Physical Adaptations to High-Intensity Multimodal Training in Recreationally Active Adults: A Randomised Control Trial.

High-intensity multimodal training (HIMT), combines aerobic and resistance exercise within a single session, offering a time-efficient training mode. However, the efficacy of HIMT for physical adaptations compared to other combined training models (e.g., inter-session concurrent training [ISCT]) remains unclear. This two-arm parallel randomised controlled trial examined the physical adaptations of 7 weeks of HIMT compared to a matched active control (ISCT) in recreationally active adults. The HIMT group completed 4 × 45-min sessions/week integrating aerobic and resistance exercises. The ISCT group completed 2 × 45-min resistance sessions/week and 2 × 45-min aerobic sessions/week. Training intensity was prescribed at ≥ 7 RPE (CR-10) with weekly volume and exercise selection matched across groups. Maximal strength, aerobic capacity, anthropometry and body composition were assessed pre and post-intervention. Both HIMT (n = 38) and ISCT (n = 37) demonstrated small improvements in upper- and lower-body strength, peak oxygen uptake and maximum work rate (p < 0.05). Trivial but significant improvements were also observed in fat mass, body fat percentage, lean mass, waist circumference and waist-to-hip ratio (p < 0.05). A modest group × time interaction favoured ISCT for reducing body fat percentage (b = -0.628, 95% CI [-1.21 to -0.046], p = 0.035 and d = -0.082). Seven weeks of HIMT and ISCT improved muscular strength, aerobic fitness and body composition. Separating high-intensity aerobic and resistance sessions across days may offer a small advantage for reducing relative body fat. Longer interventions may be needed for greater adaptations. TRIAL REGISTRATION: ETH24-9364, ACTRN12624000556549, Protocol: available on the Open Science Framework.