 SAN FRANCISCO--(BUSINESS WIRE)--The following statement is being issued by Lieff Cabraser Heimann & Bernstein, LLP: 
 
 A comprehensive new study conducted by researchers at California State Polytechnic University, Pomona (“Cal Poly Pomona”) reveals that the PurePulse™ heart rate monitors in the Fitbit Surge™ and Charge HR™ bear an “extremely weak correlation” with actual users’ heart rates as measured by a true echocardiogram (ECG) and are “highly inaccurate during elevated physical activity.” 
 
 With this study, Dr. Brett Dolezal and Dr. Edward Jo set out to test the accuracy of the Fitbit heart rate monitoring devices and to determine once and for all whether they were statistically valid heart rate monitors. It is the most thorough examination of the Fitbit heart rate monitors performed to date, and includes results from 43 separate subjects tested for 65 minutes each during a variety of activities depicted by Fitbit when marketing the devices such as jogging, stair climbing, jumping rope, and plyometrics. While performing these activities, each subject wore a Fitbit heart rate device on different wrists, which were measured against a time-synchronized ECG, the gold standard of heart rate monitoring. At moderate to high exercise intensities, the average difference between the Fitbit devices and the ECG was approximately 20 beats per minute, well beyond any reasonable or expected margin of error. The report concludes: “Overall, the results of this investigation fail to support Fitbit® Surge™ and Charge HR™ wearable fitness trackers and the integrated PurePulse™ technology as valid methods for heart rate measurement.” In other words, “[t]he 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.” 
 
 Although this is the by far the most comprehensive study of the devices’ accuracy, it is not the first. The data from the Cal Poly Pomona study corresponds closely with results obtained in February 2016 by researchers at Ball State University in Indiana (available at http://www.wthr.com/story/31285468/sometimes-your-fitness-tracker-lies-a-lot-fitbit-jawbone-garmin-ifit-misfit-accuracy), in an unrelated and independent study. They too found that the Fitbit heart rate devices were off by “20 or 30 beats per minute,” a margin of error they concluded was unacceptably high and “dangerous – especially for people at high risk of heart disease.” As that report put it, “The box for the Fitbit Charge HR says ‘every beat counts,’ but despite what the package says, the tracking device inside missed lots of them.” 
 
 The new study was included in an amended complaint filed in the consumer fraud class action case filed earlier this year by several purchasers represented by attorneys at Lieff Cabraser and co-counsel against Fitbit, Inc., over complaints that various Fitbit heart rate monitors—now including three Fitbit models equipped with the PurePulse™ technology, the Fitbit Blaze™, Fitbit Charge HR™ and the Fitbit Surge™—fail to accurately measure user heart rates during exercise, the precise use for which Fitbit markets them and for which it charges a premium price. Consumer Protection Attorneys at Lieff Cabraser 
 
 If you purchased a Fitbit Heart Rate Monitor (Fitbit Charge HR™, Blaze™, or Surge™), we invite you to visit our Fitbit Heart Rate Monitor lawsuit page to contact a consumer attorney at Lieff Cabraser.
– The heart rate tracker technology in fancier models of Fitbit starts to become inaccurate when people start exercising, according to a study included in an amended class-action lawsuit against the company. In a press release, plaintiffs' lawyers say California State Polytechnic University put both Fitbits and ECG sensors on 43 separate subjects tested for 65 minutes of moderate to high-intensity exercise, and found that the PurePulse technology in the Fitbits had an "extremely weak correlation" with the heart rate recorded by the ECGs. The researchers say the Fitbit measurement was up to 20 beats per minute off during exercise. In some cases, Fitbits on both wrists recorded different rates—and heart rates of zero were recorded on subjects who were definitely not zombies. Fitbit argues that the study, which was funded by the lawyers, "lacks scientific rigor and is the product of flawed methodology." The company notes that the ECGs were consumer-grade ones, not clinical devices. Alex Montoye, an assistant professor of clinical exercise physiology at Ball State University tells CNN that his own research has found that Fitbits are pretty good at giving a "ballpark estimate of activity levels, but these are difficult elements to measure perfectly." He says the Fitbit is not a medical device and doesn't claim to be one, which is why the company tends to use words like "track" instead of "measure" in marketing materials and never promises 100% accuracy. (Doctors say heart rate data from this man's Fitbit helped save his life.)