Chong Raymond K Y, Chastan Nathalie, Welter Marie-Laure, Do Manh-Cuong
Department of Physical Therapy, Medical College of Georgia, EC-1342 Augusta, GA, USA.
Neurosci Lett. 2009 Jul 10;458(1):23-7. doi: 10.1016/j.neulet.2009.04.022. Epub 2009 Apr 15.
During walking, the body center of mass oscillates along the vertical plane. Its displacement is highest at mid-swing and lowest at terminal swing during the transition to double support. Its vertical velocity (CoMv) has been observed to increase as the center of mass falls between mid- and late swing but is reduced just before double support. This suggests that braking of the center of mass is achieved with active neural control. We tested whether this active control deteriorates with aging (Experiment 1) and during a concurrent cognitive task (Experiment 2). At short steps of <0.4m, CoMv control was low and similar among all age groups. All groups braked the CoMv at longer steps of >0.4m but older subjects did so to a lesser extent. During the cognitive task, young subjects increased CoMv control (i.e. increase in CoMv braking) while maintaining step length and walking speed. Older subjects on the other hand, did not increase CoMv control but rather maintain it by reducing both step length and walking speed. These results suggest that active braking of the CoM during the transition to double support predominates in steps >0.4m. It could be a manifestation of the balance control system, since the braking occurs at late stance where body weight is being shifted to the contralateral side. The active braking mechanism also appears to require some attentional resource. In aging, reducing step length and speed are strategic to maintaining effective center of mass control during the transition to double support. However, the lesser degree of control in older adults indicates a true age-related deficit.
在行走过程中，身体重心在垂直平面内振荡。其位移在摆动中期最大，在向双支撑过渡的摆动末期最小。研究发现，随着重心在摆动中期和后期之间下降，其垂直速度（CoMv）会增加，但在双支撑之前会降低。这表明重心的制动是通过主动神经控制实现的。我们测试了这种主动控制是否会随着年龄增长而退化（实验1）以及在同时进行认知任务时是否会退化（实验2）。在步长小于0.4米的短步幅行走时，所有年龄组的CoMv控制水平都较低且相似。在步长大于0.4米的长步幅行走时，所有组都会对CoMv进行制动，但老年受试者的制动程度较小。在认知任务期间，年轻受试者在保持步长和步行速度的同时增加了CoMv控制（即CoMv制动增加）。另一方面，老年受试者没有增加CoMv控制，而是通过缩短步长和步行速度来维持控制。这些结果表明，在向双支撑过渡期间，CoM的主动制动在步长大于0.4米的行走中占主导地位。这可能是平衡控制系统的一种表现，因为制动发生在身体重量向对侧转移的站立后期。主动制动机制似乎也需要一些注意力资源。在衰老过程中，缩短步长和速度是在向双支撑过渡期间维持有效重心控制的策略。然而，老年人控制程度较低表明存在与年龄相关的真正缺陷。
