Lower-Body Strength and Hypertrophy Adaptations in Response to Concurrent Training in Trained Young Males

ABSTRACT: Gomes, M, Costa, M, Pezarat-Correia, P, and Mendonca, GV. Lower-body strength and hypertrophy adaptations in response to concurrent training in trained young males. J Strength Cond Res XX(X): 000-000, 2026-This study examined the interference effect of concurrent training (CT) on maximal and explosive strength and muscle morphology in trained young males. Thirty subjects were randomly assigned to endurance training (E), resistance training (R), or CT for 11 weeks. The intervention comprised 2 mesocycles: weeks 1-5 emphasizing maximal strength, and weeks 6-11 targeting explosive strength. Assessments were conducted at baseline, mid-training, and post-training, and included leg-press maximal voluntary isometric contraction (MVIC), rate of force development (RFD), countermovement jump kinetics, and vastus lateralis cross-sectional area and pennation angle. Maximal voluntary isometric contraction increased only in the R group (18.4 ± 10.2%, p = 0.015). Peak RFD improved in both R (31.8 ± 23.2%) and CT (23.1 ± 27.9%), although with distinct time courses: R improved progressively across both mesocycles, whereas CT improved only during the second. Early-phase RFD (0-50 ms) increased in the R group from mid-training onward, whereas the CT group improved only from mid- to post-training (38.3 ± 40.4%, p = 0.021), accompanied by greater quadriceps electromyographic activity (p < 0.05). No changes in RFD were observed in E during training. Countermovement jump positive impulse improved in both R (12.7 ± 9.0%) and CT (8.8 ± 8.3%, p < 0.05), with no evidence of interference in jump-related explosive performance. Cross-sectional area increased in both R (17.0 ± 13.0%) and CT (8.8 ± 9.4%, p < 0.05). Pennation angle increased in CT (10.1 ± 12.9%) and R (18.6 ± 15.1%). These findings indicate that, although CT may limit MVIC development and delay early-phase RFD adaptations, it does not hinder explosive performance when resistance training is oriented toward rapid-strength development. Thus, CT can be effectively implemented in trained individuals when resistance training is periodized to emphasize neural-driven explosive or hypertrophy-related adaptations.