The journal JAMA Cardiology has published a research letter that found that the Apple Watch’s heart rate monitor is more accurate than the one in Fitbit’s Charge HR, and is matched only by the Mio Alpha.
The study, led by doctors at the Cleveland Clinic, compared the heart rates reported by monitors in a range of wrist-worn consumer devices to the rates reported by an EKG and a Polar H7 chest strap. The chest strap had a 99 percent correlation with the EKG — not a surprise, as chest-worn sensors are known to be pretty accurate.
Generally speaking, the study found, the consumer devices were most accurate when at rest and less accurate during vigorous activity. Apple and Mio’s products had a 91 percent correlation with the EKG; the Charge HR correlated 85 percent. A Basis Peak (no longer sold) over-counted heart rate, but the Charge HR under-counted — meaning it reported a heart rate lower than reality. The authors referred to the Basis and Fitbit’s results as “suboptimal.” (It’s worth noting that Fitbit’s Charge HR has been updated to the Charge 2, which was not tested.)
Researchers said that if accuracy is important, stick with a chest strap.