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Department of Life Sciences (Sports Sciences), The University of Tokyo, Meguro, Tokyo 153-8902, Japan
Behavior of fascicles and
tendinous structures of human gastrocnemius medialis (MG) was
determined by use of ultrasonography in vivo during jumping. Eight male
subjects jumped vertically without countermovement (squat jump, SQJ).
Simultaneously, kinematics, kinetics, and electromyography from lower
leg muscles were recorded during SQJ. During phase I (
350
to 100 ms before toe-off), muscle-tendon complex (MTC) length was
almost constant. Fascicles, however, shortened by 26%, and tendinous
structures were stretched by 6%, storing elastic energy of 4.9 J
during phase I. During phase II (100 ms to
toe-off), although fascicles generated force quasi-isometrically, MTC
shortened rapidly by 5.3%, releasing prestored elastic energy with a
higher peak positive power than that of fascicles. Also, the compliance
of tendinous structures in vivo was somewhat higher than that of
external tendon used in the simulation studies. The results demonstrate
that the compliance of tendinous structures, together with no yielding
of muscle fibers, allows MTC to effectively generate relatively large
power at a high joint angular velocity region during the last part of
push-off.
ultrasonography; compliance; elastic energy
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