Respiratory muscle strength, peripheral muscle strength, and balance in adolescents with idiopathic scoliosis: A cross-sectional comparative study

Background Adolescent idiopathic scoliosis (AIS) is a three-dimensional spinal deformity that may affect respiratory function, neuromuscular performance, and postural control. Objective To compare respiratory muscle strength, peripheral muscle strength, and balance between adolescents with AIS and healthy controls and to explore associations between respiratory muscle strength and postural stability in AIS. Methods This cross-sectional comparative study included 70 adolescents (40 AIS, 30 controls). Respiratory muscle strength was assessed using maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP), peripheral muscle strength using handgrip and hand-held dynamometry, and balance using the Postural Stability Test and Limits of Stability test. Group comparisons, exploratory Spearman correlations with false discovery rate (FDR) correction, and linear regressions were performed. Strength outcomes were adjusted for sex, age, and weight. Results MIP and MEP were lower in AIS than controls (64.95 ± 23.03 vs. 85.40 ± 25.08cmH2O and 67.54 ± 18.96 vs. 85.13 ± 27.47cmH2O, respectively). After adjustment for sex, age, and weight, the between-group differences remained significant for MIP, MEP, and bilateral knee extensor strength, but not for handgrip strength. Static stability indices did not differ between groups, whereas selected dynamic balance measures were impaired in AIS. Three of 42 exploratory correlations had unadjusted p < 0.05; none remained significant after false discovery rate correction. Conclusion AIS was associated with lower respiratory and knee extensor strength after adjustment and with differences in selected dynamic balance measures. Exploratory correlations did not survive FDR correction. These findings support comprehensive functional assessment of respiratory muscle strength, knee extensor strength, and balance in AIS. The cross-sectional design precludes causal inference.