| Summary: | Cycling has become a popular model in recent years for the study of muscle mechanics.
The purpose of this study was to manipulate bicycle seat heights in order to perturbate muscle
lengths and contraction velocities of three lower leg muscles, the soleus, medial gastrocnemius,
and tibialis anterior, and to measure subsequently the effects on the muscles’ contribution to the
cycling task as measured by EMG.
Two groups of female subjects, riders (n=7) and non-riders (n=6), rode a bicycle mounted
on a Schwinn Velodyne® at 200 Watts and cadence of 80 rpm. Individuals rode at a self-selected
seat height, a 10% lowered, and 5 % raised seat position. It was hypothesized that responses in
muscle EMG would differ on the basis of cycling experience but results showed this to not be
true. It was also hypothesized that because the three muscles would operate at decreased
contraction velocities at the low seat, the integrated EMG would be less for the lowest seat
position. This hypothesis was based on the force-velocity relationship of muscle, where muscles
operating at the lower end of the velocity spectrum can produce greater forces and thereby
require the recruitment of fewer fibers to perform the same task. Although the soleus and medial
gastrocnemius muscles did show a decrease in integrated EMG value with decreases in seat
height, the tibialis anterior showed unexpected results, with the chosen seat height resulting in
the lowest integrated EMG. This suggests either that EMG responses occurred independently
from the calculated muscle lengths and contraction velocities or that electromyography may not
be a sensitive enough tool to reflect changes in muscle force induced by altered muscle lengths
and/or contraction velocities.
As seat height decreased, it was also observed that the absolute muscle lengths increased
for both the soleus and medial gastrocnemius muscles, but decreased for the tibialis anterior
muscles. The absolute peak muscle lengths did not show a large variation across seat heights,
with only an average difference of 2 %. Therefore, it is unlikely that the changes in muscle
lengths affected the force production of the muscles to a significant extent.
Although the muscle length and contraction velocity variables add considerably more
insight into the mechanics of muscle action than either EMG or kinematic analyses of limb
motion alone, their use in predicting muscle forces and muscular contributions to movement
remains very limited. Furthermore, the choice of using the cycling model for investigating
certain aspects of muscle mechanics should be examined further. === Education, Faculty of === Kinesiology, School of === Graduate
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