Department of Mechanical Engineering, University of Washington, Seattle, USA.
Department of Applied Mathematics, University of Washington, Seattle, USA.
Sci Rep. 2024 Jan 10;14(1):1031. doi: 10.1038/s41598-023-50999-0.
Ankle exoskeletons alter whole-body walking mechanics, energetics, and stability by altering center-of-mass (CoM) motion. Controlling the dynamics governing CoM motion is, therefore, critical for maintaining efficient and stable gait. However, how CoM dynamics change with ankle exoskeletons is unknown, and how to optimally model individual-specific CoM dynamics, especially in individuals with neurological injuries, remains a challenge. Here, we evaluated individual-specific changes in CoM dynamics in unimpaired adults and one individual with post-stroke hemiparesis while walking in shoes-only and with zero-stiffness and high-stiffness passive ankle exoskeletons. To identify optimal sets of physically interpretable mechanisms describing CoM dynamics, termed template signatures, we leveraged hybrid sparse identification of nonlinear dynamics (Hybrid-SINDy), an equation-free data-driven method for inferring sparse hybrid dynamics from a library of candidate functional forms. In unimpaired adults, Hybrid-SINDy automatically identified spring-loaded inverted pendulum-like template signatures, which did not change with exoskeletons (p > 0.16), except for small changes in leg resting length (p < 0.001). Conversely, post-stroke paretic-leg rotary stiffness mechanisms increased by 37-50% with zero-stiffness exoskeletons. While unimpaired CoM dynamics appear robust to passive ankle exoskeletons, how neurological injuries alter exoskeleton impacts on CoM dynamics merits further investigation. Our findings support Hybrid-SINDy's potential to discover mechanisms describing individual-specific CoM dynamics with assistive devices.
踝关节外骨骼通过改变质心（CoM）运动来改变整个身体的行走力学、能量学和稳定性。因此，控制CoM 运动的动力学对于维持高效稳定的步态至关重要。然而，踝关节外骨骼如何改变 CoM 动力学尚不清楚，如何优化个体特定的 CoM 动力学模型，尤其是在神经损伤患者中，仍然是一个挑战。在这里，我们评估了正常成年人和一名脑卒中偏瘫患者在穿着普通鞋子和零刚度及高刚度被动踝关节外骨骼时的 CoM 动力学的个体特异性变化。为了确定描述 CoM 动力学的最佳物理可解释机制集，我们利用混合稀疏非线性动力学识别（Hybrid-SINDy），这是一种从候选功能形式库中推断稀疏混合动力学的无方程数据驱动方法。在正常成年人中，Hybrid-SINDy 自动识别了弹簧加载倒立摆样模板签名，这些签名不会随外骨骼而改变（p>0.16），除了腿部休息长度略有变化（p<0.001）。相反，零刚度外骨骼会使脑卒中偏瘫腿的旋转刚度机制增加 37-50%。虽然正常成年人的 CoM 动力学对外骨骼具有很强的适应性，但神经损伤如何改变外骨骼对 CoM 动力学的影响值得进一步研究。我们的研究结果支持了 Hybrid-SINDy 发现描述个体特定 CoM 动力学的辅助设备机制的潜力。
