Resting energy expenditure

Indirect calorimetry is the study or clinical use of the relationship between respirometry and bioenergetics, where measurements of the rates of oxygen consumption (VO₂) and the generation of waste products such as carbon dioxide, metabolic water, and less often urea are used to quantify rates of resting energy expenditure. These parameters approximate direct calorimetry measurements of body heat generation to about 98%, and they are the ones most commonly used to represent RMR, expressed as the ratio between i) energy and ii) the time frame of the measurement. For example, following analysis of oxygen consumption of a human subject, if 5.5 kilocalories of energy were estimated during a 5-minute measurement from a rested individual, then the resting metabolic rate equals = 1.1 kcal/min rate. Unlike some related measurements (e.g. METs), RMR itself is not referenced to body mass and has no bearing on the rate of cellular energy metabolism itself.