Williams Genevieve K R, Vicinanza Domenico, Attias Michael, Armand Stéphane
Department of Public Health and Sports Sciences, University of Exeter, Exeter, United Kingdom.
Faculty of Science and Engineering, Anglia Ruskin University, Cambridge, United Kingdom.
Front Hum Neurosci. 2024 Sep 5;18:1367952. doi: 10.3389/fnhum.2024.1367952. eCollection 2024.
To investigate the dynamics of the motor control system during walking by examining the complexity, stability, and causal relationships of leg motions. Specifically, the study focuses on gait under both bilateral and unilateral constraints induced by a passive exoskeleton designed to replicate gastrocnemius contractures.
Kinematic data was collected as 10 healthy participants walked at a self-selected speed. A new Complexity-Instability Index (CII) of the leg motions was defined as a function of the Correlation Dimension and the Largest Lyapunov Exponent. Causal interactions between the leg motions are explored using Convergent Cross Mapping.
Normal walking is characterized by a high mutual drive of each leg to the other, where CII is lowest for both legs (complexity of each leg motion is low and stability high). The effect of the bilateral emulated contractures is a reduced drive of each leg to the other and an increased CII for both legs. With unilateral emulated contracture, the mechanically constrained leg strongly drives the unconstrained leg, and CII was significantly higher for the constrained leg compared to normal walking.
Redundancy in limb motions is used to support causal interactions, reducing complexity and increasing stability in our leg dynamics during walking. The role of redundancy is to allow adaptability above being able to satisfy the overall biomechanical problem; and to allow the system to interact optimally. From an applied perspective, important characteristics of functional movement patterns might be captured by these nonlinear and causal variables, as well as the biomechanical aspects typically studied.
通过研究腿部运动的复杂性、稳定性和因果关系，来探究步行过程中运动控制系统的动态变化。具体而言，该研究聚焦于由旨在模拟腓肠肌挛缩的被动外骨骼所引发的双侧和单侧约束条件下的步态。
在10名健康参与者以自选速度行走时收集运动学数据。将腿部运动的一种新的复杂性 - 不稳定性指数（CII）定义为关联维数和最大Lyapunov指数的函数。使用收敛交叉映射探索腿部运动之间的因果相互作用。
正常行走的特征是每条腿对另一条腿有较高的相互驱动作用，此时双腿的CII最低（每条腿运动的复杂性低且稳定性高）。双侧模拟挛缩的影响是每条腿对另一条腿的驱动减少，且双腿的CII增加。在单侧模拟挛缩时，机械受限的腿强烈驱动未受限的腿，与正常行走相比，受限腿的CII显著更高。
肢体运动的冗余性用于支持因果相互作用，在我们步行过程中降低腿部动力学的复杂性并提高稳定性。冗余的作用是允许适应性，而不仅仅是能够解决整体生物力学问题；并允许系统进行最佳交互。从应用角度来看，这些非线性和因果变量以及通常研究的生物力学方面可能会捕捉到功能运动模式的重要特征。
