This post is part ofFind Your Fit Tech, Lifehacker’s fitness wearables buying guide.
Sure, you could calculate a rough estimate based on your body size, sex, and age.
You could choosewhether or not to believe the calorie readouton the treadmills and bikes at the gym.
It was also wrong.
Even as fitness wearables have gotten more advanced, it’s still wrong.
Most trackers use accelerometers to figure out when your body is moving, and by how much.
If there is quicker bouncing and your wrist makes a smaller movement, youre probably running.
This is the basic idea behind how trackers detect how many steps youre taking.
Your age, weight, and sex may figure into this equation.
But humans are complicated, and technology often gets confused.
For example, you may get different step countsif you put a gadget on your right versus left wrist.
And the optical heart rate sensors that a lot of trackers usemay be less accurate on dark skin.
Researchers are interested in fitness trackers accuracy, which would seem like a good thing.
They want to be able to use wearables in research or recommend them for individuals and healthcare providers.
Areanyof them good at estimating your calorie burn?
What studies say about fitness trackers accuracy
Time for the bad news.
Heres how some of the top brands fared:
Garmins underestimated calorie burn 69% of the time.
Apple watches overestimated calorie burn 58% of the time.
Polar devices overestimated calorie burn 69% of the time.
Fitbits underestimated calorie burn 48% of the time and overestimated 39% of the time.
The fact that Fitbits were roughly correcton averagedoesnt mean they were useful.
If these devices are all inaccurate, how can you know how many calories you’re burning?
Its probably most useful if you think of your calorie burn as a number you cannot measure directly.
Treat it as a black box: I burnsome unknowable numberof calories, now what?
Lets say youre training for a marathon and you want to ensure you fuel yourself appropriately.
Well, if youre under-eating, youll start to lose weight.
If, after that adjustment, your weight stays steady, then you know youre eating the right amount.
