Analysis Of Kinematic Characteristics Affecting The Serving Speed Of Chinese Elite Female Tennis Players

Objective: The purpose of this study was to explore the main factors influencing the serve speed of China’s elite female tennis players,to understand the characteristics of China’s elite female tennis players’ service technology,and to provide theoretical basis for the improvement of women’s tennis players’ service technology in the future.Methods: Two z-camera high-speed cameras were used to shoot the service movements of 18 high-level female tennis players.Use a radar gun to record ball speed.The obtained service action video is digitized by video recording analysis system and the 3d coordinates are obtained it.According to the purpose of each stage of the serve movement,the serve movement was divided into three stages: Back Swing Phase,Extension Phase,and Forward Swing Phase.The four characteristic moments were the moment when the ball was off the hand,the end of Back Swing Phase,the end of Extension Phase and hitting.Qualisys Track Manager and Excel software were used to calculate the kinematic parameters.Select the fastest individual serve,divide into two groups according to the ball speed from big to small,set as high speed group and low speed group respectively.Statistical analysis was conducted on the corresponding kinematic parameters of each stage,the difference between the two groups was analyzed by the independent sample t test,and the correlation between the kinematic parameters of each group and the service speed was analyzed by Pearson correlation coefficient.Significance level is defined as p < 0.05.Results: Back Swing Phase: The height of the ball off hand,the speed of the ball off hand,the maximum height of the ball rising and the height of the ball were not significantly different between the two groups.The difference in the height of the ball,the difference in the height of the ball off hand and the height of the highest point was significantly higher in the high speed group(1.02±0.15m;2.11±0.33 m)than in the low speed group(0.81±0.24m;1.78±0.33 m)(p<0.047).At the end of Back Swing Phase:there was no significant difference between the two groups in knee Angle and shoulder and hip torsion Angle,while the high-speed group(101.11±0.63°)was significantly higher than the low-speed group(98.64±1.83°).There was a significant negative correlation between shoulder and hip torsion Angle and service speed in the low-speed group(r=-0.871,p=0.002**),while other parameters had no significant correlation with service speed in the two groups.The trunk posterior elevation had a significant positive correlation with the maximum rise of the center of gravity in both the lowspeed group and the high-speed group(r=0.720,p=0.029).R =0.817,p=0.007),and the correlation between other parameters and the maximum rising velocity of the center of gravity was not significant.Extension Phase: The maximum angular velocity of the right hip,knee and ankle joint had no significant difference between the two groups.The maximum angular velocity of the right ankle joint had a significant positive correlation with the service speed in the low speed group(r=0.668,p=0.049),while the other parameters had no significant correlation with the service speed in the two groups.There was no significant difference between the two groups in the range of extension,the maximum speed of center of gravity and extension time.In the low speed group,there was a significant positive correlation between the change range of kick extension of the left knee and the service speed(r=0.723,p=0.028),while the correlation between other parameters and the service speed was not significant in the two groups.At the end of Extension Phase: right elbow joint Angle,right shoulder joint flexion Angle,right Angle,right shoulder shoulder joint flexion and adduction abducent angles,right shoulder joint spin spin outside,inside,right Angle of hip flexion and extension,right hip adduction abducent angles,shoulder elevation after hip twist Angle,trunk,trunk roll Angle in the two groups had no significant difference,right Angle and shoulder joint flexion and extension serve speed has significant negative correlation(r = 0.743,p = 0.022),and other parameters in the two groups with ball velocity correlations were not significant.Forward Swing Phase: the maximum speed of right shoulder,elbow,wrist,hip and knee had no significant difference between the two groups.Time used in each service stage: there was no significant difference between the two groups in the three stages.The total time in the high speed group(1.11±0.08s)was significantly higher than that in the low speed group(1.00±0.11s).The correlation between the time spent in each stage and the total time and the service speed was not significant.Conclusions: 1.Keeping the shoulder-hip twist Angle smaller at the end of the throwing shot can better increase the shoulder-hip twist Angle in the process of scratching the back,thus improving the service speed.2.Improve the speed growth rate and increase amount of the shoulder,elbow,wrist,hip and knee during the swing stage,shorten the time interval of the peak speed of the hip-shoulder joint,and faster braking can produce faster serve speed.3.In the batting stage of swing,the upper limb part delivers force in the order of shoulder-elbow-wrist in accordance with the whip action principle,which can better carry out momentum transfer and improve the serve speed.4.The parameters such as the difference in the hitting height,the difference in the height between the departure point and the peak point,the Angle of the left and right knee and the Angle of the back of the trunk at the end of the throwing shot,the time of each stage of the serve and the total time of the serve do not directly affect the serving speed,but these parameters can affect the structure of the player’s serve and the effect of the kicking and extending of the lower limbs.