| Purpose:The open stance is more suitable for the development of the today's tennis technical and the tactical play because of its quick-moving,returning rapidly,easily playing a more stable topspin and other advantages.By studying the kinematic characteristics of double-handed backhand with an open stance at baseline and the features of surface myoelectric activities in terms of the major muscles(upper and f lower limbs).The experiment effectively gets the corresponding kinematic dates of lower limbs and each joint and the results of surface muscles discharge activity.It helps to analyze to find out the influences(upper and f lower limbs)of double-handed backhand return with high quality for baseline open stance,which mainly includes the changes in the centre of gravity of the backswing,the rotation of the shoulder and hip angle for racket,the range of the stability angle before and after hitting,the condition of supporting leg,stretching in buffer and the pedal of the leg and the factors about balance of body.Accordingly,with the usual teaching and training,the coaches will provide more training skills targeted to open stance backhand for college athletes who major in professional sports and tennis.Meanwhile,the coaches could help them to reduce the forced mistakes in case of opponent's backhand hit at baseline in match,and improve the quality and the stability of the return at that station,which lead to the situation from passive attitude to positive emotion.Methods:in this paper,10 male students of Xi'an Physical Education University who majored in tennis(age from 20 to 25,second-level athletes)are the studying subjects.In this experiment,high-speed imaging(120Hz)and EMG test synchronization(1000Hz)are applied simultaneously to simulate the practice of double-handed backhand with an open stance at baseline in game in the case of forced ball,and to select the best results of three teams.With using EMG analysis software(Mage Win6000)on the EMG amplitude,frequency and other changes in qualitative or quantitative analysis included four muscles of left and right legs,and with anglicizing the various stages of RMS and muscle activation sequence of two muscle of the trunk and the United States APAS three-dimensional image analysis system to process a total of 19 points on the human body,the relevant speed,angle,angular velocity,time,and other results can be obtained by using statistical methods.Results:(1)The order of swing force when one takes baseline open stance double-handed backhand are as follows:the ankle joint,knee joint,hip joint,and then from the trunk to the shoulder joint,elbow joint,wrist,hand and the racket.(2)There is a significantly positive correlation between the variation degree value of hip-shoulder angle and hand speed by correlation analysis.(P<0.01).(3)The mean value of the forward stability angle at the time of hitting the ball is 12.02°(±3.76)and the backward stability angle is 13.46°(±6.04).Obviously,the forward stability angle is less than the backward stability angle.The angle of equilibrium is 25.49°(±7.14),the maximum value is 39.23°and the minimum is 15.04°.(4)When swings,the ratios of the electrical discharge from the related muscle to the muscles in the 1RM group were the left gastrocnemius(1.17)-the right lateral ventral oblique(0.99)-the left radial muscle(0.73)-the left biceps(0.72)-the left deltoid muscle(0.68)-the left tibialis anterior muscle(0.56)-the left rectus femoris muscle(0.54).(5)The sequences of electrical discharge between in each muscle at the swinging stage are the inside of the left deltoid muscle(0.005)-the left brachioradialis(0.013)-the left rectus femoris muscle(0.212)-the left biceps(0.025)-the left gastrocnemius(0.039)-the left tibialis anterior muscle(0.043)-the right lateral ventral oblique(0.049).Conclusions:(1)The forcing order of double-handed backhand with an open stance at baseline conforms to the order principle of the physical strength.(2)There is a significant positive correlation between the variation degree value of shoulder hip angle and hand speed at the swinging stage.(3)When hits the ball,the forward stabilization angle is less than the backward stabilization angle and the body center of gravity follows the direction of the ball.At this time the body balance angle has a characteristic value between 150 and 39°.(4)The muscles of the lower limbs are the main working muscles in double-handed backhand with an open stance.The left gastrocnemius muscle is the largest force in all stages.In addition,the force degree of left deltoid,left radial and right lateral ventral oblique muscle in the swing shot stage are more obvious than other stages of force. |
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