Fat is broken down aerobically. Once aerobic exercise is no longer performed and anaerobic exercise begins, the body will start to retrieve glucose molecules from other areas of the body for immediate energy needs. Anaerobic exercise initially affects skeletal muscle tissue. The muscle tissue can no longer completely contract when there is an inadequate oxygen supply, which decreases ATP production. The goal of exercise is to utilize the readily available glucose molecules, and then to utilize fat molecules stored in adipose tissue to increase the body's metabolic rate.
Metabolic rate is the rate at which heat is produced as the body breaks down ingested foods.
Some energy not used by the cell is given off as heat. To determine the amount of heat given off by food substances as they are broken down, scientists who research this phenomenon actually burn food to measure the amount of heat produced. The heat produced is measured as temperature in units known as calories. A calorie is the amount of energy, in the form of heat, that will raise 1 gram of water 1E Celsius. To determine BMR, nutritionists have derived gender specific formulae.