<p> The present study was undertaken to investigate the mechanism
underlying the observation that the maximal voluntary strength
of the two legs acting together or bilaterally in isometric leg
extension was less than the summed unilateral (sum of the left
and right legs tested separately) strength. Observations were
made on this phenomenon under both isometric and concentric contraction
conditions by testing young adult males performing unilateral and
bilateral leg press contractions on a modified isokinetic dynamometer. </p> <p> Electromyographical evidence indicated that there was a
lesser activation of motor units in bilateral contraction as
compared to unilateral, under isometric conditions and at a low and
high concentric velocity. To determine whether a particular type
of motor unit was being activated to a lesser extent in bilateral
contractions, two physiological parameters of unilateral and bilateral
contractions were compared: the strength-velocity relation and
fatigability. This investigative method was based on the known
physiological differences between the motor unit types; namely
fast-twitch (FT), type two motor units have a faster twitch contraction
time, greater force output at high velocities of shortening and
lesser resistance to fatigue than the slow-twitch (ST), type one units. </p> <p> Results showed a greater relative decline in the strength
of bilateral contractions as the velocity of contraction was increased
through a range from 0°/s to 424°/s (0 to 7.40 radians/s). The bilateral to summed unilateral strength ratio (B/U-ratio) decreased
from 0.91 under isometric conditions to 0.51 at the highest test
velocity. Lesser fatigability was found in the bilateral condition
in a 100 consecutive concentric contraction fatigue test. These
results provided complementary evidence for the conclusion that FT
motor units were active to a lesser degree in bilateral contractions. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20595 |
| Date | 05 October 2016 |
| Creators | Vandervoort, Anthony |
| Contributors | Sale, D. G., Adapted Human Biodynamics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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