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Inter-Limb Muscle Asymmetries in Youth Athletes: A Comprehensive Systematic Review and Meta-Analysis of Single-Leg
Adam Maszczyk1, Mariola Gepfert1, Przemysław Pietraszewski1
1Institute of Sport Sciences, Academy of Physical Education, 41-065 Katowice, Poland.
Abstract:
The aim of this meta-analysis was to synthesize current evidence on inter-limb asymmetries in youth athletes and to determine their magnitude, developmental determinants, and functional relevance. The review followed PRISMA 2020 guidelines, and the protocol was registered in PROSPERO. Six databases were searched from inception to October 2025. Studies assessing asymmetry as a between-limb difference in athletes aged 6-18 years were included. A total of 25 studies (N = 4125) were included qualitatively, with 24 included in the quantitative analyses. Meta-analyses were conducted for comparable outcomes (single-leg countermovement jump [SLCMJ], change of direction speed [COD], association with sprint performance, and maturation effects) using random-effects models and heterogeneity assessment (I2, τ2). Mean asymmetry was 10.8% for SLCMJ (95% CI: 6.7-14.9; I2 = 78%) and 7.4% for COD (95% CI: 0.5-14.2; I2 = 64%). The association between asymmetry and sprint performance was small and not statistically significant (r = -0.27; 95% CI: -0.55 to 0.07). Maturation analysis showed a moderate effect (d = 0.35; 95% CI: 0.18-0.52), with peak asymmetry around peak height velocity (PHV). Heterogeneity was mainly explained by sport-specific demands and methodological differences. Asymmetries of approximately 10% are commonly observed in youth athletes in single-leg jump and change of direction tests, but their clinical relevance likely depends on sport-specific demands, maturation status, and testing modality, and should not be interpreted as a universal normative threshold. The lack of prospective injury data prevents the establishment of universal clinical thresholds. In conclusion, inter-limb asymmetries are common and developmentally dynamic in youth athletes, with functional relevance depending on biological and sport-specific context. Future research should prioritize methodological standardization and prospective designs.
