Energy metabolism in infants and children.

Energy is used continuously in the body and is fundamental to physiologic processes. Requirements of individuals vary in relation to a wide variety of factors, making energy metabolism an issue of great importance to the pediatrician. Techniques are available for short- and long-term measurements of energy expenditure, which serve different purposes. The principal techniques are suitable for the age range from birth to adolescence. The theory of energy metabolism is briefly discussed, including a summary of the different working definitions. The principles and practicalities of classical indirect calorimetry, the doubly labeled water method, the bicarbonate method, and heart rate monitoring are then described.