Unilateral muscle weakness often leads to asymmetric gait, disrupting interlimb coordination and stance timing. This study presents a reinforcement learning (RL) based musculoskeletal simulation framework to (1) quantify how progressive unilateral muscle weakness affects gait symmetry and (2) evaluate whether ankle exoskeleton assistance can improve gait symmetry under impaired conditions. The overarching goal is to establish a simulation- and learning-based workflow that supports early controller development prior to patient experiments. Asymmetric gait was induced by reducing right-leg muscle strength to 75%, 50%, and 25% of baseline. Gait asymmetry was quantified using toe-off timing, peak contact forces, and joint-level symmetry metrics. Increasing weakness produced progressively larger temporal and kinematic asymmetry, most pronounced at the ankle. Ankle range of motion symmetry degraded from near-symmetric behavior at 100% strength (symmetry index, SI = +6.4%; correlation r=0.974) to severe asymmetry at 25% strength (SI = -47.1%, r=0.889), accompanied by a load shift toward the unimpaired limb. At 50% strength, ankle exoskeleton assistance improved kinematic symmetry relative to the unassisted impaired condition, reducing the magnitude of ankle SI from 25.8% to 18.5% and increasing ankle correlation from r=0.948 to 0.966, although peak loading remained biased toward the unimpaired side. Overall, this framework supports controlled evaluation of impairment severity and assistive strategies, and provides a basis for future validation in human experiments.

翻译：单侧肌力减弱常导致步态不对称，破坏肢体间协调性与站立相时序。本研究提出一个基于强化学习（RL）的肌肉骨骼仿真框架，旨在（1）量化渐进性单侧肌力减弱对步态对称性的影响，以及（2）评估在损伤条件下踝关节外骨骼辅助能否改善步态对称性。总体目标是建立一个基于仿真与学习的工作流程，为患者实验前的早期控制器开发提供支持。通过将右腿肌力分别降低至基线水平的75%、50%和25%来诱导不对称步态。步态不对称性采用足尖离地时序、峰值接触力及关节层面对称性指标进行量化。肌力减弱程度的增加导致时间和运动学不对称性逐步扩大，在踝关节处最为显著。踝关节活动范围对称性从100%肌力时的近对称状态（对称指数SI = +6.4%；相关系数r=0.974）恶化至25%肌力时的严重不对称状态（SI = -47.1%，r=0.889），并伴随负荷向未受损肢体转移。在50%肌力条件下，踝关节外骨骼辅助相较于未辅助的损伤状态改善了运动学对称性，将踝关节SI幅值从25.8%降至18.5%，并将踝关节相关系数从r=0.948提升至0.966，尽管峰值负荷仍偏向未受损侧。总体而言，该框架支持对损伤严重程度与辅助策略进行受控评估，并为未来人体实验验证奠定了基础。