Fat Burning: High vs. Low

Q: Will people lose body fat more efficiently by performing their aerobic workouts at a low, rather than  a high, intensity?

A: Unfortunately, many fitness professionals advocate low-intensity workouts as a way to maximize fat burning. The theory is that low-intensity aerobic exercise training will allow the body to use more fat as the energy source, thereby accelerating the loss of body fat.

While it is true that a greater percentage of calories burned during low-intensity exercise come from fat (about 60 percent as opposed to about 35 percent from high-intensity exercise workouts), high-intensity exercise still burns more calories from fat in the final analysis. Thirty minutes of low-intensity exercise (e.g., 50 percent of maxžmal exercise capacity) burns approximately 200 Calories, and about 120 of those come from fat (i.e., 60 percent). However, exercising for the same amount of time at a high intensity (e.g., 75 percent of maximal exercise capacity) burns approximately 400 calories. At the 35 percent fat utilization figure, 140 Calories burned come from stored fat.

The more vigorous exercise burns both more total and fat calories, but the milder has its benefits as well. For example, many overweight people find lower-intensity exercise to be more comfortable and, therefore, are more willing to engage in such workouts. And low-intensity workouts do promote weight and fat loss. They just have to be performed for longer durations.

Low-intensity exercise, however, is not a better or more effective way to lose weight than more intense physical activity. It really doesn’t matter which substrate your clients burn when they exercise. Expending energy (i.e., burning calories) is what’s important The bottom line is that your clients will lose weight and body fat when they expend more calories than they consume — not because they burn fat (or anything else) when they exercise.

Q: Does stepping backward on a stair climbing machine cause greater  involvement of the gluteals?

A: Retrograde stair climbing (e.g., stepping backward) reduces lumbar flexion (i.e., forward body lean), thus promoting a more erect and improved body posture during exercise. Many individuals erroneously believe that retrograde stair climbing places a greater emphasis on the gluteal muscles, resulting in specific firming and toning of the buttocks.

However, EMG (electromyographic) studies conducted by the Department of Physical Therapy at Iowa University have revealed that retrograde stair climbing places slightly greater (when compared to forward stair climbing) emphasis on the quadriceps (the large group of muscles located on the front of the thigh) and the hamstrings (muscles on the back of the thigh), while slightly reducing the emphasis placed on the gluteals and strocnernius (calves). In our opinion, using a stepping machine in the retrograde position is generally not justified due to the awkwardness associated with exercising in this manner. FM Cedric X. Bryant, Ph.D., FACSM, is director of sports medicine at StairMaster Sports/Medical Products L.P., Kirkland, Wash., and James A. Peterson, Ph.D., FACSM, is a sports medicine specialist residing in Mesa, Ariz. Both Bryant and Peterson are former faculty members in the physical education department at the United States Military Academy at West Point.


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