Department of Biomechanical Engineering, University of Twente , Enschede , The Netherlands.
J Neurophysiol. 2019 May 1;121(5):1711-1717. doi: 10.1152/jn.00752.2018. Epub 2019 Mar 13.
The ankle joint muscles can contribute to balance during walking by modulating the center of pressure and ground reaction forces through an ankle moment. This is especially effective in the sagittal plane through ankle plantar- or dorsiflexion. If the ankle joints were to be physically blocked to make an ankle strategy ineffective, there would be no functional contribution of these muscles to balance during walking, nor would these muscles generate afferent output regarding ankle joint rotation. Consequently, ankle muscle activation for the purpose of balance control would be expected to disappear. We have performed an experiment in which subjects received anteroposterior pelvis perturbations during walking while their ankle joints could not contribute to the balance recovery. The latter was realized by physically blocking the ankle joints through a pair of modified ankle-foot orthoses. In this article we present the lower limb muscle activity responses in reaction to these perturbations. Of particular interest are the tibialis anterior and gastrocnemius medialis muscles, which could not contribute to the balance recovery through the ankle joint or encode muscle length changes caused by ankle joint rotation. Yet, these muscles showed long-latency responses, ~100 ms after perturbation onset. The response amplitudes were dependent on the perturbation magnitude and direction, as well as the state of the leg. The results imply that ankle muscle responses can be evoked without changes in proprioceptive information of those muscles through ankle rotation. This suggest a more centralized regulation of balance control, not strictly related to the ankle joint kinematics. Walking human subjects received forward-backward perturbations at the pelvis while wearing "pin-shoes," a pair of modified ankle-foot orthoses that physically blocked ankle joint movement and reduced the base of support of each foot to a single point. The lower leg muscles showed long-latency perturbation-dependent activity changes, despite having no functional contributions to balance control through the ankle joint and not having been subjected to muscle length changes through ankle joint rotation.
踝关节肌肉可以通过踝关节力矩来调节中心压力和地面反作用力，从而有助于行走时的平衡。这在矢状面通过踝关节跖屈或背屈尤其有效。如果踝关节被物理阻挡以使踝关节策略无效，则这些肌肉在行走时对平衡没有功能贡献，也不会产生关于踝关节旋转的感觉输出。因此，预计为平衡控制目的而激活的踝关节肌肉会消失。我们进行了一项实验，其中受试者在行走时接受前后骨盆扰动，而他们的踝关节无法为平衡恢复做出贡献。通过一对改良的踝足矫形器物理阻挡踝关节来实现后者。在本文中，我们介绍了下肢肌肉对这些扰动的反应。特别有趣的是胫骨前肌和腓肠肌内侧肌，它们不能通过踝关节或编码由踝关节旋转引起的肌肉长度变化来帮助平衡恢复。然而，这些肌肉表现出长潜伏期反应，在扰动开始后约 100 毫秒。响应幅度取决于扰动幅度和方向以及腿部状态。结果表明，即使没有踝关节旋转引起的本体感觉信息变化，也可以诱发踝关节肌肉反应。这表明平衡控制的调节更加集中，与踝关节运动学没有严格的关系。 行走的人体受试者在穿着“销钉鞋”（一对改良的踝足矫形器）时，在前-后方向上受到骨盆的扰动，该矫形器物理阻挡了踝关节的运动，并将每个脚的支撑基础减小到一个点。尽管小腿肌肉在踝关节没有功能贡献平衡控制，并且没有受到踝关节旋转引起的肌肉长度变化的影响，但它们表现出与扰动相关的长潜伏期活动变化。
