*Department of Physical Education

The purpose of this study was to explore the two different serving pattems---flat serve and spin serve, using a motion analysis system to discover the 3-D kinematic changes of the ankle, knee, hip, pelvis and trunk in the overall serving motion, in conjunction with force plates that helped to measure the ground reaction force (GRF) and worked out the center of pressure (COP). The moment formed by COP with the whole body center of mass would then be analyzed to explore the kinematic characteristics of the body. A further understanding of the role of joints in the lower extremity during a serve will provide a reference to motions and techniques on training and teaching, with a view to improve serving efficiency and avoid sports injury. KEY WORDS: tennis, serve, kinematics, moment, COP, CaM. INTRODUCTION: The serve is one of the most important techniques in tennis. Tennis serve can generally be divided into three patterns: flat, spin, and slice. Tennis serve transfers the GRF to the trunk by tiptoeing of the lower extremity, utilizing an effective integrity of body segments and the continuity of limb motion from proximal end to distal end. Such a rotation plus a chain of mechanical effects of the customary arm will produce a "whipping motion " to complete th