A STUDY ON THE MECHANICAL CHARACTERISTICS OF MUSCULAR FORCES IN THE VERTICAL JUMP

Abstract

In order to improve human performance in competitive sports, human motions have been analyzed from various viewpoints. One of the well-known methods is to compare the patterns of joint torques with those of top athletes during the motions. However, such comparisons are not necessarily sufficient to evaluate human motion, since individual differences in muscular forces and anatomical characteristics are not taken into consideration. The aim of this study is to investigate the relationship between the optimal vertical jump (squat jump) motion and the mechanical characteristics of muscular forces. The vertical jump motions of four male subjects were analyzed; their anatomical characteristics are similar, but the muscular force characteristics are different. Each subject performed a squat jump, in response tothe command "jump ashigh as possible," from an initial squat position with 90°hip and knee angles. The reaction force from the platform, the motions of the limb and the body, and the electromyographic (EMG) data were recorded. In order to estimate the optimal control for vertical jump motion under various conditions, a simulation system is applied which is based on the musculoskeletal model with the mean characteristics of muscular forces and the anatomical parameters of the four subjects chosen. In order to investigate the relationship between the optimal vertical jump motion and the mechanical characteristics of muscular force, a series of simulations was carried out by varying the parameters of the musculoskeletal model, such as the force-velocity relationship and the maximum contraction force. The following conclusions are derived from the results of the experiments and the simulations. (1) Change in the force-velocity relationship of human muscles results in a change in the optimal vertical motion and the sequence of the firing pattern of muscles, so that the contraction velocity of muscles does not become extremely large. (2) Changes in maximum contraction forces of some muscles result in changes in the optimal vertical motion and the sequence of the firing pattern of muscles, so that each muscle contracts under the optimal condition for the vertical jump. (3) The firing pattern of muscles is governed by the relationship between the anatomical characteristics and the muscular forces, and the timing of firing is determined by the relationship between the firing patterns and the maximum muscular forces. (4) The maximum contraction forces and the force-velocity relationship have to be improved in order to improve vertical jump performance.