Coordination control of the muscles including the bi-articular and mono-articular muscles in the ballistic jump movement.

The hypothesis that the bi-articular muscle gastrocnemius controls the ground reaction force direction in jumping was constructed by means of the functionally effective muscle model including bi-articular muscle. The relationship between the activities of lower limb muscles and the jump direction was examined by means of electromyogram and computer simulation during the vertical and broad jump. In the result, it was clarified that jump direction was controlled by changing the timing of gastrocnemius muscle activation.