Can you rely on your smartwatch to monitor your heart rate?

You see people wearing them all the time these days, the smart watches. They come in many different shapes and brands and most people use them to track their workouts and heart rates. But are they reliable? And how do they actually measure your heart rate?

How do they measure your heart rate?

Smart watches essentially work upon one simple idea: blood is red because it reflects red light and absorbs green light. The smart watch projects a green light on the skin and the light that isn’t absorbed by the tissue beneath the skin is reflected back to the sensor. So, when your heartbeat is high, there’s more blood flow in your wrist, and more green light absorption. Using an algorithm, the watches then work out how high your heart rate is.

Ok enough smart talk, I bet you just want to know if they are reliable.

Are they reliable?

There has been a number of studies that have looked at this. The commonly accepted gold standard of heart rate monitoring when exercising is a mobile Electrocardiogram (ECG) device. A study published in the Journal of Medical Internet Research compared a number of smart watches against the mobile ECG to see how accurate they were over a 24-hour period. What they found that the Fitbit and Apple watches were the most accurate. The Apple Watch had an average difference of 1.8 beats per minute (bpm) while the Fit bit had an average difference of 3.4 bpm.

What they concluded was that smart watches in particular the two mentioned above provided an acceptable level of accuracy during day to day activities. It did find also that the heart rate was most inaccurate during interval training where the heart rate changes quickly.

So, should I use them?

These findings should be taken with a grain of salt though. This shows that there is still a difference between what your heart rate is and what the smart watches are telling you. This can become problematic, especially if you have a heart condition and you can’t elevate your heart rate too high.

In the end, smart watches are a really good bit of equipment to give you an idea of what your heart rate is. I wouldn’t be relying on it as the be-all and end-all but I wouldn’t be throwing it in the bin either.