Final answer:
Basal Metabolic Rate (BMR) is the energy expenditure of a body at rest in a postabsorptive state. It comprises about 70% of total daily energy usage and is influenced by factors such as muscle mass, with leaner individuals typically having higher BMRs.
Step-by-step explanation:
The Basal Metabolic Rate (BMR) is defined as the rate at which your body uses energy while at rest in a neutrally temperate environment, during the postabsorptive state (meaning that the digestive system is inactive, which requires about 12 hours after the last meal). It represents the minimum amount of energy needed to keep your body functioning, including breathing and keeping your heart beating. BMR accounts for about 70 percent of your daily energy expenditure, with the rest being physical activity (around 20 percent) and thermoregulation or temperature control (about 10 percent).
BMR is not the energy burned during exercise; instead, it measures the energy expended for normal, basic daily bodily functions. It's affected by several factors including age, gender, body weight, and muscle mass. Notably, muscle mass burns more calories than body fat, so a person with more lean muscle mass typically has a higher BMR. As such, BMR is inversely related to body fatness, meaning that people with higher body fat percentages tend to have lower BMRs.