Characterization of muscle synergy organization in adolescents with idiopathic scoliosis

Objectives Previous studies of adolescent idiopathic scoliosis (AIS) have primarily examined paraspinal muscle function using pairwise comparisons between the convex and concave sides, focusing on asymmetry. However, such approaches cannot capture the spatial and temporal coordination of muscles required exercise. This study aimed to characterize paraspinal muscle synergy patterns during trunk movement in AIS and to compare them with healthy controls. Methods Surface electromyography was recorded from eight pairs of bilateral paraspinal muscles in adolescents with AIS (n=13) and age-matched healthy participants (n=13) during a standardized trunk flexion–extension task. Muscle synergies were extracted using non-negative matrix factorization. Between-group differences were assessed using the Mann–Whitney U test. Results Compared with healthy controls, adolescents with AIS required a greater number of synergies to meet the reconstruction criterion (median 4 vs. 3, p=0.005). The variance accounted for (VAF) of the target-muscle-related synergy was significantly lower in AIS (median 42 vs. 62 %, p=0.006). Although similar synergies associated with target muscles were identified in both groups, AIS showed a reduced contribution of this synergy to overall muscle activation. AIS participants exhibited a more distributed coordination structure characterized by increased reliance on additional, subject-specific synergies. Conclusions Adolescents with AIS demonstrate altered paraspinal muscle coordination characterized by reduced contribution of target-muscle-related synergies and increased synergy dimensionality during functional trunk movement. Muscle synergy analysis provides a quantitative framework for assessing coordination structure beyond traditional pairwise-muscle-level measures and may offer objective features for individualized evaluation and rehabilitation monitoring.