Effects of Controlling the Velocity of Shortening on Force-Velocity-Length and Time Relations in Cat Papillary Muscle: VELOCITY CLAMPING

Abstract

A new technique-velocity clamping-was used to study the effects of a constant total velocity of shortening on the interrelation between force, velocity, length, and time in cat papillary muscle. With decreasing values of clamped total velocity, the duration of the contraction increased but never exceeded the duration of an isometric contraction. Hence these findings confirm that the mode of contraction-isometric or isotonic-has a marked effect on the duration of the contraction. The active state can be prolonged when less shortening occurs and more tension is developed. This phenomenon seems mainly due to the amount of shortening rather than to the velocity of shortening of the muscle. The data were also plotted on a threedimensional graph and compared with velocity-length tracings of afterloaded contractions. The force-length trajectories of the muscle during velocity clamping did not fall on the surface described by the force-velocity-length relations as derived from afterloaded isotonic contractions. This finding could be ascribed to the masking effect of the series elastic component due to the continuous adjusting of the load.