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

Background: 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. Methods: 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. Results: There were no significant changes in RMR (kcal/day) between exercise groups vs. controls ( p  > 0.05). All exercise groups decreased visceral fat (-0.2 ± 0.02 kg; p  < 0.05) compared to control. Increases in fat-free mass (FFM) were only seen in the combined group (2.3 ± 0.4 kg; p  < 0.05), whereas increases in skeletal muscle mass were observed in both resistance (1.2 ± 0.2 kg; p  < 0.05) and combined (1.5 ± 0.3 kg; p  < 0.05) groups vs. control. Change in FFM, but not fat mass (FM), visceral fat, or skeletal muscle mass ( p  > 0.05), was a significant determinant of changes in RMR, independent of exercise modality ( p  = 0.04). Conclusion: 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.