The One Big Thing Fitness Trackers Haven't Mastered

Photographed by Jessica Nash.
For those of you who rely on your fitness trackers big-time, beware – they might not be as accurate as you think.
A new study from Stanford University has called into question the accuracy of seven different fitness trackers.
Advertisement
Researchers looked at the Apple Watch, the Fitbit Surge, Basis Peak, Microsoft Band, PulseOn, Samsung Gear S2 and the Mio Alpha 2, testing them on 60 volunteers who were asked to walk, run and cycle while wearing them.
Most of the trackers were good at measuring heart rate – just one performed poorly, the Samsung Gear S2, which had an error rate of 6.8%. However, when it came to measuring calories burned through working out, it was another game entirely.
Even the most accurate device was off by 27%, while the least accurate was off by a huge 93%.
Although lead author Euan Ashley was impressed with the accuracy of the heart rate measurements from the fitness trackers, when it came to the calorie-counting element he was shocked. "The energy expenditure measures were way off the mark," he said. "The magnitude of just how bad they were surprised me."
He added that he was concerned because "people are basing life decisions on the data provided by these devices."
As to why the fitness trackers are so off the mark, he and his co-author Anna Shcherbina were unsure but they suspect it has to do with the problems of tailoring algorithms to individuals who were all very different. "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." Anna said.
Euan says his takeaway message is that it is safe to rely on fitness trackers for heart rates but, if you are using your fitness tracker in a bid to maintain or lose weight, you might run into problems. "Basing the number of doughnuts you eat on how many calories your device says you burned is a really bad idea."
Advertisement