Fitness trackers are great, but a Stanford study reports that they're terrible at measuring fitness.
Fitness trackers are great -- they're getting us up and moving, and most doctors probably agree that's a good thing. But before you binge on flourless chocolate cake, a team of researchers at Stanford have concluded that fitness trackers like the Fitbit and the Apple Watch -- just to name a few -- are grossly inaccurate. [gallery ids="16469,16470"] In fact, the team put seven different fitness trackers to the test, including the Fitbit, the Apple Watch, the Fitbit Surge, Basis Peak, Microsoft Band, Mio Alpha 2, PulseOn, and the Samsung Gear S2. The team then asked 60 participants to perform various exercises where they were monitored using medical-grade echocardiographs and other devices that measured oxygen and carbon dioxide in breath. The results? "The heart rate measurements performed far better than expected but the energy expenditure measures were way off the mark," says Professor Euan Ashley, senior author of the study. The Fitbit Surge was the most accurate of the group with a median error rate of 27 percent, and the worst was the PulseOn with a staggering 92.6 percent error rate. The team could not offer a wholly complete explanation as to why there was such a gap, but they recognize that each device uses its own algorithm to calculate total energy expenditure.
"My take on this is that it's very hard to train an algorithm that would be accurate across a wide variety of people because energy expenditure is variable based on someone's fitness level, height and weight, etc.," suggests the study's lead author, graduate student Anna Shcherbina.
The study also discovered that a higher body mass index, large wrist circumference, and darker skin tone also correlated with higher error rates.
Considering fitness trackers have been under scrutiny lately (Fitbit has been battling a class action lawsuit over the device's accuracy), the results come as no surprise. The good news is, however, that you can still accurately measure your heart rate. But if you're using it to see how much ice cream you can eat at the end of the day, you might want to reconsider.
