Health study finds Apple Watch has the most accurate heart-rate monitor

Measuring heart rate accurately is pretty easy, comparatively speaking. Electrocardiograph methods have been in (basic) use for over a century, but even today, they’re not really practical for use outside of a medical practice. Hooking electrodes up to the skin is somewhat impractical for day-to-day use, to put it mildly.

Health study finds Apple Watch has the most accurate heart-rate monitor

That means that fitness trackers promising heart-rate monitoring have to make compromises. While some offer support for chest straps to measure the heartbeat directly, most of them plump for optical heart-rate sensors. These work by illuminating the capillaries in the wrist with an LED light, while an adjacent sensor measures the frequency at which blood flows underneath the skin, giving you an estimated rate at which the heart is pumping blood.

That’s the intent anyway – a compromise solution based on the practicalities of fashion and technology – but how accurate are they? The Cleveland Clinic has just published a study of four fitness trackers that provides some interesting reading for fitness fans.

The researchers took four fitness trackers (the Apple Watch, Fitbit Charge HR, Mio Fuse and the Basis Peak) and measured their results against a chest strap and an EKG on 50 healthy adults at rest, walking and running on a treadmill. In all, they recorded 1,773 heart-rate readings across all the devices, with readings ranging from between 49 and 200bpm.fitbit_charge_hr_optical_heart_rate

Overall, the chest strap was almost as good as the EKG, measuring 99% accuracy, which isn’t too surprising as both technologies work the same way, capturing electrical activity directly from the heart.

Things dropped off for the commercial fitness bands, but it was the Apple Watch that maintained the most accuracy, managing around 91%, beating the Mio Fuse by a nose. The Fitbit Charge HR and Basis Peak had around 84% and 83% accuracy, respectively.

The reduced accuracy of wrist-based tracking isn’t surprising to study co-author Dr Gordon Blackburn, director of cardiac rehabilitation at the Cleveland Clinic. “You need to have good contact between the photosensing cells; as a person is exercising more vigorously, there’s more bounce, so you may lose some of that contact,” he explained.

However, that’s not to say that wearables shouldn’t be consulted anymore, but perhaps take it with a pinch of salt – especially at higher activity levels. “What we really noticed was all of the devices did not a bad job at rest for being accurate for their heart rate, but as the activity intensity went up, we saw more and more variability,” said Blackburn. “At the higher levels of activity, some of the wrist technology was not accurate at all.”

The moral of the story is that if you’re serious about measuring your heart rate, it might be time to consider a chest strap.

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