The Influence Of The Direction Of External Interference On The Postural Stability Of The Elderly

Purpose: With the increasing aging population,the health of the elderly has become a research hotspot in health science.In daily life,falls caused by various perturbations pose a great threat to the elderly health.In addtion,the elderly adopt different postural control mechanisms in different ways of interference.This study investigated the changes of center of pressure(COP)and center of mass(COM)and the relationship between anticipatory postural adjustment(APAs)and compensatory postural adjustment(CPAs)of the elderly during step initiation under external perturbation conditions(Backward perturbation stepping condition,BS.Forward perturbation stepping condition,FS).To explore the influence of the direction of external perturbation on the elderly's postural stability during step initiation could provide a theoretical basis for the prevention of falls and the evaluation of balance of the elderly under support surface perturbation.Methods: Eghit healthy older subjects(73.1 ± 5.6yr,165.1 ± 7.7cm,63.2 ± 8kg)participated in this study.A "human mobile device" was used to move the force platform under the subject's feet forward or backward by 5 cm(peak speed: 5cm / s,peak acceleration: 0.05g).Informing the subject of the perturbations direction in advance,subjects were asked to use their dominant legs to take a step forward.The experimental instruments were a Kistler force plateform,Inline 3D accelerometer,DTS footswitch sensors and "human moving device".The following parameters were analyzed: COP and COM displacements,velocities and accelerations in the anterior-posterior(AP)or medial-lateral(ML)directions during the steps in different perturbation directions,as well as the step duration and percentage.Results: 1)Temporary parameters: the step duration and percentage of the pre-unloading phase were relatively small;under the FS condition,the percentage of the post-unloading phase was relatively large;and the duration and percentage of the APAs period were relatively large.2)COP displacement: except for the swing period in the AP direction,there were significant differences between the maximum and average values of the COP displacement.Under the FS condition,the range of displacements in the APAs phase,the post-unloading phase,and the unloading phase were large.The difference in the maximum value in the ML direction was significant;BS made the range and average of the imbalance period larger;FS made the range and average of the swing period and the entire stride period larger;FS made the average of the APAs period,pre-unloading period and unloading period smaller.3)COP velocity:except for the imbalance phase in the APAs period in the AP direction,there were significant differences in the maximum and average values;FS made the range of APAs and imbalance periods larger;under the FS condition,the range of pre-unloading was smaller.In the ML direction,the difference between the maximum value and range of the pre-unloading period,the maximum value of the unloading phase,the range of the post-unloading period,and the average value of the imbalance phase were all significant.4)COM acceleration: in the AP direction,the maximum and average values of the imbalance period were smaller under the condition of BS;BS made the range of pre-unloading larger;FS made the average of the APAs period and the entire stride period larger.In the ML direction,except for the imbalance phase and swing period,the differences between the maximum value and the range were significant;BS made the average of the pre-unloading period and the entire stride period larger.5)COM velocity: In the AP direction,FS made the range of APAs period,imbalance period and the entire stride period larger.In the ML direction,the range of APAs period and pre-unloading period was larger under the BS condition.6)Relevance: Overall,APAs and CPAs were positively correlated.Conclusions: 1)BS perturbation hindererd the execution of step initiation,and the elderly adopt a rapid step strategy to maintain balance;under the FS and BS conditions,the APAs of the elderly did not significantly weakened.2)The elderly need to increase the step width to maintain postural stability under the BS condition;FS perturbation made CPAs strengthen to deal with the lack of APAs in the AP direction.However,the lateral postural stability was poor,indicating that the APAs itself caused another kind of perturbation to the elderly under the FS condition.3)The elderly entered a normal gait during the swing period;the BS perturbation made the AP direction occupied more APAs resources,resulting in a lower level of APAs in the ML direction.4)COM and COP moved in the opposite direction first,then moved in the same direction;the postural adjustment mechanism of the elderly had the specificity of the perturbation direction.5)Postural control systems were complex and irregular.6)Under the FS and BS conditions,if the degree of APAs activation of the elderly in the AP and ML directions increases,the corresponding level of CPAs would also increase.