EMG activity and the load applied. For running, however, only the gastrocnemius muscle showed a significant, but low correlation ( r=0.33). The correlation coefficients of the vastus lateralis and biceps femoris muscles were not significantly different from 0. The results were interpreted as follows. In contrast to cycling, which includes only concentric contractions, during running up inclines eccentric muscle actions play an important role. With steeper inclines, more concentric contractions must be produced to overcome the external force, whereas the amount of eccentric muscle actions decreases. This change in the relative contribution of concentric and eccentric muscle actions, in combination with the fact that eccentric muscle actions require much less metabolic energy than concentric contractions, can explain the difference between the running and cycling delta efficiency.
Content may be subject to copyright.
ORIGINAL ARTICLE
K.E. Bijker ÆG. de Groot ÆA.P. Hollander
Differences in leg muscle activity during running
and cycling in humans
Accepted: 29 May 2002 / Published online: 13 July 2002
Springer-Verlag 2002
Abstract Delta (D) efficiency is defined as the ratio of an
increment in the external mechanical power output to
the increase in metabolic power required to produce it.
The purpose of the present study was to investigate
whether differences in leg muscle activity between run-
ning and cycling can explain the observed difference in D
efficiency between the two activities. A group of
11 subjects performed incremental submaximal running
and cycling tests on successive days. The Defficiencies
during running and cycling were based on five exercise
stages. Electromyograph (EMG) measurements were
made of three leg muscles (gastrocnemius, vastus later-
alis and biceps femoris). Kendall’s correlation coeffi-
cients between the mean EMG activity and the load
applied were calculated for each muscle, for both run-
ning and cycling. As expected, the mean Defficiency
during running (42%) was significantly greater than that
during cycling (25%). For cycling, all muscles showed a
significant correlation between mean EMG activity and
the load applied. For running, however, only the gas-
trocnemius muscle showed a significant, but low corre-
lation (r=0.33). The correlation coefficients of the vastus
lateralis and biceps femoris muscles were not signifi-
cantly different from 0. The results were interpreted as
follows. In contrast to cycling, which includes only
concentric contractions, during running up inclines ec-
centric muscle actions play an important role. With
steeper inclines, more concentric contractions must be
produced to overcome the external force, whereas the
amount of eccentric muscle actions decreases. This
change in the relative contribution of concentric and
eccentric muscle actions, in combination with the fact
that eccentric muscle actions require much less metabolic
energy than concentric contractions, can explain the
difference between the running and cycling Defficiency.
Keywords Locomotion ÆEfficiency ÆMuscle
contraction type ÆElectromyography
Introduction
The Defficiency of an activity is the ratio of an increment
in the external mechanical power output to the increase
in metabolic power required to produce it, and is
expressed as a percentage. The Defficiency during run-
ning is significantly greater than that during cycling
(Zacks 1973; Asmussen and Bonde-Petersen 1974; Bijker
et al. 2001). Furthermore, the Defficiency of running is
also much greater than the muscle efficiency, which is
estimated to have a maximal value of 29% (Cavanagh
and Kram 1985). Poole et al. (1992) compared efficien-
cies during cycling, using measurements of both pul-
monary and leg oxygen uptake (
_
VV O
2
). No significant
difference between these Defficiencies was observed and
therefore Poole et al. (1992) concluded that, during cy-
cling, processes other than those in the exercising leg
muscles do not substantially contribute to the increased
metabolic cost at greater power outputs. For running,
changes in the metabolic energy cost of processes other
than the exercising legs can only explain the great D
efficiency if the metabolic energy cost of these processes
decreases with running against greater applied loads
(steeper inclines). This seems unlikely. Therefore, as-
suming that for cycling as well as for running the exer-
cising legs determine the metabolic cost of the
movement, the difference in the Defficiency between
running and cycling must be due to a difference in the
functioning of the exercising leg muscles.
Electromyography (EMG) can be used to study
muscle activity non-invasively. Quantified EMG mea-
surements of muscles can indicate if the muscle force is
increasing or decreasing (Deluca 1997). In addition,
Eur J Appl Physiol (2002) 87: 556–561
DOI 10.1007/s00421-002-0663-8
K.E. Bijker (&)ÆG. de Groot ÆA.P. Hollander
Institute for Fundamental and Clinical Human
Movement Sciences, Faculty of Human Movement Sciences,
Vrije Universiteit Amsterdam, Van der Boechorststraat 9,
1081 BT Amsterdam, The Netherlands
E-mail: k.bijker@fbw.vu.nl
Tel.: +31-20-4448459
Fax: +31-20-4448529
Komi et al. (1987) and Praagman (2001) have shown
clear relationships between the mean EMG activity of
concentric exercise and energy expenditure. However,
for eccentric muscle actions, no relationship between
mean EMG signals and applied load can be observed
(Komi et al. 1987). Therefore, the estimation of mean
EMG activity seems to be a good way of investigating
possible differences in the actions of the leg muscles
during running and cycling.
The purpose of the present study was to investigate
differences between running and cycling in the relation-
ships between mean EMG activity of the exercising leg
muscles and the external power output. Further, we in-
vestigated if such differences in muscle actions can ex-
plain the observed difference in Defficiency between
running and cycling.
Methods
Subjects
A group of 11 healthy (7 men, 4 women) subjects participated in
this study. All subjects were informed about the protocol to be used
and gave written informed consent. Their [mean (SD)] age was
23.7 (4.0) years, body mass was 69.3 (7.9) kg and height was
1.79 (0.10) m.
Protocol
All subjects performed a submaximal running and cycling test on
different days. After a warm up period of 10 min, the subjects
started the test protocol. Each test consisted of five, 6 min-long
exercise stages to ensure steady-state measurements, followed by a
rest of 4 min. Heart rate values (beatsÆper minute) were collected
using a heart rate monitor (Polar Vantage). To ensure that only the
aerobic energy system was involved, only those exercise trials with
heart rate values less than 85% of the maximal heart rate (Snyder
et al. 1994) and respiratory exchange ratios (R) values less than 0.95
were used in the calculation of Defficiency. Maximal heart rate was
estimated as (220 minus age in years).
During the running test, the subjects ran on a treadmill at a
freely chosen comfortable velocity (between 2.81 and 3.75 mÆs
–1
).
Stride frequency was controlled with help of a metronome. The
subjects ran up inclines between 0% and 5% in random order. The
mechanical power (P
mech
) increment between two successive incli-
nation values was about 20 W.
The study of Marsh et al. (2000) showed that pedal cadence
does not influence cycling Defficiency. Therefore, for practical
reasons, in the present study during the cycling test all subjects
cycled at a cadence of 80 r.p.m. The mean (SD) P
mech
output
during the initial cycling stage was 56.2 (8.7) W. The difference
between two successive stages during cycling was about 25 W.
