The effects of HIIT and MICT on body fat composition and cardiopulmonary fitness in adults: a meta-analysis of randomized controlled trials

HIIT is a time-efficient aerobic exercise with potential for obesity prevention and control, as it achieves comparable or superior effects to traditional exercise in a shorter duration. This meta-analysis examines the differential effects of HIIT and MICT on body fat composition and cardiorespiratory fitness in adults, providing evidence for optimized exercise prescriptions. Searched PubMed, Embase, Cochrane Library, and Web of Science for RCTs assessing HIIT cycling’s effects on fat reduction and cardiorespiratory fitness. Data were pooled using SMD in Review Manager 5.4 and Stata 18. Heterogeneity was evaluated via the I 2 statistic, with subgroup analyses stratified by population (disease, obese, sedentary). Nineteen RCTs were included. Compared to MICT, HIIT significantly reduced BMI in obese populations (SMD = -0.59 kg/m 2 , 95% CI: -0.84 to -0.34, P < 0.001), but slightly increased BMI in disease populations (SMD = 0.40 kg/m 2 , 95% CI: 0.03 to 0.77, P = 0.042). For cardiorespiratory fitness, HIIT outperformed MICT in improving VO₂peak in obese populations (SMD = 0.23 ml·kg⁻ 1 ·min⁻ 1 , 95% CI: 0.01 to 0.45, P = 0.041) and sedentary populations (SMD = 6.21 ml·kg⁻ 1 ·min⁻ 1 , 95% CI: 4.68 to 7.74, P < 0.001). HIIT cycling demonstrates comparable efficacy to MICT for improving body composition, including body fat percentage, fat mass, and lean body mass in adults, while outperforming MICT in reducing BMI among obese individuals and enhancing cardiorespiratory fitness VO 2 peak across obese and sedentary populations.