Do Optical Sensors Provide Reliable Heart Rate Data? 26787

Used in so-called activity trackers by fitness buffs, the devices offer comfort advantages for wearers, but some users are starting to question their accuracy, especially during exercise.

The trackers, which use a tiny sensor package to monitor blood flow through the wrist, were never expected to have such problems. Engineers initially saw the wristband format as a natural -- a more comfortable alternative to the existing “EKG straps” that fit tightly around the chest. With their unobtrusive design, the optically based devices could potentially be worn all day, during activities ranging from walking and standing to sitting and sleeping, manufacturers predicted.

FitBit’s Charge HR tracker employs a technology called PurePulse that uses optical sensors to measure heart rate.
(Source: FitBit Inc.)

"If you want to sleep with the device, you should be able to do that, and you should be able to get a really good sense of your heart rate while you’re asleep,” Shelten Yuen, vice president of research for FitBit Inc., told Design News. “It’s very different than an EKG strap. Most people won’t wear an EKG strap while they’re asleep, unless they suspect a problem or are just really curious.”

Still, the technology has come under fire, especially when it comes to its ability to track heart rates during exercise. Earlier this year, a user group filed a class-action lawsuit alleging that FitBit’s PurePulse technology was inaccurate and, therefore, a safety hazard. FitBit denied the claim.

As far back as 2014, however, CNET reported in a product analysis that optically based products from Garmin, Basis, Withings, and Samsung displayed problems during tests, with errors climbing as high as 57% for fast heart rates.

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User reviews have been mixed. On FitBit’s message boards, some customers have called the technology “downright illogical” and “woefully inaccurate.” Some use a pejorative -- “sitbit” -- to refer to its ability to produce accurate results at rest, but not during exercise.

To be sure, though, many users are happy with their results. A healthy percentage of FitBit message posters have no issues during exercise, saying it “very accurately measures my heart rate” and “works like a dream.”