KINETICS OF THE COMPUTER-SIMULATED TENNIS STROKE WITH DIFFERENT RACKETS

Abstract

INTRODUCTION: The aim of this biomechanical analysis of the tennis stroke is the determination of the effects of the mass properties of different tennis rackets' on the kinetics of the striking arm. In contrast to experimental investigation the computer simulation gives an infinite temporal resolution so that the arm movements could be investigated especially during the racket-ball-contact phase. The planar model of the tennis stroke consisting of the immovable trunk, the upper arm, the lower arm, the hand and• the racket was derived from the mo ei of the human body by GLITSCH (1993). The striking arm with a racket tightly fixed to the hand was constructed as a pendulum of three rigid bodies which are connected with frictionless revolute joints. An elastic spring (0=45000 N/m) represents the ballracket-contact. The arm-racket-system• rotates around the shoulder joint and hits the resting ball in the respective" racket area centre. Considering rigid body mechanics the mass distributions of three different tennis rackets were measured and served as input for the model. The computer simulation with the initial conditions referring to real tennis strakes registered by KNUDSON (1990) was carried out with the software-packet DADS (Dynamic Analysis and Design System) by CADSI (Computer Aided Design Software Inc.). RESULTS: As it is shown in figure 1 the computer simulation has calculated an elbow flexion when rackets 1 or 2 are used. When the tennis forehand stroke is carried out with racket 3 the elbow is kept extended during the ball-racket-contact phase. The quite different arm movements during the impact with different tennis rackets are the result• of the separate locations of the centres of percussion with respect to the rigid handracket-system. The centre of percussion of racket 3 (5.3 cm) is located more distally than its centre of area because of the different mass distribution and finally because of its greater moment of inertia. In contrast to that the centre of percussion of the other two rackets (racket 1: -3.6 cm, racket 2: -3A cm) are located more proximally than the hitting point. CONCLUSION: The mechanical properties of tennis rackets, particularly the mass distribution, are responsible for different and movements during the ball-racket-contact phase. Obviously, there is no consensus of the preferable mass distribution of modern tennis rackets. This model can objectively assist in choosing one's individual favourable racket. REFERENCES: Glitsch U., Farkas R. (1993): Applications of a multi-body simulation model in human movement studies. Proc. Int. Soc. of Biomech., XIV1h congress, Paris. Knudson, DV (1990): Intrasubject variability of upper extremity angular kinematics on the tennis forehand drive. Int. J. of Sport Biomech., 6, 415-421.