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Yesterday I posted about an online toy that lets you estimate the calorie burns for different activities by entering your weight and the duration of the activity. It’s not great for getting specific numbers, but it helps to show the different levels of effort for different activities.

Gina Kolata, in a 2007 article called Putting Very Little Weight in Calorie Counting Methods, has quite a nice roundup of the ways that cardio machines in the gym, in particular, can mislead us. The “calories” readout on an exercise machine looks so precise, it’s tempting to believe it’s real, but it’s almost impossible that it’s accurate:

  • Some cardio machines do measure power output, but that doesn’t necessarily translate into calories: “One reason for the calorie-count skepticism is that two individuals of the same age, gender, height, weight and even the same level of fitness can burn a different amount of calories at the same level of exertion.”
  • “Part of that is genetic and part is familiarity with the exercise. The more familiar you are with an exercise, the fewer calories you use at the same level of effort, he found in a research study.”
  • “There also is a seldom mentioned complication in calculating calories burned during exercise: you should subtract off the number of calories you would be using if you did nothing.” (This could be 50 to 100 calories per hour.)
  • How you use the machine matters — a lot: “Hanging onto the rails reduced the number of calories burned by 40 to 50 percent. The same thing happened with stair-climbing machines.”
  • And then there’s just plain machine maintenance: “A major problem is that the machines get out of calibration. ‘They drift in speed and grade,’ Dr. Haskell said. ‘If you go from one machine to another, it is obvious that at the same setting you are working much harder on one and much less on the next.’”

Does this mean it just doesn’t matter what you do in the gym? Not at all, but it may help you more to keep track of information like distance and time, and heart rate (if available), and look for changes in your performance and total time spent over time. That kind of tracking, plus being aware of your intake (with some kind of tracking there, too), can help you any needed make adjustments over time.

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