Kinematic Characteristics Of The Head And Trunk During Stepping Under Simple Reaction Time Condition

Purpose: Gait initiation requires body to generate forward propulsion to break the body’s relative stability,while gait termination requires the body to generate sufficient braking force to maintain balance and restore a stable upright posture,both of which require the integration of central nervous system(CNS).Simple reaction time stepping(RTS)increases cognitive interference at a faster gait speed(single task),and both cognitive interference and increased gait speed are detrimental to postural control.Therefore,this study focused on the analysis of acceleration and velocity data from head,neck and center of mass(COM);comparing the changes in temporal and spatial parameters during gait initiation and termination in healthy adults in different phases and directions under different conditions;and investigating the relationship between gait initiation and termination in RTS condition.The relationship between gait initiation and termination was investigated to understand the kinematic characteristics of the head and trunk in dual-task stepping,and to further understand the postural control mechanisms of healthy adults during gait.Methods: This study was conducted with a dual-task and two single-task stepping at different speeds.12 healthy adults with the dominant right leg participated in the study.Kistler 3D forceplates and Noraxon 16-conductor telemetry surface EMG system were used to collect raw data.The subjects were asked to perform: normal stepping without interference(NS),quick stepping without interference(QS)and a simple reaction time stepping(RTS)task.Acceleration and velocity parameters were analyzed from the head,neck and COM,as well as parameters related to the center of pressure(COP).Results:(1)The duration of the unloading phase was significantly smaller in both the RTS and QS conditions than in the NS condition;the duration of the swing phase was significantly larger in both the RTS and NS conditions than in the QS condition;the duration of the unbalanced and stride phases was significantly smaller in the RTS condition than in the QS condition.The duration of the stabilization and stopping posture adjustments(SPAs)were greater in the RTS condition than in the QS and NS conditions.(2)In the anterior-posterior(AP)direction,the COM acceleration parameters showed RTS > QS and RTS > NS in both the swing and stride phases,and the neck acceleration variation range showed RTS > NS in both the swing and stride phases.(4)In the medio-lateral(ML)direction,the velocity maxima of the head,neck and COM showed RTS > NS at multiple stages of gait termination;the acceleration parameters of the head,neck and COM in the RTS condition were significantly different at multiple stages of gait termination.(5)In the ML direction,COM and head in the RTS and QS conditions showed weak positive correlations between anticipatory postural adjustments(APAs)and the swing phase.The peak velocity of the head in the AP direction in the RTS condition and QS condition had a weak positive correlation in SPAs.Conclusions:(1)In the RTS condition,healthy adults maintained their body stability during gait by prolonging the CPAs duration during gait initiation,while restored body to a quiet stance by increasing the SPAs duration during gait termination.(2)During gait initiation,healthy adults in the RTS condition showed "false APAs" in the COM and neck movements in the AP and ML directions,as compared to the QS and NS conditions.The head was affected and showed a deficit in the expected postural regulation,with compensatory postural adjustments maintaining the spatial position of the head and postural stability.In particular,compensatory postural adjustments were more pronounced in the AP direction.(3)During gait termination,to reduce the body’s greater propulsive force in the AP direction,healthy adults in the RTS condition regulated body posture by increasing motor performance in the ML direction and generating greater braking force in the AP direction.Braking was completed in the COM and neck during the BR phase,but the head propulsive force was still not sufficiently reduced during the transition phase until the stabilization phase.(4)Dualtask RTS posed a significant challenge to postural control in healthy adults during gait initiation and termination.The head,neck and COM generated greater forward forces in the AP direction during the cognitive-gait task,making postural control during the gait termination phase extremely important for maintaining postural stability.Both cognitive interference and increased gait speed could affect balance in healthy adults.