Background The relationship between the frequency of high-intensity interval training (HIIT) and the resultant adaptations is largely unclear.
Purpose This study compared the effects of different frequencies of HIIT with those of moderate-intensity continuous training (MICT) on body composition in overweight or obese adults.
Methods Fifty-six overweight or obese (BMI: 26.4±2.9) men aged between 18 and 30 years (age: 22.8±3.1) were randomly assigned to the following groups: no-intervention control (CON; n=14), MICT performed thrice weekly (MICT×3/wk; n=9), HIIT performed thrice weekly (HIIT×3/wk; n=14), HIIT performed twice weekly (HIIT×2/wk; n=10), and HIIT performed once weekly (HIIT×1/wk; n=9). Each HIIT session consisted of 12×1-min bouts at 90% heart rate reserve (HRR), interspersed with 11×1-min bouts at 70% HRR. Aerobic capacity, body composition, resting heart rate, vascular function, insulin resistance, and biomarkers of metabolic syndrome risk factor were examined at baseline, after 4 weeks and after 8 weeks of intervention.
Results Aerobic capacity and percent fat-free mass significantly increased in all exercise groups compared with those in the CON group (CON vs. all exercise groups: p<0.05), whereas body fat mass and systolic blood pressure significantly decreased after 8 weeks of intervention in all exercise groups compared with those in the CON group (CON vs. all exercise groups: p<0.05). Body fat mass significantly decreased after 4 weeks in all HIITgroups compared with those in the CON group (CON vs. all HIIT groups: p<0.05) but not in the MICT×3/wk group.
Conclusion These novel results demonstrated that performing HIIT once weekly, even with a lower weekly volume of exercise, improved cardiorespiratory fitness, body composition, and blood pressure in overweight/obese adults. Low-frequency HIIT might be a feasible and effective strategy for the prescription of an initial exercise program for inactive, overweight or obese young men.