Differential physiological adaptations and perceptual responses to high-intensity functional versus interval training in young adults with obesity: a randomized controlled trial

This study compared the effects of high-intensity functional training (HIFT) and high-intensity interval training (HIIT) on body composition, muscular strength, cardiorespiratory fitness, and exercise-related perceptual responses in insufficiently active young adults with obesity. Twenty-four participants were randomized to the CON, HIFT, and HIIT groups (n= 8 each); 22 completed the study and were included in the final analysis (CON, n= 8; HIFT, n= 7; HIIT, n= 7). Both exercise groups were prescribed three supervised sessions per week for 8 weeks. After baseline adjustment, HIIT showed significantly lower waist circumference (<i>P</i>< 0.01), hip circumference (<i>P</i>< 0.05), waist-to-hip ratio (<i>P</i>< 0.01), gynoid fat mass (FM) (<i>P</i>< 0.05), and leg FM (<i>P</i>< 0.05) than CON, whereas these measures did not differ significantly between HIIT and HIFT. No significant between-group differences were observed for whole-body FM, body fat percentage, or fat-free mass. After baseline adjustment, relative peak oxygen consumption (both <i>P</i>< 0.05) and the first ventilatory threshold (HIFT, <i>P</i>< 0.05; HIIT, <i>P</i>< 0.01) were significantly higher in both HIFT and HIIT than in CON, with no significant differences between exercise groups. Baseline-adjusted absolute upper-body strength was higher in HIFT than HIIT (<i>P</i>< 0.05), whereas lower-body strength did not differ. First-session-adjusted affective valence and exercise enjoyment were higher in HIFT than HIIT (both <i>P</i>< 0.05), whereas perceived exertion and heart rate did not differ. These findings indicate that both HIFT and HIIT improved aerobic fitness, while HIFT showed higher postintervention upper-body strength and more favorable affective and enjoyment responses than HIIT. These distinct profiles may inform individualized exercise prescription by considering both training outcomes and exercise experience in young adults with obesity.