Can we trust Heart Rate Monitors?

If you’re dark skinned, your heart rate monitors may not be accurate. But should you worry about it?

Nothing grabs attention like putting ‘racist’ and ‘technology’ together in the same sentence. STAT, a US-based health and medicine publication, did an article claiming that wearable fitness trackers were less accurate for dark-skinned people than for the light-skinned.

There is a science behind the development of this wearable: most fitness trackers use PSM or photoplethysmography technology to track blood volume changes using light, to read heartbeat. Here is how it works: a green light is sent to the bloodstream, and a receptor reads the light reflected. (Why green? Because human blood cells absorb light in this wavelength.) In between heartbeats, the bloodstream is lower, and so less light is absorbed and more is reflected. In this way, by reading how the light reflected goes up and down, the gadgets can keep a count of your heartbeat.

The absorption of green light increases in the presence of melanin in the skin. Since dark-skinned people have a higher melanin content, the light absorbed is greater, leading to an inaccurate reading.

A 2017 study published in the Journal of Personalized Medicine tested the accuracy of wrist-worn, sensor-based devices such as Apple Watch, Fitbit Surge, Microsoft Band, Samsung Gear S2, and more. It found that the error margins were higher when tested on people with dark skin tones.

Does this mean that those with darker skins should avoid fitness trackers? Not really.

 Dr Rajat Chauhan, founder of Back 2 Fitness, a sports-medicine clinic, says that the point of fitness trackers is “to find out what kind of zone you’re exercising in: high intensity, or low intensity, depending on what your resting heart rate is.” That works even if your heart rate reading is not accurate. Also, let’s remember that these are not medical devices.

In this column we decode health trends and decide if it’s all just ‘hype’ or actually ‘happening’

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