You’ve just spent an hour on the treadmill, and the number on the screen tells you that you’ve burned 300 calories. Do you believe it? How did it get that number?

Your treadmill got that number the same way that the EPA gets gas mileage numbers: estimations and averages. Scientists had a lot of people run on a treadmill hooked up to a mask that calculated the amount of air they breathed, then used that to estimate the amount of calories were required to do the effort. Then they got an average over the sample and put that average into the treadmill, which spits out a number based on how much you weigh and how fast the drums were turning.

This number is pretty good … if you’re close to the average and do everything the way the people in the tests did. But did you?

Do you weigh what they weighed? Did you put your hands on the rails? Do you have the same ratio of fat to muscle? Did you work as hard per minute?

The number on that treadmill is probably wrong as it relates to you and not the testers (unless you are very close to the average and do everything the same as the testers did). But the more you deviate from the mean, the less likely the mean is an accurate way to predict your actual calorie usage. Let me show you what I mean with gas mileage.

I own a car. Can you tell me how much gas it uses on my way to work? According to the EPA, the average fuel economy for a car in the United States is 24.6 MPG combined cycle, so would that be a pretty good guess? It would be a terrible way to guess! What kind of car I own, how I maintain it, what kind of driving I do on my commute and how much of a lead foot I have all matter if you want an accurate guess of how much gas I use during my commute. Even if I told you my car has four doors and weighs 3,500 pounds, it could be a Prius or a BMW M5. I’ve owned both and let me tell you, there’s a 4x difference in gas bills for the exact same commute.

And this is not just a math problem. According to a 2014 study by Fenzl, Bartsch and Koenigstorfer, the harder we think a workout was, the more we will eat afterward. For this study, the researchers told half the participants they were working out in a “fat-burning zone” and the other half in an “endurance zone,” even though the exercise was of the exact same intensity and duration. The participants were then offered water and pretzels. The participants who were told they were “working harder” ate more pretzels than those who did not.

The more we think we exercise, the more we eat. So don’t let the number on that treadmill fool you. “I exercised so I deserve this,” is one of the most dangerous thoughts you can have if you are trying to lose weight.

Written by Coach Stevo, the nutrition and behavior change consultant at San Francisco CrossFit. He is a Certified Strength and Conditioning Specialist, holds a BA in Philosophy from the University of Chicago and an MA in Sport Psychology from John F. Kennedy University. He teaches habit-based coaching to wellness professionals all over the world and he contributed to Intervention by Dan John in 2012.

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