In obese adolescent females, 12 weeks of high-intensity interval training at 100% maximal aerobic speed performed three times per week results in greater reductions in body mass, body fat percentage, and waist circumference compared to moderate-intensity interval training at 80% maximal aerobic speed, with effect sizes of 0.67–0.76 for body composition changes.

High-intensity exercise burns more energy during and after workouts, which shrinks fat cells. Smaller fat cells release less of a hormone that signals fullness, which helps the body keep burning fat. The body also gets better at using sugar from the blood, so the pancreas doesn't have to work as hard. Losing weight makes movement easier, so the heart doesn't have to pump as hard, and the person feels less tired during activity. All these changes work together to remove more fat from the body.