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Pulses rise as Fitbit defends accuracy of fitness trackers

A study funded by a law firm suing the wearables maker raises questions about the accuracy of Fitbit technology.

The Fitbit Charge HR is the best-selling fitness tracker on the market.

Sarah Tew

A study of Fitbit heart monitors has set pulses racing.

The San Francisco wearables company on Monday defended the accuracy of its fitness trackers after a study conducted by researchers at California State Polytechnic University, Pomona, found its PurePulse technology didn't correctly monitor heart rates. The study was commissioned by lawyers representing a group of customers who are suing Fitbit over the accuracy of its products.

The study found an average difference of 20 beats per minute between Fitbit devices and an electrocardiogram when used at moderate to high exercise intensities. The researchers said the devices "cannot be used to provide a meaningful estimate of a user's heart rate."

Fitbit blasted the study, challenging its purpose and methodology, as well as the quality of the electrocardiogram used.

"What the plaintiffs' attorneys call a 'study' is biased, baseless, and nothing more than an attempt to extract a payout from Fitbit," the company said. "It lacks scientific rigor and is the product of flawed methodology."

The feud over Fitbit's technology, which is used in its Surge and Charge devices, isn't the first time the accuracy of the company's products has been called into question. Fitbit's products accurately measured the number of steps a wearer had taken, but were less precise about distance traveled and calories burned, according to a 2014 article in Berkeley Science Review.

The researchers compared data recorded from the trackers with data taken from a BioHarness -- a chest-worn heart rate monitor -- hooked up to an electrocardiogram. The study used a sample group of 43 participants and found Fitbit devices could be out of kilter by as many as 25 beats per minute.

Fitbit took issue with the electrocardiogram used, which it called "consumer-grade" and "not a true clinical device." It cited a January study by Consumer Reports that gave its heart monitors an excellent rating.

Jonathan Selbin of Lieff Cabraser, the law firm bringing the case, said the fact that the study was funded by the plaintiffs' is "meaningless."

The case could head to court, where blood pressure will almost certainly be elevated.