Capacity of Skeletal Muscle to Develop Isometric Tension After Prolonged Shortening

Abstract

A study was made of the relationships between the shortening and the degree of functional impairment which occurs in skeletal muscle subjected to prolonged and severe experimental shortening. Rat gastrocnemius muscles caused to shorten by tetanus toxin injection, tenotomy and immobilization were found to exhibit varying degrees of atrophy and functional impairment in studies made after 14 days. Although atrophy was greater after immobilization, tenotomy produced more marked functional damage. The isometric tensions developed by contralateral control and experimental muscles at initial lengths ranging from 70-140% of the resting length were used to construct active length-tension diagrams. In tenotomized and in immobilized muscles the optimal length for maximum tension development was essentially the preshortened resting length. In contrast, shortening evoked by tetanus toxin injection was accompanied by a shift in the optimal length to the newly acquired resting length.