Excerpt from: Burning Calories with Exercise

People choose to exercise for a variety of reasons: to feel more energetic during the day, because they enjoy the challenge of becoming fit, to get the health benefits, and because they want to look good. These are all fine motivations to get you started and usually help somewhat to keep you going. But on a day-to-day basis, most of us want the gratification of knowing how many calories we burned with that agony and sweat.

Metabolism at Rest and with Exercise

A completely sedentary person burns between 800 and 1,500 food calories per day, creating the energy for the daily obligatory functions of all the cells in the body. This is called our basal metabolic rate, or BMR. A food calorie is actually equal to 1,000 chemical calories; that is why the abbreviation for a food calorie is Kcal.

Most types of cells in the body have a limited capacity to increase energy expenditure because the demands for energy are just not there. These cells might need to work a little harder if they need to fight an infection or correct a chemical imbalance, for example. On the other hand, muscle cells have a much greater ability to cycle Adenosine Triphosphate and thereby increase energy expenditure and calorie burning.

Howard LeWine, M.D., is chief editor of Internet publishing, Harvard Health Publications. He is a clinical instructor of medicine at Harvard Medical School and Brigham and Women's Hospital. Dr. LeWine has been a primary care internist and teacher of internal medicine since 1978.