Data from: Neural control of balance during walking

Neural control of standing balance has been extensively studied. However, most falls occur during walking rather than standing, and findings from standing balance research do not necessarily carry over to walking. This is primarily due to the constraints of the gait cycle: Body configuration changes dramatically over the gait cycle, necessitating different responses as this configuration changes. Notably, certain responses can only be initiated at specific points in the gait cycle, leading to onset times ranging from 350 to 600ms, much longer than what is observed during standing (50–200ms). Here, we investigated the neural control of upright balance during walking. Specifically, how the brain transforms sensory information related to upright balance into corrective motor responses. We used visual disturbances of 20 healthy young subjects walking in a virtual reality cave to induce the perception of a fall to the side and analyzed the muscular responses, changes in ground reaction forces and body kinematics. Our results showed changes in swing leg foot placement and stance leg ankle roll that accelerate the body in the direction opposite of the visually induced fall stimulus, consistent with previous results. Surprisingly, ankle musculature activity changed rapidly in response to the stimulus, suggesting the presence of a direct reflexive pathway from the visual system to the spinal cord, similar to the vestibulospinal pathway. We also observed systematic modulation of the ankle push-off, indicating the discovery of a previously unobserved balance mechanism. Such modulation has implications not only for balance but plays a role in modulation of step width and length as well as cadence. These results indicated a temporally-coordinated series of balance responses over the gait cycle that insures flexible control of upright balance during walking.站立平衡的神经调控机制已得到广泛研究。然而，绝大多数跌倒事件发生于行走过程中而非站立时，且站立平衡研究所得结论未必能直接推广至行走场景。这主要源于步态周期（gait cycle）的约束特性：人体肢体构型在步态周期中会发生剧烈变化，这要求随构型改变采取不同的调控响应。值得注意的是，部分响应仅能在步态周期的特定时刻触发，其响应启动时长介于350至600毫秒之间，远长于站立状态下观测到的50至200毫秒。 本研究聚焦行走过程中的直立平衡神经调控机制，具体探究大脑如何将与直立平衡相关的感觉信息转化为校正性运动响应。 本研究招募20名健康青年受试者，令其在虚拟现实舱（virtual reality cave）中行走，并通过视觉扰动诱导其产生向侧方跌倒的感知，随后分析其肌肉响应、地面反作用力（ground reaction forces）变化以及人体运动学（body kinematics）特征。 研究结果显示，摆动腿的足位调整与支撑腿的踝关节滚动动作会使身体向视觉诱导跌倒刺激的反方向加速移动，这与既往研究结论相符。 令人意外的是，踝关节肌肉活动会快速响应该刺激，这提示存在一条从视觉系统直达脊髓的直接反射通路，其机制与前庭脊髓通路（vestibulospinal pathway）类似。 此外，本研究还观测到踝关节蹬地动作的系统性调控现象，这表明我们发现了一种此前未被报道过的平衡调控机制。 这类调控不仅对平衡调控具有意义，还可对步幅宽度、步幅长度以及步频产生调节作用。 上述研究结果证实，行走过程中存在一系列随步态周期时序协调的平衡响应机制，可保障直立平衡的灵活调控。