Cycling exercise stages were also presented in random order.
Calculation of Defficiency
During the last 2 min of each exercise stage, the volume flow rate,
O
2
and CO
2
concentrations of the expired gas were measured
breath-by-breath (Oxycon Champion, Mijnhart). The Rvalues
were calculated over the same period of time. Assuming purely
aerobic energy production, metabolic power (P
met
, in watts) was
calculated as (Garby and Astrup 1987):
Pmet ¼ð4940 Rþ16040Þ=60½
_
VV O2ð1Þ
where
_
VV O
2
is in litres per minute.
In the cycling test, the external P
mech
was calculated from the
product of crank torque and crank angular velocity. In the running
test, extra external P
mech
was calculated as:
Pmech ¼mbgvsinðaÞð2Þ
where m
b
is the mass of the subject (kilograms), gis the acceleration
due to gravity and equal to 9.81 mÆs
–2
,vis the velocity of the tread-
mill (metres per second) and ais the angle of inclination (degrees).
For each subject, linear regression equations were calculated
from the extra external P
mech
and associated P
met
data. The D
efficiencies were calculated from the regression coefficient of the
regression lines.
EMG measurements
The EMG signals from three superficial leg muscles [gastrocnemius
(lateral head), vastus lateralis and biceps femoris] were recorded
using Ag-AgCl surface electrodes with an inter electrode distance of
approximately 2.0 cm. Before attaching the electrodes, a skin im-
pedance below 2.5 kWwas ensured by shaving, sanding and cleaning
the skin. The EMG signals were amplified, analogue band-pass fil-
tered (10–200 Hz) and sampled at a frequency of 1,000 Hz. During
the running and cycling tests, EMG signals were recorded during the
first 20 s of the 5th min of each exercise stage. Off-line, the digital
EMG signals were corrected for offset, full-wave rectified and low-
pass filtered (12 Hz). From the 20 s recordings, mean EMG values
were calculated from ten successive running and cycling cycles.
Statistical analysis
For running as well as for cycling, for each muscle the non para-
metric Kendall’s correlation coefficient (Siegel and Castellan 1988)
was calculated between the mean EMG value and the external
P
mech
output. Differences in Defficiency between running and cy-
cling were tested for significance using a Student’s t-test for paired
comparisons (P=0.05).
Results
In Fig. 1 a typical example of the two regression lines
and the resulting Defficiencies is presented. As expected,
Fig. 1. Typical example of the regression lines for running and
cycling, calculated from the data for the extra external mechanical
power output and the metabolic power required. Both Defficiencies
(eff) are presented in the figure
557
the mean (SEM) Defficiency during running was sig-
nificantly greater than that during cycling [42% (3.2)
compared to 25% (1.5), P<0.001].
For cycling, all muscles showed a substantial increase
in mean EMG activity with increased P
mech
output
(Fig. 2). For running however, only the gastrocnemius
muscle showed an increase in mean EMG activity
(Fig. 2). For the vastus lateralis muscle, the difference in
increase in EMG activity between cycling and running is
illustrated in Fig. 3, where raw rectified EMG data are
presented for each exercise stage of the running and
cycling test.
For cycling, all three leg muscles measured showed a
significant relationship between mean EMG activity and
the external P
mech
output. For running however, only
the correlation coefficient of the gastrocnemius muscle
was significantly different from 0 (see Table 1).
Discussion
The main finding of the present study was that during
running the vastus lateralis and biceps femoris muscles
did not show a relationship between the mean EMG
activity and the increased external P
mech
output. For
cycling, all muscles measured did show a relationship
between EMG activity and external P
mech
output.
Ericson et al. (1985), van Ingen Schenau et al. (1997)
and Miura et al. (2000) concur that during cycling only
concentric muscle actions are involved. Komi et al.
(1987) and Shinohara et al. (1997) showed that there is a
positive relationship between the EMG activity of con-
centric exercise and the load applied. The results of the
present study therefore support the idea that during
cycling concentric muscle actions dominate. Since the
efficiency of concentric exercise has a maximal value of
30% (Cavanagh and Kram 1985), the Defficiency during
cycling should not exceed this value. In the present study
the mean cycling Defficiency was 25%. Results from
previous studies (Asmussen and Bonde-Petersen 1974;
Suzuki 1979; Coyle et al. 1992; Bijker et al. 2001) have
also shown that the Defficiency of cycling is indeed less
than the efficiency of concentric exercise.
Since Komi et al. (1987) did not observe a relationship
between EMG activity during eccentric muscle actions
and external P
mech
output, our data for running suggest
that during running up shallow inclines non-concentric
muscle actions play an important role. There is little
doubt that level running includes stretch-shortening
cycles (Margaria 1976; Taylor 1985; van Ingen Schenau
et al. 1997). During the landing phase the active muscles
are stretched to decelerate body mass whereas during the
push off phase the active muscles are shortening. The
active stretch allows the tendons of the muscles to store
elastic energy, which can be re-used during the subse-
quent concentric phase. As a result, the gross efficiency
during running can be much greater than the muscle
efficiency (van Ingen Schenau et al. 1997; Ettema 2001).
Fig. 2. Increases in mean electromyogram (EMG) activity of three
leg muscles resulting from increases in external mechanical power
output during running (circles) and cycling (squares). The increase
in mean EMG activity is calculated as the percentage increase with
respect to the exercise stage having the lowest mechanical power
output
558
Previous studies suggested that during running up
inclines storage and re-use of elastic energy also takes
place, which could explain the large Defficiencies ob-
tained during running (Lloyd and Zacks 1972; Asmus-
sen and Bonde-Petersen 1974). According to van Ingen
Schenau (1984), however, during running up inclines,
work produced by the muscles to overcome the external
force is lost and can therefore not be stored. Since
muscles can only recover energy that has been previously
stored, the storage and re-use of elastic energy could not
explain the great running Defficiency. In such reasoning,
however, van Ingen Schenau (1984) assumes that
stretching of the muscle also implies a stretch of the
contractile elements of the muscle-tendon complex. Of
course, if that is the case it is difficult to explain how a
muscle can contribute to external work (De Haan et al.
