How good are smartwatches at measuring heart rate?

Question and answer

A reader wonders how good the heart rate measurement actually is on the wrist. We answer.

Question: Hi, have read your and many others reviews of heart rate monitors and no one even mentions the most important thing about a heart rate monitor. That is, the ability to measure the pulse. I myself have gone from a watch that measures with a chest strap to one that measures on the wrist. It differs quite a lot. On the one hand, a pulse of approx. 10-20% lower is shown on the wrist, on the other hand the watch seems to be sensitive to various external influences, such as sunlight, skin differences, the structure of the wrist (ie thin, thick wrist etc.) and possibly empty step frequency?
It can be useful to know if all watches that measure heart rate on the wrist are equally sensitive and what differentiates them.

Elias Nordling answers: In general, it is difficult to comment on the accuracy of the heart rate measurement. Partly because it is difficult to test more than two watches (and one heart rate band) at a time, and partly because, if they differ, it is difficult to decide who is more right. Usually, however, in tests we have rarely discovered major differences in heart rate measurement accuracy between different watch models, expensive or cheap.

What we can say after testing many watches and sometimes even compared to heart rate bands, is that the results can differ somewhat in the moment, but usually become similar over time and broadly speaking. That is, at any given moment it can differ quite a lot in what they show for heart rate, but if you look at the sum of the number of heart rate minutes in different heart rate zones, the result is usually similar.

That the wrist generally gives a 10-20 percent lower heart rate does not match my experience, but on the other hand, I have noticed that, for example, falling sunlight can sometimes cause it, and on some days I get too high or too low a heart rate in the watch for unknown reasons. This is also difficult to comment on in individual tests, if we notice it we will of course point it out, but it may not happen during the test period. Therefore, it is also difficult to determine whether a watch is better or worse at this.

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