The Acute Effect Of Different Time Cross-legged Sitting Posture On Lower Extremity Electromyogram Characteristic And Jumping Ability During A Countermovement Jump

Objective: To study the relationship between the acute effects of cross-legged and the physiological mechanism in different time points by using the method of exercise biomechanics.In order to understand the acute effect of different time cross-legged sitting posture on lower extremity electromyogram characteristic and jumping ability during a countermovement jump.At the same time,the effects of different time on the injury of knee joint were analyzed.Through experimental research to make people more comprehensive understanding of cross-legged sitting behavior,in order to better guide people to take a reasonable time to cross-legged sitting.Methods: In this study,16 young college students were selected after repeated screening by healthy screening.The typical stretch-shortening cycle action-CMJ was performed by different time.The high speed camera,three dimensional forceplate,electromyography instrument were synchronous,we obtained kinematics,kinetics,EMG data.After treatment with Ariel,Excel,Origin and Matlab,the effect of cross-legged sitting on the CMJ dependent variables(kinematics,kinetics and EMG)was analyzed by single factor repeated measurement of variance.The main effect of each time point,if it is statistically significant.Then select a variable that needs to be observed for one-way ANOVA and Tukey post-hoc.Using independent sample T test on the subject of bilateral lower extremity EMG indicators whether the difference between the statistical significance of the test.In additio,each subject was required to complete the test,including three different time cross-leg sitting(5,10 and 15min)and four times CMJ.Lottery to determine each subject cross-legged sitting in time order,cross-legged sitting 30 s after the start of CMJ test,5min after the completion of the test by the order of the next time to take the ball in the order of each subject in each day to complete the test.Results: 1.The jumping ability: with the prolonged cross-legged sitting time,CMJ-Fi and jump height didn’t have statistically significant.2.Muscle’s EMG characteristics: pedal extension pre-activation phase in addition to BF,G are a downward trend;pedal extension activation stage,in addition to RF are rising trend,lower extremity muscle group were no statistical difference;pre-activation stage,The frequency of TA activation increased;in the buffer activation phase,RF electromyography difference was statistically significant,showing a downward trend,BF electromyography,although there is no statistical difference but also a downward trend;MF value in each stage of the number of repeated tests And there was no significant differences between each stage.With the prolonged cross-legged sitting time,VM and VL contribution rates were significantly higher and higher than RF and BF.3.The impact characteristics: 10 min and 15 min cross-legged sitting Kleg are increased;passive impulse were down;the time from landing to the peak force is about 80 ms,the peak force is about 3.5 times the body weight;The time of the maximum instantaneous loading rate is higher and the time is shorter than 50 ms.The stabilization time in the vertical direction is longer and longer,but there is no statistically significant difference in the stabilization time.Conclusion: 1.The longer the time to cross-legged sitting,the influence is more obvious to the the performance of the movement and knee extensor muscles.Long-term cross-legged sitting will reduce the jumping ability,such as jumping height.After a long time sitting cross-legged,it will have a negative impact on the rectus muscle activation,In the buffer phase after landing,knee joint co-contraction index decreased,knee joint injury risk were increased.2.The longer the time to cross-legged sitting,bilateral lower extremity VL,VM in the buffer period to bear the buffer action more.Landing strategy have changed,in the landing moment,the ankle angle is different from the landing strategy by increased the hip and knee angle.3.With the prolonged cross-legged sitting time,muscle elasticity caused by negative impact lead to lower extremity stiffness and lower extremity lack of impact capacity.Lower extremity neuromuscular control capacity decreased,the direction of the required stabilization time extended.The longer the cross-legged sitting time,the higher the maximum instantaneous load rate,the greater the instantaneous load rate occurs more time in advance.In addition,the time to stabilization in each direction are also increased...