A successful backward step correlates with hip flexion moment of supporting limb in elderly people

PurposeThe objective of this study was to determine the positional relationship between the center of mass (COM) and the center of pressure (COP) at the time of step landing, and to examine their relationship with the joint moments exerted by the supporting limb, with regard to factors of the successful backward step response.MethodsThe study population comprised 8 community-dwelling elderly people that were observed to take successive multi steps after the landing of a backward stepping. Using a motion capture system and force plate, we measured the COM, COP and COM-COP deviation distance on landing during backward stepping. In addition, we measured the moment of the supporting limb joint during backward stepping. The multi-step data were compared with data from instances when only one step was taken (single-step). Variables that differed significantly between the single- and multi-step data were used as objective variables and the joint moments of the supporting limb were used as explanatory variables in single regression analyses.ResultsThe COM-COP deviation in the anteroposterior was significantly larger in the single-step. A regression analysis with COM-COP deviation as the objective variable obtained a significant regression equation in the hip flexion moment (R2 = 0.74).ConclusionsThe hip flexion moment of supporting limb was shown to be a significant explanatory variable in both the PS and SS phases for the relationship with COM-COP distance. This study found that to create an appropriate backward step response after an external disturbance (i.e. the ability to stop after 1 step), posterior braking of the COM by a hip flexion moment are important during the single-limbed standing phase.## 研究目的 本研究旨在明确迈步落地时刻重心（center of mass, COM）与压力中心（center of pressure, COP）的位置关系，并结合成功向后迈步反应的相关影响因素，探讨二者与支撑肢体所产生的关节力矩之间的关联。 ## 研究方法 本研究的受试对象为8名社区居住的老年人，观察其在完成向后迈步落地后连续完成多步迈步的情况。研究采用运动捕捉系统与测力平台，测量向后迈步落地过程中的COM、COP以及COM与COP的偏差距离；同时采集向后迈步时支撑肢体的关节力矩数据。将多步迈步数据与仅完成单次迈步（单步）的数据进行对比，将单步与多步数据间存在显著差异的变量作为因变量，以支撑肢体关节力矩作为解释变量开展一元回归分析。 ## 研究结果 单步迈步时前后方向的COM-COP偏差显著更大。以COM-COP偏差为因变量的回归分析显示，髋屈曲力矩对应的回归方程具有统计学显著性（决定系数R²=0.74）。 ## 研究结论 本研究证实，支撑肢体的髋屈曲力矩在与COM-COP距离相关的PS与SS阶段中均为显著的解释变量。本研究发现，在外来干扰后产生恰当的向后迈步反应（即完成1步后即可停止的能力）时，于单腿站立阶段通过髋屈曲力矩对重心进行向后制动，是至关重要的。