Biorobotics Laboratory, École polytechnique fédérale de Lausanne, School of Engineering, Institute of Bioengineering, Lausanne, Switzerland.
Kinesiology Laboratory, Geneva University Hospitals and University of Geneva, Geneva, Switzerland.
PLoS Comput Biol. 2021 May 19;17(5):e1008594. doi: 10.1371/journal.pcbi.1008594. eCollection 2021 May.
The central nervous system of humans and other animals modulates spinal cord activity to achieve several locomotion behaviors. Previous neuromechanical models investigated the modulation of human gait changing selected parameters belonging to CPGs (Central Pattern Generators) feedforward oscillatory structures or to feedback reflex circuits. CPG-based models could replicate slow and fast walking by changing only the oscillation's properties. On the other hand, reflex-based models could achieve different behaviors through optimizations of large dimensional parameter spaces. However, they could not effectively identify individual key reflex parameters responsible for gait characteristics' modulation. This study investigates which reflex parameters modulate the gait characteristics through neuromechanical simulations. A recently developed reflex-based model is used to perform optimizations with different target behaviors on speed, step length, and step duration to analyze the correlation between reflex parameters and their influence on these gait characteristics. We identified nine key parameters that may affect the target speed ranging from slow to fast walking (0.48 and 1.71 m/s) as well as a large range of step lengths (0.43 and 0.88 m) and step duration (0.51, 0.98 s). The findings show that specific reflexes during stance significantly affect step length regulation, mainly given by positive force feedback of the ankle plantarflexors' group. On the other hand, stretch reflexes active during swing of iliopsoas and gluteus maximus regulate all the gait characteristics under analysis. Additionally, the results show that the hamstrings' group's stretch reflex during the landing phase is responsible for modulating the step length and step duration. Additional validation studies in simulations demonstrated that the modulation of identified reflexes is sufficient to regulate the investigated gait characteristics. Thus, this study provides an overview of possible reflexes involved in modulating speed, step length, and step duration of human gaits.
人类和其他动物的中枢神经系统调节脊髓活动以实现几种运动行为。以前的神经机械模型研究了通过改变属于中央模式发生器（CPG）的前馈振荡结构或反馈反射回路的参数来调制人类步态变化。基于 CPG 的模型可以通过仅改变振荡的特性来复制慢走和快走。另一方面，基于反射的模型可以通过优化大维参数空间来实现不同的行为。然而，它们不能有效地识别负责步态特征调制的单个关键反射参数。本研究通过神经机械模拟研究哪些反射参数调节步态特征。使用最近开发的基于反射的模型对不同目标行为（速度、步长和步幅持续时间）进行优化，以分析反射参数与它们对这些步态特征的影响之间的相关性。我们确定了九个关键参数，这些参数可能会影响从慢走到快走的目标速度（0.48 和 1.71 m/s）以及大范围的步长（0.43 和 0.88 m）和步幅持续时间（0.51、0.98 s）。研究结果表明，站立期间的特定反射对步长调节有显著影响，主要是由踝跖屈肌组的正力反馈引起的。另一方面，在摆腿阶段活跃的伸肌反射调节分析中的所有步态特征。此外，结果表明，股二头肌在着陆阶段的伸展反射负责调节步长和步幅持续时间。在模拟中的额外验证研究表明，所确定的反射的调节足以调节所研究的步态特征。因此，本研究提供了参与调节人类步态速度、步长和步幅持续时间的可能反射的概述。
