DEPENDENCE OF HUMAN MAXIMUM JUMP HEIGHT ON MOMENT ARMS OF THE BIARTICULAR M GASTROCNEMIUS - A SIMULATION STUDY

In this study the dependence of maximum jump height on moment arms of m. gastrocnemius at the knee and ankle joint was investigated, using a forward dynamic simulation model of the human musculoskeletal system. Input of the model was the stimulation of six muscles of the lower ex tremity as a function of time, output was the movement of body segment s. For many different combinations of moment arms, maximum jump height was determined by optimizing muscle stimulation. It was found that (1 ) maximum jump height depends on the combination of moment arms of m. gastrocnemius at the knee and ankle, (2) at a given moment arm at the ankle there is an optimal moment arm at the knee joint, and (3) this m oment arm differs from zero, i.e. there is an advantage in the bi-arti cularity of m. gastrocnemius. This advantage, which amounted to less t han 2 cm, was explained as follows. When m. gastrocnemius is bi-articu lar, it causes a particular combination of net joint moments at the kn ee and ankle joint during the last part of the push-off. This combinat ion is such that the acceleration of the body's mass centre remains ve rtical, even at maximal stimulation of all muscles. Such a profitable situation cannot be achieved when m. gastrocnemius is mono-articular. Finally, it was shown that moment arm values derived from cadaver data reported in the literature were close to the optimal values determine d for the model.