Resting Metabolic Rate (RMR) measures the number of calories your body requires to maintain itself at rest. These calories are expended on bodily functions such as breathing and heartbeat. Resting Metabolic Rate varies with age and body composition. A human body doesn't require any energy to store fat, but it does for muscle. That.s why most diets fail. Abrupt reduction in calorie intake leads to muscle and fat realignment. The dieter quickly loses weight, muscle and fat. When normal consumption is resumed the weight quickly rebounds because the body is now burning fewer calories to sustain itself.