Strength and balance asymmetries in children and adolescents: comparison between single- and multi-sport participants

Abstract

Background: Prior research has suggested links between youth sport special-ization, inter-limb asymmetries, and injury risk, but findings remain inconsistent regarding whether single-sport athletes show greater asymmetries than their multi-sport peers. This study examined differences in inter-limb asymme-try (global, balance, strength) between single- and multi-sport athletes, and explored the prevalence of exceeding clinical thresholds, sex- and sport-specific interactions, and associations with training volume and injury history. Methods: A cross-sectional study was conducted on 76 youth athletes (24 single-sport, 52 multi-sport; mean age 12.6 ± 1.7 years) using standardized assessments of dynamic balance (Y-Balance Test) and isometric strength (hand-held dynamometry). Inter-limb asymmetry was calculated using Index-9 in three domains: global asymmetry, balance asymmetry, and strength asymmetry. Differ-ences between single-sport specialists and multi-sport athletes were tested using linear mixed effect models, adjusted for sex, maturity status, BMI, training vol-ume, and sport type. Sensitivity and interaction analyzes (e.g., sport symmetry, sex, injury history) were also performed. Results: Inter-limb strength asymmetries greater than 10% were observed in more than half of the participants, especially for ankle plantarflexion and hip abduction. Balance asymmetries were smaller, with fewer than 15% of athletes exceeding the 10% threshold. Training volume was higher in the single-sport group, but was not associated with greater asymmetry. No significant differences were found between single and multisport athletes for global (β = 0.039, p =.597), balance (β = 0.037, p =.745) or strength asymmetry (β = 0.013, p =.879). These null results persisted across the sensitivity analyses and interaction models. Conclusions: Despite higher training volumes, single-sport youth athletes did not exhibit greater balance or strength asymmetries than their multi-sport peers. Inter-limb asymmetries were common across the cohort but were not associated with sport specialization. These findings highlight the need for cautious, individ-ualized interpretation of asymmetry measures in youth athletes, and underscore the importance of further research to clarify their developmental and clinical significance. Trial registrations: ClinicalTrials.gov (NCT06325228); registered on 10/03/2024.