Author(s): SHARP, T., HIGHAM, S., SLATTERY, K., MARQUES, C.D., COUTTS, A.J., MAGEROPOLOUS, N., NOVAK, A., BREWER, M., WALLACE, L., Institution: UNIVERSITY OF TECHNOLOGY SYDNEY FACULTY OF HEALTH, Country: AUSTRALIA, Abstract-ID: 1259

INTRODUCTION:
High-Intensity Multimodal Training (HIMT) is promoted as a time‑efficient method for meeting physical activity guidelines by combining high-intensity aerobic and resistance exercise within a single session. However, poor standardisation in prescription and reporting has limited comparisons with other combined training modes (e.g., Inter‑Session Concurrent Training [ISCT]). This study examined the feasibility, acceptability, physical and biochemical outcomes of a 7‑week HIMT intervention compared to an active matched ISCT control, delivered across three community sites.
METHODS:
A two‑arm parallel randomised controlled trial was conducted. Recreationally active adults were allocated to HIMT (4 × 45‑min sessions/week of combined aerobic and resistance exercise in a circuit format) or ISCT (2 × 45‑min resistance circuits + 2 × 45‑min aerobic circuits/week). Training volume, session duration, exercise intensity (RPE ≥ 7/10 [CR‑10]) and exercise selection were matched between groups. Feasibility and acceptability were evaluated using a convergent mixed-methods approach, integrating qualitative data (thematic content analysis of open-ended survey responses) and quantitative data (Likert scale scores, training session intensity, retention). Physical outcomes (maximal strength, aerobic capacity, anthropometry, body composition) and acute and chronic exercise-induced biochemical responses (cortisol, testosterone, growth hormone) were assessed using linear mixed effect models, pre to-post intervention. A priori sample size n = 47 (α=0.05, power =0.80, f=0.42).
RESULTS:
79 participants were randomised and 75 completed post-testing (HIMT n=39, ISCT n=36). Participants attended 91.4% of sessions, with an average training S-RPE of 7.47 ± 1.40. The program was safe, tolerable and enjoyable. Both groups showed small within‑group improvements in lower and upper‑body strength, peak oxygen uptake, and maximum work rate, alongside trivial improvements in fat mass, body fat percentage, lean mass, and waist circumference (p<0.05). A modest group × time interaction favoured ISCT for reduced body fat percentage (b=-0.628, 95% CI [-1.21 to -0.046], p=0.035, d=−0.082). An attenuated exercise-induced growth hormone response was observed following 7-weeks of ISCT compared to HIMT in females only (b= -8.135, 95% CI [-14.737 to -1.533], p=0.017, d=-0.836). Further expected biochemical responses were observed in both groups.
CONCLUSION:
HIMT is a safe, feasible and acceptable intervention for recreationally active adults, eliciting meaningful physical adaptations over 7-weeks. Both training modes produced expected biochemical adaptations, with more pronounced exercise-induced hormonal responses in females. These findings support the use of HIMT to promote structured exercise engagement and physical fitness, while advancing community based prescription standards for combined training. This may inform future implementation of scalable, time efficient models to promote population health and fitness.