1989). Roberts et al. (1997), however, showed that in the
gastrocnemius muscle of turkeys who ran on the level,
no stretch of the contractile elements occurred. Fur-
thermore, Kram and Taylor (1990) based their cost-of-
generating-force hypothesis on the idea that during level
running the contractile elements of the muscle operate
isometrically. Therefore, assuming that during running
on the level, as well as up inclines, in the stretching phase
no stretch of the contractile elements takes place, it is
likely that in both running situations (level and incli-
nation) storage and re-utilization of elastic energy plays
a role. Elastic energy storage and re-use can only explain
the great Defficiency during running if during running
up inclines the amount of elastic energy stored and re-
used increases. Minetti et al. (1994), however, asserted
that during running up any gradient a fixed maximal
amount of elastic energy is stored and re-used. There-
fore, although storage and re-use of elastic energy
probably improves the economy of running up inclines,
it cannot explain the great Defficiency during running.
As stated above, stretch-shortening cycles include
both eccentric and concentric muscle actions. During
running up inclines, the amount of concentric contrac-
tions has to increase to overcome the external force (i.e.
gravity) whereas the contribution of eccentric muscle
decreases (Minetti et al. 1994; Taylor 1994), but will still
be substantial. It is well known that the metabolic cost
of eccentric muscle actions is much less than that of
concentric contractions (Asmussen 1953; Bigland-
Ritchie and Woods 1976; Rall 1985). As Minetti et al.
(1993) showed, a change in the relative contribution of
concentric and eccentric muscle actions, combined with
the difference in metabolic costs between both muscle
actions will lead to very small increases in the metabolic
cost for running up shallow inclines. Consequently, for
running up shallow inclines, as used in the present study,
the Defficiency will be much greater than the concentric
muscle efficiency. During running up steep inclines,
concentric contractions will probably dominate, just as
they do during cycling. As a result, the Defficiency
during running up steep inclines should be much less
than the Defficiency during running up shallow inclines.
It would be interesting to test this hypothesis in further
research.
Fig. 3. A typical example of raw rectified electromyogram (EMG)
data of the vastus lateralis muscle for the different exercise stages
during cycling (left column) and running (right column)
Table 1. Kendall’s correlation
coefficients between mean
electromyogram (EMG) values
and external P
mech
Gastrocnemius muscle Vastus lateralis muscle Biceps femoris muscle
Cycling 0.55
a
0.92
a
0.64
a
Running 0.33
a
0.02 0.06
a
Correlation coefficient is significantly different from 0
559
The gastrocnemius muscle has a large compliant
Achilles tendon, which seems to be ideal for stretching.
Therefore, at first sight it seems strange that this muscle
shows a significant relationship between the mean EMG
activity and the load applied during running up shallow
inclines, suggesting that concentric contractions play an
important role. Hof and van den Berg (1983) showed
that there is a difference between ankle plantar flexor
and knee extensor muscles in their contribution of ec-
centric and concentric muscle actions during level run-
ning. Whereas, during level running, for the knee
extensors the contribution of eccentric muscle actions
was substantial, for the ankle plantar flexors concentric
contractions already played a prominent role. Conse-
quently, during running up inclines, where more con-
centric contractions must be produced, the
gastrocnemius muscle (which is an ankle plantar flexor)
will show a much better relationship between EMG
activity and the load applied than the vastus lateralis
muscle (knee extensor).
In our explanation of the great Defficiency of run-
ning, as well as a constant amount of elastic energy
stored and re-used, we have also assumed that the
amount of internal P
mech
produced remained constant
during running up shallow inclines. Minetti et al. (1994),
indeed, showed that for the range of inclines that was
used in the present study, the amount of internal P
mech
produced remained nearly constant and would therefore
not influence the Defficiency during running. Another
assumption we made was that the average vertical
ground reaction force will not change substantially
during running up shallow inclines. Since the metabolic
cost of running seems to be directly proportional to the
average vertical ground reaction force (Kram 2000) a
change in this force would influence the Defficiency.
However, the inclines used in the present study were so
small that the change in the average vertical ground
reaction force, and consequently also in the metabolic
cost of supporting the mass of the body, would have
been negligible and would not have influenced the D
efficiency during running.
In conclusion, the present study showed a difference
between running and cycling in the relationship between
the mean EMG activity of leg muscles and the load
applied. This difference can be used to explain the ob-
served difference in Defficiency between the two types of
locomotion. For cycling, the high correlation coefficients
confirm the theory that concentric contractions are the
main muscle actions. For running, the lack of a rela-
tionship between EMG activity and the load applied
suggests that during running up shallow inclines, ec-
centric muscle actions also play an important role. A
change in the relative contributions of concentric and
eccentric muscle actions, combined with the large dif-
ference in metabolic cost between both muscle action
types can explain the great Defficiency during running.
Acknowledgements The authors gratefully acknowledge J. Gerrit-
sen and L. Snel for their assistance in collecting the data and Dr.
R. Kram for his useful comments on a previous version of the
manuscript.
References
Asmussen E (1953) Positive and negative muscular work. Acta
Physiol Scand 28:364–382
Asmussen E, Bonde-Petersen F (1974) Apparent efficiency and
storage of elastic energy in human muscles during exercise. Acta
Physiol Scand 92:537–545
Bigland-Ritchie B, Woods JJ (1976) Integrated electromyogram
and oxygen uptake during positive and negative work. J Physiol
(Lond) 260:267–277
Bijker KE, De Groot G. Hollander AP (2001) Delta efficiencies of
running and cycling. Med Sci Sports Exerc 33:1546–1551
Cavanagh PR, Kram R (1985) The efficiency of human movement
– a statement of the problem. Med Sci Sports Exerc 17:304–308
Coyle EF, Sidossis LS, Horowitz JF, Beltz JD (1992) Cycling
efficiency is related to the percentage of type I muscle fibers.
Med Sci Sports Exerc 24:782–788
De Haan A, Ingen Schenau GJ van, Ettema GJ, Huijing PA,
Lodder MA (1989) Efficiency of rat medial gastrocnemius
muscle in contractions with and without an active prestretch.
J Exp Biol 141:327–341
Deluca CJ (1997) The use of surface electromyography in biome-
chanics. J Appl Biomech 12:135–163
Ericson MO, Nisell R, Arborelius UP, Ekholm J (1985) Muscular
activity during ergometer cycling. Scand J Rehabil Med 17:53–
61
Ettema GJC (2001) Muscle efficiency: the controversial role of
elasticity and mechanical energy conversion in stretch-short-
ening cycles. Eur J Appl Physiol 85:457–465
Garby L, Astrup A (1987) The relationship between the respiratory
quotient and the energy equivalent of oxygen during simulta-
neous glucose and lipid oxidation and lipogenesis. Acta Physiol
Scand 129:443–444
Hof AL, Geelen BA, Van den Berg J (1983) Calf muscle moment,
work and efficiency in level walking; role of series elasticity.
