Effects of Resistance Training on Isometric Force and Muscle Thickness in Prepubertal and Pubertal Boys: A Randomized Controlled Trial.

Komm, YN, Held, S, Gavanda, S, Comfort, P, Faigenbaum, AD, Geisler, S, and Augste, C. Effects of resistance training on isometric force and muscle thickness in prepubertal and pubertal boys: a randomized controlled trial. J Strength Cond Res XX(X): 000-000, 2026-While increases in strength in youth are largely attributed to neural adaptations, evidence regarding hypertrophic adaptations in prepubertal youth remains inconsistent. This study compared the effects of resistance training on hypertrophy and strength between prepubertal and pubertal adolescents. Sixty-eight male subjects were classified as prepubertal (11.58 ± 1.04 years) or pubertal (14.28 ± 0.88 years) using maturity offset estimates and randomized into 4 groups: prepubertal resistance training (n = 19), prepubertal active control (n = 20), pubertal resistance training (n = 14), and pubertal active control (n = 15). The 9-week intervention consisted of 2 weekly sessions of lower-body resistance training, while the active control groups continued their regular soccer training. Strength was assessed using the isometric mid-thigh pull, and hypertrophy was assessed using muscle thickness. Data were analyzed using linear mixed-effects models. Statistical significance was set at p < 0.05. No significant Time × Intervention interactions were observed for rectus femoris and vastus intermedius (p = 0.295), and for vastus lateralis (p = 0.711). A significant Time × Intervention interaction (p = 0.042) was found for peak force, indicating superior strength improvements in the training groups. No significant Time × Maturity × Intervention interactions were detected for absolute strength (p = 0.289), relative strength (p = 0.656), rectus femoris and vastus intermedius thickness (p = 0.451), or vastus lateralis thickness (p = 0.731), although these analyses had limited statistical power. These findings indicate that the resistance training protocol in this study increased isometric mid-thigh pull force in prepubertal and pubertal adolescent boys.