Effect of stress relaxation on the contraction response of cardiac muscle.

Abstract

Isolated papillary muscles from the rabbit were subjected to series of quick stretches of increasing magnitude. Each stretch was maintained for 5 min. Muscle tension was recorded during the entire period of the stretch. A maximal square wave stimulus was applied every 3 sec throughout the experimental procedure. The maximum isometric contraction tension produced during the period of stress relaxation following each stretch increased up to a mean extension ratio of 24.37%. For stretches of less than this amount, the isometric contraction tension continuously decreased during the period of stress relaxation. With stretch of greater than this value, the magnitude of the isometric contraction response increased throughout the period of stress relaxation. These data are interpreted to suggest there is a viscous muscle unit in series with both the elastic and contractile elements.