Relative effects of interval training with different intensities and interval structures on cardiometabolic health...

Sedentary behavior is closely associated with early cardiometabolic dysfunction in young populations. However, under approximately matched prescribed active-work-load conditions, it remains unclear whether interval-training protocols differing in exercise intensity and interval structure induce different cardiometabolic responses in sedentary individuals.

Forty sedentary young males (22.85 ± 0.22 years) were randomized to four 8-week interval-training protocols: moderate-intensity short-interval group (MISI: 60%-70% maximal heart rate (HRmax), 60 s work/30 s rest), moderate-intensity long-interval group (MILI: 60%-70% HRmax, 60 s work/120 s rest), high-intensity short-interval group (HISI: 85%-95% HRmax, 30 s work/30 s rest), and high-intensity long-interval group (HILI: 85%-95% HRmax, 30 s work/120 s rest) (n = 10 per group). Two-way repeated-measures ANOVA was used to compare pre-post changes in body fat percentage (BFP), skeletal muscle mass (SMM), visceral fat area (VFA), basal metabolic rate (BMR), total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C).

BFP, VFA, TC, and TG decreased significantly in all four protocols, whereas SMM and HDL-C increased significantly. BMR increased significantly in MILI, HISI, and HILI, but not in MISI. VFA decreased in all groups, and post-intervention VFA was significantly lower in HISI than in MILI (p < 0.05). TG decreased in all groups, and post-intervention TG was significantly lower in HISI than in MISI (p < 0.05). Improvements in LDL-C were observed only in the high-intensity training groups (p < 0.05). HDL-C increased significantly in all four protocols, and post-intervention HDL-C was significantly higher in HISI and HILI than in MILI.

Eight weeks of interval training was associated with favorable changes in selected body composition and lipid-profile indicators in sedentary young males. Compared with the moderate-intensity protocols, the high-intensity protocols showed more favorable changes in selected outcomes, including VFA, TG, and LDL-C. The HISI protocol may represent a promising option for improving selected cardiometabolic risk indicators related to visceral adiposity and lipid metabolism in sedentary young males; however, these findings should be interpreted cautiously given the small sample size, the absence of a non-exercise control group, and the lack of direct physiological-load measurements.