["Tendon" action of two-joint muscles during human locomotion: transfer of mechanical energy between links in shock-absorbing and push-off phases].

We hale evaluated experimentally the amounts of the mechanical energy transferred by the two-joint muscles between the links of legs during squat vertical jumps and landings after jumping down from a height of 0.5. The experiments have been conducted on file healthy subjects in the course of locomotions. The coordinates of markers attached to the subjects' bodies and the ground reaction forces have been registered. The energy transferred by the two-joint muscles from and to the links forming each joint has been determined by integration of the difference between the power developed in the joint by the control moment and the total power of the muscles serving the given joint. It has been shown, that at squat vertical jump (the push-off phase) the two-joint muscles transfer mechanical energy from the proximal links of the leg to the distal ones: from pelvis to shank (by the rectus femoris m.), and from thigh to foot (by the gastrocnemius m.). At landing (the shock-absorbing phase) the two-joint muscles transfer energy from the distal to proximal links: from foot to thigh (by the gastrocnemius m.), and from shank to pelvis (by the rectus femoris m.). Thus the one-joint muscles of the proximal links compensate for the deficiency in the force developed by the one-joint muscles of the distal links due to the "tendon action" of the two-joint muscles. During push-off, the muscles of the proximal links contribute to increase in the energy of the distal links, and in the shock-absorbing phase, to its dissipation.