NEW YORK (TheStreet) -- Fitbit (FIT) - Get Report  shares are taking a hit, down 3.98% to $13.99 on Tuesday after researchers at the California State Polytechnic University, Pomona, found that the company's PurePulse device is "highly inaccurate," CNBC reports. 

Researchers tested the heart rates of 43 healthy adults wearing Fitbit's PurePulse trackers. The subjects were observed during their exercise, which included jump roping, outdoor jogging, and stair climbing.

The results were then compared with a separate study where researchers hooked the same individuals up to a medical device called BioHarness that measures heart rates.

Overall, the study showed that Fitbit products were off by 20 beats per minute on average during more intensive workouts.

Lieff Cabraser, the law firm behind the class action lawsuit against Fitbit hired the researchers at the university to conduct the studies, CNBC noted. 

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

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