If a recent study by California State Polytechnic University rings true, FitBit could be in trouble.

The study, commissioned by plaintiffs after a class action lawsuit against the tech company, claims that the heart trackers found in the Fitbit Blaze, Fitbit Charge HR and Fitbit Surge produce “highly inaccurate” readings during moderate to intense physical activity. The setup for the study was fairly simple: forty-three subjects were monitored while they used the Fitbit Surge and Charge HR trackers. The FitBit PurePulse™ results were compared with an electrocardiograph (ECG). The disparity between the two devices was concerning.

SEE ALSO: The Bodybuilder’s Problem With Fitness Wearables

“The Charge HR exhibited an aggregate mean bias of -6.1 beats per minute (bpm) and a mean absolute differential of 12.2 bpm. During higher exercise intensities, the mean bias was -12.5 bpm and the mean absolute difference increased to 15.5 bpm,” the study says. In layman’s terms, the study purports that the Fitbit’s reading was up to 15.5 bpm off during heavy exercise. 


To put that into perspective, the ideal heart rate for a healthy individual is 60-100 bpm.

FitBit’s response? They’re going nuclear. Gizmodo published FitBit’s full statement, the reiterates the fact that this study was conducted after the lawsuit and by the plaintiffs. FitBit says the ECG used in the study wasn’t up to par.

“What the plaintiffs’ attorneys call a “study” is biased, baseless, and nothing more than an attempt to extract a payout from Fitbit,” the statement reads. “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.”