The Relationship Of Variability In Dynamic Balance Control And Eccentric Strength Of Ankle

Purpose:People have different response to the external disturbances.By exert external force on health young man and collect their response in terms of kinetics and kinematics,the research will investigate the characteristics of variability and time variant structural of postural control in people with different eccentric muscle strength ratio and try to make further understanding of postural control mechanism when people are expose to external disturbances.Methods:24 young male subjects who are health and without ankle sprains history are recruited in this study,dorsiflexion/plantarfiexion eccentric strength ratio and eversion/inversion eccentric strength ratio were calculated and subjects were separate into two groups according to dichotomy respectively.Trajectory of COM and COP and force were recorded for 15s after the load was released and 3 available tests were conducted for each direction.Oscillation SD,the 95%ellipse area of COP,the time to recover and the largest Lyapunov exponent(λ1)of the trajectory of COM,COP and COM-COP were calculated in MatLab.Two-way repeated measure ANOVA were used and p<0.05.Results:(1)In the back direction,interaction occurs in λ1 of trajectory of COMCOP between eccentric strength ratios while other indexes are independent.Dorsiflexion/plantarfiexion eccentric strength ratio has significant effect on λ1 of anterior-posterior and medio-lateral trajectory of COM-COP,oscillation SD of COP in medio-lateral while eversion/inversion eccentric strength ratio has significant effect onλ1 of anterior-posterior and medio-lateral trajectory of COM-COP and oscillation SD of COP in anterior-posterior;(2)In the front direction,interaction occurs in λ1 of medio-lateral trajectory of COP,oscillation SD of COP in anterior-posterior and vertical recovery time between eccentric strength ratios while other indexes are independent.Dorsiflexion/plantarfiexion eccentric strength ratio has significant effect on λ1 of anterior-posterior trajectory of COP and anterior-posterior recovery time while eversion/inversion eccentric strength ratio has significant effect on λ1 of mediolateral trajectory of COM-COP;(3)In the left direction,interaction occurs in λ1 of anterior-posterior trajectory of COM between eccentric strength ratios while other indexes are independent.Dorsiflexion/plantarfiexion eccentric strength ratio has significant effect on λ1 of medio-lateral trajectory of COP while eversion/inversion eccentric strength ratio has significant effect on λ1 of medio-lateral trajectory of COM and of anterior-posterior trajectory of COM-COP;(4)In the right direction,interaction occurs in λ1 of anterior-posterior trajectory of COM-COP,oscillation SD of COP in medio-lateral and the 95%ellipse area of COP between eccentric strength ratios while other indexes are independent.Dorsiflexion/plantarfiexion eccentric strength ratio has significant effect on λ1 of medio-lateral trajectory of COM-COP while eversion/inversion eccentric strength ratio has significant effect on λ1 of medio-lateral trajectory of COP and of anterior-posterior trajectory of COM-COP.Conclusion:eccentric strength ratios have interaction in postural control.the traditional linear index and non-linear index were different between groups,higher dorsiflexion/plantarfiexion eccentric strength ratio showed a larger 95%ellipse area of COP.However,had a smaller λ1.It indicated that in the health young man,the postural variability and time-variant structure were different based on their eccentric strength ratio.Moreover,the linear index was not sensitive enough to distinguish the difference of postural control.When compare the non-linear index,it showed that subjects with higher eccentric strength ratio show higher stability,which represent higher eccentric strength ratio were helpful for the postural control under the external disturbances.