When trying to determine the calories burned during exercise, you most often will find lists or charts with common exercises and a static number of calories burned for a given duration. For example, you might see, "Walking for one hour burns 300 calories." The problem with these types of tables is that they make gross assumptions about the style and intensity of the exercise and also about the person engaging in the activity. Although it's a bit more work, figuring out your individual calorie-burning rate for your exercise of choice is a much more accurate approach.
The MET
The modern, scientific method for calculating calories burned in exercise requires determining your resting metabolic rate (RMR) and multiplying it by the MET, or metabolic equivalent task, of an activity. MET numbers represent the energy consumption of an activity, relative to rest (defined as sitting still in a chair). When the MET number is multiplied by your hourly RMR, it yields the specific number of calories that you personally burn when doing that exercise.
For example, the METs are given for various types of ice skating: general ice skating, 9 miles per hour or less, has a MET of 5.5; ice skating rapidly, greater than 9 mph, has a MET of 9; competitive speed skating has a MET of 15.
Interpret this as general ice skating burns 5.5 times as many calories as resting, and speed skating burns almost three times as many calories as regular ice skating. You can find a list of hundreds of common activities at the University of South Carolina School of Public Health website, where research was done to produce the most recent "Compendium of Physical Activities" in 2000.
Resting Metabolic Rate
Your resting metabolic rate (RMR) is the number of calories you use when completely at rest, at least 12 hours after consuming any food or beverage. The most accurate measure of RMR is made by a testing process called "indirect calorimetry," but because that is not readily available or affordable for most people, there are equations you can use to estimate it.
A simple but still quite accurate equation is the John J. Cunningham equation, published in the November 1991 edition of the "American Journal of Clinical Nutrition." This equation takes only fat-free mass in kilograms as its input: RMR = 370 + 21.6 x FFM.
An Example RMR Calculation
Here is an example of how to use the equation to calculate RMR. If Jane weighs 135 lbs and has 21 percent body fat, her RMR is calculated as follows:
1) Jane's FFM = (135 lbs / 2.2 lbs/kg) x (1 - 0.21) = 61.4 kg x 0.79 = 48.5 kg
2) Jane's RMR = 370 + 21.6 x 48.5 = 1,417 calories per 24 hours, or 59 calories/hour
Jane's resting metabolic rate--the number of calories she burns when sitting still in a chair, doing nothing, for one hour--is 59.
Calculating Exercise Calorie Burning
With your RMR in hand, you can calculate your individual calorie burning for any exercise by multiplying the hourly RMR by the activity's MET. Jane goes ice skating for 90 minutes. Because her hourly RMR is 59 calories, when she skates, Jane burns 59 x 5.5 = 324.5 calories per hour. So if she skates for 90 minutes, that will be 324.5 x 1.5 = 487 calories burned. Note that 487 calories is the total calories she used in that 90 minutes, including both her RMR and her activity, not in addition to her RMR.
Caveats
It is important to realize that all of these concepts, equations and tables are based on statistical averages and do not necessarily apply to everyone. If you suffer from a chronic illness, autoimmune disorder or metabolic disease, they might not apply to you. Likewise, if you are a very fit person, an elite athlete or extremely under- or overweight, they probably won't give you accurate results. For the majority, however, these calculations provide an excellent means of determining individual exercise calorie consumption.
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