Each calorimeter precisely measures the oxygen uptake (VO2)and carbon dioxide production (VCO2) of research subjects from childhood through adulthood, including pregnant and lactating women, in a controlled environmental chamber. The VO2 and VCO2 (in liters per minute) are measured in real time and are converted into kilocalories per minute to provide measurements in sleeping metabolic rate, basal metabolic rate, 24 hour total energy expenditure, and exercise energy expenditure (e.g. biking, walking, running, aerobics, or video game play). All research volunteers are closely monitored during the entire stay in the calorimeter whether short or long term. Heart rate, activity, body temperature, blood and urine collection are also available to be measured during any calorimeter study.