Gym Hacks: Improving Accuracy of Cardio Machines

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gym hacks quantified self fitness tips by measured me blogI am not a huge fan of cardio, but generally try to spend at least 15-30 minutes on a treadmill or elliptical machine every time I go to the gym. Instead of the distance or time, I often use “calories burned” as a benchmark: “I will stay on this treadmill until I burn 200 calories”. Unfortunately, there is no way to see the BodyMedia report on how many calories were burned until I get home and plug the tracker into computer. So to track my progress in real time, I often rely on calorie counters that you can nowadays find on every cardio machine at the gym. People regard these estimates with suspicion, knowing that the numbers on display are always overestimated. But if you think that the error is only 5-10%, read this article.

Yep, most of the gym machines tend to overestimate the caloric expenditure with much higher error. Here is the average error by the type of machine:

Treadmill: 13%
Stationary bike: 7%
Stair Climber: 12%
Elliptical: 42%

It means that instead of 500 calories that you thought you burned while working out on elliptical machine, you actually burned only 500*(1-.42) = less than 300! It’s a considerably big difference, especially if you work out more than once a week. To help myself get more accurate benchmark estimates, I put together a conversion table that shows what results one need to get on the machine display in order to burn the desired number of calories.

If you are good with math, the formula is

DisplayCalories = TargetCalories/(1-MeasurementError)

Of course, these are just adjusted estimates and should be used only for informative purposes. For the self-tracking purposes, you will be better off using BodyMedia or advanced heart rate monitors. And don’t forget to enter your age and weight before you program your workout:  it substantially increases the accuracy.

Speaking of manually entering your parameters. Question for manufacturers of the cardio machines: why should we manually enter our weight, when you can easily build scales into the machine? And how about using those heart-rate monitors that are built into the handrails? Why their data feed is not used in estimation of the calories burned?

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3 Responses to Gym Hacks: Improving Accuracy of Cardio Machines

  1. James says:

    I agree, when I do cardio, my Polar watch readings and those on the machine are never even close. Not sure your formula can help, though. The best way is to use a better tracking device like HRM monitor.

  2. Scot says:

    Your points are right on. One thing I found to at least get a more accurate read on the heart rate readings provided was to avoid the built in sensors on the hand grips and instead wear a polar chest strap of my own. I don’t need to wear the watch portion (uncomfortable) but this way the feed to the read out is consistent even when changing machines. I found the fail rate on the hand grips to be very high.

    Thanks for the great table for the calories.

  3. Silva says:

    It feels that the error of caloric expenditure depend on body movement. The more movement the more error. I think that it’s easier to use calorie counters for monitering.

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