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Do Optical Sensors Provide Reliable Heart Rate Data?

Charles Murray

August 17, 2016

2 Min Read
Do Optical Sensors Provide Reliable Heart Rate Data?
WearablesThe 2010s saw technology grow from something we carry to an actual accessory that we can wear. From consumer focused products like the Apple Watch, Samsung Galaxy Gear, and even the FitBit, to serious medical devices like the AlivCor EEG, intended to track and help diagnose diseases, wearables found their way onto millions of bodies. There was certainly a wearables bubble that has since burst, but the digital health sector owes much of its success to wearables. And Google's recent major acquisition of Fitbit shows that the tech industry believes there's more to wearables than being a high-tech fashion statement.(Image source: Fitbit)

Optical heart rate monitors, hailed as a promising new technology when they hit the market a few years ago, are starting to see some backlash.

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.

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"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.

MD&M Minn logoMedical Product Development. Advanced electronics such as optical sensors are playing a greater role in healthcare than ever before. Learn what is happening now and what to expect for the future in the "Medical: Achieving Product Development Goals With Sensors and Data Management" track at Medical Design & Manufacturing. Sept. 21-22, 2016 in Minneapolis. Register here for the event, hosted by Design News’ parent company UBM.

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."

About the Author(s)

Charles Murray

Charles Murray is a former Design News editor and author of the book, Long Hard Road: The Lithium-Ion Battery and the Electric Car, published by Purdue University Press. He previously served as a DN editor from 1987 to 2000, then returned to the magazine as a senior editor in 2005. A former editor with Semiconductor International and later with EE Times, he has followed the auto industry’s adoption of electric vehicle technology since 1988 and has written extensively about embedded processing and medical electronics. He was a winner of the Jesse H. Neal Award for his story, “The Making of a Medical Miracle,” about implantable defibrillators. He is also the author of the book, The Supermen: The Story of Seymour Cray and the Technical Wizards Behind the Supercomputer, published by John Wiley & Sons in 1997. Murray’s electronics coverage has frequently appeared in the Chicago Tribune and in Popular Science. He holds a BS in engineering from the University of Illinois at Chicago.

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