Vo2max Is Associated With Energy Expenditure Measures, Including Diet Induced Thermogenesis, Under Sedentary Conditions

Low cardiorespiratory fitness predicts subsequent weight gain independently of physical activity. However, the physiological mechanisms underlying this relationship have not been fully explained. One hypothesis is that VO2max is related to measures of energy expenditure, in particular diet induced thermogenesis. Results from previous studies exploring these associations have been mixed. However, these studies may have been limited by methodological issues regarding the adjustment for energy expenditure (EE) by confounding factors and small sample size. PURPOSE: To determine the association between VO2max and measures of 24-h thermogenesis under predominantly sedentary condition and in particular awake fed thermogenesis (AFT) a measure of diet induced thermogenesis. METHODS: Two hundred twenty-nine American Indians from the southwest (132 men, 97 women) had measures of body composition by hydrodensitometry, resting metabolic rate (RMR) by the ventilated hood method, and then performed the intermittent treadmill run test for assessment of VO2max. On a separate day, they spent 24 hours in a whole-room calorimeter for assessment of 24-h EE, AFT, sleeping metabolic rate (SMR), and spontaneous physical activity (SPA) by radar system. As we have reported previously, AFT was calculated as the intercept of EE vs. SPA at zero activity minus SMR. RESULTS: After adjustment for fat free mass, fat mass, age and sex, multiple regression analysis showed that a higher VO2max (L/min) was associated with a higher RMR (beta = 45.9 kcal/ day per L/min, standardized beta = 0.184, p = 0.010, n = 181) and 24-h EE (beta = 62.1, standardized beta = 0.125, p = 0.028, n = 229) and including additional adjustment for energy intake higher AFT (beta = 65.8, standardized beta = 0.334, p = 0.012, n = 179). Neither SMR (p = 0.64) nor SPA (p = 0.80) were associated with VO2max. CONCLUSION: VO2max was associated with RMR, AFT and 24-h EE. In particular the association with AFT indicates a possible common mechanism regulating both processes and that the protective effect of higher VO2max on weight change reflect its association with measure of 24-h thermogenesis.