Dingwell Jonathan B, Cusumano Joseph P
Department of Kinesiology & Health Education, University of Texas, Austin, Texas, United States of America.
Department of Engineering Science & Mechanics, Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2015 Apr 24;10(4):e0124879. doi: 10.1371/journal.pone.0124879. eCollection 2015.
Variability is ubiquitous in human movement, arising from internal and external noise, inherent biological redundancy, and from the neurophysiological control actions that help regulate movement fluctuations. Increased walking variability can lead to increased energetic cost and/or increased fall risk. Conversely, biological noise may be beneficial, even necessary, to enhance motor performance. Indeed, encouraging more variability actually facilitates greater improvements in some forms of locomotor rehabilitation. Thus, it is critical to identify the fundamental principles humans use to regulate stride-to-stride fluctuations in walking. This study sought to determine how humans regulate stride-to-stride fluctuations in stepping movements during treadmill walking. We developed computational models based on pre-defined goal functions to compare if subjects, from each stride to the next, tried to maintain the same speed as the treadmill, or instead stay in the same position on the treadmill. Both strategies predicted average behaviors empirically indistinguishable from each other and from that of humans. These strategies, however, predicted very different stride-to-stride fluctuation dynamics. Comparisons to experimental data showed that human stepping movements were generally well-predicted by the speed-control model, but not by the position-control model. Human subjects also exhibited no indications they corrected deviations in absolute position only intermittently: i.e., closer to the boundaries of the treadmill. Thus, humans clearly do not adopt a control strategy whose primary goal is to maintain some constant absolute position on the treadmill. Instead, humans appear to regulate their stepping movements in a way most consistent with a strategy whose primary goal is to try to maintain the same speed as the treadmill at each consecutive stride. These findings have important implications both for understanding how biological systems regulate walking in general and for being able to harness these mechanisms to develop more effective rehabilitation interventions to improve locomotor performance.
变异性在人类运动中无处不在，它源于内部和外部噪声、固有的生物冗余以及有助于调节运动波动的神经生理控制作用。步行变异性增加会导致能量消耗增加和/或跌倒风险增加。相反，生物噪声可能是有益的，甚至是必要的，以提高运动表现。事实上，鼓励更多的变异性实际上有助于某些形式的运动康复取得更大的改善。因此，确定人类用来调节步行中步幅间波动的基本原则至关重要。本研究旨在确定人类在跑步机行走过程中如何调节步幅间的波动。我们基于预定义的目标函数开发了计算模型，以比较受试者从每一步到下一步是试图保持与跑步机相同的速度，还是相反地停留在跑步机上的同一位置。这两种策略预测的平均行为在经验上彼此无法区分，也与人类的行为无法区分。然而，这些策略预测的步幅间波动动态却非常不同。与实验数据的比较表明，人类的步行动作通常能被速度控制模型很好地预测，但不能被位置控制模型预测。人类受试者也没有表现出他们仅在间歇性地纠正绝对位置偏差的迹象，即更接近跑步机边界时。因此，人类显然没有采用一种主要目标是在跑步机上保持某个恒定绝对位置的控制策略。相反，人类似乎以一种最符合一种策略的方式调节他们的步行动作，该策略的主要目标是在每连续一步中试图保持与跑步机相同的速度。这些发现对于理解生物系统一般如何调节步行以及对于能够利用这些机制开发更有效的康复干预措施以改善运动表现都具有重要意义。
