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.