J Biomech 16:523–537
Ingen Schenau GJ van (1984) An alternative view of the concept of
utilisation of elastic energy in human movement. Hum Mov Sci
3:301–336
Ingen Schenau GJ van, Bobbert MF, Haan A de (1997) Does
elastic energy enhance work and efficiency in the stretch-
shortening cycle? J Appl Biomech 13:389–415
Komi PV, Kaneko M, Aura O (1987) EMG activity of the leg
extensor muscles with special reference to mechanical efficiency
in concentric and eccentric exercise. Int J Sports Med 8 [Suppl
1]:22–29
Kram R (2000) Muscular force or work: what determines the
metabolic energy cost of running? Exerc Sport Sci Rev 28:138–
143
Kram R, Taylor CR (1990) Energetics of running: a new perspec-
tive. Nature 346:265–267
Lloyd BB, Zacks RM (1972) The mechanical efficiency of treadmill
running against a horizontal impeding force. J Physiol (Lond)
223:355–363
Margaria R (1976) Biomechanics and energetics of muscular ex-
ercise. Clarendon Press, Oxford
Marsh AP, Martin PE, Foley KO (2000) Effect of cadence, cycling
experience, and aerobic power on delta efficiency during cy-
cling. Med Sci Sports Exerc 32:1630–1634
Minetti AE, Ardigo LP, Saibene F (1993) Mechanical determinants
of gradient walking energetics in man. J Physiol (Lond)
472:725–735
Minetti AE, Ardigo LP, Saibene F (1994) Mechanical determinants
of the minimum energy cost of gradient running in humans.
J Exp Biol 195:211–225
Miura H, Araki H, Matoba H, Kitagawa K (2000) Relationship
among oxygenation, myoelectric activity, and lactic acid
560
accumulation in vastus lateralis muscle during exercise with
constant work rate. Int J Sports Med 21:180–184
Poole DC, Gaesser GA, Hogan MC, Knight DR, Wagner PD
(1992) Pulmonary and leg VO2 during submaximal exercise:
implications for muscular efficiency. J Appl Physiol 72:805–810
Praagman M (2001) A method for biomechanical modelling of
energy consumption. J Clin Biomech 15 [Suppl 1]: S53-S54
Rall JA (1985) Energetic aspects of skeletal muscle contraction:
implications of fiber types. Exerc Sport Sci Rev 13:33–74
Roberts TJ, Marsh RL, Weyand PG, Taylor CR (1997) Muscular
force in running turkeys: the economy of minimizing work.
Science 275:1113–1115
Shinohara M, Kouzaki M, Yoshihisa T, Fukunaga T (1997)
Mechanomyography of the human quadriceps muscle during
incremental cycle ergometry. Eur J Appl Physiol 76:314–319
Siegel S, Castellan NJ Jr (1988) Non parametric statistics for the
behavioral sciences. McGraw-Hill, Singapore
Snyder AC, Woulfe T, Welsh R, Foster C (1994) A simplified ap-
proach to estimating the maximal lactate steady state. Int J
Sports Med 15:27–31
Suzuki Y (1979) Mechanical efficiency of fast- and slow-twitch
muscle fibers in man during cycling. J Appl Physiol 47:263–267
Taylor CR (1985) Force development during sustained locomotion:
a determinant of gait, speed and metabolic power. J Exp Biol
115:253–262
Taylor CR (1994) Relating mechanics and energetics during exer-
cise. Adv Vet Sci Comp Med 38A:181–215
Zacks RM (1973) The mechanical efficiencies of running and bi-
cycling against a horizontal impeding force. Int Z Angew
Physiol 31:249–258
561
... For instance, swimming demands the recruitment of arms and legs limbs for propulsion (Figueiredo, Rouard, Vilas-Boas, & Fernandes, 2013;Gourgoulis et al., 2014). Differently, cycling demands prolonged quadriceps concentric contractions during a large proportion of the pedal rotation (Bijker, de Groot, & Hollander, 2002;Brownstein, Metra, Pastor, Faricier, & Millet, 2022), whereas running demands body weight support while performing repeated gait cycles with forward and upward propulsion using stretch-shortening cycle muscle actions (Bijker et al., 2002;Hamner, Seth, & Delp, 2010). Due to these different patterns of movements, neuromuscular fatigue may vary throughout the triathlon race. ...
... For instance, swimming demands the recruitment of arms and legs limbs for propulsion (Figueiredo, Rouard, Vilas-Boas, & Fernandes, 2013;Gourgoulis et al., 2014). Differently, cycling demands prolonged quadriceps concentric contractions during a large proportion of the pedal rotation (Bijker, de Groot, & Hollander, 2002;Brownstein, Metra, Pastor, Faricier, & Millet, 2022), whereas running demands body weight support while performing repeated gait cycles with forward and upward propulsion using stretch-shortening cycle muscle actions (Bijker et al., 2002;Hamner, Seth, & Delp, 2010). Due to these different patterns of movements, neuromuscular fatigue may vary throughout the triathlon race. ...
... Previous studies demonstrated similar levels of quadriceps muscle peripheral fatigue (from −24% to −31%) after cycling time trials performed without previous swimming (Brownstein et al., 2022;Thomas et al., 2015). Cycling involves prolonged repeated quadricep concentric contractions during a large proportion of the pedal rotation (Bijker et al., 2002), contributing to a great contractile function impairments of quadriceps muscle following cycling (Brownstein et al., 2022). The switch from an upper limb dependence during swimming to a lower limb dependence (mainly quadriceps muscle) during cycling explains a greater level of quadriceps muscle fatigue in post-cycling compared to post-swimming. ...
Article
This study compared central and peripheral fatigue development between Sprint and Olympic distance triathlon. Fifteen male triathletes performed Sprint and Olympic triathlon simulations in a randomized and counterbalanced order. Central and peripheral fatigue was evaluated from changes in voluntary activation level (VAL) and twitch responses of quadriceps muscle (Qtw,pot), respectively. Qtw,pot reduced from baseline to post-swimming similarly between triathlon simulations (Sprint, -17±11%; Olympic, -13±9%). In post-cycling, Qtw,pot further declined to a similar extent between triathlon distances (Sprint, -31±15%; Olympic, -28±11%). In post-running, Qtw,pot was fully recovered in Olympic triathlon (-4±10%), whereas there was only a partial recovery of Qtw,pot in Sprint triathlon (-20±11%). VAL was not reduced in post-swimming, but reduction was similar between triathlon distances in post-cycling (Sprint, -10±9%; Olympic, -8±8%) and post-running (Sprint, -15±14%; Olympic, -16±8%). In Sprint triathlon, the swimming speed (1.07±0.13 m ·s-1) was above (p<.001) critical speed (1.01±0.14 m ·s-1), the cycling power (179.7±27.2W) was below the respiratory compensation point (216.3±27.8W, p<.001) and running speed (13.7±1.05km·h-1) similar to the respiratory compensation point (13.2±0.70 km·h-1, p=.124). In Olympic triathlon, swimming speed (1.03±0.13m·s-1) was similar to critical speed (p=.392), and both cycling power (165.3±27.3W) and running speed (12.6±1.05km·h-1) were below the respiratory compensation point (p≤.007). In conclusion, peripheral fatigue progressed until post-cycling regardless of triathlon distances. However, peripheral fatigue was fully recovered after running in Olympic but not in Sprint triathlon. The central fatigue started in post-cycling and progressed until post-running regardless of triathlon distances.
