Incorrect HR during Tennis - Fenix 7

As said, the watch was working much much better up until 3 weeks ago. My problem is this; the fact that it has gotten way way worse. It used to be pretty ok and now it simply isn't. Nonetheless, I do know that with a chest HRM the results are much more reliable.

You were just lucky - the more data you acquire, the more the inherent inaccuracy of the WHRM for active sports becomes obvious.  Correlation does not equal causation.

HTH

I beg to differ. I recorded like 15+ tennis activities, and they were all fine. And since the latest software update, it is really bad. It has to be something else, probably the software update.

Maybe the phase of the moon?

Tennisfan said:

Otherwise, how can it be that it used to work fine and now it doesn't?

Tweaks and adjustments have been made to the algorithm ever since the arrival of wrist heart rate. The result has always been improvement for some who were having problems but made worse for some who were not. It's possible you fall into the latter category. 

Tennisfan said:

HR during tennis was accurate more or less.

It can't be both ways. It's either accurate or it's not. What were you comparing it with to determine its accuracy? 

As noted, for consistency you need a strap. Then you can compare the wrist heart rate with the strap and better determine how accurate the wrist heart rate is/was.

It can actually be both ways. IN the sense that it is one thing having an error of +- 5 bpm and another thing having an error of +- 30 bpm. Before, it used to be pretty accurate, in the sense that what the watched showed agreed with how I measured my bpm by counting my beats (by pressing the carotid artery with my fingers). On top of that, the watch showed, say, 140 bpm, and I did feel like 140 (ofc it could be +-5 or even +- 10). Now, it is completely different. The watch shows 105 bpm, and my bpm is certainly above 130 bpm. This is a huge difference wrt how it used to be.

You spent 1k on a watch...get a hrm pro....start the activity leave the watch on or dump in your bag...now the hr will always be 100%

I see it differently. After spending 1k on a watch with marketed function that worked properly, there is no justifiable reason to spend more just to have something working as it was working before the software update.

This might be the same issue: https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-7-series/306474/has-9-33-ruined-heart-rate-monitoring

Garmin - Chris