Dynamic Contribution Analysis of Tennis-serve-motion in Consideration of Torque Generating Mode

The purpose of this study was to quantify dynamic functional roles of upper body joint torques to the generation of racket head speed in consideration of the joint torque generating mode in the tennis serve motion. The upper body with a racket was modelled as a linked eleven-segment system consisting of the upper limbs, shoulder girdles, head, upper trunk and the racket. The contributions of the joint torque term, motion-dependent term, gravitational term and external force term to the generation of racket head speed were calculated from the equation of motion for the system. Furthermore, the joint torque was divided into two components, such as eccentric torque component, which shows negative sign of its torque power, and concentric torque component, which shows positive sign of its torque power. An algorithm which converts the motion dependent term into other terms was proposed. The results obtained in this study showed that 1) motion dependent term was the great contributor to the generation of racket head speed prior to the impact and 2) after converting motion dependent term into other terms, racket head speed was mainly obtained by eccentric torque component about internal rotational axis at racket side shoulder joint.