... Increased muscle force at high workloads could be produced by increasing muscle activation magnitude and contraction timing. [9][10][11][12] Interestingly, with the workload increase, VL's activation time decreased, while SO's muscle activation time increased. 13 Assuming that knee joint extensors act mostly concentrically during the crank cycle, increases in workload might determine a need for decreasing the knee extensors' concentric contribution with an increase in the eccentric's contraction time due to its reduced metabolic cost. 2 Also, although plantar flexor bi-articular muscles' (e.g., gastrocnemius) timing of contraction adapted to changes in saddle height, it is not known if this adaptation also occurs with a workload increase. ...
... Increased muscle force at high workloads could be produced by increasing muscle activation magnitude and contraction timing. [9][10][11][12] Interestingly, with the workload increase, VL's activation time decreased, while SO's muscle activation time increased. 13 Assuming that knee joint extensors act mostly concentrically during the crank cycle, increases in workload might determine a need for decreasing the knee extensors' concentric contribution with an increase in the eccentric's contraction time due to its reduced metabolic cost. 2 showing especial benefits from improvements in aerobic power/capacity, exercise tolerance, strength and muscle mass in clinical populations. ...
Article
Background: The mechanical energy required to drive the cranks during cycling depends on concentric and eccentric muscle actions. However, no study to date provided clear evidence on how workload levels affect concentric and eccentric muscle actions during cycling. Therefore, the aim of this study was to investigate the workload effects on the timing of lower limb concentric and eccentric muscle actions, and on joint power production. Methods: Twenty-one cyclists participated in the study. At the first session, maximal power output (POMAX) and power output at the first (POVT1) and second (POVT2) ventilatory thresholds were determined during an incremental cycling test. At the second session, cyclists performed three trials (2-min/each) in the workloads determined from their POMAX, POVT1 and POVT2, acquiring data of lower limb muscle activation, pedal forces and kinematics. Concentric and eccentric timings were computed from muscles' activations and muscle-tendon unit excursions along with hip, knee and ankle joints' power production. Results: Longer rectus femoris eccentric activation (62%), vastus medialis concentric (66%) and eccentric activation (26%) and biceps femoris concentric (29%) and eccentric (133%) activation at POMAX were observed compared to POVT1. Longer positive (12%) and shorter negative (12%) power were observed at the knee joint for POMAX compared to POVT1. Conclusions: We conclude that, to sustain higher workload levels, cyclists improved the timing of power transmission from the hip to the knee joint via rectus femoris eccentric, vastus medialis concentric and eccentric and biceps femoris concentric and eccentric contractions.
... Cycling primarily affects the lower body and the muscular system, causing a more local and muscular internal load. By contrast, running is more challenging for the whole body, with more influence on the vestibular, proprioceptive, and visual systems, causing a global internal load (Bijker, De Groot, & Hollander, 2002;Nardone et al., 1997). Nevertheless, since the latter are the systems primarily involved in dynamic postural control (Fusco et al., 2020), the effect was expected to be greater after running than after cycling (Paillard, 2012;Wright et al., 2013). ...
Article
Full-text available
Dynamic postural control is one of the essential factors in situations where non-contact injuries mainly occur, i.e., landing, cutting, or stopping. Therefore, testing of dynamic postural control should be implemented in injury risk assessment. Moreover, non-contact injuries mainly occur under loaded conditions when the athlete is physically stressed. Therefore, risk factors and mechanisms of these injuries should also be regarded under loading conditions and not only when the athlete is recovered. Current studies examining the influence of physical load on risk factors, such as dynamic postural control, often use cycling protocols to stress the participants. Nevertheless, most types of sports require running as a central element and the induced internal load after cycling might not be the same after running. Therefore, the current study aimed to examine the influence of a running and a cycling protocol on dynamic postural control and to determine the potential injury risk under representative conditions. In total, 128 sport students (64 males and 64 females, age: 23.64 ± 2.44, height: 176.54 ± 8.96 cm, weight: 68.85 ± 10.98 kg) participated in the study. They were tested with the Y Balance Test before and after one loading protocol. A total of 64 participants completed a protocol on a cycle ergometer and the other 64 on a treadmill. A mixed ANOVA showed significant interactions of time and load type. Dynamic postural control was reduced immediately after cycling but did not change after running. These findings indicate a load type dependence of dynamic postural control that must be considered while assessing an athlete’s potential injury risk and they support the need for more representative designs.
... These results could partly be explained by the contraction types. Indeed, plyometric contractions, during running, might cause greater muscle damage as compared with the concentric-dominant nature of cycling [23][24][25]. However, the comparison between cycling and running aerobic exercises during concurrent training are scarce and mainly apply to long-duration, low-intensity exercises [21]. ...
Article
Full-text available
Exercise modality has been proposed to reduce the interferences between aerobic and resistance sessions during concurrent training. The aim of the study was to examine the acute effects of cycling or running sprint interval exercise on subsequent resistance training sessions. Twenty-five competitive male rugby union players were recruited. Players were tested during three conditions: CONTROL (resistance training session only), CYCLE and RUN (corresponding to a concurrent training scheme with cycling or running sprint interval exercise conducted on the morning, followed by a resistance training session). Four hours rest was proposed between the aerobic and resistance training session. Muscle performance (bar velocity during bench press and box squat, counter movement jump height) and subjective ratings (rate of perceived exertion, wellbeing) were assessed during and after aerobic or resistance training sessions. No significant difference was observed for muscle performance (vertical jump height and bar velocity). However, significant higher perceived exertion and low-value scaled subjective wellbeing were observed in RUN (7.7 ± 1.1 and 17.9 ± 4.1, respectively) as compared with the two other conditions (6.7 ± 1.5 and 21.1 ± 3.6 for CONTROL and 7.4 ± 1.1 and 20.1 ± 3.9 for CYCLE). It was concluded that the exercise modality (running or cycling) during the aerobic exercise using a sprint interval exercise did not impact the quality of the resistance session. However, subjective ratings were affected the following days. Cycling exercises might be more adequate when performing a sprint interval training session during concurrent training programs.
