Abstract

Background: After stroke, neuromuscular coordination during gait is commonly characterized by increased co-activation between lower-limb muscles. Although such alterations are well described during steady walking, their relevance for reactive balance control following unexpected perturbations remains unclear. Objective: To examine the association between vastus lateralis-gastrocnemius medialis (VL-GM) co-activation during gait and reactive balance performance following unexpected slip-like perturbations in individuals with chronic stroke. Methods: Thirty-seven individuals with chronic stroke completed overground gait assessment with surface electromyography to quantify VL-GM coordination during stance. Peak Activation Interval between VL-GM (PAI_VL-GM) and Co-activation Amplitude Index (CAI_VL-GMmax and CAI_GM-VLmax) were computed. In a separate protocol, participants were exposed to unexpected slip-like perturbations induced by a moveable platform during walking. Reactive balance performance was quantified using a dimensionless center-of-mass (CoM) stability metric at the first recovery step. Results: Higher PAI_VL-GM was associated with greater CoM stability. Additoinally, participants who fell showed lower PAI_VL-GM and higher CAI_GM-VLmax than those who recovered balance. Conclusion: Gait-phase VL-GM EMG coordination is closely associated with reactive balance control after slip-like perturbations in chronic stroke.