A Stanford University study of fitness trackers indicated that while devices did a good job at tracking a person's heart rate, those devices did not accurately record calorie burning.
Stanford researchers studied the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2. Researchers said that some devices were more accurate than others, but all six devices had a relatively large margin of error.
Sixty volunteers participated in the Stanford study, and wore devices while walking or running on treadmills or using stationary bicycles. According to researchers, their heart rate was measured with a electrocardiograph. For calorie burning, Stanford estimated with an instrument for measuring the oxygen and carbon dioxide during breathing.
Stanford's evaluation of fitness devices' abilities to track calorie burning showed that the most accurate devices had a margin of error of 27 percent. The least accurate device had a margin of error of more than 90 percent.
“People are basing life decisions on the data provided by these devices,” said Euan Ashley, professor of cardiovascular medicine, of genetics and of biomedical data science at Stanford.
Part of the problem, researchers warn, is that devices cannot factor every variable.
"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.” researcher Anna Shcherbina said.
According to Stanford, the Apple Watch had the most accurate readings in both measuring heart rate and metabolic rate. The PulseOn was considered the worst-performing device.
Although Stanford's findings were damning of fitness trackers for their ability to estimate calorie burning, all six devices were able to measure heart rate accurately within a 5 percent margin of error.