LCHB: Comprehensive Testing Confirms Fitbit’s PurePulse™ Heart Rate Monitors “Highly Inaccurate”

Exhaustive new study submitted in class action lawsuit confirms
Fitbit heart rate monitors are “highly inaccurate” and measurements bear
“extremely weak correlation” with true heart rates during exercise.

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

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.

Jonathan Selbin of Lieff Cabraser stated: “We commissioned this
comprehensive, peer-review quality study by academics with expertise in
this area to further test our allegations, and it proved them to be
true. These devices simply are not accurate at measuring heart rates
during moderate or high intensity exercise.” Co-counsel, and former
Assistant to the United States Solicitor General, Robert Klonoff added:
“We are unaware of any comprehensive testing performed by Fitbit prior
to releasing the Fitbit devices with the PurePulse™ technology or since.”

After carefully analyzing the more than 46 hours’ worth of comparative
data—including hundreds of thousands of individual data points—that
resulted from this testing, Dr. Jo and Dr. Dolezal concluded that the
Fitbit devices simply do not accurately track users’ actual heart rates,
particularly during exercise. 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. Moreover, this analysis disregards the
thousands of discrete data points in which the Fitbit devices recorded
literally no heart beat at all. As the authors note, incorporating those
null data points increased the average discrepancy at moderate to high
intensities to approximately 25 beats per minute, an even worse result.
In addition, the study also reported a “startling inconsistency” between
Fitbit devices simultaneously recording the same user’s heart rate on
different wrists.

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,
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
. We welcome the opportunity to
learn of your experiences with your Fitbit Heart Rate Monitor and to
answer any questions you may have about your legal rights.

About Lieff Cabraser and Counsel

Recognized as “one of the nation’s premier plaintiffs’ firms” by The
American Lawyer
, Lieff Cabraser Heimann & Bernstein, LLP, has
successfully litigated and settled hundreds of class action lawsuits in
federal and state courts, including dozens of cases requiring
manufacturers to remedy a defect, extend warranties, and refund to
purchasers the cost of repairing the defective product. It has recovered
billions of dollars for consumers in such cases. With sixty-plus
attorneys in offices in San Francisco, New York, Nashville, and Seattle,
we are among the largest law firms in the United States that represent
only plaintiffs.

Robert Klonoff is the Jordan D. Schnitzer Professor of Law at Lewis &
Clark Law School and served as Dean of the Law School from 2007-2014. He
has vast experience as a class action attorney and expert, and has
written leading textbooks in the field. He is a former Assistant to the
Solicitor General and has argued numerous cases in the U.S. Supreme

The consumer plaintiffs are also represented by Lori Feldman of Levi &
Korsinsky LLP.


Lieff Cabraser Heimann & Bernstein, LLP
Jonathan D. Selbin,
H. Klonoff, LLC
Robert Klonoff, 503-768-6935