Effects of Exercise on Resting Metabolic Rate in Adolescents with Overweight and Obesity.

We examined the effects of exercise training on resting metabolic rate (RMR), and whether changes in body composition are associated with changes in RMR in adolescents with overweight and obesity. One hundred forty adolescents (12-18 years, BMI ≥85th percentile) participated in randomized exercise trials (3-6 months) at UPMC Children's Hospital of Pittsburgh (18 control, 51 aerobic, 50 resistance, and 21 combined aerobic and resistance exercise). All participants had RMR assessments by indirect calorimetry after a 10-12 hour overnight fast, and body composition by magnetic resonance imaging and dual-energy X-ray absorptiometry. There were no significant changes in RMR (kcal/day) between exercise groups vs. controls ( > 0.05). All exercise groups decreased visceral fat (-0.2 ± 0.02 kg;  < 0.05) compared to control. Increases in fat-free mass (FFM) were only seen in the combined group (2.3 ± 0.4 kg;  < 0.05), whereas increases in skeletal muscle mass were observed in both resistance (1.2 ± 0.2 kg;  < 0.05) and combined (1.5 ± 0.3 kg;  < 0.05) groups vs. control. Change in FFM, but not fat mass (FM), visceral fat, or skeletal muscle mass ( > 0.05), was a significant determinant of changes in RMR, independent of exercise modality ( = 0.04). Although exercise modality was not associated with changes in RMR, change in FFM, but not skeletal muscle or FM, was a significant correlate of changes in RMR in adolescents with overweight and obesity. Clinicaltrials.gov registration numbers: NCT00739180, NCT01323088, NCT01938950.