External postural perturbations induce multiple anticipatory postural adjustments when subjects cannot pre-select their stepping foot
External postural perturbations induce multiple anticipatory postural adjustments when subjects cannot pre-select their stepping foot
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DOI：
10.1007/s00221-006-0763-5
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发表时间：
2007-05-01
影响因子：
2
通讯作者：
Horak, Fay B.
中科院分区：
文献类型：
--
作者：
Jacobs, Jesse V.;Horak, Fay B.
先前关于人体平衡恢复的研究表明，在外部触发的姿势扰动之前，健康受试者可以基于环境背景预先选择他们的姿势反应，但目前尚不清楚这种预先选择是否包括在执行补偿步骤时选择步进腿。我们试图确定如何预先选择一个步进肢体影响代偿步骤和稳定性的年轻，健康的受试者时，应对姿势扰动。9例健康受试者（24-37岁）在扰动之前，受试者要么知道他们是用左腿还是右腿向视觉目标迈步，（可预测条件）或不知道是否用左腿或右腿行走，直到两个目标之一出现在扰动开始时（不可预测的条件）。不可预测的条件还包括随机插入的脚趾向上旋转试验和无目标向后平移试验（接球试验）。结果表明，在可预测的条件下，受试者始终表现出一个预期的姿势调整（阿帕;一个横向重量转移到站立肢体），然后用正确的腿准确地踩到目标。在不可预测的条件下，受试者（1）表现出多个APA，晚步开始和向前的质心（CoM）位移，这些位移远远超出了他们的支撑基础，或者（2）表现出只有一个阿帕的早期步骤，并保持他们的CoM更接近支撑基础，但也更经常用不正确的腿走路。因此，当受试者必须在扰动开始时选择一条踏步腿时，他们要么变得更不稳定，并使用多个APA来延迟踏步，以便提供足够的时间来选择正确的踏步腿，要么他们更早地踏步以保持稳定，但经常用不正确的腿踏步。此外，在不可预测的条件下，捕捉试验的反应包括扭曲的步骤放置，类似于预期目标的步骤，尽管允许受试者用他们选择的腿和他们选择的位置。最后，受试者对视觉目标的无扰动的自愿步行时间是他们对向后平台平移的步行时间的两倍。因此，健康受试者似乎预先选择他们的踏步肢体，即使当扰动特性是不可预测的，因为依赖于在扰动开始时提供的视觉输入需要延迟的响应，导致更大的不稳定性。
Previous research on human balance recovery suggests that, prior to an externally triggered postural perturbation, healthy subjects can pre-select their postural response based on the environmental context, but it is unclear whether this pre-selection includes the selection of a stepping leg when performing compensatory steps. We sought to determine how pre-selecting a stepping limb affects the compensatory steps and stability of young, healthy subjects when responding to postural perturbations. Nine healthy subjects (24-37 years of age) stepped in response to backward translations of a platform under their feet when, prior to the perturbations, the subjects either knew whether they were to step with their left or right leg to a visual target (the Predictable condition) or did not know whether to step with their left or right leg until one of two targets appeared at perturbation onset (the Unpredictable condition). The Unpredictable condition also included randomly inserted trials of toes-up rotations and backward translations without targets (catch trials). The results showed that, in the Predictable condition, the subjects consistently exhibited one anticipatory postural adjustment (APA; a lateral weight shift toward the stance limb) before stepping accurately to the target with the correct leg. In the Unpredictable condition, the subjects either (1) exhibited multiple APAs, late step onsets, and forward center-of-mass (CoM) displacements that were farther beyond their base of support, or (2) exhibited an early step with only one APA and kept their CoM closer to the base of support, but also stepped more often with the incorrect leg. Thus, when the subjects had to select a stepping leg at perturbation onset, they either became more unstable and used multiple APAs to delay stepping in order to provide enough time to select the correct stepping leg, or they stepped earlier to remain stable but often stepped with the incorrect leg. In addition, responses to catch trials in the Unpredictable condition included distorted step placements that resembled steps to anticipated targets, despite allowing the subjects to step with a leg of their choice and to a location of their choice. Lastly, the subjects' voluntary stepping latencies to visual targets presented without perturbations were twice as long as their stepping latencies to the backward platform translations. Therefore, healthy subjects appear to pre-select their stepping limb, even when the perturbation characteristics are unpredictable, because relying on visual input provided at perturbation onset requires a delayed response that leads to greater instability.