Beyond unilateral motor impairments: Role of bilateral force control and strength asymmetry in gait coordination and falls post-stroke

Coordination between lower extremities is a fundamental aspect of walking, yet it has received limited attention in locomotor recovery post-stroke. We aimed to compare the impact of unilateral versus bilateral force impairments on gait coordination and examine the relationship between gait coordination and incidence of falls post-stroke. In adults with stroke (N = 22) and age-similar healthy controls (N = 22), we measured gait coordination with phase coordination index (PCI) during overground walking. We measured force control for ankle dorsiflexors in unilateral and bilateral conditions. Unilateral force impairments were quantified with force error during visuomotor tracking and maximum voluntary contraction force for each leg. Bilateral force impairments were measured with cross-correlation coefficient, time lag, and strength symmetry. We recorded the history of falls in the previous year for adults with stroke. Compared with controls, adults with stroke showed significantly increased PCI, decreased cross-correlation coefficient and increased time lag between bilateral forces. Force error of both paretic and non-paretic legs was increased in the stroke group. Strength symmetry and cross-correlation coefficient explained 59.5 % of the variance in PCI (p < 0.001). However, unilateral force impairments were not associated with PCI. Adults with stroke reported a previous fall incidence rate of 59.09 %. Stroke survivors with a history of fall showed significantly higher PCI relative to stroke survivors without a history of fall (p < 0.01). We found a significant relationship between falls and PCI (p < 0.05) such that poor gait coordination was related to past incidence of falls in stroke survivors. The current study provides novel insights that impairments in bilateral, but not unilateral force control influences coordination during overground walking post-stroke. Specifically, impaired timing between bilateral ankle forces and strength asymmetry negatively impacts gait coordination post-stroke. Impaired gait coordination elevates the risk for falling post-stroke, thereby compromising safe mobility in individuals with stroke.