How Do Optical Heart Rate Monitors Work?

Technology has come pretty far and in many ways, we’re finally living in the future that was promised to us by The Jetsons. We have the screens that talk to us and now we’re wearing smartwatches that can track our health and even take photos and make calls.

And when you really think about it, these smartwatches are pretty amazing. No longer do we need to strap something around our chest and shave ourselves to get a reading of our heart rate – now we can do it through our watch all throughout the day. Even most phones now often basic heart rate readings!

But just how effective is this form of heart rate monitoring? And how exactly does it work?

Optical Heart Rate Monitors: The Basics

If you turn on your heart rate monitor on your phone, or flip over your FitBit, you’ll find that they feature a bright light that shines right where the devices take your pulse. This is the ‘optical’ part of the equation.

On a phone, this light will normally be right by what looks like a little camera and this is no accident – rather the two will be working in conjunction with one another in order to get your heart rate.

Specifically, the infrared light is going to shine on your skin which will allow a camera to ‘look through’ it and see your blood vessels underneath. From there, they will then use something called ‘pulse oximetry’. This is a technique that looks for changes in the appearance of your blood – which in turn reflect levels of oxygenation. As the purpose of your heartbeat is to circulate blood and oxygen, each beat will alter the amount of oxygen that is in your veins and this in turn will alter the amount of infrared light that is getting absorbed or reflected. Your phone or smartwatch can read these changes and in turn, that allows those devices to take a reading of your pulse.

Drawbacks and Limitations

Unfortunately, these devices are still not as accurate as chest straps and nor are they as rapid in picking up changes. If you want the most accurate reading possible then, you should still probably opt for a chest strap from a company like Polar or alternatively, something that measures skin conductivity.

One of the issues with a wrist-worn optical heart rate monitor is that other things can also affect the oxygenation of your blood. Among these are muscle contractions – so if you are working out, this can actually upset the accuracy of the readings you’re getting.

The smarter fitness trackers on the market though do attempt to mitigate this factor. The Microsoft Band for instance can reduce this inaccuracy using a complex algorithm that combines user input (you tell it when you’re training) alongside other sensors such as the galvanic skin response, skin temperature and gyroscope/gyrometer. The idea is that these devices can work out what kind of movements you’re engaging in and thus adjust the heart rate reading accordingly.

These meet with varied amounts of success however – so if you’re going to be shelling out a lot of money on a tracker, make sure to do your research first to ensure that the readings it provides will be as accurate as possible!

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