Basal metabolism is the energy (calories) a body burns when completely at rest. Basal metabolism rate (BMR) is the level of energy needed to keep involuntary body processes going.
These processes include heartbeat, breathing, generating body heat, perspiring to keep cool, and transmitting messages to the brain.
For a sedentary person, BMR accounts for about 60-70 percent of daily energy expenditure; the remaining 30-40 percent is from physical activity and from body heat produced after a eating a meal.
Physical activity is responsible for as much as 50-60 percent of the total energy expenditure in people who include frequent aerobic activity into their lifestyles.
Reprinted from the International Food Information Council Foundation