... In addition to the structural anatomy, the functional context of each muscle should be taken into account when interpreting relaxation times. While running in general has been shown to involve predominantly eccentric contractions, the plantar flexor muscle group (including the gastrocnemius muscle) performs more concentric contractions during running, which have been shown to be associated with higher metabolic costs and greater impact on T2 relaxation times [45,46]. This could be another possible reason for the tendency of the plantar flexor muscle group (MG, LG, SOL, TP, PER), especially the MG and LG, towards a more pronounced initial increase in T2 � and T2 relaxation time in comparison to the dorsiflexor muscle group (TA, EDL). ...
Article
Full-text available
Objectives Previous studies on T2* and T2 relaxation time of the muscles have shown that exercise leads to an initial increase, presumably representing different intramuscular physiological processes such as increase in intracellular volume or blood oxygenation level dependent effects with a subsequent decrease after cessation of exercise. Their behaviour during prolonged exercise is still unknown but could provide important information for example about the pathophysiology of overuse injuries. The aim of this study was to evaluate the temporal course of T2* and T2 relaxation time in extrinsic foot muscles during prolonged exercise and determine the optimal mapping technique. Methods Ten participants had to run a total of 75 minutes at their individual highest possible running speed, with interleaved MR scans at baseline and after 2.5, 5, 10, 15, 45 and 75 minutes. The examined extrinsic foot muscles were manually segmented, and relaxation time were analysed regarding its respective time course. Results T2* and T2 relaxation time showed an initial increase, followed by a plateau phase between 2.5 and 15 minutes and a subsequent decrease. For the T2* relaxation time, this pattern was also apparent, but less pronounced, with more muscles not reaching significance (p<0.05) when comparing different time points. Conclusions T2* and T2 relaxation time showed a similar course with an initial rapid increase, a plateau phase and a subsequent decrease under prolonged exercise. Moderate but long-term muscular activity appears to have a weaker effect on T2* relaxation time than on T2 relaxation time.
... A number of differences exist in the active muscle mass and contractile characteristics associated with running and cycling, with potential implications for quadriceps neuromuscular function. First, the overall active muscle mass is lower during cycling than running, with a relatively greater proportion of force production from the quadriceps, whereas hip and ankle extensors play a comparatively greater role in force production during running (14). Thus, for a given whole-body metabolic demand, the metabolic demands in the quadriceps are likely to be greater for cycling than running. ...
Article
Introduction Running and cycling represent two of the most common forms of endurance exercise. However, a direct comparison of the neuromuscular consequences of these two modalities after prolonged exercise has never been made. The aim of this study was to compare the alterations in neuromuscular function induced by matched intensity and duration cycling and running exercises. Methods During separate visits, 17 endurance-trained male participants performed 3 h of cycling and running at 105% of the gas exchange threshold. Neuromuscular assessments were taken are pre-, mid- and post-exercise, including knee extensor maximal voluntary contractions (MVC), voluntary activation (VA), high- and low-frequency doublets (Db100 and Db10, respectively), potentiated twitches (Qtw,pot), motor evoked potentials (MEP) and thoracic motor evoked potentials (TMEPs). Results Following exercise, MVC was similarly reduced by ~25% following both running and cycling. However, reductions in VA were greater following running (−16 ± 10%) than cycling (−10 ± 5%; p < 0.05). Similarly, reductions in TMEP were greater following running (−78 ± 24%) than cycling (15 ± 60%; p = 0.01). In contrast, reductions in Db100 (running: −6 ± 21% vs. cycling: −13 ± 6%) and Db10:100 (running: −6 ± 16% vs. cycling: −19 ± 13%) were greater for cycling than running (p ≤ 0.04). Conclusions Despite similar decrements in the knee extensor MVC following running and cycling, the mechanisms responsible for force loss differed. Running-based endurance exercise is associated with greater impairments in nervous system function, particularly at the spinal level, while cycling-based exercise elicits greater impairments in contractile function. Differences in the mechanical and metabolic demands imposed on the quadriceps could explain the disparate mechanisms of neuromuscular impairment following these two exercise modalities.
... Alongside the vastus medialis and vastus lateralis (VL), the GM and GL are the most activated muscles during cycling on a bicycle (Ericson et al., 1985). Athletes specialized in conventional cycling, where the gastrocnemius is predominantly activated concentrically (Ericson et al., 1985;Bijker et al., 2002), could have structural adaptations different to locomotive sports athletes. Basketball is a locomotive sport where the gastrocnemius muscle of an athlete is activated eccentrically as well as concentrically, at different joint angles and muscle lengths during running, sprinting, accelerating, sudden stopping, changing direction, jumping, and landing (Savelberg and Meijer, 1985;Vogt and Hoppeler, 1985;Ben Abdelkrim et al., 2007;Ullrich and Brueggemann, 2008). ...
Article
Full-text available
Eccentric and concentric actions produce distinct mechanical stimuli and result in different adaptations in skeletal muscle architecture. Cycling predominantly involves concentric activity of the gastrocnemius muscles, while playing basketball requires both concentric and eccentric actions to support running, jumping, and landing. The aim of this study was to examine differences in the architecture of gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) between elite basketballers and cyclists. A trained sonographer obtained three B-mode ultrasound images from GM and GL muscles in 44 athletes (25 basketballers and 19 cyclists; 24 ± 5 years of age). The images were digitized and average fascicle length (FL), pennation angle (θ), and muscle thickness were calculated from three images per muscle. The ratio of FL to tibial length (FL/TL) and muscle thickness to tibial length (MT/TL) was also calculated to account for the potential scaling effect of stature. In males, no significant differences were identified between the athletic groups in all parameters in the GM, but a significant difference existed in muscle thickness in the GL. In basketballers, GL was 2.5 mm thicker (95% CI: 0.7–4.3 mm, p = 0.011) on the left side and 2.6 mm thicker (95% CI: 0.6–5.7 mm, p = 0.012) on the right side; however, these differences were not significant when stature was accounted for (MT/TL). In females, significant differences existed in the GM for all parameters including FL/TL and MT/TL. Female cyclists had longer FL in both limbs (MD: 11.2 and 11.3 mm), narrower θ (MD: 2.1 and 1.8°), and thicker muscles (MD: 2.1 and 2.5 mm). For the GL, female cyclists had significantly longer FL (MD: 5.2 and 5.8 mm) and narrower θ (MD: 1.7 and 2.3°) in both limbs; no differences were observed in absolute muscle thickness or MT/TL ratio. Differences in gastrocnemius muscle architecture were observed between female cyclists and basketballers, but not between males. These findings suggest that participation in sport-specific training might influence gastrocnemius muscle architecture in elite female athletes; however, it remains unclear as to whether gastrocnemius architecture is systematically influenced by the different modes of muscle activation between these respective sports.
