Investigating muscle synergies in individuals with spinal cord injury: A scoping review

Context. Spinal cord injury (SCI) disrupts central motor control, leading to significant alterations in neuromuscular function. Muscle synergy analysis, which identifies coordinated patterns of muscle activation, has emerged as a promising approach to investigate motor impairment and compensatory strategies in neurorehabilitation. Although increasingly applied in other neurological populations, no comprehensive synthesis has yet focused on individuals with SCI. Objective. This scoping review aimed to map the methodologies and applications of studies employing muscle synergy extraction in individuals with SCI. Methods. Following the Joanna Briggs Institute methodology, a systematic search was conducted across MEDLINE, CINAHL Complete, Scopus, IEEE Xplore, and Web of Science from inception to May 2025. Eligible studies included adults with SCI in which muscle synergies were extracted from electromyographic (EMG) data collected during motor task execution using decomposition algorithms. Two reviewers independently performed study selection and data extraction. Results. Twenty-one studies involving 205 individuals with SCI were identified. Protocols covered diverse motor tasks involving upper and lower limbs, trunk, and hand. Most studies used surface EMG and non-negative matrix factorization, to extract between one to six synergies. Considerable heterogeneity was observed in sample characteristics and synergy extraction methods. Only a few studies examined associations with clinical outcomes, which remained inconclusive. Conclusion. Muscle synergy analysis is a feasible and promising tool for characterizing motor function after SCI. However, current evidence is constrained by small samples, methodological variability, and limited clinical integration. Future research should prioritize protocol standardization and clinically oriented designs to clarify its translational value in SCI rehabilitation.