Impact Vibrations of a Racket Handle and the Wrist Joint in Tennis.

The performance of a tennis racket concerning the shock vibrations of the racket handle during impact is one of the important factors for the optimum design of rackets. This paper investigates the mechanism of shock vibrations caused by the impact between a ball and a racket on the basis of the approximate nonlinear impact model and the vibration model of the racket, identified using the experimental modal analysis, and gives physical explanations for the recorded waveform of measured acceleration of the racket handle and the wrist joint when a male tournament player hits flat forehand drives. The results show that the shock vibrations at the racket handle are composed of the reaction force and the vibrations of the racket frame when the ball hits the strings, and also show that there is no reaction force when the ball hits the center of percussion on the racket face. Furthermore, the reaction force due to ball-racket impact and the vibrations at the racket handle are rather small when the ball hits near the center of the racket face with the normal grip position.