The energy liberated by an isolated muscle during the performance of work

Abstract

The investigation of Fenn (1) (2) established the fundamental fact that the total energy liberated by a stimulated muscle depends upon the amount of work which it does, and also upon the manner, and the phase of contraction, in which that work is performed. The extreme importance of Fenn's results, in any theory of muscular contraction, has long made a further study of the subject desirable. This, and the development of various improvements in technique, particularly of the ergometer of Levin and Wyman (3) which we used in the experiments described in a recent paper (9), have caused us during the last 18 months make the experiments described below; these have led us to a new standpoint in relation to the thermodynamics of muscle. We had no difficulty in confirming Fenn's most important conclusion, that the performance of work by a muscle causes a considerable increase in the total energy liberated, but with the provision that the contraction is of a tetanic nature . Most unexpectedly, however, we found that in a single twitch the total energy is the same whether work be done or not . This point was clearly of great theoretical significance. One statement of Fenn's, moreover, we were unable to verify, viz., that work done during the phase of relaxation causes a decrease in the total energy set free. Finding it impossible to explain this disagreement, and wishing to confirm our observation that the energy liberated in a twitch is unaffected by work done, we made a further series of 34 complete experiments, of which 23 employed the thermopile wound on a silver-frame described recently (11). By using this thermopile we hoped to eliminate any possibility of temperature differences along the length of the shortening muscle. The second series of experiments confirmed the first.