Characteristics Of Body Dynamic Stability During Stepping Under Simple Reaction Time Condition

Research objectives: Gait initiation and termination requires good postural control and motor coordination ability.As a kind of time pressure,dynamic stability of the body changes in the stepping movement under the simple reaction condition.Basic data of normal stepping(NS)task,quick stepping(QS)task and simple reaction time stepping(RTS)task of healthy adults were studied.It would be helpful to deeply understand the changes of body dynamic stability and the mechanism of postural regulation in the gait of healthy adults,and provide reference data for the follow-up study of special populations.It provides reference for formulating rehabilitation training program and guaranteeing walking safety.Methods: Sixteen healthy adults(24.29±0.59 yr,170.79±7.83 cm,66.94±11.47kg)performed the normal stepping task,quick stepping task and the simple reaction time stepping task,respectively.The subjects were asked to stand quietly on the left and right forceplates and keep their body stable.Within 5 seconds after the tester gave the command,the subject took a step forward to the right forceplate with the dominant leg(right leg)at the normal/as fast as possible/as fast as possible in response to simple reaction.The non-dominant leg(left leg)then took a step forward to the left forceplate.A Kistler three-dimensional force platform and Noraxon16 guided telemetry surface EMG system were used to collect data.Gait duration and duration proportion indexes,center of pressure(COP)displacement and velocity indexes,force and torque indexes,TA/SOL activation time,maximum amplitude and occurrence time,root mean square amplitude,integrated EMG and contraction index were analyzed.Research results: 1)Temporal parameters: Under the three conditions,the duration of anticipatory postural adjustments 1(APA1),APA2 a,APA2b,locomotor phase(LOC),stopping postural adjustment 1(SPA1)and SPA2 a stages were significantly different(p < 0.05,p < 0.01),and the percentage of duration of APA1 stage was significantly different(p < 0.01).2)COP displacement parameters: In the anterior-posterior(AP)direction,the displacement range of COP at APA1,APA2 a,LOC,and SPA3 stages,the average velocity of COP at APA1,LOC,SPA1,SPA2 b and SPA3 stages,and the maximum velocity of COP at APA1,LOC and SPA1 stages were significantly different(p < 0.05,p < 0.01).In the medio-lateral(ML)direction,COP displacement range of APA1,LOC,SPA2 a and SPA2 b stages,average COP velocity of APA1,APA2 a,APA2b,LOC,SPA1 and SPA2 a stages,APA1,APA2 a,APA2b,LOC,SPA1 and SPA2 a were significantly different(p < 0.05,p < 0.01).In the AP direction,APAs and compensatory postural adjustments(CPAs)showed moderate positive correlation(r=0.561,p=0.00)and SPA1-2 showed moderate positive correlation(r=0.488,p=0.00)in COP displacement range under QS condition.In the ML direction,SPA1-2 was positively correlated with SPA3 in the COP displacement range under the NS condition(r=0.697,p=0.00),and SPA1-2 was positively correlated with SPA3 under the QS condition(r=0.614,p=0.00).3)Force and torque parameters: in the AP direction,the normalization of APA1,APA2 a,APA2b,LOC,SPA2 a,SPA2b and SPA3 stages were the most vigorous,and the maximum torque of SPA2 b stage had a significant difference(p < 0.05,p < 0.01).In the ML direction,the standardization force of APA2 b stage was the highest,and the maximum torque of APA2 b stage and LOC stage was significantly different(p < 0.05).In the vertical direction,the standardization of APA1,APA2 b,SPA1 and SPA2 a stages were the most vigorous,and the maximum torque of APA2 b,LOC,SPA1,SPA2 a and SPA2 b stages had a significant difference(p < 0.05,p < 0.01).4)EMG parameters:there were significant differences in the activation time of TA and SOL under the three conditions(p < 0.05,p < 0.01).There were significant differences in the occurrence time of TA’s maximum amplitude,integrated EMG’s maximum amplitude,SOL’s maximum amplitude,root mean square amplitude,and SOL and TA’s maximum amplitude in the stepping stop stage(p < 0.05,p < 0.01).There was significant difference between APA1 and LOC in the three conditions(p < 0.01).Conclusions: 1)There was no significant change in the proportion of each stage of the stepping movement under the RTS condition.Healthy adults can achieve a rapid response to the simple response by shortening the duration of each stage of step initiation and termination in a coordinated manner.2)When healthy adults performed the stepping task under RTS condition,the central nervous system can adapt to the characteristics of postural regulation,which can not only accelerate the stepping movement,but also maintain a certain dynamic stability.3)Postural regulation was axial dependent.Postural regulation in the stepping movement had relatively independent neural control in three directions and played an independent role.Postural adjustment mechanism can adapt to the requirements and characteristics of autonomous movement,and play an independent and complementary role in the three directions.4)In the RTS condition,the stepping action tended to be parallel model,that is,anticipatory postural regulation and autonomous movement were two independent movement instructions that can be executed independently.