The mechanism of muscular contraction

A contracting muscle gives maximal values for the force exerted only when it is allowed to shorten very slowly. The force exerted decreases as the speed of shortening increases. The nature of the physical property which underlies the contractile mechanism, and which is responsible for the variation of force exerted with speed of shortening, is not definitely known. It may be any of the properties of heterogeneous systems which attain equilibrium slowly, such as the properties of viscous elastic systems, the generation of interfacial tension, etc. The properties of viscous elastic systems have already been applied to the problem of a muscle shortening at varying speeds, and as Gasser and A. V. Hill (1) have shown, equilibrium is established in a viscous elastic system under stress at rates which show many analogies with those observed during the contraction of muscle.