Fitbit heart rate tech 'puts consumers at risk' according to lawsuit scientist

We speak with the scientist at the centre of Fitbit's PurePulse legal row

Fitbit trackers boasting the company's PurePulse heart rate monitoring technology are "dangerous" and pose a risk to general consumers. That's according to Dr. Edward Jo, assistant professor of Applied Physiology at California State Polytechnic University.

Jo, along with his colleague Dr Brett Dolezal were instructed by Lieff Cabraser Heimann & Bernstein to research the accuracy of the Fitbit Charge HR, the Fitbit Surge and the Fitbit Blaze, as part of an ongoing class action lawsuit it has filed against the wearable tech company.

"The legal group wanted me to do a validation study – me, as an unbiased independent researcher – and whatever the outcome was, I was to do a comprehensive study and provide them with the results," Jo explained to Wareable.

The result of which, as you may have read earlier this week, concluded that Fitbit's heart rate accuracy is, on average, 20 beats per minute inaccurate during moderate to high-intensity exercise.

"This inaccuracy that we've seen can definitely pose a danger to not only the clinical population, but those population of individuals who may not know that they have any cardiac related conditions," said Jo. "It can definitely put them at risk."

However, Fitbit has quickly moved to counter the results of the study, and contacted us to state: "What the plaintiffs' attorneys call a 'study' is biased, baseless, and nothing more than an attempt to extract a payout from Fitbit. It lacks scientific rigor and is the product of flawed methodology. It was paid for by plaintiffs' lawyers who are suing Fitbit, and was conducted with a consumer-grade electrocardiogram – not a true clinical device, as implied by the plaintiffs' lawyers. Furthermore, there is no evidence the device used in the purported 'study' was tested for accuracy."

Firm words indeed, but words that didn't take Dr. Jo by surprise.

"It's expected obviously," he responded. "They're not going to say, 'Oh great job Dr. Jo'. If the result of an independent study is not in the favour of the product, obviously the manufacturer will come up with a generic rebuttal – and one of the most generic ones is to say it's flawed methodology."

Fitbit on the ropes

"Mudslinging in a litigation contest is not that unfamiliar but I was a little bit insulted on their behalf to the depths that Fitbit has stooped to call out independent researchers who have done many validation studies," Kevin Budner, one of the attorneys working on the case against Fitbit, told us.

"There is absolutely zero incentive for an academic to sully their reputation with a biased report. If anybody is misrepresenting the facts and the reality of the world to gain a profit, then it's Fitbit. They very aggressively market a heart rate feature, knowing it's a big selling point, saying 'every beat counts' and 'know your heart'," he added.

With regards to the Zephyr Technology BioHarness, the device used in the study to compare the Fitbits to, Jo himself had this to say: "The device has been validated twice to the traditional 12-lead ECG and also a 3-lead ECG for heart rate measurement. It's FDA approved, so for them to say it's not a clinical grade device – well, I don't even know what that means."

A Fitbit spokesperson also highlighted an additional study, one by Consumer Reports, that gave the Surge and HR an 'excellent' rating. However, that study is useless according to Dr. Jo, as there were only two individuals tested.

"If they're talking about flawed methodology, this one had the most minimal amount of scientific rigor you could possibly have," argued Jo. "It's crude, not sophisticated and has minimal data. They say they did statistical analysis – you can't do statistical analysis with just two data points. And this is their go-to reference?"

Jo told us that his study involved 43 subjects simultaneously wearing a Surge and Charge HR on each wrist, resulting in over 120,000 data points in controlled conditions.

Surge and Charge HR inaccuracies

Jo also explained that the inaccuracies he reported were not consistent and, more worryingly, he also noted differences between Fitbit's own devices, while the individual user was wearing both at the same time.

"If the difference was systematic, that would be one thing – say always underestimating by 20 beats all the time compared to the ECG," he said. "But those differences were sporadic. It was ambiguous and all over the place.

"Another separate analysis that we did was comparing the data from the Charge HR versus the Fitbit Surge," he added. "They are purported to have the same optical heart rate sensor. So you'd think the results for an individual would be the same for a given time point but we saw inconsistencies. It was off. From a statistical standpoint it was significantly off."

Fitbit disputes the report and has always maintained that its devices are consumer products and not medical devices. However, the attorney Budner has issues with that distancing.

"They're bandying about this term 'medical device' like it's the be-all and end-all," he told us. "But it's kind of a red-herring. The issue is they advertise it and sell it, at a premium, to do something – monitor your heart rate during exercise.

"It doesn't matter if it's a medical device or not a medical device, they tell the consumers it will do one thing, consumers buy it and it turns out that it doesn't do that thing. That's classic consumer fraud and I think that's what we're dealing with here.

