Study On The Characteristics Of Forehand Stroke Of Students With Different Practice Time

Research purposes: To collect the EMG information of muscle activity of tennis students and the kinematic information of human joints and rackets in the course of forehand stroke,and to explore the internal relationship between racket acceleration,swing trajectory,racket surface stability and joint movement and muscle activity.To understand the rules of tennis forehand technique,strengthen the scientific teaching of tennis technique and the pertinence of training guidance.Research methods:(1)Subjects: Sports College of Yan shan University 18 tennis students(male).(2)Experimental scheme: 18 tennis students were divided into 3 groups,including 6players of 1 year,6 players of 2 years and 6 players of 3 years.Electrodes and Mark balls were pasted on the corresponding positions of subjects’ bodies.The ball will be sent to the forehand position of the subject’s bottom line using the server,and the subject is required to hit the ball as close to the opponent’s bottom line as possible.Each subject will complete 15 shots.Qualisys motion capture system was used to record the subjects’ complete forehand strokes.Subjects’ surface EMG data were recorded using Delsys surface EMG acquisition and analysis system.(3)Data collection: From Qualisys motion capture system,9 effective shots of each subject in 15 shots were selected for kinematic information collection,and the data of relevant joint angles,angular velocity,racket track,racket face Angle,racket speed and other key nodes in the action process were derived.The original surface EMG data in the Delsys surface EMG acquisition and analysis system were filtered,rectified and smoothed,and the muscle discharge timing sequence,discharge duration,root mean square value,integrated EMG value and contribution rate were calculated.(4)Excel2019 was used to sort out the relevant test data,and SPSS17.0 was used for statistical analysis of the test data.Univariate ANOVA was used to compare the differences between the movements of three groups of tennis students.P < 0.05 indicates significant difference,and P < 0.01 indicates very significant difference.Results:(1)The racquet speed at the time of hitting was significantly different among the three groups(P < 0.01),with 3 years of age(11.93m/s)> 2 years of age(10.35m/s)> 1year of age(7.79m/s).At the time of hitting,the velocity of hip,shoulder,elbow and wrist Angle increased successively at the age of 3 years,which was consistent with the "whipping" action.The angular velocity of each joint at the age of 1 year and 2 years was disordered.In the hitting stage,there were differences in the active muscles of the three groups of tennis students: 1 year old active muscle was the upper band of trapezius muscle,contributing rate of 16.64%;2 years old active muscle was the anterior band of deltoid muscle,contributing rate of 17.00%;3 years old active muscle was biceps brachii muscle,contributing rate of 20.52%.(2)The trajectory stability at the time of hitting was as follows: 2 years of age(16.67±2.6°)> 3 years of age(17.94±3.76°)> 1 year of age(20.22±4.47°).There was no significant difference in trajectory Angle(impact Angle)among the three groups(P >0.05).At the time of hitting,the fluctuation range of shoulder abduction Angle and hip joint Angle at 2 years of age is small,while the fluctuation range of shoulder abduction Angle and hip joint Angle at 1 year of age is large.(3)The stability of racquet face at the time of hitting was as following: 3 years(2.11±1.43°)> 2 years(3.16±2.04°)> 1 year(1.94±2.09°),and there was no significant difference in racquet face Angle among the three groups(P > 0.05);At the time of hitting,the fluctuation range of wrist internal rotation Angle of 3-year old ball is small,while that of 1-year old ball is large.Research Conclusions:(1)1 year of playing experience: insufficient rotation leading racket,excessive tension of latissimus dorsi muscle during hitting,stiff and uncoordinated action,premature closing of racket after hitting,resulting in too much rotation and relatively slow racket speed.(2)The fluctuation of hip and shoulder joint angles is small and the joint stability is good.The stable joint Angle is the main factor to keep the swing track stable.But its upper and lower limbs force is not smooth,joint angular velocity upper and lower limbs force disorder.(3)The main driving muscles between the links of the 3-year old ball are the biceps brachii and the upper band of the trapezius muscle.The joint angular velocity is controlled reasonably,and its hitting matches the law of whipping action,which helps to form a stable running track of the hit ball.