Your body uses about 50 to 60 percent of the calories from fat during low- to moderate-intensity exercise, according to exercise physiologist William McArdle. The remainder of the calories comes from carbohydrates with a trace amount of protein. During high-intensity exercise, your body uses 15 to 30 percent of the calories from fat. However, the amount of calories you use is higher than during low-intensity exercise. In some cases, the net number of calories you burn from fat is higher during high-intensity exercise than low- to moderate-intensity exercise.
Fat-burning Zone
On most aerobic machines, there is a chart that indicates two heart-rate training zones -- the fat-burning zone and the cardio zone. The heart rate of the fat-burning zone falls between 50 to 70 percent, while the cardio zone is above 70 percent. Although a large percentage of calories come from fat, exercise physiologist Jason Karp, a contributing writer for IDEA Fitness Association, states that the number of calories burned is lower than at a higher-intensity aerobic exercise.
Calories Burned
According to McArdle, a 150 lb. man burns about 130 calories for 30 minutes of walking at a rate of 3 mph, which puts his aerobic exercise in a fat-burning zone. About 50 percent of his total calories come from fat, which is about 65 fat calories. If he runs for 30 minutes at a rate of 9 mph, he would burn about 440 calories. About 25 percent of his calories come from fat, which is 110 fat calories. High-intensity exercise burns more fat calories and net calories than the fat-burning zone.
EPOC
Your body continues to burn calories at a higher rate after exercise than before exercise. This condition is called excess post-exercise consumption, or EPOC, where your body requires oxygen at a higher rate after exercise, according to McArdle. If you exercise in the fat-burning zone, you burn fewer calories than someone who exercises at a higher intensity. During EPOC, your metabolism is elevated above your resting state for two to six hours after exercise. You can burn between 100 to 300 additional calories per day during rest.
Considerations
Aerobic exercise in the fat-burning zone is ideal for those who are new to exercise or are recovering from a cardiovascular disease. You can always increase the intensity under the supervision and guidance of an exercise physiologist, a physician or a qualified medical or fitness professional.
References
- IDEA Fitness Journal: Burning Fat: Myths and Facts
- "Exercise Physiology: Energy, Nutrition, and Human Performance"; William McArdle; 2003
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