"We're not saying that this is supposed to be an ECG; it's a consumer device. But there are a lot of consumer devices out there that actually do provide close and meaningful heart data to consumers – and these Fitbit devices simply don't."

Fitbit leading the way

Fitbit has told us that its research team rigorously researched and developed PurePulse technology for three years before introducing it "and continues to conduct extensive internal studies to test the features of our products."

The company was also keen to express us that the Fitbit Charge HR is the top selling fitness tracker on the market, and is "embraced by millions of consumers around the globe."

We at Wareable actually rate the Fitbit Blaze, featuring PurePulse technology, as our best all-round fitness tracker. However, as we lamented the sporadic bpm recordings of both the Surge and the Charge HR in their reviews in 2015, we also had big concerns about the Blaze's performance during exercise.

We've written at length about the accuracy and shortcomings of optical heart rate technology, and the usefulness of the data, especially at high intensity. And in our own testing against consumer grade HR straps, we found Fitbit's PurePulse technology to be unreliable during high-intensity workouts.

"As we upped the pace, things fell apart," wrote executive editor James Stables in his review. "As our heart rate rose up from 150bpm to 165bpm, the Fitbit remained static, locked to 150bpm. As we started to sprint the chest strap reported 170–180bpm, yet still the Fitbit stayed at 150.

"Later in the run it came back to the chest strap at around 165 as we started to cool down. It's a disaster zone… The Blaze's tracking can't handle high intensity, and what's more, it suffers from a dreadful lag time, making its suitability for hardcore sessions non-existent."

Fitbit may have the fitness tracker market sewn up but it seems it has a long way to go before it can truly boast about its HRM credentials.

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  • Indydoc90·

    It makes sense that the optical monitor would have trouble at high intensity. The movement and changes in the skin as blood flow changes and sweat scatters the light used to measure the HR. Blood flow at high heart rates will have less of a wave in the skin that far from the heart. The technology is not up to the task. The chest strap is measuring the electrical impulses. The optical system is looking at changes in the capillary blood flow. I suspect it looks for the wave/ pulse of blood past the sensors. 

    A medical physiologist would be able to make this occurrence much more clear that I can. 

  • spiney·

    I have compared to the heart rate readers at gyms and have no had any issues with consistency. I don't need to be as concerned about my heart rate at this point, but I hope if it is an issue they will address it at some point. Nonetheless, I didn't purchase the Blaze solely for the heart monitor and am happy with the product.

  • AveragePerson·

    I fail to see how the claim 'puts consumers at risk' holds water as it's a completely impractical statement when put in the context of wearing a fitbit while exercising. One of the most important indicators in understanding your own personal health is your resting heart rate, and I've found that optical HR sensors do a pretty decent job at monitoring this. Not once have I worried about how accurate the band is at high intensity. At that point I don't care about what's on my wrist, what it's saying, or anything else for that matter. My priorities are to get as much air into my lungs as possible, stop the sweat from getting into my eyes, and retain some sort of dignity while I work my bollocks off. Max heart what?...who bloody cares! 

    Don't get me wrong a more accurate HR sensor would be great, but at the moment the current technology does exactly what I was hoping it did - provide me with a decent estimate of my movements, activity and over all health over a period of time. What I find most interesting is the effect of things like coffee, lack of sleep, or alcohol on resting HR - very interesting data. 

    If someone want's a very accurate HR sensor for specific sporting activities then they get a chest strap. I would hope that an average consumer doesn't expect optical HR sensors to be on par. Two products which at the moment, have two very different uses. Anyone fancy wearing a chest strap all day and night? didn't think so. 

  • Otter888·

    Fitbit seems to do more harm than good

    I've had a Fitbit charge 2 as a belated Christmas gift (late delivery) and started wearing it constantly from February 2017 onward. Only recently I discovered - after wearing it for 2 1/1 months - that the low energy & tiredness, blurry vision and severe inability to focus and concentrate I experienced during this time was connected to wearing the Fitbit.

    As I had a virus over Christmas I thought that its the symptoms that are dragging on - in a strange kind of way. Apart from questioning my 'sanity', I had started on a health regimen about a month ago, went for acupuncture, taking Ginkgo, Ginseng, etc... which all had no effect on the symptoms I experienced. Then last week - while staring at my computer trying to make sense of what I was doing - my Fitbit alarmed me to charge.......

    .......low and behold - I took it off to charge - and within a couple of minutes my vision and concentration sharpened - as if a switch was flipped! My energy returned and I am now back to feeling myself again.

    So for me that's the end of using Fitbit or any tracking measuring device! Thus I can only put out a word of caution warning fitness trackers constantly!