Abstract
BACKGROUND: This study aims to investigate the effects of 8 weeks equivalent-volume resistance training (RT) and high-intensity interval training (HIIT) performed within same session or alternated weekly on body composition, cardiorespiratory function, and muscular fitness in young adult males. METHODS: Twenty-three young adult males were randomly assigned to either the A group (RT and HIIT performed within the same session, n = 11) or the B group (RT and HIIT were alternated weekly, n = 12). Body composition, cardiorespiratory function, and muscular fitness were assessed at baseline (T1), the fifth week (T2), and the ninth week (T3). Baseline differences and training effects were analyzed using independent sample t-tests and repeated measures ANOVA, respectively. RESULTS: No significant group differences were found at baseline (P > 0.05). Post-intervention, body fat percentage, skeletal muscle mass, and thickness significantly improved over time (P < 0.05), but no significant group or interaction effects. Maximum power output significantly increased at T2 and T3 compared to T1 (P < 0.05), while VO₂max, METs, and Maximum Minute Ventilation significantly increased only at T3 compared to T1 (P < 0.05), with no significant group or interaction effects. Both groups showed significant improvements in maximal strength during the intervention (P < 0.05). Endurance repetitions, particularly in the squat exercise, showed significant improvement initially (P < 0.05), followed by a downward trend, and no significant group or interaction effects were found. CONCLUSIONS: Concurrent training, whether performed within the same session or alternated weekly, elicited comparable improvements in body composition, cardiorespiratory, and muscular outcomes in young adult males. Both arrangements promoted beneficial adaptations, indicating flexibility in concurrent training design. TRIAL REGISTRATION: The study was retrospectively registered on 24 June 2025 at www.chictr.org.cn with identification number ChiCTR2500104848.