Kibushi Benio, Hagio Shota, Moritani Toshio, Kouzaki Motoki
Laboratory of Neurophysiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
Japan Society for the Promotion of Science, Tokyo, Japan.
Front Hum Neurosci. 2018 Dec 11;12:485. doi: 10.3389/fnhum.2018.00485. eCollection 2018.
In order to achieve flexible and smooth walking, we must accomplish subtasks (e. g., loading response, forward propulsion or swing initiation) within a gait cycle. To evaluate subtasks within a gait cycle, the analysis of muscle synergies may be effective. In the case of walking, extracted sets of muscle synergies characterize muscle patterns that relate to the subtasks within a gait cycle. Although previous studies have reported that the muscle synergies of individuals with disorders reflect impairments, a way to investigate the instability in the activations of muscle synergies themselves has not been proposed. Thus, we investigated the local dynamic stability and orbital stability of activations of muscle synergies across various walking speeds using maximum Lyapunov exponents and maximum Floquet multipliers. We revealed that the local dynamic stability in the activations decreased with accelerated walking speeds. Contrary to the local dynamic stability, the orbital stability of the activations was almost constant across walking speeds. In addition, the increasing rates of maximum Lyapunov exponents were different among the muscle synergies. Therefore, the local dynamic stability in the activations might depend on the requirement of motor output related to the subtasks within a gait cycle. We concluded that the local dynamic stability in the activation of muscle synergies decrease as walking speed accelerates. On the other hand, the orbital stability is sustained across broad walking speeds.
为了实现灵活且顺畅的行走，我们必须在一个步态周期内完成子任务（例如，负重反应、向前推进或摆动起始）。为了评估步态周期内的子任务，肌肉协同作用分析可能是有效的。在行走的情况下，提取的肌肉协同作用集表征了与步态周期内子任务相关的肌肉模式。尽管先前的研究报告称，患有疾病的个体的肌肉协同作用反映了功能障碍，但尚未提出一种研究肌肉协同作用自身激活不稳定性的方法。因此，我们使用最大Lyapunov指数和最大Floquet乘数，研究了不同步行速度下肌肉协同作用激活的局部动态稳定性和轨道稳定性。我们发现，随着步行速度加快，激活的局部动态稳定性降低。与局部动态稳定性相反，激活的轨道稳定性在不同步行速度下几乎保持不变。此外，最大Lyapunov指数的增加速率在不同肌肉协同作用之间有所不同。因此，激活的局部动态稳定性可能取决于与步态周期内子任务相关的运动输出需求。我们得出结论，随着步行速度加快，肌肉协同作用激活的局部动态稳定性降低。另一方面，轨道稳定性在较宽的步行速度范围内得以维持。
