Humans rely on ankle torque to maintain standing balance, particularly in the presence of small to moderate perturbations. Reductions in maximum torque (MT) production and maximum rate of torque development (MRTD) occur at the ankle with age, diminishing stability. Ankle exoskeletons are powered orthotic devices that may assist older adults by compensating for reduced muscle force and power production capabilities. They may also be able to assist with ankle strategies used for balance. However, no studies have investigated the effect of such devices on balance in older adults. Here, we model the effect ankle exoskeletons have on stability in physics-based models of healthy young and old adults, focusing on the mitigation of age-related deficits such as reduced MT and MRTD. We show that an ankle exoskeleton moderately reduces feasible stability boundaries in users who have full ankle strength. For individuals with age-related deficits, there is a trade-off. While exoskeletons augment stability in low velocity conditions, they reduce stability in some high velocity conditions. Our results suggest that well-established control strategies must still be experimentally validated in older adults.

翻译：人类依赖踝关节扭矩维持站立平衡，尤其在受到中小型扰动时。随着年龄增长，踝关节最大扭矩（MT）产生能力和最大扭矩变化率（MRTD）会下降，从而降低稳定性。踝关节外骨骼是一种动力辅助矫形装置，可通过补偿肌肉力量和功率生成能力的衰退来帮助老年人。它们还可能协助维持平衡的踝关节控制策略。然而，目前尚无研究探讨此类设备对老年人平衡能力的影响。本文通过基于物理学的健康青年与老年成人模型，研究踝关节外骨骼对稳定性的影响，重点关注其对年龄相关缺陷（如MT和MRTD下降）的改善作用。研究表明，对于具备完整踝关节力量的用户，踝关节外骨骼会适度缩小其可行稳定性边界。对于存在年龄相关缺陷的个体，则存在权衡关系：外骨骼在低速度条件下能增强稳定性，但在某些高速度条件下会降低稳定性。我们的结果表明，现有成熟的控制策略仍需在老年群体中进行实验验证。