Fitness wearable company Fitbit Inc recently became the subject of a class action lawsuit that claimed that its devices are not as accurate as it claims, and now that lawsuit may have some evidence to back it up thanks to a new study by researchers at the California State Polytechnic University, Pomona.

The researchers conducted a test using Fitbit PurePulse wearables on 43 healthy individuals. To determine the accuracy of the devices, the test subjects engaged in varying levels of physical activity, and the results of their Fitbit were compared to the results of an external heart rate monitor.

According to the researchers, the heart rate measured by the Fitbit was sometimes more than 20 beats per minute off of the rate measure by the other monitors, and the greater the level of physical activity, the more inaccurate the Fitbit wearables seemed to be.

“The PurePulse Trackers do not accurately measure a user’s heart rate, particularly during moderate to high intensity exercise, and cannot be used to provide a meaningful estimate of a user’s heart rate,” the researchers said.

While the study certainly seems to be damning of Fitbit’s accuracy, it is important to note that it was commissioned by the plaintiffs in the case against Fitbit, something that the company has been quick to point out in a particularly harsh statement that it released to Gizmodo.

“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 in its statement. “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.”

Fitbit said that its devices had undergone rigorous testing prior to being released to the market, and the company pointed to an independent study conducted by Consumer Reports, which rated Fitbit’s wearables as “excellent.”

Image courtesy of FitBit Inc