When working out in the gym, machines, such as treadmills and stationary bikes, show how many calories you are burning. Are these calculations correct, or is it just something to keep the participants happy?

— Just Wondering

Dear Just Wondering,

The reliability of these calculations in figuring out the number of calories you expend during a workout depends on your size, body composition, workout intensity, and level of fitness. If the machine doesn't ask for your body weight, you can be sure the calorie count is not accurate. People who weigh less burn fewer calories than people who weigh more when doing otherwise equivalent workouts.

If the machine does ask for your weight, it is giving you an approximate count of calories burned. The reliability of the numbers varies by manufacturer and depends on what formula the machine uses. Excercise machines, like many website calorie calculators, use various formulas to calculate the approximate number of calories burned.  Some are more accurate than others: a number of sites have you plug in your weight, exercise mode, and time to calculate your caloric expenditure. For a rough estimate, this is fine. However, you may also be interested in calculating more a more accurate picture of calories burnes; here's a partial listing from a well-respected text, Exercise Physiology, by McArdle, Katch, & Katch:

Activity Calories/lb/minute
Moderate 0.065
Vigorous 0.095
Step 0.070
5.5 mph 0.033
10 mph 0.050
13 mph 0.071
Jump rope 0.060
11 min/mile 0.070
8.5 min/mile 0.090
7 min/mile 0.102
6 min/mile 0.114
Moderate 0.070
Vigorous 0.090
Stationary Cycling  
Moderate 0.055
Vigorous 0.090

Note: "Moderate" and "vigorous" are not specific terms. But generally "moderate" means you will notice some increase in your breathing or heart rate, and "vigorous" means you'll notice a large increase in your breathing and heart rate. For example, moderate activity might include brisk walking, playing catch, or yoga. Vigorous activity might include running, swimming, basketball, or soccer.

Also consider that a person who has a high percentage of lean body mass will spend more calories than a person with a greater fat mass, because lean tissue is more metabolically active. In addition, as an athlete adapts to a certain mode of exercise, the muscles become more efficient and work becomes easier, causing slightly fewer calories to be used up. So, you can keep your muscles guessing by cross-training or switching activities. Technique also matters — for example, if you're leaning on an elliptical machine (putting your weight on your arms), you're reducing your body weight load and burning far fewer calories than the machine says. The same holds true for a treadmill. You're better off setting the machine at a lower intensity and swinging your arms at your sides (touching the side bars occasionally for balance).

If you'd prefer to put energy your into working out, rather than mastering the myriad ways of calculate calories burned, you can simply keep some general physical activity guidelines in mind:

  • Participate in moderate physical activity for at least 30 minutes, five or more days each week
  • Participate in vigorous physical activity for at least 20 minutes, three or more days per week
You may also be interested in reading the related Q&A below to learn more about burning calories and working out. Wishing you "happy" workouts, regardless of whether you're calculating calories burned! Alice!

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