Potentiation of the mechanical behavior of the human skeletal muscle through prestretching

Abstract

Force–velocity and power–velocity curves in a vertical jump involving movements around several joints were derived from vertical ground reaction forces and knee angular velocities. The jumps were performed with weights from 10 to 160 kg added on the shoulders. The obtained curves from a semi–squatting static starting position resembled those reported for isolated muscles or single muscle groups. Vertical jumps were also performed in the conditions where the shortening of the leg extensors was preceded by prestretching of the active muscles either through a preparatory counter–movement or dropping down on the force–platform from the various heights ranging from 20 to 100 cm. Prestretching modified through a range of velocities the force–velocity and power–velocity curves by increasing both the ground reaction forces and the calculated mechanical power. Thus the results are similar to those reported in isolated muscles. In studies with isolated muscle preparation the nervous connections have not been intact and therefore it is suggested that increase in the performance of the skeletal muscles through prestretching, in the conditions of the present study, was attributed to the combined effects of the utilization of stored elastic energy and the reflex potentiation of muscle activation.