Resting metabolic rate and postprandial thermogenesis in highly trained and untrained males

The purpose was to compare the resting metabolic rate (RMR) and thermic effect of a meal (TEM) in exercise trained and untrained individuals. TEM was measured for 180 min and blood samples were drawn for determination of plasma insulin, glucose, triiodothyronine (T₃) and thyroxine (T₄). Results indicated that highly trained subjects demonstrated a higher RMR when expressed in kilocalories per minute and per kilogram fat-free weight (FFW) than do untrained subjects. TEM was lower in trained (55.8 ± 3.1 kcal) than in untrained (79.2 ± 3.7 kcal) subjects. No differences were noted between the two groups for plasma levels of insulin, glucose, T₃, and T₄. A higher RMR and lower TEM persisted in the trained group compared with the untrained group when groups were matched for FFW and body fat. Results support a higher RMR in endurance athletes and a lower TEM even after control is exerted over differences in body composition.