Production and Absorption of Work by Muscle

Abstract

The relation between work and heat, under various conditions of shortening, lengthening and tension were investigated to determine the possibility of thermodynamic ''reversibility'' during contraction of toad sartorius muscle at 0[degree] C. Muscles were stretched 11-22% of their resting lengths shortly after stimulation and were then allowed to relax. Despite this procedure, total heat production was the same as in muscles which were not stretched. Since the muscle produced a large part of its normal heat before the stretch began, the author postulated a reversal of the chemical reactions occurring during the contraction. The net energy of the whole cycle of contraction and relaxation was never negative, but a long, negative phase of net energy occurred soon after the stretch. With the negative phase, there was a concomittant absorption of energy during the extension of the contractile component; therefore, a ther-moelastic effect was postulated and its nature and quantity discussed. The application of these experiments to man is considered briefly.