Fat burning-myths and truths.

If you have ever worked out at a gym you may have noticed treadmill ergometer notations of "fat burning zone" in the area of 65% of maximum heart rate. And if your workout is generally at a higher intensity, you may have wondered whether you may be running too fast to burn fat. Nothing could be more ridiculous.

The idea that low intensity aerobic activities are better for fat burning than high intensity exercise was given credence when several research studies indicated that low intensity activities burned a greater percentage of fat calories than high intensity activities. These studies validated that the body prefers to use fat as its fuel source during low-intensity exercise. This equates roughly to 60% of the total calories burned, as opposed to about 40% from high intensity exercise.

While this fuel preference is true, it is misguided to believe that the selective use of fat for fuel will translate into burning more total fat calories. High-intensity exercise burns more fat calories, as well as carbohydrate calories, on an absolute basis than lower intensity activities. Because an important aspect of training intensity is the total amount of fat calories burned--not the percentage from fat--higher intensity exercise has the decided edge. Further, reduced body fat results from total calorie deficits--that is, burning more calories than you take in from your foods.

When you consider the time-related efficiency of training, low-intensity exercise provides a very poor cost/benefit dividend. You bum about the same number of calories walking a mile as running a mile--it just takes a bit longer walking them off. If fat burning is one of your aims, performing cardiovascular exercise at a higher intensity gives you more bang for your workout buck.

(Brad Schoenfeld, C.P.T., is the author of Sculpting Her Body Perfect, 1999, Human Kinetics, 195 pp. Champaign, IL. Visit his Web site at www.highnrg.com for other fitness tips.)