Comparative Study On Muscle Movement Control Characteristics Of Tennis Flat Serve And Kick Serve

Objective: Serving as the basic technical link in tennis competition,is one of the most difficult and effective and accurate execution of hitting action in the game.The hitting effect of different serving techniques has an extremely important influence on the level of competitive performance.The variation characteristics of human motion kinematics,dynamics and muscle activity at T inner corner and Wide outer corner of tennis flat serve and kick serve were explored,and the differences between different tennis serve movements were compared and analyzed from the perspective of biomechanics – muscle motion control.In order to provide data support and theoretical basis for tennis researchers to study the movement characteristics of tennis serve,and provide reference for tennis enthusiasts,athletes and coaches to avoid sports injury and scientific sports training programs.Methods: In this study,18 national junior male tennis players(average age: 16.67±1.03 years old,height:181.17±7.22 cm,weight:71.33±12.75kg)were selected to conduct biomechanical tests on the step up technique of tennis flat stroke and side topspin serve.Eight Qualisys 3D infrared motion capture cameras were used to collect the kinematic data of the ball,and the sampling frequency was 200Hz/s.Four Kistler three dimensional force measuring tables were used to collect the dynamic data of the ball at a sampling frequency of 2000Hz/s.The Delsys Trigno 16-channel wireless surface EMG system was used to collect surface EMG data synchronically with kinematics and dynamics at a sampling frequency of 2000Hz/s.Results:(1)Kinematics index: There was no significant difference in the throwing speed during the throwing period(P>0.05).At the moment of throwing,the shoulder rotation angle of the throwing arm at the inner angle of the flat serve was the largest(P<0.05),and the wrist retraction angle of the kick serve at the outer angle was the largest(P<0.05),and the angular velocity variation of the left knee and left shoulder joint at the inner angle of the kick serve was the largest(P<0.05).There was no significant difference in the peak flexion of the knee joint during the lead period(P>0.05),and the Angle characteristics of shoulder external rotation,elbow adduction and wrist abduction were the most obvious at the peak moment of the knee joint torque(P<0.05).During the period of ‘back scratching’,the change of the left knee flexion ROM of the flat hit inside corner serve was the most obvious(P<0.05),while the ROM of the right knee had no significant difference(P>0.05).The change characteristics of the shoulder flexion and the outside corner ROM of the swing arm were the most significant(P<0.05),and the change of the elbow flexion ROM of the flat hit inside corner serve was the most significant(P<0.05).The ROM of elbow internal rotation had the least change(P<0.05),while the ROM of wrist joint had no significant change(P>0.05).The characteristics of knee flexion and extension Angle of the lateral swing arm were obvious(P<0.05),while the variation of hip Angle was not obvious(P>0.05).The characteristics of shoulder extension and elbow flexion Angle were the most significant(P<0.05),while the characteristics of wrist flexion and wrist internal rotation Angle were the most significant(P<0.05).There was no significant change in the angular velocity of knee joint of lower limbs at swinging arm side(P>0.05),and the maximum angular velocity of hip rotation at the outside Angle of the flat serve(P<0.05).The Angle velocity of shoulder adduction and elbow adduction of upper limb was the largest(P<0.05),while the Angle velocity of wrist flexion was the largest(P<0.05).At the time of hitting the ball,the speed of hitting the ball was the highest,while the speed of hitting the ball was the highest,but there was no significant difference(P>0.05).(2)Dynamic index: There was no significant difference in the average and peak value of vertical ground reaction force between flat serve and kick serve(P>0.05),and the lower limb stiffness of strike in the flat inner serve was the highest(P<0.05).(3)Surface electromyography index: There was no significant difference in RMS between flat serve and kick serve(P>0.05).There were common characteristics in muscle force timing and muscle activation contribution rate.The muscles with the highest contribution rate of muscle activation in flat serve were superior bundle of right trapezius,left rectus abdominis and lateral left gastrocnemius.The muscles with the highest contribution rate of muscle activation in kick serve were superior bundle of right trapezius,left rectus abdominis and right wrist extensor.Conclusion:(1)The flat serve adopts the increase of the rotation angle of the elbow during the lead time,and the increase of the left knee flexion ROM and the ROM of the shoulder and elbow joint during the ‘back scratching’ period to improve the movement performance of the whip effect.The stroke strategy is to increase the shoulder abduction and wrist flexion angle,and the hip abduction and the angular velocity of the shoulder and elbow.The characteristics of kick serve whiplash action are that the shoulder rotation,elbow adduction and wrist abduction increase during the shooting period,and the left knee abduction ROM and shoulder rotation ROM increase during the ‘back scratching’ period.The shot strategy is used to improve the knee flexion and adduction angle,wrist flexion and internal rotation angular velocity.(2)Tennis players’ left leg is the main driving leg for lower limb stretching and jumping,and right leg provides more stretching range for lower limbs.Therefore,it is suggested to increase the plyometric training and muscle strength balance based on SSC characteristics of lower limbs to prevent muscle asymmetry injury.(3)The s EMG index of flat serve and kick serve suggests that the lateral left gastrocnemius is the first muscle to activate and contribute to serve,suggesting that the increase in the recruitment ability of the right wrist extensor muscle may also be one of the factors that distinguish flat serve and kick serve.It is suggested that tennis players and enthusiasts should strengthen the explosive training of lower limb muscles,strengthen the functional training of upper limb muscles,and avoid excessive shoulder rotation of whiplash.