The information on cardio machines can be deceiving. The "fat burning zone" is a myth that is based on a fact, but taken out of context.
It's true that higher intensity exercise uses more glucose and glycogen (the form of energy your body gets from foods) in proportion to fat, but remember that "high intensity" in this context means exercise that you can only maintain for a couple of minutes before becoming exhausted (i.e. anaerobic exercise). It’s also true that low intensity exercise uses more fat as fuel; moderate intensity exercise that you can maintain for 20 minutes or more is aerobic exercise, and will burn both fat and glucose.
You're better off exercising in the aerobic zone as much as you can because exercising at higher intensities burns more total calories. The "fat burning zone" business is very misleading. You will burn a larger percentage of fat in relation to glucose when you are working at a lower intensity, but you will also burn fewer total calories and less total fat.
Bottom line: The relative percentage of fat burned has nothing to do with weight loss—it's the total amount calories burned that counts. So just ignore the machine and continue to exercise aerobically. As a bonus, aerobic exercise also strengthens your heart and cardiovascular system, lowers blood pressure, and improves cholesterol levels.
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