A Comparative Biomechanical Study Of Straight-arm And Flexed-arm Striking In Men’s Tennis Forehand

Object:Through the biomechanical analysis of tennis amateur players’ forehand straight-arm and flexed-arm hitting movements,we compare and study the differences between the two hitting styles,find out the relationship between the two hitting styles and intrinsic muscle properties through kinematic indexes,so that players can choose a more suitable hitting style in the process of hitting,and provide data support to improve the quality of hitting and reduce or even avoid sports injuries.The significance is that by comparing and studying the differences between the two hitting styles,the weaknesses of the study can be supplemented and scientific guidance can be given to athletes or students,which is of positive significance to improve the quality of students’ hitting and prevent injuries.Methods:Eight amateur tennis players(male)between 25-55 years old in Liaocheng city were selected,and video images of the subjects’ forehand straight-arm and flexed-arm strokes and surface EMG signals were collected using a three-dimensional high-speed camera(500 Hz)synchronized with a surface EMG signal acquisition system(1500 Hz).The kinematic analysis was performed by using Si Mi Motion to calibrate 21 points,including head,shoulders,elbows,wrists,hands,hips,knees,heels,tips and racket,to obtain the ball speed,rotational speed,velocity,angle,angular velocity and angular acceleration of each joint(angle)of the human body,and to calculate the root mean square amplitude and other relevant parameters by combining with the surface EMG signal analysis system.After the kinematic images were acquired,the maximum joint torques were collected from eight subjects using an isokinetic muscle tester(slow 60°/s for 5 times and fast 180°/s for 10 times)for eight movements: elbow flexion and extension,wrist flexion and extension,shoulder flexion and extension,shoulder horizontal flexion and extension,shoulder abduction and adduction,shoulder rotation in natural position,forearm rotation and trunk rotation.The average values of the slow and fast movements were then combined with kinematic image data to analyze the similarities and differences between the two striking styles.Results:1)In terms of stroke effect,the straight arm had a faster stroke speed than the flexed arm(P<0.05),while it showed similar characteristics in terms of ball speed.2)The brachioradialis muscle had the highest root mean square standardized value during the whole action phase of both stroke types,while the biceps,triceps and wrist extensors had the smallest root mean square standardized value,and the wrist flexors had a higher root mean square standardized value in the straight arm stroke than in the flexor stroke during the swing stroke phase.3)During the swing phase,the muscle contribution of wrist flexors was higher in the straight-arm stroke than in the flexor stroke,with a significant difference,while the muscle contribution of biceps and triceps was higher in the flexor stroke than in the straight-arm stroke,with a highly significant difference.Combined with the root mean square standardized mean value of EMG and the muscle activity contribution value of the whole phase of stroke,it can be found that the muscle activity contribution of wrist extensor group and wrist flexor group is second only to brachioradialis,but the root mean square standardized mean value of EMG is small compared with brachioradialis and middle deltoid muscles,and the muscle strength is relatively small,which may produce sports fatigue and risk of injury.4)Combined with kinematic analysis and joint peak torque data,the peak torque of forearm internal rotation and shoulder joint natural position rapid internal rotation were linearly correlated with the stroke speed of the two striking methods,and the peak torque of shoulder joint horizontal position rapid flexion and trunk rapid left rotation were linearly correlated with the ball speed of the two striking methods of tennis stroke,respectively.However,the straight arm used the wrist joint more than the flexed arm to improve the ball quality,while the flexed arm used the elbow joint more to improve the ball quality.Conclusions:1)The straight-arm stroke has a higher quality of stroke,but the flexed-arm stroke has a more fluid motion.2)The straight-arm stroke used the wrist joint more during the stroke,while the flexed-arm stroke used the elbow joint more during the stroke.3)The wrist extensor group and wrist flexor group muscles do more work but have a relatively weak muscle recruitment capacity,which may produce sports fatigue and risk of injury.4)The peak torque of internal arm rotation and rapid internal rotation in the natural position of the shoulder joint were linearly correlated with the stroke speed of the two stroke modes,respectively,and the peak torque of rapid flexion in the horizontal position of the shoulder joint and rapid left rotation of the trunk were linearly correlated with the ball speed of the tennis ball of the two stroke modes,respectively.