Data from: Walking with wider steps changes foot placement control, increases kinematic variability and does not improve linear stability

Walking humans respond to pulls or pushes on their upper body by changing where they place their foot on the next step. Usually, they place their foot further along the direction of the upper body perturbation. Here, we examine how this foot placement response is affected by the average step width during walking. We performed experiments with humans walking on a treadmill, both normally and at five different prescribed step widths. We prescribed step widths by requiring subjects to step on lines drawn on the treadmill belt. We inferred a linear model between the torso marker state at mid-stance and the next foot position. The coefficients in this linear model (which are analogous to feedback gains for foot placement) changed with increasing step width as follows. The sideways foot placement response to a given sideways torso deviation decreased. The fore–aft foot placement response to a given fore–aft torso deviation also decreased. Coupling between fore–aft foot placement and sideways torso deviations increased. These changes in foot placement feedback gains did not significantly affect walking stability as quantified by Floquet multipliers (which estimate how quickly the system corrects a small perturbation), despite increasing foot placement variance and upper body motion variance (kinematic variability).

行走过程中的人体可通过调整下一步落脚位置，对上身受到的牵拉或推挤作出响应。通常，其落脚位置会沿上身扰动的方向偏移更远。本研究旨在探究行走过程中的平均步宽对该落脚位置调整反应的影响。我们开展了人体行走实验：受试者在跑步机上分别以正常步宽与五种预设步宽进行行走，实验通过要求受试者踩踏跑步机跑带上绘制的标线来限定步宽。我们基于站立中期的躯干标记点状态与下一步落脚位置构建了线性模型，该模型中的系数（类比于落脚位置调整的反馈增益）随步宽增加呈现如下变化规律：针对给定侧向躯干偏移的侧向落脚调整反应减弱，针对给定前后向躯干偏移的前后向落脚调整反应同样减弱，且前后向落脚位置与侧向躯干偏移之间的耦合效应增强。尽管落脚位置变异度与上身运动变异度（即运动学变异性）均有所上升，但落脚位置反馈增益的上述变化并未对行走稳定性造成显著影响——行走稳定性通过弗洛凯乘子（Floquet multipliers）量化，该指标用于评估系统校正微小扰动的速率。