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Background: This study investigated the associations of muscular strength measures with anthropometry, chronological age, biological maturation, and training experience in trained prepubertal and pubertal males. Another aim was to investigate if handgrip strength can predict general or overall muscle strength in the same population.

Method: Forty-one (n = 41) trained male children and adolescents aged 10–16 participated in the study. The 10-repetition maximum (RM) leg press and bench press were used to assess upper- and lower-body muscular strength, handgrip strength was used as an overall strength assessment, and a countermovement jump with arm swing (CMJa) was used to estimate extensor muscle power of the lower extremity. The maturity status was determined using the Tanner scale. Anthropometric factors included height, body mass, two skinfolds, limb length, and lean leg volume. Multivariable linear regressions were performed on absolute strength values to explore predictors of muscular strength and power.

Results: Body mass explained 81% of the variance in leg press strength (p < 0.001), whereas bench press was associated with body mass and chronological age, explaining 83% of the variance (p < 0.001). The countermovement jump (CMJa) height was positively associated with lean leg volume, which explained 52% of the variance (p < 0.001). Chronological age and fat-free mass explained 87% of the variance in handgrip strength (p < 0.001). Biological maturity (Tanner) did not contribute to the final models. Handgrip strength was strongly associated with total muscle strength (r = 0.89–0.91, p < 0.001).

Conclusion: The results indicate that anthropometrical factors, rather than biological maturity, are associated with muscular strength in trained male children and adolescents. Our findings suggest that handgrip strength may be a quick and effective screening tool for assessing total muscle strength in youth.