Department of Mechanical Engineering and Robotics Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America.
PLoS One. 2013 Aug 28;8(8):e73597. doi: 10.1371/journal.pone.0073597. eCollection 2013.
Human walking exhibits small variations in both step length and step width, some of which may be related to active balance control. Lateral balance is thought to require integrative sensorimotor control through adjustment of step width rather than length, contributing to greater variability in step width. Here we propose that step length variations are largely explained by the typical human preference for step length to increase with walking speed, which itself normally exhibits some slow and spontaneous fluctuation. In contrast, step width variations should have little relation to speed if they are produced more for lateral balance. As a test, we examined hundreds of overground walking steps by healthy young adults (N = 14, age < 40 yrs.). We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01). The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations. Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect. That difference was further magnified by walking with eyes closed, which appears detrimental to control of lateral balance. Humans appear to modulate fore-aft foot placement in precise accordance with slow fluctuations in walking speed, whereas the variability of lateral foot placement appears more closely related to balance. Step variability is separable in both direction and time scale into balance- and speed-related components. The separation of factors not related to balance may reveal which aspects of walking are most critical for the nervous system to control.
人类行走时步长和步宽都会有小的变化，其中一些可能与主动平衡控制有关。人们认为，横向平衡需要通过调整步宽而不是步长来进行综合的感觉运动控制，这导致了步宽的更大变化。在这里，我们提出步长的变化在很大程度上可以解释为人类通常倾向于随着步行速度的增加而增加步长，而步行速度本身通常会有一些缓慢的自发波动。相比之下，如果步宽的变化更多是为了横向平衡，那么它们与速度的关系应该不大。作为一个测试，我们检查了数百名健康年轻成年人（N=14，年龄<40 岁）在地面上行走的步伐。我们发现，自我选择的步行速度的缓慢波动（2.3%的变异系数）可以解释步长变化的大部分（59%，P<0.01）。速度无法解释的剩余可变性很小（1.5%的变异系数），这表明如果没有缓慢的速度波动，步长实际上是相当精确的。步宽的变化发生在更快的时间尺度上，与速度波动无关，在考虑速度影响后，其方差是步长方差的 4.3 倍（P<0.01）。这种差异在闭眼行走时进一步放大，这似乎对横向平衡的控制不利。人类似乎以精确的方式根据步行速度的缓慢波动来调节前后脚的位置，而横向脚位置的变化似乎与平衡更密切相关。步长的可变性可以在方向和时间尺度上分为与平衡和速度相关的两个组成部分。将与平衡无关的因素分开，可能会揭示出哪些方面的行走对神经系统的控制最为关键。
