Each year hundreds of claims are published regarding the ideal fat-burning exercise. Various products claim to be superior at utilizing fat and reducing inches. How can you distinguish between wishful thinking and the realities of exercise and fat burning? The following information will help you to dispel the misconceptions. The Secret: Total Calories Fat supplies a relatively large percentage of the energy requirements during prolonged low-intensity exercise (30-plus minutes at less than 50 percent aerobic capacity). But at this low intensity, fat (as well as carbohydrate) is burned at a relatively slow rate (approximately three to five kilocalories per minute). By contrast, higher-intensity aerobic exercise uses a smaller percentage of fat but results in a greater total calorie expenditure.

When total fat use is calculated, researchers have found that more total fat is burned at higher exercise intensities (70 to 75 percent of aerobic capacity), at least up to the highest intensity an exerciser can sustain without going to exhaustion. The selective use of fat as a fuel, specifically at lower intensities, does not translate into greater fat loss, regardless of how tempting it is to draw this conclusion. The more important focus with regard to energy production, or calories expended, is not the percentage of energy coming from fat, but rather the total volume of fat used and the total number of calories expended.

For Sedentary of Older Individuals
The faster you walk, step, dance, cycle or run, the more calories you use per minute. However, for those who have been sedentary, high-intensity exercise compromises the ability to sustain exercise for a long time. For that reason, lower-intensity exercise is more effective in the initial stages of training and is a prerequisite to higher calorie-burning intensities. In addition, older, sedentary individuals tend to rely more on carbohydrate utilization than do younger individuals. This does not imply that older people can't lose fat weight as a result of training. It does mean they may need to exercise at a lower relative intensity to keep going longer, thus enhancing duration and total calorie expenditure. Exercise training studies on an elderly population have demonstrated that over time the elderly can increase the ratio of fat to carbohydrate use.

Take-Home Lessons
To help you in your weight management and exercise efforts, use the following guidelines:

1.Exercise fuel utilization and post-exercise energy expenditure should not be primary considerations in fat weight control. The total amount of fat used, not the percentage of calories contributed by fat, is most important. Total calorie expenditure during exercise ultimately determines the amount of fat used.

2.The primary reason to use the aerobic energy system is to avoid fatigue so the exercise session can be sustained as long as possible. Using intervals (alternately speeding up and slowing down) potentially enables an exerciser to burn more total calories in a given session.

3.Because of the individual nature of exercise metabolism and the many factors involved, no single exercise/weight control prescription is ideal for everyone.

4.In general, the guidelines for becoming a "calorie-burning machine" include the following:

• Develop a reasonable level of cardiorespiratory fitness. (Exercise three to four times per week for 25 to 40 minutes at moderate intensities.)
• To increase the rate of fat loss, gradually increase exercise duration to 50 to 60-plus minutes at least three to five days per week and raise the intensity as high as you can safely sustain it.
• Try to include strength training twice a week to increase muscle mass.
• Allow at least six months to realize most physiological changes and an additional six to nine months for final adaptive changes in body composition.

Ralph LaForge, MS, is director of health promotion at the San Diego Cardiac Center Medical Group. Daniel Kosich, PhD, is president of EXERFIT Lifestyle Consulting and consulting senior director of professional development for IDEA.

This handout is a service of IDEA, the international association of fitness professionals, the leading organization serving personal trainers, exercise instructors and business operators.

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