... Dieser Effekt lässt sich jedoch durch die kurzfristige Zufuhr von Kohlenhydraten nach einer mehrtägigen fettdominanten Diät reduzieren, ohne dabei die enzymatischen Anpassungen im Fettstoffwechsel zu beeinträchtigen (Stellingwerff et al., 2006 (Chenevière, Malatesta, Gojanovic & Borrani, 2010;Knechtle et al., 2004). Als mögliche Ursache kann die erhöhte muskuläre Aktivität beim Laufen gelten (Arkinstall, Bruce, Nikolopoulos, Garnham & Hawley, 2001), aber auch eine verbesserte Bewegungsökonomie durch den Einfluss des Dehnungs-Verkürzungs-Zyklus, welcher beim Radfahren ausbleibt (Bijker, Groot & Hollander, 2002). Verlässliche Angaben zum Ausmaß des Einflusses der Belastungsart sowie zu möglichen Gewöhnungseffekten oder Reduktionsmöglichkeiten durch Training sind unbekannt (Purdom et al., 2018). ...
Thesis
Die Arbeit beleuchtet den Einsatz algorithmischer Datenbearbeitungen bei sportwissenschaftlichen Spiroergometrien aus praktischen und theoretischen Gesichtspunkten. Die aktuelle Verbreitung von algorithmischen Datenbearbeitungen aus Breath-by-Breath Untersuchungen wird über die Ergebnisse eines Fragebogens und einer systematischen Literaturübersicht dargestellt. Zudem erfolgt die Analyse der durch Algorithmen verursachten Messwertvarianzen der Sauerstoffaufnahme in diskontinuierlichen Belastungsuntersuchungen, bei Jugendlichen und im submaximalen Belastungsbereich.
... Torres-Peralta et al. (2014) reported that the RMS EMG activity showed an increase in the muscle contraction burst duration with the exercise intensity due to muscle activation during exercise that increased almost linearly with exercise intensity. According to Bruce-Low et al. (2012) and Bijker et al. (2002), a faster trunk movement during bending exercises demands a high amount of force to induce greater muscle activity. As such, the FB task in the present study suggests a particular demand to increase the muscle activity of LD and LES muscles. ...
Article
This study investigates the effects of standing exercise tasks with an incline-slope surface on the activation of latissimus dorsi (LD) and lumbar erector spinae (LES) muscles, and low-back pain (LBP) intensity. Sixteen LBP symptomatic subjects were equally and randomly divided into two groups, such as experimental and control groups based on standing interventions. The experimental group performed the exercise tasks with an incline-slope surface and the control group completed these tasks on a level surface. Electromyography and subjective LBP data were collected for five weeks to understand the intervention effects on the muscles and LBP intensity. The intervention significantly influenced trunk muscle activations and LBP intensity. The intensity of LBP was lowered in the experimental group as compared to the control group. Changes in trunk muscle activations suggested that standing exercises with an incline-slope surface intervention can positively influence the activation of trunk muscles and potentially reduce LBP intensity.
Chapter
Cycling and running are aerobic activities that represent two different means of exercising, rarely combined. Both cycling and running are essential for overall health, proper function of the cardiovascular system, and weight balance, with few differences between them. Although not widely known, running can contribute to a cyclist’s training and performance. Running and cycling seem to result in different physiological and metabolic responses having different physiological effects. There are certain benefits of running for cyclists, though. These include an increase in bone density, an increased cardiovascular and muscular strength, better exercise tolerance, and psychological benefits as well. Nevertheless, drawbacks also exist. Running in cyclists has been correlated to an increased risk for injury. More specifically, a combination of running and cycling without a proper periodization of the training can lead to overload and injury. The perfect merge of these two activities, running and cycling, is cyclo-cross.
Article
Full-text available
The amount of energy used to run a mile is nearly the same whether it is run at top speed or at a leisurely pace (although it is used more rapidly at the higher speed). This puzzling independence of energy cost and speed is found generally among running animals, although, on a per gram basis, cost is much higher for smaller animals. Running involves little work against the environment; work is done by muscles and tendons to lift and accelerate the body and limbs. Some of the work is recovered from muscle-tendon springs without metabolic cost and work rate does not parallel metabolic rate with either speed or size. Regardless of the amount of work muscles do, they must be activated and develop force to support the weight of the body. Load-carrying experiments have shown that the cost of supporting an extra newton of load is the same as the weight-specific cost of running. Size differences in cost are proportional to stride frequency at equivalent speeds, suggesting that the time available for developing force is important in determining cost. We report a simple inverse relationship between the rate of energy used for running and the time the foot applies force to the ground during each stride. These results support the hypothesis that it is primarily the cost of supporting the animal's weight and the time course of generating this force that determines the cost of running.
Article
This lecture explores the various uses of surface electromyography in the field of biomechanics. Three groups of applications are considered: those involving the activation timing of muscles, the force/EMG signal relationship, and the use of the EMG signal as a fatigue index. Technical considerations for recording the EMG signal with maximal fidelity are reviewed, and a compendium of all known factors that affect the information contained in the EMG signal is presented. Questions are posed to guide the practitioner in the proper use of surface electromyography. Sixteen recommendations are made regarding the proper detection, analysis, and interpretation of the EMG signal and measured force. Sixteen outstanding problems that present the greatest challenges to the advancement of surface electromyography are put forward for consideration. Finally, a plea is made for arriving at an international agreement on procedures commonly used in electromyography and biomechanics.
Article
It is widely accepted that the series elastic component (SEC) of muscles and tendons plays an important role in dynamic human movements. Many experiments seem to show that during a pre-stretch movement energy can be stored in the SEC which is re-used during the subsequent concentric contraction. Mechanical calculations were performed to calculate the capacity for muscles and tendons to store elastic energy. The storage of elastic energy in muscle tissue appears to be negligible. In tendons some energy can be stored but the total elastic capacity of the tendons of the lower extremities appears far too small to explain reported advantages of a pre-stretch during jumping and running.Based on literature concerning chemical change and enthalpy production during experiments on isolated muscles, a model is proposed which can explain the advantages of a preliminary counter movement on force and work output during the subsequent concentric contraction. The main advantage of a pre-stretch, as seen in movements like jumping, throwing and running, seems to be to prevent a waste of cross bridges at the onset of a contraction in taking up the slack of the muscle. The model can explain why the mechanical efficiency in running can be much higher than in cycling. A muscle which is stretched prior to concentric contraction can do more work at the same metabolic cost when compared with a concentric contraction without pre-stretch.
