Reactive Muscle Force Modulation Following Induced Belt Deceleration in Treadmill Gait

Background: Gait stability requires rapid and coordinated neuromuscular responses to unexpected perturbations, yet the muscle-specific forces underlying reactive recovery remain poorly understood. The present study investigated changes in peak lower-limb muscle forces during the recovery step following treadmill belt decelerations applied in the pre-swing phase of the gait cycle in young, healthy females. Methods: Twenty-one participants completed treadmill walking trials with controlled unilateral belt decelerations while kinematic and kinetic data were recorded and processed using OpenSim musculoskeletal modeling to estimate individual muscle forces. Results: Across all examined muscles, peak muscle forces were higher during the recovery step compared to unperturbed walking, with the largest relative increases observed in the tensor fasciae latae (118.86%), iliacus (115.57%), and gluteus maximus (101.37%). Cluster analysis revealed a hierarchical response pattern: proximal hip stabilizers generated the greatest forces, intermediate muscles contributed to hip and ankle stabilization, and distal or postural muscles exhibited smaller adjustments. Conclusions: These results highlight the central role of hip and ankle musculature in restoring dynamic balance and support previous evidence on coordinated multi-muscle responses during reactive control. Furthermore, the findings indicate that effective recovery relies on sufficient muscle capacity across nearly all lower-limb muscles, emphasizing the potential importance of strength and power in balance interventions. Limitations of static optimization and treadmill-based perturbations are acknowledged, but relative changes in muscle forces provide robust insight into reactive control strategies. Overall, this study elucidates muscle-specific contributions to balance recovery following pre-swing deceleration, informing the design of targeted interventions for fall prevention and stability enhancement.