A new study released by Stanford University suggests that while wrist-worn fitness trackers do a decent job measuring a person’s heart rate, they aren’t very good at recording how many calories they have burned.
A 60-person trial was conducted to test the trackers’ effectiveness after cardiologist Euan Ashley, an associate professor of medicine at the Stanford University Medical Center, noticed that many of his patients were bringing in their health trackers during visits. The study tested 7 of the most popular wrist-worn trackers. The results?
They looked at two metrics: heart rate and calories burned. For heart rate, the fitness trackers were compared to findings from an electro-cardiogram, or EKG. It turned out the devices were “surprisingly accurate”, says Ashley. “Most devices most of the time were ‘off’ by only about 5 percent.”
However, when it came to measuring how many calories a person burned, the findings were way off, says Ashley, showing a degree of inaccuracy that ranged from 20 percent to 93 percent, meaning 93 percent of the time the worst-performing device was wrong. Researchers compared the findings of the wrist devices to a sophisticated system of calculating metabolism which measures oxygen and carbon dioxide in people’s breath.
The findings reaffirm a 2016 study by the University of Pittsburgh that suggested people wearing fitness trackers actually lost less weight than people who did not. In fact, the study suggested that the group least likely to see erroneous readings were fit, Caucasian women, meaning the error rate was greater for demographics most in need of accuracy.