Stretch-shortening cycle in skeletal muscle function : with special reference to elastic energy and potentiation of myoelectrical activity

Abstract

Mechanical behaviour of human leg extensor muscles was investigated under conditions of varied stretch-shortening (eccentric-concentric) cycle movements of the vertical jump. In these exercises the muscular performance was always greater than that in pure concentric contraction. The enhanced performance was due to the storage and re-use of elastic energy. When examined with 226 subjects this elastic potentiation was observed to be both sex and age dependent. In another series of experiments the pre-stretch movement prior to shortening shifted the force-velocity curve to the right. Similarly the net mechanical efficiency of the positive work was increased from 20 % (no rebound jumps) to 30-40 % (rebound jumps). The results also indicated that not only the mechanical behaviour of muscle was modified due to stretching of active muscle, but the electromyographic activity was also increased, but primarily during the eccentric phase of the cycle. Elastic potentiation was also sensitive to the duration and velocity of the stretch and suggestion was made that, although the influence of muscle structure was not examined directly in the present study, utilization of elastic energy may occur differently according to whether slow or fast muscles were activated under various conditions of the stretch-shortening cycle.