How accurate are fitness gadgets?

By March 20, 2018May 23rd, 2023blood pressure, exercise, fitness, health

How accurate are fitness gadgets that monitor heart rate?

Robina 7 Day Doctors and Acupuncture recommends this article.

Wearable tech including smartwatches and fitness bands are now owned by 1 in 7 of us. These devices claim to monitor everything from our heart rates to the amount of calories we burn and the number of steps we take.

 But are they accurate?

Heart rate

You can estimate you maximum heart rate with a simple calculation:

220 – your age

(So if you are 50 then your maximum heart rate should be 170).

When carrying out exercise, use this as a marker of how intensely you are exercising.

If you are aiming for high intensity exercise, your pulse should be 70–90% of your maximum heart rate.


How do heart monitors work?

Wrist worn monitors have sensors that assess the colour of the blood vessels near the surface. As your blood vessels fill and empty with each heart beat, they change colour. The sensors detect this and determine your pulse from that. Some smartphone apps work in the same way, asking you to put your finger over the phone camera.

How accurate are they?

To put some wrist monitors to the test, we got a group of volunteers to wear two different wrist straps at the same time as a professional-standard heart rate monitor.

What we found was there was often a big difference between the wrist monitors and the accurate chest monitor. Particularly once the volunteers started exercising and their heart rates went up.

So, what’s going on?

Well, we thought there were two major problems with using the wrist straps to record pulse.

Firstly, those with dark skin in our experiment seemed to have more problems with one of the commercial wrist devices than those with paler skin. This could well be due to difficulties detecting the subtle colour changes caused by varying blood flow.  People with tattoos on the wrist have also reported similar problems.

Secondly, the wrist monitors can easily be too loosely fitted, this can cause problems with the sensor used to monitor the pulse.

If you want to find your heart rate while you are exercising, or at any other time, the best advice is to measure your own. This is easily done by placing your first two fingers against the vein in your neck as shown below, then feel each strong beat and count how many you feel in a minute – no fancy gadgets needed!



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