A 3-DIMENSIONAL KINEMATIC METHOD FOR DETERMINING THE EFFECTIVENESS OFARM SEGMENT ROTATIONS IN PRODUCING RACQUET-HEAD SPEED

The contribution that a segment's anatomical rotations make to racquet -head speed depends on both the segment's angular velocity and the ins tantaneous position of the head of the racquet with respect to the seg ment's axes of rotation. Any analysis of racquet swing technique that does not consider both of these factors simultaneously is, at best, in complete. With this in mind, a three-dimensional kinematic method was developed to determine the effectiveness of the anatomical rotations o f the upper arm, forearm, and hand in producing racquet-head speed. Th e method entailed developing a system of vector equations for three-di mensional upper limb rotations that used displacement histories of 10 selected landmarks as input. The required three-dimensional displaceme nt histories were obtained using three cine cameras and the DLT approa ch. To test the diagnostic capabilities of the method, a tennis serve was selected for analysis. For the player and serve analyzed, the grea test contribution to racquet-head speed at impact was produced by inte rnal rotation of the upper arm (8 m s(-1)). Forearm pronation, althoug h exhibiting the fastest rotation at impact (24 rad s(-1)), ranked onl y fourth in terms of its contribution (4 m s(-1)) to racquet-head spee d. To test the performance of the method, a comparison was made betwee n the racquet-head speed measured directly from film and the racquet-h ead speed computed by summing all of the individual segment contributi ons to speed commencing at the start of forward swing and ending at ba ll contact. The results indicate that the method can successfully dete rmine the individual contributions that the different anatomical rotat ional velocities of the arm segments make to the measured instantaneou s racquet-head speed.