Article
This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch- shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch- shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanisms and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves under in-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.
The mechanical activity of the human quadriceps muscle during maximal incremental cycle ergometry was investigated by mechanomyography (MMG). MMG and surface electromyography (EMG) recordings of vastus lateralis muscle activity were obtained from nine males. Cycle ergometry was performed at 60 rev/min and work load was incremented step wise by 20 W (3.2 Nm) every minute until volitional fatigue. The mean amplitudes of MMG (mMMG) and EMG (mEMG) during the contraction phase were calculated from the last six contractions in each load. The duration, load and work rate of exercise at exhaustion were 13.3 (1.6) min, 44.1 (5.5) Nm, 276.7 (34.7) W, respectively. A linear relationship between mMMG and load was evident in each subject (r = 0.868–0.995), while mEMG seemed to dissociate as the load became greater. In the grouped mean data, mMMG was linearly related to load whether aligned to the absolute (r = 0.995) or maximal (r = 0.995) load. Involvement of the noise component was further investigated by studying passive cycling by four subjects. Pedals were rotated passively for the first half of each stage (PAS) and the subject then pushed the pedals for the second half (ACT). In the lighter load region, the mMMG of ACT was as small as that of PAS. However, the change in the mMMG of PAS was very small compared with that of ACT. In conclusion, this study demonstrates a linear relationship between the mMMG of the quadriceps muscle and work load during maximal incremental cycle ergometry. The effect of movement noise was thought to be small and stable.
Article
The influence of different percentages of slow-twitch (ST) and fast-twitch (FT) fibers in vastus lateralis on delta efficiency expressed by delta work (x)/delta energy liberation (y) in y = a + bx was studied in six subjects during cycling on an ergometer at 60 or 100 rpm at work loads below 80% of VO2max. Three subjects had an average of 78% ST fibers (ST group) and the other subjects had an average of 76% FT fibers (FT group). There was no difference between the two groups in delta efficiency at 60 rpm, but at 100 rpm the efficiency of the ST group was significantly lower than that of the FT group (19.6 vs. 28.8%, P less than 0.01). In the ST group respiratory exchange ratio (R) was higher at 100 rpm than at 60 rpm, but the FT group had similar R values at both pedal revolution rates. The most important finding was the reduced efficiency when pedaling frequency was increased from 60 to 100 rpm in the ST group (23.3 to 19.6%). Predominant use of ST fibers at rapid pedal rates may require a substantial increase in energy expenditure.
Article
1. Integrated electromyogram (e.m.g.) from the vastus lateralis muscles, and steady-state rates of oxygen uptake, were measured simultaneously during the performance of set rates of positive (concentric) and negative (eccentric) work at 50 rev/min on a motorized bicycle ergometer. 2. Similar experiments were also carried out at other pedalling rates and using other leg muscles. 3. The relationships between each of the variables (integrated e.m.g., oxygen consumption) and mean torque on pedals were found to be linear (r greater than 0-98) with a remarkable degree of reproducibility in surface e.m.g. for each subject over several months. 4. The ratio of the e.m.g. slopes at 50 rev/min (positive/negative) was 1-96 +/- 0-12 while the same ratio for the oxygen uptake slopes was 6-34 +/- 0-82. The discrepancy between the ratios suggests that not only is less muscle fibre activity required to maintain the same exerted force during negative work exercise, but there is also a substantial reduction in the oxygen uptake when the fibres are stretched. This was observed for all speeds of pedalling.
Article
We determined that the variability in the oxygen cost and thus the caloric expenditure of cycling at a given work rate (i.e., cycling economy) observed among highly endurance-trained cyclists (N = 19; mean +/- SE; VO2max, 4.9 +/- 0.1 l.min-1; body weight, 71 +/- 1 kg) is related to differences in their % Type I muscle fibers. The percentage of Type I and II muscle fibers was determined from biopsies of the vastus lateralis muscle that were histochemically stained for ATPase activity. When cycling a Monark ergometer at 80 RPM at work rates eliciting 52 +/- 1, 61 +/- 1, and 71 +/- 1% VO2max, efficiency was determined from the caloric expenditure responses (VO2 and RER using open circuit spirometry) to steady-state exercise. Gross efficiency (GE) was calculated as the ratio of work accomplished.min-1 to caloric expenditure.min-1, whereas delta efficiency (DE) was calculated as the slope of this relationship between approximately 50 and 70% VO2max. The % Type I fibers ranged from 32 to 76%, and DE when cycling ranged from 18.3 to 25.6% in these subjects. The % Type I fibers was positively correlated with both DE (r = 0.85; P less than 0.001; N = 19) and GE (r = 0.75; P less than 0.001; N = 19) during cycling. Additionally, % Type I fibers was positively correlated with GE (r = 0.74; P less than 0.001; N = 13) measured during the novel task of two-legged knee extension; performed at a velocity of 177 +/- 6 degrees.s-1 and intensity of 50 and 70% of peak VO2 for that activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Insights into muscle energetics during exercise (e.g., muscular efficiency) are often inferred from measurements of pulmonary gas exchange. This procedure presupposes that changes of pulmonary O2 (VO2) associated with increases of external work reflect accurately the increased muscle VO2. The present investigation addressed this issue directly by making simultaneous determinations of pulmonary and leg VO2 over a range of work rates calculated to elicit 20-90% of maximum VO2 on the basis of prior incremental (25 or 30 W/min) cycle ergometry. VO2 for both legs was calculated as the product of twice one-leg blood flow (constant-infusion thermodilution) and arteriovenous O2 content difference across the leg. Measurements were made 3-5 min after each work rate imposition to avoid incorporation of the VO2 slow component above the lactate threshold. For all 17 subjects, the slope of pulmonary VO2 (9.9 +/- 0.2 ml O2.W-1.min-1) was not different (P greater than 0.05) from that for leg VO2 (9.2 +/- 0.6 ml O2.W-1.min-1). Estimation of "delta" efficiency (i.e., delta work accomplished divided by delta energy expended, calculated from slope of VO2 vs. work rate and a caloric equivalent for O2 of 4.985 cal/ml) using pulmonary VO2 measurements (29.1 +/- 0.6%) was likewise not significantly different (P greater than 0.05) from that made using leg VO2 measurements (33.7 +/- 2.4%). These data suggest that the net VO2 cost of metabolic "support" processes outside the exercising legs changes little over a relatively broad range of exercise intensities. Thus, under the conditions of this investigation, changes of VO2 measured from expired gas reflected closely those occurring within the exercising legs.