Burning Calories at the Gym

"Calories burned" readings on gym equipment are only estimates, but they provide a pretty good measure, depending on how honest you are with your information.

You finish your workout on the treadmill and the machine reads 300 calories. But how do you know if that number is truly accurate? Experts say there's a good chance it's not.

Burning Calories at the Gym: Crunching the Numbers

At the end of your workout, most cardio machines provide you with the number of calories you burned. Keep in mind though that this reading is an estimate — and often an overestimate — and should not be taken as gospel. "If you see that you expended 300 calories for a workout, there is probably about a 10 percent margin of error," says Pete McCall, MS, an exercise physiologist with the American Council on Exercise. "The number you see on the treadmill, stationary bike, elliptical machine, stair climber, etc., is just an estimate, but it is a relatively accurate estimate. It is based on what is called metabolic equivalents, or METs, which refers to how much oxygen your body uses."

McCall says that one MET is equal to 3.5 milliliters of oxygen per kilogram of your body weight per minute. This is the amount of oxygen your body requires at rest. When you work harder (e.g., when you exercise), your body burns more METs. "Your body has to expend energy to use oxygen. If you're running, your body needs more oxygen and your body spends more energy," McCall says.

The cardio equipment at the gym uses information on the number of METs it takes to perform a given exercise, as well as your weight if you enter it, to give you an estimate of how many calories you burned. "It is more accurate if you enter your weight and your age than if you don't," McCall notes.

If you are trying to lose weight, you may be particularly interested in finding out the exact number of calories you burned during your workout.

"If people are really concerned about monitoring weight loss, the gym equipment is a good estimate, but the best estimates are going to come from heart rate monitors," says McCall.

Newer heart rate monitors allow you to program in your resting heart rate and your age, and they use this information to give you a more precise estimate of the calories you expend.

Burning Calories at the Gym: Maximizing Your Burn

When deciding which piece of gym equipment will give you the best burn, don't count on the calories-burned estimates from the machine. In order to burn more calories, you simply have to work harder. So the best way to determine which piece of equipment will help you burn the most calories is by gauging how hard you are able to work on it — if you're not able to sustain a workout on the elliptical machine, for instance, use the treadmill instead.

While you can use the calorie counters on gym equipment as rough guidelines, the most important way to maximize the number of calories you are burning is to find a piece of equipment you enjoy using and to use it often.