EFFECTS OF MUSCLE STRENGTHENING ON VERTICAL JUMP HEIGHT - A SIMULATION STUDY

In this study the effects of systematic manipulations of control and m uscle strength on vertical jump height were investigated. Forward dyna mic simulations of vertical squat jumps were performed with a model of the human musculoskeletal system. Model input was STIM(t), stimulatio n of six lower extremity muscles as function of time; model output was body motion. The model incorporated all features of the musculoskelet al system of human test subjects considered salient for vertical jumpi ng, and the initial body configuration was set equal to that of the te st subjects. First, optimal STIM(t) was found for a standard version o f the model (experiment A). A satisfactory correspondence was found be tween simulation results and kinematics, kinetics and electromyograms of the test subjects. Subsequently, optimal STIM(t) for the standard m odel was used to drive a model with strengthened muscles (experiment B ). Jump height was now lower than that found in experiment A. Finally, optimal STIM(t) was found for the model with strengthened muscles (ex periment C). Jump height was now higher than that found in experiment A. These results suggest that in order to take full benefit of an incr ease in muscle strength, control needs to be adapted. It is speculated that in training programs aimed at improving jumping achievement, mus cle training exercises should be accompanied by exercises that allow a thletes to practice with their changed muscles.