Background

Persons with lower limb amputation often experience decreased physical capacity, difficulty walking, and increased fall risk. To either prevent or recover from a loss of balance, one must effectively regulate their stepping movements. It is therefore critical to identify how well persons with amputation regulate stepping. Here, we used a multi-objective control framework based on Goal Equivalent Manifolds to identify how persons with transtibial amputation (TTA) regulate lateral stepping while walking without and with lateral perturbations.

Research question

When walking in destabilizing environments, do otherwise healthy persons with TTA exhibit greater difficulty regulating lateral stepping due to impaired control? Or do they instead continue to use similar strategies to regulate lateral stepping despite their amputation?

Methods

Eight persons with unilateral TTA and thirteen able-bodied (AB) controls walked in a virtual environment under three conditions: no perturbations, laterally oscillating visual field, and laterally oscillating treadmill platform. We analyzed step-to-step time series of step widths and absolute lateral body positions. We computed means, standard deviations and Detrended Fluctuation Analysis scaling exponents for each time series and computed how much participants directly corrected step width and position deviations at each step. We compared our results to computational predictions to identify the underlying causes of our experimental findings.

Results

All participants exhibited significantly increased variability, decreased scaling exponents, and tighter direct control when perturbed. Simulations from our stepping regulation models revealed that people responded to the increased variability produced by the imposed perturbations by tightening their control of both step width and lateral position. Participants with TTA exhibited only a few minor differences from AB in lateral stepping regulation, even when subjected to substantially destabilizing lateral perturbations.

Significance

Since control of stepping is intrinsically multi-objective, developing effective interventions to reduce fall risk in persons with amputation will likely require strategies that adopt multi-objective approaches.

中文翻译：

---

胫骨截肢患者在横向不稳定环境中行走时如何调节横向踏步

背景

下肢截肢者通常会出现体力下降、行走困难和跌倒风险增加的情况。为了防止或从失去平衡中恢复，必须有效地调节他们的踏步动作。因此，确定截肢者如何调节踏步是至关重要的。在这里，我们使用基于目标等效流形的多目标控制框架来确定经胫骨截肢 (TTA) 的人如何在没有和有横向扰动的情况下行走时调节横向踏步。

研究问题

在不稳定的环境中行走时，其他健康的 TTA 患者是否会由于控制能力受损而表现出更大的侧向踏步困难？或者，尽管他们截肢了，他们是否继续使用类似的策略来调节横向踏步？

方法

8 名单侧 TTA 人和 13 名健全 (AB) 控制者在三种条件下在虚拟环境中行走：无扰动、横向摆动视野和横向摆动跑步机平台。我们分析了步长和绝对横向身体位置的逐步时间序列。我们计算了每个时间序列的均值、标准差和去趋势波动分析缩放指数，并计算了每一步有多少参与者直接纠正了步宽和位置偏差。我们将我们的结果与计算预测进行了比较，以确定我们实验结果的根本原因。

结果

所有参与者都表现出显着增加的可变性、降低的缩放指数以及在受到干扰时更严格的直接控制。我们的步进调节模型的模拟表明，人们通过加强对步宽和横向位置的控制来应对强加扰动产生的增加的可变性。TTA 参与者在横向步进调节方面与 AB 仅表现出一些微小的差异，即使在受到严重不稳定的横向扰动时也是如此。

意义

由于控制踏步本质上是多目标的，因此开发有效的干预措施以降低截肢者的跌倒风险可能需要采用多目标方法的策略。