The effect on human body at the impact of tennis racket and balls from the viewpoints of mechanical characteristics of the grip

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Experiments reveal clearly that when the vibration occurred at the impact of a ball and a racket, there are two kinds of frequency, one is high frequency around 130 Hz and another one is low frequency around 10 to 50 Hz. These results lead us to the conclusion that the racket acts as one is a vibration body and another one is a rigid object at the impact. This high frequency vibration disappeared when a ball impacts only just on the center of racket face, and low frequency remains on the racket. This law frequency vibration transmits to a hand and a forearm though. At the off center impact, when changing the rigidity of the grip from tight to loose, it was found that the high frequency was hard to transmit to a hand, but low frequency passed through the grip. Yoneyama, S. (2003) and other studies reported that the vibration after the impact may causes the "tennis elbow". The results of this experiment reveal that not only the vibration of high frequency but also the low frequency origi … More nates in the tennis elbow, when the racket is regarded as a rigid body.Findings from the experimental results show that the racket acts as a body with two types of properties, one is a vibration body and another one is a rigid object at the impact. From this point of view, we made a model of impact as a rigid body, and the racket links to a hand through a grip that has the characteristics of visco-elasticity. By means of this model, the characteristics of grip are investigated. The model was identified by comparing the experiment data such as the duration time of contact with the ball and racket, the coefficient of restitution of ball, the characteristics of damping of vibration, the frequency and the peak value of vibration. From the simulation of the model, it is inferred that the coefficient of viscosity of grip changes 1.0 to 5.5 N/m/s and the coefficient of elasticity changes from 50 to 500 N/m, according to the tightness of grip. As the tightness of the grip changes, the visco-elasticity coefficients of wrist joint are also influenced. Less