This just in: the data from your fitness tracker may not be as accurate as you think it is, new research shows.
A study out of Stanford which looked into the accuracy of different wristband activity monitors found that, while fitness trackers tend to do a good job tracking heart rate, they’re not so good with measuring energy expenditure (AKA calories burned).
The study observed a group of 60 different people and evaluated the accuracy of seven activity monitors—the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2. When it came to measuring heart rate, 6 of the 7 activity monitors had an error rate of less than 5 percent, but that error rate jumped quite a bit when measuring energy expenditure. The most accurate had an error rate of 27 percent, and the least accurate? A whopping 93 percent.
So, why is the margin of error so huge—more specifically, why is it so hard to accurately measure calories burned?
According to Euan Ashley, senior author on the study and a Stanford professor of cardiovascular medicine, genetics and biomedical data science, consumer fitness trackers like these aren’t held to the same standards as medical-grade devices, and it’s hard for medical professionals to even know what to make of the data these activity monitors provide.
Anna Shcherbina, a lead author on the study, also noted that energy expenditure is different for everyone and depends on a person’s fitness level, height, weight, and more, so it might just be that the algorithms the activity trackers depend on don’t work for every individual.
What does this mean for your workouts?
While you shouldn’t base any fitness or diet decisions based on the number of calories your activity monitor shows you may or may not have burned, you can still benefit from your fitness tracker. Instead of focusing on calories when you’re getting active (it’s also important to note that focusing on calories in general can also become harmful), focus on the quality of your workouts instead—something you can do with the help of your fitness tracker’s heart rate data, since hitting your target heart rate during a workout helps you exercise more effectively.
You may not know your exact energy expenditure when you’re through with a run or your favorite fitness class, but you’ll still feel the results, and truly, how you feel after a workout is way more important than any number.
Note: If you’re struggling with an eating disorder, you can find resources at NEDA or contact their helpline at 1-800-931-2237.