Background. Common understanding is that adequate foot placement (stepping strategy) is crucial in maintaining stability during walking at normal speed. The aim of this study was to investigate strategies that humans use to cope with lateral perturbations during very slow walking. Methods. Ten healthy individuals underwent an experimental protocol whereby a set of perturbations directed inward (medially to a stance leg) and outward (laterally to a stance leg) of three intensities (, , and of body weight), applied at three instances of a stance phase, were delivered in random order to the pelvis using a balance assessment robot while walking on a treadmill at three walking speeds (, , and ). We analyzed the peak center of mass displacements; step length, step width, and step times; and the lateral component of ground reaction force for perturbations that were delivered at the beginning of the gait cycle. Results. Responses after inward perturbations were similar at all tested speeds and consistently employed stepping strategy that was further facilitated by a shortened stance. Wider and shorter steps were applied with increased perturbation intensity. Responses following outward perturbations were more complex. At S₁, hip strategy (impulse-like increase of mediolateral ground reaction force) augmented with ankle strategy (mediolateral shift of the center of pressure) mainly contributed to responses already during the stance phase. The stance duration was significantly longer for all perturbation intensities. At S₂, the relative share of hip strategy was reduced while with increased perturbation intensity, stepping strategy was gradually added. The stance duration was significantly longer for F₁ and F₂. At S₃, stepping strategy was mainly used while the duration of stance was similar to the one in unperturbed walking. Responses following both inward and outward perturbations at all speeds were characterized by temporary slowing down movement in a sagittal plane that was more pronounced with increased perturbation intensity. Conclusions. This study provides novel insights into balancing strategies used at slower walking speeds which may be more relevant to understand the challenges of gait stability following perturbations in the frontal plane in clinical populations.

中文翻译：

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跑步机速度和扰动强度对正面平面扰动慢走时平衡策略选择的影响。

背景。普遍的理解是，适当的足部放置（踏步策略）对于以正常速度行走时保持稳定性至关重要。这项研究的目的是研究人类在非常缓慢的步行过程中用来应对横向扰动的策略。方法。10 名健康人接受了一项实验方案，其中一组扰动向内（在站立腿的内侧）和向外（在站立腿的外侧）定向，具有三种强度（, ,和体重），在站立阶段的三个实例中应用，使用平衡评估机器人以随机顺序传递到骨盆，同时以三种步行速度在跑步机上行走（, ,和）。我们分析了质心位移的峰值；步长、步宽和步数；以及在步态周期开始时传递的扰动的地面反作用力的横向分量。结果。向内扰动后的反应在所有测试速度下都是相似的，并且始终采用步进策略，缩短的站姿进一步促进了这种策略。随着扰动强度的增加，应用更宽和更短的步骤。外部扰动后的反应更为复杂。在S ₁, 髋部策略（中外侧地面反作用力的脉冲样增加）与踝部策略（压力中心的中外侧移动）增强主要有助于在站立阶段已经做出反应。对于所有扰动强度，站姿持续时间明显更长。在S ₂时，臀部策略的相对份额减少，而随着扰动强度的增加，逐步增加了步进策略。F ₁和F ₂的站姿持续时间明显更长。在S ₃, 主要采用步进策略，而站立时间与无干扰步行相似。在所有速度下，向内和向外扰动后的反应的特点是在矢状面上的运动暂时减慢，随着扰动强度的增加，这种运动更加明显。结论。这项研究为在较慢步行速度下使用的平衡策略提供了新的见解，这可能更有助于理解临床人群额面扰动后步态稳定性的挑战。