| This research takes the four tennis players from the 2016 International Youth League Youth Masters and the 2014 China Tennis Open Men's Singles Competition as the objects.Two Japanese high-speed cameras has been applied in the game site to make video capture and collection on the players' whole forehand topspin technology.According to the research needs,the captured video is intercepted,and then imported into 3D—SignalTEC analytical system for the 3D kinematics analysis,thus to gain the kinematic parameters such as the joints of upper and lower limbs,the angle of the links and the line velocity required in this study.The analyzing method combining the quantitative and qualitative analysis has been used for the kinematic comparative analysis,to reflect players' technical advantages and disadvantages in the batting process via players' joints of upper and lower limbs,the duration of the links,spatial parameters as well as the coordination with the body and torso,and reveal the biomechanical characteristics and laws of their action technologies.By the comparison on the similarities and differences in the technical characteristics of these four tennis players and the technical gaps,the players' shortcomings during the batting process could be found on the one hand,and one the other hand,certain data reference would be provided for our tennis players and coaches to improve the forehand topspin technology.Through the comparison and analysis,the main research conclusions are as follows: 1 Stage of Backswing:(1)Djokovic and Murray lowered the gravity center of the human body and transited to the right feet,which was beneficial for the lower limb to storage the elastic potential energy,while Rude's gravity center of the human body was lifted higher and not completely transited to the right foot,and Hong Chengcan's right knee angle had too large changing range,which was not good to maintain the balance of the human body.(2)Djokovic and Murray's right shoulder angle changes were 25.56 ° and 22.62 ° respectively,indicating that the two had used the ring backswing technology,and the ring backswing were done by driving the entire arm back after lifting the elbow in the early stage of the backswing;Hong Chengcan used the traditional straight pulling method without fully lifting the arm,which was not good for fully extending the shoulder muscles,while Rude failed to raise the right elbow high enough during the backswing,thus to affect the backswing effect.(3)These four players' joints of the arm holding the racket all went through the adjustment process of first acceleration and then slowing down at this stage.In the end of thebackswing,both Djokovic and Murray's right wrists maintained the faster speeds,3.56 m/s and 3.31m/s respectively,indicating the ideal backswing effect;while Rude and Hong Chengcan's right wrist speed were relatively slow,and the backswing effect was poor.2 Stage of Swing and Striking Ball:(1)Djokovic and Murray made the body rotation range of 59.60° and 62.93° respectively,and the time consumed during this stage of 0.18 s and 0.20 s,respectively,indicating a large body rotation range of the two and a significant effect in the swing towards the ground;while Hong Chengcan and Rude had insufficient swing and body rotation range and longtime duration during this stage,resulting in the poor swing effect towards the ground during the batting.(2)Djokovic and Murray had such a reasonable control on the deceleration brake and the acceleration time of each link during the batting that the speed of the racket head reached the maximum,indicating that the batting of the two completely fit the law of the whipping;while both Hong Chengcan and Rude had violated the law of the whipping during the batting,causing the poor momentum transmission effect and the slow speed of the racket head.(3)0.10 s before the swinging the racket at the tennis ball,Djokovic and Murray's right wrists were in passive stretching,and the arm and wrist joints holding the racket were in centripetal contraction with actions of wrist shake and brushing the ball forward0.10 s after touching the tennis;while Hong Chengcan and Rude's arms were relatively rigid,Hong Chengcan's batting was passive and Rude's right wrist had quite a small range to bend and stretch forward.(4)Djokovic and Murray had bigger difference value of the ratio between the height of gravity center and their height,reaching 0.13 m and 0.14 m,indicating that the two's lower limb had more significant pedal and stretch effect in the batting,and the elastic potential energy had been fully released;Hong Chengcan had the pause during the convergence of these two stages,resulting in the loss of partial energy and poor pedal and stretch effect.(5)During the swinging the racket at the tennis ball,the four players all had a better control on the angle of the racket face during the batting,there was no significant difference for the inclined angle of the upper body,and all of them could better coordinate the upper and lower limbs of the human body in a stable batting state.3 Stage of Follow-Through:(1)Djokovic and Murray's angles of right shoulders had increased from 46.83° and 45.13° to 104.24° and 108.73°,respectively,indicating that right elbow joints of both the two were lifted higher to stay away from the body and torso,which obeys the principle of follow-through at a large scale and at the long distance;right elbow angles were reduced from 117.25° and 120.19° to 77.46° and 72.93°,respectively,indicating that the two's right elbows significantly moves forward during the batting to prolongs the time of racket upon ball.The follow-through action of the two all ended in the outside of the left upper arms,this mode of follow-through could effectively prevent shoulder damage at the time of ensuring the power of the batting.(2)Hong Chengcan's follow-through action ended at the top of the left shoulder,this mode of follow-through could easily cause the arm excessively rotate towards the back of the left shoulder,bringing the shoulder a greater rotational pressure and increasing the possibility of the strains on the right shoulder and right elbow joints;after the batting,Rude failed to continue to push forward the entire arm and the center of gravity,and the follow-through action ended at the upper right of the body,which would bring a greater rotational pressure to the right shoulder and right elbow and more easily cause injures. |
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