Effect of surface electromyography normalisation methods over gait muscle synergies

This study investigates the effect of different normalisation methods on muscle synergy extraction from EMG data collected while walking in typically developing young people. Six methods were evaluated: Raw, Within-Trial Maximum, Inter-Trial Maximum, Task-Specific Maximum, Magnitude Percentile, and Unit Variance. Eighteen healthy children aged 8-15 participated, performing walking trials while their EMG signals were recorded and processed. Synergies were extracted using non-negative matrix factorisation, and the influence of normalisation methods on synergy complexity, structure, and activation coefficients was assessed. Normalisation choice significantly influenced synergy number, structure, and temporal characteristics. TSM and ITM methods yielded more consistent synergies, while MP and WTM exhibited greater variability. This study highlights the importance of selecting appropriate normalisation methods for robust muscle synergy analyses, enhancing understanding of motor control strategies, and contributing to a unified processing workflow.