None, however, measured energy expenditure well.
The findings, published online in the Journal of Personalized Medicine, were based on an evaluation of the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2 in a diverse group of 60 volunteers.
Millions of people wear some kind of activity tracker and often share the data with their physician.
“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 University.
But consumer devices aren’t held to the same standards as medical-grade devices, and it’s hard for doctors to know what to make of heart-rate data and other data from a patient’s wearable device, he said.
In the study, the volunteers, including 31 women and 29 men, wore the seven devices while walking or running on treadmills or using stationary bicycles.
Each volunteer’s heart was measured with a medical-grade electrocardiograph. Metabolic rate was estimated with an instrument for measuring the oxygen and carbon dioxide in breath - a good proxy for metabolism and energy expenditure.
Results from the wearable devices were then compared to the measurements from the two instruments.
“The heart rate measurements performed far better than we expected,” noted Ashley, the senior author on the study, “but the energy expenditure measures were way off the mark. The magnitude of just how bad they were surprised me.”
Neither Ashley nor graduate student Anna Shcherbina, a lead author on the study, could be sure why energy-expenditure measures were so far off. Each device uses its own proprietary algorithm for calculating energy expenditure.
“All we can do is see how the devices perform against the gold-standard clinical measures,” Shcherbina was quoted as saying in a news release.
“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.”
Heart rate, she said, is measured directly, whereas energy expenditure must be measured indirectly through proxy calculations.
The team of researchers at the Stanford University School of Medicine is working on the next iteration of their study, in which they are evaluating the devices while volunteers wear them as they go about a normal day, including exercising in the open, instead of walking or running on a laboratory treadmill. - ANA-Xinhua