Physical activity related energy expenditure in children by doubly labeled water as compared with the Caltrac accelerometer

OBJECTIVE: The objective of this study was to determine whether the Caltrac accelerometer was a meaningful predictor of physical activity related energy expenditure (AEE) in free-living, pre-adolescent children. SUBJECTS: The sample consisted of 31 children (14 girls, 17 boys; 22 Caucasian, 9 Mohawk) with a mean age of 8.3 (+/- 2.0) y. MEASUREMENTS: AEE was measured by subtracting postprandial resting metabolic rate (RMR), measured via indirect calorimetry, from total daily energy expenditure (TDEE), derived from the doubly labeled water (DLW) method. Average daily activity counts (AC) were measured using a Caltrac accelerometer, which was worn for three days, two weekdays and one weekend day, within the DLW dosing period. RESULTS: AEE was related to gender (r=0.42, P=0.02), fat mass (FM, r=0.32; P=0.07), and fat free mass (FFM, r=0.32; P=0.07), but not to AC (r=-0.09; P=0.63), After adjusting for gender, race, FM and FFM using multiple correlation regression analysis (R=0.53), AC did not significantly increase the amount of variation explained in AEE. An estimate of the calories expended in physical activity was derived from AC using a formula developed by Sallis et al. This estimate was significantly higher than AEE (956 kcal/d vs 469 kcal/d, respectively, t=5.9, P < 0.001). CONCLUSION: The Caltrac was not a meaningful predictor of AEE in our sample. The caloric estimates of energy expended in physical activity derived from the Caltrac AC, were significantly higher in comparison with measured AEE in these free-living children.