Joint moment and mechanical power flow of the lower limb during vertical jump.

The purpose of this study was to examine the joint moment and the mechanical power flow in the lower limb during three types of vertical jump. A healthy male subject performed the following jumps: maximal vertical jump from a squatting position (SJ), maximal vertical jump from an erect standing position with a preliminary countermovement (CMJ), and repetitive submaximal hopping in place with preferred frequency. The jumps on the force plate were also filmed (100 frames X s-1). Film analysis on force platform records were used to obtain the joint reaction forces, moments, mechanical powers, and work. All the peak values of moments of CMJ were greater than those of SJ, but in both cases they appeared in the same rank order (hip greater than knee greater than ankle). The mechanical work of the hip extensors was much greater than that of SJ although the work by the knee extensors and the ankle plantar flexors was almost the same in these jumps. It was suggested that the performance difference between SJ and CMJ might result from the difference in work by the hip extensors rather than from the effect of the stored elastic energy. Hopping differed from SJ and CMJ and was characterized by large moment and mechanical work of the ankle plantar flexors. The results also suggest that muscle elasticity may play a greater role in hopping than in CMJ.