Fenix identifies a new maximum heart rate that’s much higher than anything observe during the run

Mine has done that a couple of times and set the max HR at 178 whereas my actual max HR is 164. I’ve turned off auto detection because I’m pretty sure my max HR is not going to increase.

mcbit said:

Mine has done that a couple of times and set the max HR at 178 whereas my actual max HR is 164

Exactly my case as well!

I have experienced the same with HRM Run + Fenix 7 Saphire Solar on 10.43 software.

One more here...

I think there's another thread here pointing to the same issue. 

Same happens with my 955. I assumed it's a predicted / estimated value using algorithms. Like VO2.

It still makes a bit of sense to have your max HR calculated to be higher than max reached on a run - esp. nor a hectic one. You very very seldom actually reach your true max HR.
My experience was worse! With a known max HR, I went for an easy run. Lo and behold, Garmin detected a new max HR, 20 bpm lower than my known max. It's just silly to guess a new much lower max HR fresh off an easy run. That said, the HRM Pro was new, so it may have been a first-wear thing as well... experience remains the same.

If you’ve set your max HR and have auto detect enabled it should only detect a higher value than the current one. I’ve certainly never had a lower HR detectect on any of my Garmin watches.

I have disabled the max HR detection very quickly after I got the Epix 2 because of this problem. I first started with 220-age, and then I tweaked the max HR value up and down until the daily suggestion workout for threshold matched my actual threshold pretty well. I made sure I kept a balanced training week between the tweaks to give anough time for the VO2 max model to adjust. It is hard to predict which way things will change, when you change the max HR, but it stated converging within a month or so. That took my max HR down to 164.

Since then, Garmin updated the max HR detection software, but it didn't change anything in my case.

Recently I did a field max HR test. This is way too hard to do on a regular basis, but that gave me 166, so pretty close to the first, much easier method.

Haha, that's exactly why I mentioned it. In many many years of using Garmin Edge and Fenix, this was a first. As mentioned, maybe it was simply due to 1st strap wearing, don't know... I just turned off auto detect on HR Max immediately thereafter.