Impaired motor control during post-stroke walking: A systematic review and meta-analysis of muscle synergies across different phases of recovery.

Background: Stroke often impairs motor control during walking. Muscle synergy analysis provides insights into motor control by evaluating how muscle groups coordinate movement.

Objective: This review has a threefold aim: (1) To compare the number of muscle synergies during walking between the paretic and non-paretic leg, as well as in perspective with healthy controls. (2) To examine eventual associations between these synergies and lower extremity motor impairment and self-selected walking speed. (3) To explore how synergy patterns differ between the sub-acute and chronic phase post-stroke.

Method: MEDLINE, Embase, and Web of Science were systematically searched (until 11/04/2025) for studies using matrix factorization to extract muscle synergies during post-stroke walking. Meta-analyses were conducted using standardized mean differences (SMD) and associations with clinical measures were analyzed using correlations and Chi-square statistics.

Results: Twenty-four studies (624 individuals post-stroke) were included. The paretic leg showed significant fewer synergies than the non-paretic leg (SMD: -0.73; p < 0.00001) and healthy controls (SMD: -1.04; p < 0.00001). Additionally, the non-paretic leg revealed a small but statistically significant reduction in synergies compared to healthy controls (SMD: -0.40; p = 0.02). The number of synergies in the paretic leg strongly correlated with lower extremity motor function (r = 0.827; p < 0.001). Fewer synergies were more prevalent in the sub-acute than chronic phase (χ² = 15.611; p < 0.001). Synergy composition showed increased co-activation and prolonged activation timing.

Conclusion: Stroke leads to fewer and less distinct muscle synergies during walking in the paretic leg, especially in the sub-acute phase and in persons with severe lower extremity motor impairments.