The Effect Of Different Visual Conditions On The Ankle Muscle Adjustment When Young People Stand On One Foot

Background: During upright standing,the body center of mass is high and the supporting area is small.In addition,there are many segments between the feet and the center of mass,so the posture is unstable.When standing is disturbed internally or externally,mechanical coupling between body segments can cause postural disturbances on balance.Ankle strategy is often used to restore the interference degree is small or the support surface does not change,in which the ankle joint muscle activity plays an important role.Vision is one of the important sensory information to keep balance,but visual impairment is also easy to happen in life.Many studies have shown that the stability of human posture will be affected when the visual condition is interfered,but the influence of the neural control and sensory information integrated adjustment caused by the visual condition and the absence of visual condition on the posture regulation,especially the influence on the ankle muscle activity state,is not clear.Motion control of equilibrium hypothesis suggests that the nervous system by changing the motion parameter,cause muscle activity which drive the body from the original equilibrium position shifts to new balance position,eventually makes the body in the new referent position restores balance,different visual feedback may cause the nervous system to make different motion parameter setting and control muscle activity.Therefore,researching ankle muscle activity characteristics and posture adjusting parameter change rule of healthy people in single-leg stance under different visual conditions,helps reveal visual effects on ankle muscle.In addition,the analysis of the time-varying characteristics of the surface EMG activity of the tibial anterior(TA)/soleus(SOL)in different time intervals(T1:0-10 s,T2:10-20 s,T3:20-30s)is helpful to explore the possible mechanism of maintaining the balance of the upright body posture under different visual conditions.Objectives:1)To study the effects of different visual conditions on ankle joint muscle regulation of healthy people in single-leg stance.2)To investigate the time-varying characteristics of surface EMG activity of tibial anterior(TA)and soleus(SOL)at different time intervals.Methods: The subjects of this study were 8 healthy adults(4 males and 4 females).The dominant leg of the subjects was the right leg.Experimental conditions were 35 seconds standing on one foot and two feet with eyes opened(EO)and eyes closed(EC).Experimental requirements: when standing on one foot,the subjects crossed their hands in front of their chest,stood on the right foot(dominant foot),bent the knee joint of the left leg about 90 degrees closer to the right foot supporting the standing,kept the knee joint of the right leg straight,and maintained the body balance for 35 seconds.When standing on two feet,kept legs straight.Experimental instruments: Kistler 3D force plate,Tele Myo 2400 T G2 16 EMG system.Data parameters: COP displacement area,scope,anterior-posterior /medio-lateral displacement length,displacement range of the center of pressure(COP),contraction index(C index,R index),maximum amplitude,root mean square(RMS),integral EMG and other parameters of TA/SOL surface EMG.It was proposed that healthy adults can control the stability of the body in single-leg stance under different visual conditions through their postural adjustment.Results: 1)when standing on one foot/two feet,all COP parameters were larger in the EC condition than in the EO condition,showing relatively poor postural stability.2)when standing on one foot,the maximum amplitude of surface EMG,integral EMG,root-mean-square amplitude and common contraction index of the ankle muscles were greater in the EC condition than in the EO condition,but the reciprocal contraction index was greater in the EO condition than in the EC condition,showing a stronger reciprocal contraction relationship of the ankle muscles.3)when standing on one foot in the EC condition,the COP parameters increased significantly in T2,and in the EO condition,the COP parameters increased significantly in T3.4)when standing on one foot in the EC condition,the TA integral EMG and the common contraction index significantly increased from T2,however,in the EO condition,the integral EMG and the common contraction index of the ankle muscles did not significantly increase,the reciprocal contraction index significantly increased from T2.Conclusions: 1)when standing on one foot,different visual conditions caused different dominance characteristics of the central nervous system to the ankle muscles(TA/SOL Reciprocal contraction was the main one in the EO condition,and co-contraction was the main one in the EC condition),thus resulting in different postural stability.2)TA/SOL activity state and contraction mode under different visual conditions had different time-varying characteristics,which led to different sequence of postural instability.In the EC condition,the common contraction with a strengthening trend made postural instability appear earlier,while in the EO condition,the reciprocal contraction with a strengthening trend made stable postural stability last longer,which provided some theoretical basis for exploring the possible mechanism of controlling postural standing on one foot under different vision.