the difference between the fat-burning mode and the cardio mode on the machines at the gym

Q. What's the difference between the fat-burning mode and the cardio mode on the machines at the gym?

There are problems with the fat burning option on the cardio machines, and it really ought to be eliminated.

The idea behind the fat burning option is this: Because fat is denser than carbohydrate, it requires more oxygen to burn. So, to maximize the percentage of fat you burn, compared to carbohydrate, the fat-burning mode would have you work out at a pace at which your body can deliver lots of oxygen to your muscles. That generally means a slow pace, to keep you from getting breathless.

The problem is that when you exercise at a slower speed, you burn fewer total calories -- from both carbohydrate and fat -- because you simply don't do as much work. Further, the way to get aerobically fit is to get your heart rate into the training range (usually 60% to 85% of your maximum heart rate), which is hard to do at slower speeds. And fitness is ultimately what you're after, whether your goals are better health, burning calories, or improving heart and lung capacity.

The bottom line is that the fat burning mode probably won't be intense enough to maximize total calorie- or fat-burning, or to help you increase or maintain optimum fitness levels. Use the cardio mode to maximize your exercise benefits.

Q. What is basal metabolic rate?

Basal metabolic rate (BMR) is the rate at which your body burns calories just to sustain life. For most people, that's roughly 50 to 80 calories per hour, or 1,200 to 1,920 calories per day. Exactly what your BMR is depends on genetics, your muscle mass, and other factors.

Of course, you burn more calories when you exercise -- or just go about the activities of daily life. For example, if you work out at the gym for 60 minutes and burn 400 calories, that comes in addition to whatever your BMR burns up. (If you walk home from the gym instead of driving, you'll burn even more!) At the end of the day, if your total energy expenditure is greater than the number of calories you've eaten, you'll lose weight.

SOURCE: WebMD Weight Loss Clinic Expert Column WebMD Weight Loss Clinic: Exercise and Fitness by Richard Weil, MEd, CDE, published May 1, 2003. American College of Sports Medicine web site: "Guidelines for Healthy Aerobic Activity."