A QUANTITATIVE STUDY OF THE CHANGES IN POWER DURING MUSCULAR CONTRACTION

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Abstract
A technique is described by means of which the instantaneous tensions and lengths of the gastrocnemius of the decerebrate cat, indirectly stimulated and contracting against an inertia disc, can be recorded for each 0.011 sec. The tension-length diagram has been constructed from these data. The work done in a single twitch has also been computed from the kinetic energy of the system. The work done by the muscle during shortening is approximately equal to that of an elastic body shortening through the same distance. W/Tl has been found to be 0.0489. The power of the muscle, calculated for each 0.011 sec. is found to be approximately constant for a period of about 40 a after the maximal force has been reached. During this period of constant power, force decreases with increasing velocity. The decrease in force with increasing speed of contraction is interpreted to be a result of the physical law which governs motion under constant power. If power is constant, force must necessarily decrease as velocity increases. Power is shown to be approximately constant during that part of the muscular contraction in which 65% of the work is done.

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