basal metabolic rate

basal metabolic rate (BMR) The energy cost of maintaining the metabolic integrity of the body, nerve and muscle tone, respiration, and circulation. It depends on the amount of metabolically active body tissue, and hence can be calculated from body weight, using different factors for males and females, and at different ages. For children the BMR also includes the energy cost of growth. Experimentally, BMR is measured as the heat output from the body, or the rate of oxygen consumption, under strictly standardized conditions, 12–14 hours after the last meal, completely at rest (but not asleep) and at an environmental temperature of 26–30 °C, to ensure thermal neutrality. Measurement of metabolic rate under less rigorously controlled conditions gives the resting metabolic rate (RMR).

For people with a sedentary lifestyle and relatively low physical activity, BMR accounts for about 70–80% of total energy expenditure. The energy costs of different activities are generally expressed as the physical activity ratio, the ratio of energy expenditure in the activity to BMR.