Accuracy of popular wrist-worn heart rate monitors varies during exercise

The accuracy of four popular wrist-worn heart rate monitors varies under different conditions of physical exertion, researchers reported in JAMA Cardiology.

The four wrist-worn heart rate monitors assessed were the Apple Watch (Apple), Basis Peak (Basis), Fitbit Charge HR (Fibit) and Mio Alpha (Mio Global). Heart rate values were compared between the four wrist-worn heart rate monitors and those with standard electrocardiographic limb leads and a Polar H7 chest strap monitor (Polar).

“We found variable accuracy among wrist-worn heart rate monitors; none achieved the accuracy of a chest strap-based monitor,” Robert Wang, MD, from the Heart and Vascular Institute, Cleveland Clinic, and colleagues wrote. In a research letter published in JAMA Cardiology. “In general, accuracy of wrist-worn monitors was best at rest and diminished with exercise.”

Variable accuracy

Researchers enrolled 50 healthy adults (mean age, 37 years; mean BMI, 23.5 kg/m²; 58% women). Participants wore the chest heart rate monitor and were randomly assigned to wear two different wrist-worn heart rate monitors. The wrist-worn monitors were secured tightly above the ulnar styloid, according to the study.

Participants completed a treadmill protocol, in which heart rate was assessed at rest and at 2 mph, 3 mph, 4 mph, 5 mph and 6 mph. Heart rate was assessed again after the treadmill exercise during recovery at 30 seconds, 60 seconds and 90 seconds.

In total, 1,773 heart rate values ranging from 49 bpm to 200 bpm were recorded during the study.

The researchers observed variable accuracy of the wrist-worn heart rate monitors compared with the chest-worn monitor:

The Basis Peak overestimated heart rate during moderate exercise (median difference at 2 mph, –8.9 bpm; median difference at 3 mph, –7.3 bpm).

The Fitbit Charge HR underestimated heart rate during vigorous exercise (median difference at 4 mph, 7.2 bpm; median difference at 6 mph, 6.4 bpm).

In addition, the researchers observed variability across a spectrum of midrange heart rates during exercise. With the Apple Watch and Mio Fuse wrist-worn monitors, 95% of the heart rate differences occurred within –27 bpm and +29 bpm of the chest-worn monitor. With the Fitbit Charge HR wrist-worn monitor, 95% of the heart rate values were within –34 bpm and +39 bpm. With the Basis Peak wrist-worn monitor, 95% of the heart rate values were within –39 bpm and +33 bpm, according to the results.

Accuracy of the wrist-worn monitors was not affected by age, BMI or sex.

Call for appropriate validation

“Electrode-containing chest monitors should be used when accurate heart rate measurement is imperative,” Wang and colleagues wrote. “While wrist-worn heart rate monitors are often used recreationally to track fitness, their accuracy varies; two of the 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.” – by Cassie Homer

Disclosure: The researchers report no relevant financial disclosures.