Present study examined the impact behavior of tennis rackets during swinging by players. First, the 3D motion of racket in swing was estimated from the 2D video by transforming it into match-stick motion picture using an AI method of Openpose. As a result, it looks like that players stop their wrist to accelerate the rotation of racket head during the impact. Next, a strain gauge was glued on rackets and the bending strain was measured when hitting a ball. It was found that the acceleration of racket have bent the racket significantly before the impact; the flexure was as large as the bending vibration induced by hitting a ball.
