Effects of Resistance Training on Muscle Hypertrophy in Children and Adolescents: A Systematic Review and Meta-Analysis.

backgroundResistance training is considered safe and beneficial for young individuals, yet the extent to which it results in morphological adaptations before, during and after puberty remains unclear.

objectiveThe aim of this review was to quantify the effects of resistance training on muscle hypertrophy in children and adolescents and to examine whether the effects differ by maturational stage, sex, and hypertrophy-oriented design of the resistance training program.

methodsPubMed, Scopus, Web of Science and Google Scholar were searched in April 2025. Randomized and non-randomized controlled studies in participants younger than 18 years of age were eligible when hypertrophy was assessed with direct imaging or indirect instrumented methods. Subgroup analyses were conducted by maturational status, sex and the hypertrophy-oriented design of the resistance training program. Effect sizes (Cohen's d) with 95% confidence intervals were pooled using a random-effects model with heterogeneity quantified via the I

resultsTwenty-three studies with a total of 1443 participants were included. Overall, compared with passive controls, resistance training induced a small increase in muscle mass (Cohen's d = 0.22 95% CI 0.06-0.37), while compared with active controls, the effects were notably greater (Cohen's d =  0.61, 95% CI 0.03-1.20). Subgroup analyses revealed trivial-to-small hypertrophy across maturational stages when compared with passive controls (prepubertal Cohen's d = 0.16, 95% CI - 0.04 to 0.36; peripubertal Cohen's d =  0.30, 95% CI 0.01-0.58 postpubertal Cohen's d = 0.01, 95% CI - 0.31 to 0.33). Compared with active controls, subgroup differences by maturational stage were statistically significant (p =  0.0227), with postpubertal participants showing a large and significant effect (Cohen's d = 1.50, 95% CI 0.46-2.54) compared with smaller, non-significant effects in peripubertal and prepubertal participants. Compared with active controls, hypertrophy was large in males (Cohen's d =  1.26, 95% CI 0.29-2.22), trivial in females (Cohen's d =  - 0.12, 95% CI - 1.05-0.81) and trivial in mixed samples (Cohen's d = 0.04, 95% CI - 0.08 to 0.17). Compared with passive controls, changes were trivial in males (Cohen's d =  0.11, 95% CI - 0.12-0.34), small in females (Cohen's d = 0.20, 95% CI - 0.07 to 0.46) and small in mixed samples (Cohen's d =  0.39, 95% CI -  0.01 to 0.78).

conclusionResistance training induces small hypertrophy compared with passive controls and larger effects compared with active controls. The hypertrophic adaptations occur across various maturational stages but postpubertal youth show the greatest increases when contrasted with active comparators. Sex did not consistently influence outcomes. Resistance training promotes muscle growth in young males and females and is partly influenced by maturational stage.