Most fitness trackers accurately measure heart rate but not the calories burned: Stanford study

Cardiology researcher Euan Ashley and his team conducted a study to determine how accurately seven types of fitness trackers measure heart rate and energy expenditure. Paul Sakuma

Stanford recently conducted a study to check the accuracy of the wristband activity trackers that has become an indispensable part of many, for keeping a tab on health and exercise routine. The data generated is often shared with the physician, but is the data accurate?

A team of researchers at the Stanford University School of Medicine carried out a study in estimating if the heart rates as shown by these trackers should be taken seriously. They analyzed seven devices in a diverse group of 60 volunteers, that showed six of all the devices measuring the heart rate with an error rate of less than 5 percent. These fitness bands were—Apple watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn and the Samsung Gear S2.

They found out that some devices were more accurate than others, and factors such as skin color and body mass index affected the measurements.

The study also revealed that none of these seven devices measured the energy expenditure accurately, suggesting that even the most accurate device was off by an average of 27 percent, and the least accurate was off by 93 percent.

“People are basing life decisions on the data provided by these devices,” said Euan Ashley, DPhil, FRCP, professor of cardiovascular medicine, of genetics and of biomedical data science at Stanford. 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.

The paper was published by Ashley, who is the senior author along with lead authorship shared by by graduate student Anna Shcherbina, visiting assistant professor Mikael Mattsson, PhD, and senior research scientist Daryl Waggott.

The volunteers including 31 women and 29 men, wore the seven devices while walking or running on treadmills or using stationary bicycles. The heart rate for each of them was measured with a medical-grade electrocardiograph and metabolic rate measured with an instrument measuring the oxygen and carbon dioxide in breath—a good proxy for metabolism and energy expenditure. These results were matched with wearable devices by that the volunteers wore.

“The heart rate measurements performed far better than we expected, but the energy expenditure measures were way off the mark. The magnitude of just how bad they were surprised me”, shares Ashley.

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Srishti Deoras
Srishti Deoras

Srishti currently works as Content Strategist for Analytics India Magazine. When not covering the analytics news, editing and writing articles, she could be found reading or capturing thoughts into pictures.