What Do (And Do Not) Wearables Do Well?

Wearable health and fitness devices are all the rage these days, both inside and outside of the gym. Indeed, a recent study shows that more than 38 million Fitbits have been sold since 2010, with other data showing more than 23 million active users as of early 2017. While some devices perform only a few simple functions—for example, tracking steps—others are more elaborate, offering the ability to measure a user’s heart rate, sleep patterns, or the number of calories he or she has burned. But how effective, really, are wearable devices at performing these functions? As CNBC first reported, Stanford University’s Euan Ashley, who believes the devices could be potentially useful for improving cardiac health outcomes, and a team of researchers recently set out to answer that question.

Ashley, who serves as a professor of cardiovascular medicine, and his colleagues note that “the ability to measure physical activity through wrist-worn devices provides an opportunity for cardiovascular medicine.” This is particularly true at a time when heart disease causes so many deaths each year—about 610,000, according to recent CDC statistics. At the same time, little is known about how accurate the devices’ measurements are. To that end, the researchers tested seven popular wearables, including the Apple Watch and one Fitbit model, on 60 volunteer participants while they were sitting, walking, running, and cycling.

The results? While devices tended to be very accurate when it came to measuring heart rate (an improvement over early wearable models), their measurements of “energy expenditure” (i.e. calories burned) were far less likely to be correct. Ashley blames differences in the way people walk for this phenomenon: “Some people walk smoothly and others waddle along, and that has an impact,” he told CNBC. What’s more, there were variations among the devices themselves; the Apple Watch, for example, received high marks when it came to accuracy, while other brands did not fare as well. In addition, errors in measurement were more likely among male study participants than female participants, as well as “those with a greater body mass index, and with a darker skin tone.” The bottom line: “Individuals and practitioners should be aware of the strengths and limitations of consumer devices that measure heart rate and estimate energy expenditure.” Ashley and his colleagues also urge further data sharing from wearable device manufacturers as they continue to develop new products.

Click here for the article from CNBC on wearable device reliability.

Click here for the Stanford University Ashley Lab Web site.

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