TENDON ACTION OF 2-JOINT MUSCLES - TRANSFER OF MECHANICAL ENERGY BETWEEN JOINTS DURING JUMPING, LANDING, AND RUNNING

The amount of mechanical energy transferred by two-joint muscles betwe en leg joints during squat vertical jumps, during landings after jumpi ng down from a height of 0.5 m, and during jogging were evaluated expe rimentally. The experiments were conducted on five healthy subjects (b ody height, 1.68-1.86 m; and mass, 64-82 kg). The coordinates of the m arkers on the body and the ground reactions were recorded by optical m ethods and a force platform, respectively. By solving the inverse prob lem of dynamics for the two-dimensional, four-link model of a leg with eight muscles, the power developed by the joint (net muscular) moment s and the power developed by each muscle were determined. The energy t ransferred by two-joint muscles from and to each joint was determined as a result of the time integration of the difference between the powe r developed at the joint by the joint moment, and the total power of t he muscles serving a given joint. It was shown that during a squat ver tical jump and in the push-off phase during running, the two-joint mus cles (rectus femoris and gastrocnemius) transfer mechanical energy fro m the proximal joints of the leg to the distal ones. At landing and in the shock-absorbing phase during running, the two-joint muscles trans fer energy from the distal to proximal joints. The maximum amount of e nergy transferred from the proximal joints to distal ones was equal to 178.6 +/- 45.7 J (97.1 +/- 27.2% of the work done by the joint moment at the hip joint) at the squat vertical jump. The maximum amount of e nergy transferred from the distal to proximal joints was equal to 18.6 +/- 4.2 J (38.5 +/- 36.4% of work done by the joint moment at the ank le joint) at landing. The conclusion was made that the one-joint muscl es of the proximal links compensate for the deficiency in work product ion of the distal one-joint muscles by the distribution of mechanical energy between joints through the two-joint muscles. During the push-o ff phase, the muscles of the proximal links help to extend the distal joints by transferring to them a part of the generated mechanical ener gy. During the shock-absorbing phase, the muscles of the proximal link s help the distal muscles to dissipate the mechanical energy of the bo dy.