Effect Of Coupling Time On Biomechanical Characteristics Of Stretch-Shortening Cycle

Objective: Plyometric training is one of the frequently used methods to develop explosive muscle power of the lower leg and stretch-shortening cycle is an important feature of this method.The coupling phase between enccentric and concentric is critical to the effectiveness of plyometric training.Based on this research background,took counter-movement jump as test action,aming to investigate the effects of different coupling times on the biomechanical characteristics of stretch-shortening cycle actions,and the relationship between the coupling time and related kinematic and kinetics was analyzed on the basis.Method: 35 ordinary college students were recruited and their coupling time was tested,subjects were then divided into short coupling time group(9),moderate coupling time(17),long coupling time(9)according to the percentile method.8cameras infrared motion analysis system(Motion Analysis Rantor-4,USA,250Hz)and three-dimentional force plates(Kister 9281 CA,Switzerland,1200Hz)were synchronized to collect kinematic and kinetic data of their counter-movement jump.Kinematic data: contact time,eccentric time,concentric time,flight time,Hip Knee Ankle angle and mean angular velocity;Kinetic data: peak force,the force at end of prestretch,peak power,jump height,Eccentric Rate Force of Development(ERFD),concentric impulse,Reactive Strength Index(RSI).Using ONE WAY variance to analyse the effect of coupling time and Using pearson product-moment correlations to anlyse relationships between coupling time and above statistics.Results: The result of ONE WAY anova showed that:(1)There were significant differences in the force at the end of prestretch and eccentric rate of development between the short-coupling time group,the modermate-coupling time group and the long coupling time(p<0.05),among which the short-coupling time group was the largest,the moderate-coupling time group was the second,and the long-coupling time group was the smallest.(2)The peak force,jump height,flight time,reaction strength index and peak power of the short-coupling time group were all higher than those of the moderate-coupling time group and the long-time group(p < 0.05),and there was no difference between the moderate-coupling time group and the long-coupling time group;(3)The mean angular velocity of the knee and ankle joints in the short-coupling time group and the moderate-coupling time group were all faster than those in the long-coupling time group(p < 0.05),The hip joint angular velocity of the short-coupling time group was faster than that of the long-coupling time group(p <0.05),and there was no significant difference between the other groups.(4)Eccentric time,concentric time of short-coupling time group and the moderate-coupling time group were all faster than those in the long-coupling time group(p < 0.05),the contact time of the moderate-coupling time group was shorter than that of the long-coupling time group(p < 0.05),and there was no significant difference among other groups.(5)there was no significant difference in hip,knee and ankle joint angles and concentric impulse among the three groups.Pearson correlation analysis results show that the coupling time has a correlation with the contact time,ecentric time,concentric time,hip knee and ankle angular velocity,Reactive Strength Index,peak force,peak power,the force at end of prestretch and Eccentric Rate Force of Development,but has no correlation with hip knee and ankle Angle,flight time,jump height and concentric impulse.Conclusion: 1.The coupling time will have a significant impact on the kinematic characteristics of counter-movement jump,the longer coupling time will lead to longer contact time,eccentric time,concentric time,while shorter flight time,lower limb movement speed,but the coupling time has no effect on lower limb movement amplitude.2.The coupling time will have a significant impact on the kinematic characteristics of counter-movement jump,the shorter coupling time will lead to greater vertical ground reaction force,force at the end of prestretch,jump height,Reactive Strength Index,Eccentric Rate Force of Development and peak power,but the coupling time has no effect on concentric impluse.3.In the stretch-shortening cycle,the short coupling time is beneficial to improve the explosive force and performance.Specifically,the countermovement jump with short coupling time has a higher peak power and a higher jump height.