Wrist-worn heart rate monitors may not produce accurate results

During the past few years, fitness and heart rate monitors worn on the wrist have become popular ways for people to track their fitness goals. A recent study, though, calls into question the accuracy of such devices.

A sample of 50 young, healthy adults found that wrist-worn heart rate monitors had variable accuracy and were not as accurate as a chest strap-based monitor. The heart rate monitors were best at rest and diminished during exercise.

Lead researcher Robert Wang, MD, of the Cleveland Clinic, and colleagues published their results online in JAMA Cardiology on Oct. 12.

The study enrolled 50 healthy adults who did not have cardiovascular disease, did not use pacemakers and did not receive treatment with heart rhythm medications. The mean age was 37 years old and the mean body mass index was 23 kg/m2. Of the participants, 58 percent were women and 14 percent were African American.

The adults were randomized to wear two different wrist-worn heart rate monitors, which were placed tightly above the ulnar styloid. All participants also wore electrocardiographic limb leads and a Polar H7 chest strap monitor, which was secured tightly to the skin.

The researchers assessed the following wrist-worn monitors: Fitbit Charge HR (Fitbit), Apple Watch (Apple), Mio Alpha (Mio Global) and Basis Peak (Basis). They measured heart rates when participants were on a treadmill at rest and at 2, 3, 4, 5 and 6 miles per hour.

They found that heart rate monitors had variable accuracy compared with electrocardiogram based on the concordance correlation coefficient. The Basis Peak overestimated heart rate during moderate exercise, while the Fitbit Charge HR underestimated heart rate during more vigorous exercise.

The Apple Watch and Mio Fuse had 95 percent of differences fall within less than 27 beats per minute and greater than 29 beats per minute of the electrocardiogram reading. Meanwhile, the Fitbit Charge HR had 95 percent of values within less than 34 beats per minute and greater than 39 beats per minute of the electrocardiogram. The Basis Peak had 95 percent of values within less than 39 beats per minute and greater than 33 beats per minute of the electrocardiogram.

The researchers said that body mass index, age and sex did not influence the accuracy of the heart rate monitors.

They added that the results might not be generalizable to other populations and should be confirmed with other types of exercise and other devices.

“Electrode-containing chest monitors should be used when accurate [heart rate] measurement is imperative,” the researchers wrote. “While wrist-worn [heart rate] monitors are often used recreationally to track fitness, their accuracy varies; two of four monitors had suboptimal accuracy during moderate exercise. Because cardiac patients increasingly rely on these monitors to stay within physician-recommended, safe [heart rate] thresholds during rehabilitation and exercise, appropriate validation of these devices in this group is imperative.”