Three-dimensional Kinematics Analysis Of Chinese Male Tennis Players’ Serve

ObjectiveA study was conducted on 8 Chinese excellent tennis athletes to explore the characteristics and rules of first and second serves in the ‘T’ target area of the deuce side,to clarify the important factors affecting the effectiveness of the serve,to provide theoretical reference for the scientific training of tennis,and to help the development of Chinese tennis.MethodA high-speed camera(model: Sony DSC-RX10M4,shooting frequency: 1000fps/s)was placed behind the baseline of the tennis court and about 10 meters to the side of the sideline of the doubles serve,and the angle of the main optical axis of the two cameras was about 90°,and then the technical movements of the first and second serves of eight Chinese first-grade tennis players were collected and used the software Simi Motion 9.2.2 for 3D analysis.Result(1)When the ball was thrown away from the hand,the rise angle and left shoulder angle of the first serve were 5° and 4° smaller,and the height off the hand was 8 cm higher than those of the second serve.In terms of correlation,the ball velocity of the first serve was negatively correlated with the left knee and right ankle angles.The second serve ball velocity was negatively correlated with the trunk-plevis separation angle in vertical plane and positively correlated with the left ankle angle.(2)When the left knee was minimally flexed,the first serve right elbow angle was12° greater,and the hip vertical plane rotation amplitude was 4° smaller than the second serve.In terms of correlation,the hip vertical plane rotation amplitude was positively correlated with first serve racket velocity,and left knee angle was positively correlated with first serve ball velocity.As for the second serve,the trunk-plevis separation angle in vertical plane was positively correlated with racket velocity.In the ball throwing phase,the velocity of the second serve was negatively correlated with the trunk-plevis separation angle in horizonal plane,and positively correlated with the vertical rotation amplitude of shoulder.(3)When the racket head is lowest,the right elbow angle,left knee angle,shoulder horizontal plane and vertical plane rotation amplitude of the first serve are larger than the second serve,the left shoulder angle and trunk-plevis separation angle in vertical plane are smaller than the second serve,and the center of gravity is 9cm further forward than the second serve.In terms of correlation,the first serve velocity was positively correlated with the height of the center of gravity and the forward movement of the center of gravity.The second serve ball velocity was positively correlated with the left and right knee angles,and negatively correlated with the trunk-plevis separation angle in horizontal plane.(4)Before hitting the ball,the second serve swung upward and outward 24 and 29km/h faster than the first serve,and 20 km/h slower than the forward serve.racket,the first serve swung leftward along the Y axis(-280°/s),and the second serve swung rightward(927°/s).The second serve ball velocity was positively correlated with the racket face internal rotation and downward pressure angular velocity.(5)When hitting the ball,compared to the first serve,the second serve has a more backward center of gravity,the hitting point is more backward and left,and the racket face has less internal rotation and more left tilt,which is in line with the feeling of "brushing the ball" in the second serve.Appropriately increase the right tilt of the racket face,downward pressure and raise the height of the hitting point in the first serve to increase the ball velocity,and appropriately reduce the internal rotation of the racket face in the second serve to increase the swing velocity.(6)After hitting the ball,the first serve leftward,forward,and upward velocities were 10,43,and 9 km/h faster than the second serve,respectively,and the downward and leftward deflection angles were 2° and 2.9° more than the second serve,respectively.First and second serve ball velocity were not correlated with swing velocity,and first serve upward ball velocity was positively correlated with upward and rightward swing velocity.First serve ball velocity was negatively correlated with the angle of descent.Conclusions(1)When throwing the ball away from the hand,the first serve throws the ball forward more than the second serve.The more fully the lower limb is flexed in the first serve(the more the left knee and right ankle is flexed),the faster the swing velocity is,and the appropriate increase in the vertical angle of the trunk-plevis separation in the second serve can increase the swing velocity.(2)When the left knee was minimally flexed,the degree of right elbow flexion and hip vertical rotation is smaller in the first serve than in the second serve.The less the hip vertical plane rotation of the first serve,the faster the swing velocity,the less the left knee flexion,the faster the ball velocity.(3)When the head is lowest,compared with the second serve,the first serve has fuller upper limb folding and lower limb extension,and greater shoulder horizontal and vertical plane rotation,but the trunk-plevis separation angle in vertical plane angle is smaller.In addition,the first serve was more forward and upward in the center of gravity position,the second serve had full knee stirrups,and the increase in the trunk-plevis separation angle in horizontal plane was conducive to increasing the respective ball velocity.(4)Before hitting the ball,there is no difference in the velocity of the first and second serve,but the second serve swings upward and outward faster and forward more slowly.The angular velocity of the racket,the first serve is tilted to the left,the second serve is tilted to the right,and the appropriate increase in the external rotation of the racket face and downward pressure angular velocity is conducive to improving the ball velocity of the second serve.(5)When hitting the ball,compared to the first serve,the second serve has a backward center of gravity,the hitting point is backward and left,and the racket face has less internal rotation and more left tilt,which is in line with the feeling of “brushing the ball” in the second serve.Appropriately increase the right tilt of the racket face,downward pressure and raise the height of the hitting point in the first serve to increase the ball velocity,and appropriately reduce the internal rotation of the racket face in the second serve to increase the racket velocity.(6)After hitting the ball,the ball velocity of the first serve and its component velocities are faster than that of the second serve,and the angle of descent and offset to the left is greater than that of the second serve.The greater the angle of descent of the first serve the faster the ball velocity,the faster the upward and rightward racket velocity the faster the upward ball velocity.