THE GEOMETRY-CRITICAL FUNCTIONAL DEPENDENCE OF M. GASTROCNEMIUS

Abstract

The change in length of a muscle usually leads to a change in segment position. If a muscle is shortened the joint is being flexed. However bi-articular muscles are able to bend a joint as well as to stretch it by its contraction because of varied geometrical conditions. This phenomenon has already been analyzed in different surveys on M. biceps femoris. Until today such a consideration cannot be found for M. gastrocnemius, which is a bi-articular muscle, too. The weight- and speed-dependent activities of this muscle during fast and slow hopping, and also during running and walking, suggest that a movement-relevant function exists. This behavior pattern was the reason for a closer look on the actions of M. gastrocnemius from a geometrical point of view. The results clearly show a knee angle-dependent function. Moreover, a so-called critical angle area of the knee joint, from which the shortening of M. gastrocnemius leads from joint flexion to joint stretching, can be specified for the first time. At this, the position of the ankle joint seems to have little influence on the function of M. gastrocnemius.