The viscous elastic properties of muscle

Abstract Towards the middle of the last century Weber (1) investigated the problem of muscular contraction from the physical and mechanical points of view. He thought it possible to express the activity of the muscle solely in terms of a change in its elastic condition in response to stimulation. In other words, he assumed that the active muscle behaved as a stretched spring and that the tension-length curve of a given muscle, under a definite set of external conditions, was invariable and independent of the particular way in which it was obtained. This assumption was shown to be erroneous by Blix (2), with the help of his myographion, by means of which tension-length diagrams both of shortening, and of stretched, muscle could be automatically recorded. Blix showed that, at any length, tension developed during stretch was greater than corresponding tension developed during release. This observation was confirmed and extended by Fick (3, 4), who at first assumed an increased “physiological” response in stretch as the cause of this effect. In order to measure this response he determined the total energy of a contraction, this term denoting the algebraic sum of mechanical work and heat produced by the muscle. This quantity was found to be smaller in the case of a stretched muscle, and no satisfactory explanation was available capable of fitting the more elaborate picture which had emerged, largely from Fick’s hands.