Abstract
Players often say that some strings provide a better grip and more spin than others, but ball spin did not depend on string type, gauge or tension in the past laboratory experiment. There was no research work on the spin to uncover what is really happening during actual tennis impact owing to difficult experiment. This study made clear the mechanism of top spin and its improvement by lubrication of strings with high speed video analysis. As the main strings stretch and slide side ways more, the ball is given more spin when the main strings spring back and the ball is released from the strings. More spin produce longer contact time between ball and strings, resulting in the reduction of shock vibrations of the wrist joint during impact
