If you choose your cardio exercise based on what burns the most calories, you may have noticed that the winner seems to be the elliptical machine. (That’s the one where your legs go in a running motion, but they stay in contact with the machine the whole time.)
Unfortunately, machines’ calorie readouts are notoriously inaccurate, ellipticals included.
After all, the machine doesn’t know very much about you — often just your weight and your heart rate. It makes some guesses based on that data, plus the motion of the machine. The heavier you are, the more calories you’ll burn. The faster you go, the more calories you’ll burn.
A study published last year compared the calorie burn on a Precor elliptical with participants’ actual calorie burn measured with lab equipment. The researchers had participants hit the “quick start” button, which makes the machine start counting calories as if you are a 68kg, 35 years old, and male.
The result: after a 30-minute workout, the number on the elliptical was 128 calories higher than the more accurate lab measurement. If you were relying on that number to calculate your calorie deficit for the day (say, if you were trying to burn 500 calories more than you ate), you’d be way off.
The truth is, though, that you shouldn’t be paying too much attention to the precise number of calories you burn with exercise. Unless a scientist is following you around with a computer and an oxygen mask all day, you’re only getting a very rough estimate of what that number might be.
Gym machines typically overestimate your calorie burn because, hey, big numbers make customers happy. So if you get different numbers from your elliptical and your Fitbit, go with the lower number. But the actual winning move might be to not count activity calories at all.