Study finds inaccuracies in Fitbit's heart rate trackers, but questions remain

FitBit Surge
Bill Roberson/Digital Trends
Fitbit will happily advertise the accuracy of its PurePulse heart rate technology in both the Charge HR and Surge, but are the readings accurate? It’s a question two researchers at the California State Polytechnic University tried to answer with their recent study, and the answer does not put Fitbit in a good light.

The study, which enlisted 22 male and 21 female healthy volunteers, sought to compare the heart rate readings of a time-synced electrocardiogram (ECG) to those from the Charge HR and Surge. Both wearables were placed on either participants’ wrists, while the ECG was done using a “previously validated and calibrated” heart rate measurement system, as well as a single channel ECG sensor and circuitry.

Participants were assigned to perform several indoor and outdoor tasks, including self-paced jogging, jump roping, treadmill running, stair climbing, and plyometrics, all of which were either followed or preceded by rests and all of which were performed for five minutes. In total, participants spent 65 minutes finishing their assigned tasks.

Unfortunately for Fitbit, results showed that the Charge HR recorded a heart rate that differed from the ECG’s data by 15.5 beats per minute (bpm). Meanwhile, the Surge recorded a heart rate that differed from the ECG’s results by an average of 22.8 bpm. The study also found that the Charge HR and Surge exhibited inconsistencies, with the devices showing a differential average of 10 bpm. However, the difference increased to 12.5 bpm when a participant’s heart rate reached 124 bpm, a heart rate associated with low intensity activities.

The study concluded that not only did the Charge HR and Surge record inaccurate heart rates when compared to an ECG, especially when participating in moderate to high-intensity exercise, but that their results even differed from each other. As such, the results have added fuel to the belief that Fitbit’s wearables don’t do a great job at measuring your heart rate, as well as the ongoing lawsuit that claims as much.

There are a few things to note about the study, the biggest of which being that it was commissioned by the lawsuit’s plaintiffs. As such, one can’t help but think this nugget of information slightly skews the results. In addition, the study doesn’t include as many participants as a study might want to have, which would help with the significance of the results.

Unsurprisingly, the company took issue with the study, calling it “biased, baseless, and nothing more than an attempt to extract a payout from Fitbit.” It also brought up Consumer Reports’ retesting of the Charge HR and Surge back in January, with the retest concluding that heart rates measured by both devices were accurate, regardless of the exercise’s intensity. Finally, a source familiar with Fitbit’s background told Gizmodo that the Zephyr BioHarness, the ECG that measured the participants’ heart rate, has “no validation that it’s any more accurate than our product.”

Even so, a 2014 article in the Berkeley Science Review and a February 2016 informal investigation by Indiana news station WTHR also arrived to similar inconsistent results with Fitbit’s trackers, with inconsistencies only increasing as the exercise grew in intensity.

In other words, we do not think the lawsuit against Fitbit will go away soon.

Emerging Tech

Awesome Tech You Can’t Buy Yet: Folding canoes and ultra-fast water filters

Check out our roundup of the best new crowdfunding projects and product announcements that hit the web this week. You may not be able to buy this stuff yet, but it sure is fun to gawk!

Our favorite fitness trackers make it fun to keep moving

Looking for your first fitness tracker, or an upgrade to the one you're already wearing? There are plenty of the wrist-worn gadgets available. Here are our picks for the best fitness trackers available right now.

How to use the ECG app, set up irregular rhythm notifications on the Apple Watch

The Apple Watch Series 4 is the best smartwatch iPhone owners can own, and it just got even better with the addition of the ECG app and ability to identify irregular heart rhythms. Here's how to set it all up.
Digital Trends Live

Digital Trends Live: Amazon Go expansions, the robocall onslaught, more

On this episode of Digital Trends' live morning show, Digital Trends Live, hosts Greg Nibler and Jeremy Kaplan explored the news of the day, including Amazon Go's potential expansion, the robocall onslaught, and more.

Crush your next workout with the best Fitbit for every activity

Fitbits are amazingly helpful tools for setting fitness goals and tracking progress. However, different activities require different metrics. We've gathered a list of the best Fitbits for running, swimming, biking, and other activities.

Conquer the cold season with the best heated clothing and outdoor apparel

If you're thinking about going outside this winter, heated apparel is a must. Luckily, we've rounded up some of the best heated clothing, whether you're looking for battery-powered gloves or heated insoles.

Check out the best Green Monday deals for those last-minute gifts

Black Friday and Cyber Monday have come and gone, but that doesn't mean you've missed your chance of finding a great deal. We're talking about Green Monday, of course, and it falls on December 10.

Google Fit app finally gets a widget, among other new features

Google Fit hasn't received any new features since its redesign. This week, the company is rolling some new tools; users will be able to add a widget to their Android home screen, adjust the intensity of their workouts, and more.

Best Products of 2018

Our reception desk has so many brown boxes stacked up, it looks like a loading dock. We’re on a first-name basis with the UPS guy. We get new dishwashers more frequently than most people get new shoes. What we’re trying to say is: We…

New Apple Watch begins saving lives one week after getting EKG feature

The Apple Watch Series 4 was updated almost a week ago with a new feature that allows users to take electrocardiogram tests -- and already it seems like the new feature is saving lives.

These are the best smartwatches for everything from fashion to fitness

Tempted to buy a smartwatch? If so, then the growing number of great models available means you've got plenty to choose from. But which one should you pick? Here is our list of the best smartwatches.
Home Theater

Common AirPods problems, and how to fix them

Apple’s AirPods are among the best fully wireless earbuds we’ve seen, but they’re not perfect. If you’re having trouble, take a look at our guide to the most common problems and what you can do to fix them.

The LG V40 ThinQ, G7 ThinQ, and Watch W7 are discounted for the holidays

LG announced a series of deals for the holiday season where you can buy the company's two flagship phones, the V40 ThinQ and G7 ThinQ, as well as its latest smartwatch, for between $150 and $200 off, depending on the device.

Walmart drops prices on Apple Watches and other fitness trackers

Smartwatches, fitness trackers, and wearable heart rate monitors from Apple, Samsung, Fitbit, and Garmin are popular gifts. Wearables are smarter and more capable than in earlier years. We found the best wearables deals on Walmart.