Department of Mechanical Engineering, Stanford University, Stanford, California, United States of America.
Department of Computer Science, Stanford University, Stanford, California, United States of America.
PLoS Comput Biol. 2023 Aug 7;19(8):e1010712. doi: 10.1371/journal.pcbi.1010712. eCollection 2023 Aug.
Walking balance is central to independent mobility, and falls due to loss of balance are a leading cause of death for people 65 years of age and older. Bipedal gait is typically unstable, but healthy humans use corrective torques to counteract perturbations and stabilize gait. Exoskeleton assistance could benefit people with neuromuscular deficits by providing stabilizing torques at lower-limb joints to replace lost muscle strength and sensorimotor control. However, it is unclear how applied exoskeleton torques translate to changes in walking kinematics. This study used musculoskeletal simulation to investigate how exoskeleton torques applied to the ankle and subtalar joints alter center of mass kinematics during walking. We first created muscle-driven walking simulations using OpenSim Moco by tracking experimental kinematics and ground reaction forces recorded from five healthy adults. We then used forward integration to simulate the effect of exoskeleton torques applied to the ankle and subtalar joints while keeping muscle excitations fixed based on our previous tracking simulation results. Exoskeleton torque lasted for 15% of the gait cycle and was applied between foot-flat and toe-off during the stance phase, and changes in center of mass kinematics were recorded when the torque application ended. We found that changes in center of mass kinematics were dependent on both the type and timing of exoskeleton torques. Plantarflexion torques produced upward and backward changes in velocity of the center of mass in mid-stance and upward and smaller forward velocity changes near toe-off. Eversion and inversion torques primarily produced lateral and medial changes in velocity in mid-stance, respectively. Intrinsic muscle properties reduced kinematic changes from exoskeleton torques. Our results provide mappings between ankle plantarflexion and inversion-eversion torques and changes in center of mass kinematics which can inform designers building exoskeletons aimed at stabilizing balance during walking. Our simulations and software are freely available and allow researchers to explore the effects of applied torques on balance and gait.
步行平衡是独立移动的核心，而老年人因失去平衡而跌倒则是导致死亡的主要原因。双足步态通常不稳定，但健康的人类会使用纠正扭矩来抵消扰动并稳定步态。外骨骼辅助可以通过在下肢关节处提供稳定扭矩来为神经肌肉缺陷的人提供帮助，以替代失去的肌肉力量和感觉运动控制。然而，尚不清楚施加的外骨骼扭矩如何转化为步行运动学的变化。本研究使用肌肉骨骼仿真来研究施加在踝关节和跗骨关节上的外骨骼扭矩如何改变步行时的质心运动学。我们首先通过跟踪从五个健康成年人记录的实验运动学和地面反作用力，使用 OpenSim Moco 创建了肌肉驱动的步行模拟。然后，我们使用正向积分模拟了在保持肌肉兴奋基于我们之前的跟踪模拟结果固定的情况下施加到踝关节和跗骨关节的外骨骼扭矩的影响。外骨骼扭矩持续了步态周期的 15%，在站立阶段的足平到趾离地之间施加，并且在扭矩施加结束时记录了质心运动学的变化。我们发现，质心运动学的变化既取决于外骨骼扭矩的类型，也取决于其施加的时机。跖屈扭矩在中步时使质心速度产生向上和向后的变化，在趾离地时向上和较小的向前速度变化。外展和内翻扭矩主要在中步时分别产生速度的侧向和内侧变化。内在肌肉特性减少了外骨骼扭矩引起的运动学变化。我们的结果提供了踝关节跖屈和内翻-外翻扭矩与质心运动学变化之间的映射关系，这可以为设计旨在稳定步行时平衡的外骨骼的设计师提供信息。我们的模拟和软件是免费提供的，并允许研究人员探索施加扭矩对平衡和步态的影响。
