Cardiorespiratory and Hematological Responses to High-Intensity Interval Training in Adolescent Girls With Overweight...

This randomized controlled trial examined the effects of a 10-week high-intensity interval training (HIIT) program on physiological and hematological outcomes in 28 adolescent girls with overweight or obesity. Participants were randomly assigned to a HIIT group or a control group. The HIIT protocol comprised 4 sets of 6 × 15-s bouts at 90%-105% of maximal aerobic speed (MAS), interspersed with 15-s active recovery at 50% MAS, performed three times per week. Significant group×time interactions were observed for body composition, aerobic capacity, maximal heart rate (HRmax), erythrocytes, hemoglobin, hematocrit, creatine kinase (CK), and lactate dehydrogenase (LDH). Between-group comparisons showed greater improvements in body mass, body fat, waist circumference, MAS, estimated VO₂max, and plasma volume in the HIIT group compared with controls, though not all differences reached statistical significance. Within-group analysis in the HIIT group revealed reductions in body mass (p < 0.001, d = 0.37), body fat (p = 0.001, d = 0.78), waist circumference (p < 0.001, d = 0.54), HRmax (p = 0.020, d = 0.88), erythrocytes (p = 0.007, d = 0.46), hemoglobin (p = 0.019, d = 0.84), hematocrit (p = 0.004, d = 0.34), CK (p = 0.049, d = 0.29), and LDH (p = 0.032, d = 0.41), alongside increases in MAS (p = 0.007, d = 0.64) and estimated VO₂max (p = 0.007, d = 0.64). Plasma volume variation was also higher in the HIIT group. Overall, a 10-week HIIT intervention enhanced body composition, plasma volume, and cardiorespiratory fitness, while reducing markers of muscular and metabolic stress. These results indicate that HIIT is a feasible and effective approach for improving physiological and metabolic health in adolescent girls with overweight or obesity, supporting its potential as a targeted exercise strategy in this population.