Max Hr auto detect is displaying wrong results

I did see a post somewhere in these forums dated back a couple of years where garmin addressed this problem and they said they were concerned and wanted to hear from people who were having these problems.

ANTOS said:

When I have my Max hr zone set to auto detection it updates to a higher value than I achieved in the running activity. The watched asked if I wanted to accept the new Max hr which was previously at about 190 to 193bpm. In the activity, which was also the highest I've achieved in all activities, was at about 173bpm...

In the recent firmware updates, Garmin has improved the Max HR detectioin. It can give you a Max HR value higher than any peak HR value from your workouts.

It could also be lower, if you have bogus high HR data in some workout that the watch filtered out for Max HR detection purposes.

You can also get a max HR detected from sub-maximal activities (eg: easy or tempo run). This is because the watch is including HRV in the data used for detection.

It is rare than an athlete reaches its Max HR during any workout. Most intense workouts (like a series of uphill or 800m repeats at max speed, or a 5K personal best) will be get within about 5bpm of your Max HR. Typically, muscles will shut down because of lactic acid before you get to reach your Max HR.

Assuming you are wearing a chest strap for accuracy, the Max HR detection is spot on, but not fool proof. As recentely as last week, I had a dry chest strap giving a period of out of range HR values that triggered an absurd Max HR auto-detection.

Note: after you get a new Max HR, I recommend you check your heart rate zones. If the % are off, reset the zones. There is a bug here.

Forerunner 945 LTE just changed my max-HR from 184 to 191 and now 194 in a few weeks, is that physically possible? Only difference is maybe losing 1 kg and started swimming, now BMI is 18.9 and VO2 max 46. Female 44 yo, trail running +40km/week. Should I lower the max-HR manually?

Nico Norway said:

is that physically possible?

Well, your real Max HR doesn't change that fast: it can slowly go down with age (maybe less than 1% per year in trained athletes), or it can go down under certain training regimen and increase during de-training.

https://pubmed.ncbi.nlm.nih.gov/10688280/

In your case, it is more likely you are seeing some adjustments due to the algorithm for estimation rather than real changes.

I don't know which version of the algorithm the 945LTE has, but we can hope it is the latest.

Depending on your training workouts, including sub-maximal efforts, your estimates can vary.

I am assuming your are always wearing a good chest strap, correct?

Nico Norway said:

Should I lower the max-HR manually?

If you are a well trained athlete, you can go run a 5K personal best, take the peak HR of that PB and add 5bpm to get a pretty good estimate. You will find other ramp-based field test online.