Effectiveness of combined exercise intervention on sedentary behaviour patterns, body composition, and cardiometabolic health among middle-aged adults

Abstract Objectives Sedentary behaviour (SB) presents a health risk independent of age, sex, and clinical disease status, while exercise interventions have been shown to potentially reduce sitting time. This study examined the effectiveness of a combined moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) program on SB patterns, body composition, and exercise performance among middle-aged adults. Design Quasi-experimental intervention study without a control group. Methods Thirty-two adults (50% women, aged 38.25 ± 8.27) completed a 7-week program with three weekly sessions of cycling (MICT) and rowing (HIIT). Baseline accelerometer data were used to classify participants into Breaker (≤ 15 min sedentary bouts), Intermediator (15–20 min), and Prolonger (≥ 20 min) groups. Paired-sample t-tests and repeated measures ANOVAs assessed changes, with effect sizes reported as η²p and Cohen’s d. Results After intervention, the Breaker group showed increased breaks per sedentary hour and greater time in moderate-to-vigorous physical activity (MVPA) compared with Intermediator and Prolonger groups (all p < 0.05). Breakers also reduced body fat percentage, waist–hip ratio, and total cholesterol (p < 0.05–0.01), alongside improved maximum cycling (p = 0.001) and rowing load (p = 0.02). The Intermediator group demonstrated a reduction in body fat percentage (p = 0.005). However, mean sedentary bout duration, reflecting sedentary behaviour accumulation patterns, did not change significantly in any group (p > 0.05). Conclusions The 7-week combined exercise training improved body composition, cardiometabolic profile, and exercise performance but did not alter sedentary behaviour patterns in middle-aged adults. Nonetheless, individuals with shorter sedentary bouts experienced significant health and performance benefits than those with prolonged bouts, suggesting that baseline sedentary profiles may moderate responsiveness to exercise interventions.