There's already been a class action lawsuit filed against the company that makes the popular FitBit Heart Rate trackers, claiming they're inaccurate in calculating heart rates of consumers who wear them. The FitBit is designed to allow the wearer to see what their heart rate is throughout the day during various activities, with hopes of helping them boost physical activity and becoming healthier.

A lawfirm has filed the suit, and Lief Cabraser, the law firm, now has added the results of a study that seems to support that theory.

Researchers at Cal State University Pomona tested 43 adults using FitBit's Surge Watches and Charge HR bands. They were also hooked up to a BioHarness device that measured heart rates while jumping rope, outdoor jogging, treadmills, and stair climbing.  According to the study, the FitBit units miscalculated heart rates by an average of up to 20 beats per minute, especially during vigorous exercise.

The lawsuit was specifically targeted at what's called the PurePulse heart rate technology, which FitBit purchased. While the Cal State study claims the FitBit Blaze, Surge and Charge HR models are highly inaccurate, FitBit released a statement refuting the study.

FitBit said the study was nothing more than an attempt to extract a payout from their company. They said the study, which WAS commissioned and paid for by the law firm, was conducted with a consumer grade BioHarness device, NOT a medical grade or clinical device. They questioned the accuracy and validity of the study's data.

While the law firm and study said the inaccuracies were potentially harmful to people with heart conditions and those who have to exercise carefully, FitBit countered by saying their devices are "designed to give meaningful data" to people to help them reach their fitness goals, and  "are not intended to be scientific or medical devices."

FitBit says they studied the PurePulse technology closely for three years before making the purchase and creating the popular exercise heart rate monitors.