COLUMBUS (WFLA) — A study recently released claims that the heart rate monitors on the popular fitness tracker Fitbit are “highly inaccurate.”

According to NBC News, the researchers found that Fitbit is miscalculating heart rates with the PurePulse monitors by as many as 20 beats per minute on average.

The study was conducted at California State Polytechnic University. Researchers tested 43 adults while they wore Fitbits and were hooked up to another system to monitor their heart rates.

Comparative results from rest and moderate to high intensity – including jump rope, treadmills, outdoor jogging and stair climbing – showed that the Fitbit devices miscalculated heart rates by up to 20 beats per minute on average during more intensive workouts.

But Fitbit is fighting back. The company points out the study was commissioned by a law firm that has already filed a class action lawsuit against Fitbit. The company also questions the study’s methodology.

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

This is not the first time Fitbit’s heart rate monitors have been called into question. A separate study at Ball State University in Indiana and journalists at NBC-affiliated TV station WTHR also found that one of the Fitbit’s models missed heartbeats, marking an average heart rate error of 14 percent.What others are clicking on: