Aerobic fitness and resting energy expenditure in young adult males.

Ambiguous findings have been reported in previous studies regarding the relationships among aerobic fitness, resting metabolic rate (RMR), and the thermic effect of a meal (TEM). We reexamined the association among these variables in young nonobese men who exhibited a wide range of aerobic fitness levels. RMR was measured after an overnight fast and TEM was assessed for three hours after ingestion of a liquid meal. Preprandial and postprandial plasma levels of insulin, glucose, and thyroid hormones (total T3 and T4) were measured. Daily energy intake was estimated from three-day food diaries, body composition from underwater weighing, and aerobic fitness from a test of VO2 max. Data were analyzed with linear and curvilinear regression analysis, as well as with ANOVA to test for differences among subjects classified by fitness level (ie, untrained, moderately, and highly trained). A significant correlation was found between RMR and VO2 max (r = .77, P less than .01). RMR adjusted for body weight and FFW was higher in highly trained men when compared to moderately and untrained individuals. However, a curvilinear relationship was found between TEM and VO2 max (P less than .05). Subjects who exhibited moderate levels of fitness showed the highest TEM, whereas a lower TEM was noted in untrained and highly trained men. These findings were observed in the absence of differences in plasma concentrations of total T3 and T4 among fitness levels. These findings suggest that highly trained men have a high RMR adjusted for their metabolic size.(ABSTRACT TRUNCATED AT 250 WORDS)