| Serve technique is the only technique in tennis that can score directly without the impact and restriction of the opponent.Nowadays,the male tennis games in the world are fiercer than ever,and much attention is laid on serve technique by players and coaches.It is necessary,even for professional players,to seek offensive serve and ensure the stability of serve in order to acquire the initiative of the game.This paper mainly adopts three-dimensional video analysis of the stability of the 12 deuce area serve motions of champion Bernard Tomic and 11 deuce area serve motions of second runner-up Fabio Fognini in Chengdu Open 2018.The first serve of Tomic and Fognini are divided into four moments and three phases,and the research indicates that:(1)In the phase of ball-throwing and racket-lifting,Fognini's standard deviation of the left shoulder angle was a little larger than that of Tomic,and the standard deviation of other kinematics parameters was smaller than Tomic.So,it is considered that the stability of Fognini was better than Tomic in the first phase.The two players had high stability but low speed when the ball left their left hand.At the maximum bend of the left knee joint,the body posture of both players had changed greatly,and the stability of the lower limbs had decreased as a result.(2)In the phase of backward-swing,Tomic's range of right knee extension was larger than that of his left knee extension.While Fognini's range of left knee extension was larger than that of his right knee extension.At the moment of the lowest point of racket behind the back,both players had poor control over the right and left hip angles.Tomic had worse control of the right knee angle and the range of the right knee extension,that is,the stability of the main extension leg was worse.Besides,the stability of the lowest point of the racket was also relatively poor,and the stretching range of the upper limbs was not enough,which had damaged the coordination of upper and lower limbs.The minimum angle of Fognini's right elbow joint was bigger than Tomic.The action structure of Fognini was better than that of Tomic,but the standard deviation of Tomic's three kinematic parameters was smaller than that of Fognini,and the stability was higher.(3)In the phase of forward-swing and ball-hitting.The two players both had low batting points.Fognini's vertical distance between the highest point of the ball and the hitting point were greater than that of Tomic,which had made it more difficult for players to judge the hitting time and space,with larger standard deviation and worse stability.Fognini's horizontal distance between throwing point and hitting point was bigger than Tomic's,which further proved that Fognini with FB position can acquiremore forward ground reactive force.The standard deviation of angles of the joints of both players were still large at the moment of hitting the ball.Fognini's knees and upper limbs were more stable,whereas Tomic's hip joints were steadier.At the moment of hitting the ball,the order of joints exertion of the two players accorded with principle of whipping,but the speed of hitting the ball was lower than that of top male players in the world.Based on the comparative analysis of the stability of Tomici and Fognini's serve technique from the perspective of kinematics,the result shows that Fognini's stability was proved to be better in the phase of ball-throwing and racket-lifting.In the phase of backward-swing,both players had poor control of lower limb stability,but Tomic had better control of upper limb stability.In the phase of forward-swing and ball-hitting,Fognini's four standard deviations that affect the stroke position were smaller,and the standard deviations of left and right knee angle,right shoulder angle,right elbow angle and five velocity parameters were also smaller,which had showed higher stability.The research demonstrates that Fognini's serve stability was higher than Tomic's,thus,more suitable to be used as a reference for the kinematics analysis of serve stability. |
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