Establishing a methodological framework for evaluating gait symmetry through muscle synergies: A pilot study

Gait symmetry is vital for stable locomotion, yet conventional metrics often yield inconsistent results. Muscle synergy analysis provides a more precise understanding of neural mechanisms behind symmetric gait. A clear methodology is essential to distinguish true inter-limb differences from natural variability. This study aimed to refine the analysis of muscle synergy symmetry in healthy individuals by incorporating intra-limb similarity as a baseline for comparison, while also including muscle weightings within each synergy to explore muscle synchrony. EMG signals were collected from both lower limbs of healthy subjects during treadmill walking. Muscle synergies were extracted using non-negative matrix factorization (NMF). Intra-limb similarity was used as a baseline to assess inter-limb differences. Muscle activity, number of synergies, muscle weightings within each synergy, and weight (W) and activation coefficients (H) were compared between sides. Normalized scalar products assessed weight coefficients, while Pearson's correlation was used to compare activation coefficients. No significant differences were found in the number or structure of muscle synergies between limbs, indicating symmetrical coordination. However, significant differences were observed in activation of four of eight muscles and minor variations in muscle weightings. This study underscores the importance of a robust framework for interpreting muscle synergy symmetry.