Wearable Activity Trackers Close, Not Medically Accurate, but Improving

Wearable activity trackers such as Fitbits may not provide the most accurate recording of heart rate according to a new study published in the Annals of Internal Medicine. Researchers found activity trackers may be good for giving people an insight into their movement (or lack thereof) and encouraging more exercise, but should not be used for medical purposes in accurately measuring heart rate.

The study conducted in 2016 evaluated 40 healthy adults aged 30 to 65. Test subjects wore one of four different wrist-worn activity trackers for the study: Fitbit Surge, Fitbit Charge, Basis Peak, or Mio Fuse. Researchers analyzed the recorded heart rates from these four activity trackers and compared their accuracy to an electrocardiograph (EKG), a cardiovascular test that records a heart’s electrical activity.

Findings from the study showed differences in heart rate readings among the activity trackers and a significant drop in accuracy during exercise versus rest when compared to EKG readings. Inaccuracy ranged from an overestimation of up to 39 beats per minute with the Fitbit Surge to an underestimation of up to 41 beats per minute with the Fitbit Charge. At rest, Fitbit Surge was most accurate while the Basis Peak was least accurate.

Lead researcher and study author Lisa Cadmus-Bertram, assistant professor of kinesiology at the University of Wisconsin at Madison explained, “The heart-rate feature performed better at rest. They’re not as precise during exercise.”

Cadmus-Bertram said, generally speaking, the activity trackers were close to correct when compared with the EKG readings, adding, “At any moment, the tracker could be off by a fair bit. But at most moments, it won’t be.”

The study findings are consistent with findings released in March 2017 by the American College of Cardiology, which found a discrepancy of up to 34 beats per minute.

One explanation for the difference in findings among the activity trackers and the EKG is that wearable devices move around on the wrist during exercise which does not happen during EKG readings where electrodes remain fixed to the body during testing. Variations in readings among the trackers also may exist during exercise depending upon the type and vigorousness of the exercise.

In response to the study findings, Fitbit reminds consumers its wearable technology is not intended as a medical device and that Fitbit’s devices were “tested against properly calibrated industry standard devices like an EKG chest strap across the most popular activities performed worldwide including walking, running, biking, elliptical and more.”

Overall, study authors remain optimistic about the positive benefits of wearable activity trackers for motivating people to move and exercise more. Cadmus-Bertram also acknowledges in the time the study was done over a year ago, activity trackers have continued to advance through improvements in technology so results now may be different from those a year ago.

Bottom line…wearable activity trackers can help motivate you to move more and increase your daily exercise but should not be relied upon as a medical device for accurately measuring heart rate for health purposes.