In February 1995, the Journal of the American Medical Association published recommendations for physical activity levels for Americans, based on the findings of teams at the Centers for Disease Control and Prevention as well as the American College of Sports Medicine. The report concluded that adults should attempt to include 30 or more minutes of moderate-intensity physical activity most every day. Using a common measure for physical activity levels, the metabolic equivalent task, you can translate that recommendation into a level of calorie burning that's considered a good workout by those standards.
The Metabolic Equivalent Task
To translate workout time and intensity into calories burned, you must know the metabolic equivalent task (MET) of your chosen activity. METs represent the energy consumption of the activity, relative to rest, as in sitting still in a chair. For example, here are some exercises considered to be of very vigorous intensity in which the MET value is 8 to 10: running at a 10 minute/mile pace, calisthenics such as push-ups, pull-ups, or jumping jacks, or step aerobics. The following activities are considered moderately intense, with a MET of 3 to 4: leisure bicycling, fishing from a riverbank, mopping, vacuuming, raking the lawn, horseback riding or playing hackey sack.
More MET Values
"Compendium of Physical Activities" contains the MET values for hundreds of common activities. You can find this list at the University of South Carolina School of Public Health website. The research was done at that university.
Resting Metabolic Rate
If you know your hourly resting metabolic rate--which is the number of calories you burn in an hour of sitting still--you can combine it with the MET of your chosen activity or exercise to find the actual number of calories you burn when you engage in that activity. To find your RMR, use an on-line calculator or calculate it yourself using the Cunningham equation: RMR = 370 + 21.6 x fat-free mass in kg. For example, if your body has 70kg fat-free mass, your daily RMR would be 370 + 21.6 x 70 = 1,882. Your hourly RMR is the daily RMR divided by 24, which in this case, would be 1,882 / 24 = 78 calories per hour.
Calculating the Workout Calories Burned
With your MET value and your RMR, you can calculate the calories you burn in any exercise by multiplying the two. For example, if a 70kg person does any of the moderate-intensity activities for one hour, he burns between 234 and 312 calories. When doing the more vigorous activities, such as running or jumping jacks, he burns 624 to 780 calories per hour.
Recommended Workout Calories
Clearly, any of the above activities more than meet the CDC and American College of Medicine guidelines for 30 minutes per day of moderate physical activity--which translates to only about 125 to 150 calories per day of physical activity.
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