Twenty-four-hour energy expenditure and its components in prepubertal children as determined by whole-body indirect calorimetry and compared with young adults.

The aim of the present study was to compare total daily and circadian variations of energy expenditure (EE) in 21 prepubescent 10-y-old children (12 boys and 9 girls) and 18 23-y-old adults (9 men and 9 women) under the same conditions by using two large calorimetric chambers. The volunteers followed similar activity programs with four periods of exercise on a cyclergometer. Total daily and sleeping EE adjusted for differences in fat-free mass (FFM) and age were significantly higher in children than in adults by 35% and 27%, respectively (P < 0.001). EE during sleep decreased by 2% per hour in both age groups. Heart rate was significantly higher in girls than in boys. The energy cost of cycling, adjusted for differences in FFM and external mechanical power, was not significantly different in children and adults. The differences in EE between children and adults may partly result from a higher proportion of internal organs in the FFM.