Autodetection of Physiological Metrics

Does anyone have any info on how physiological metrics are autodetected. I'm particularly interested in the Max HR. Looking through the menu, there appears to be a setting to auto detect the max HR, but I'm not sure how or if it works. How does it interact with the setting I guessed at and put in the watch at the beginning? Will it just auto update that number once it has info (and how long does it take to get info)?

If it's the same as it was on the fenix 3, it's nothing clever. All it does is if you've set your max HR to 178, and during an activity your HR reaches 180, then it will increase your max HR to 180.

Ok, so the smart thing would be to set the Max HR low and let it set it higher rather than guessing too high in the first place.

Ok, so the smart thing would be to set the Max HR low and let it set it higher rather than guessing too high in the first place.

Yes, but only if you're going to be doing an all-out lung-bursting 100% effort activity to actually reach your max HR, otherwise your metrics will be skewed until you do so.

I don't know that I ever hit max but I'm also not sure how to figure out max based on a formula that isn't accurate. I regularly do intervals where I go all out. If I look at my max heart rate in those, it's typically 175. I dunno if I should use that or add something like 5-10 to it. I'm 43 FWIW which means according to the formulas I'm 175-180ish.

I guess maybe my basis for this question is a bit off. I originally assumed the "autodetect" feature was smart enough to interpolate my heart rate max and it sounds like that's not really the case. And now I'm back to trying to figure out my max heart rate the old fashioned way...

I don't know that I ever hit max but I'm also not sure how to figure out max based on a formula that isn't accurate. I regularly do intervals where I go all out. If I look at my max heart rate in those, it's typically 175. I dunno if I should use that or add something like 5-10 to it. I'm 43 FWIW which means according to the formulas I'm 175-180ish.

I guess maybe my basis for this question is a bit off. I originally assumed the "autodetect" feature was smart enough to interpolate my heart rate max and it sounds like that's not really the case. And now I'm back to trying to figure out my max heart rate the old fashioned way...

Ignore formulas... I'm 48 and I work on a Max HR of 200 - I know I can get it over 190 without giving it 100%. There's a bit of guesswork involved, but last year I managed to hit 196 on an all-out bike KOM attempt (I failed), and I reckon I still had that extra 4bpm in me. So yes, going for it so it's really uncomfortable and unsustainable for more than a few seconds and then adding another 5-10 isn't exactly scientific, but it's probably more accurate than something like 220 minus age.

I don't know that I ever hit max but I'm also not sure how to figure out max based on a formula that isn't accurate. I regularly do intervals where I go all out. If I look at my max heart rate in those, it's typically 175. I dunno if I should use that or add something like 5-10 to it. I'm 43 FWIW which means according to the formulas I'm 175-180ish.

I guess maybe my basis for this question is a bit off. I originally assumed the "autodetect" feature was smart enough to interpolate my heart rate max and it sounds like that's not really the case. And now I'm back to trying to figure out my max heart rate the old fashioned way...

Interpolate it with what?
No, it keeps a record of the maximum HR attained.
So if you set it 175 but you exceed that then it will autoupdate that maximum setting.

As for formulas. There are many out there. The best (such as the 25yr multi-subject study at Oakland University) still have a quoted accuracy of 2-5bpm. So go with what you have evidence for, i.e. that 175 bpm max on intervals. Now that is much better science.

Ignore formulas... I'm 48 and I work on a Max HR of 200 - I know I can get it over 190 without giving it 100%. There's a bit of guesswork involved, but last year I managed to hit 196 on an all-out bike KOM attempt (I failed), and I reckon I still had that extra 4bpm in me. So yes, going for it so it's really uncomfortable and unsustainable for more than a few seconds and then adding another 5-10 isn't exactly scientific, but it's probably more accurate than something like 220 minus age.

The 220 - Age formula has a standard deviation of 13, so it can be way off for a significant chunk of the population. A 100% lung busting effort (assuming you are healthy and exercise regularly) to understand YOUR true maximum can add a lot of value to HR zones, calorie estimates, etc, but once you know what you MHR is, you don't need to do it again for another 2-3 years.

My understanding is that a "100% lung bursting effort" is required for at least a couple minutes to accurately measure max heart rate and that it probably needs to be done after you're already pretty worn out. Suggesting to me you probably won't typically see your max HR too often. I assume I'm not seeing it intervals to be honest. The other part of the equation is trusting that the Garmin is actually measuring your HR accurately at that point...

If any of that's wrong, I'd love any help finding it as accurately as possible. My HR really doesn't seem to fit in well with "normal." I have about a 40 bpm RHR and I'm not built like an olympic athlete (at all). I also don't feel like I'm going hard enough unless I'm going all out. Maybe my max HR is 10 points higher than I think but I kinda doubt it. I appreciate all the input. Thanks.

Find a hill.
Run up the hill as fast as you can.
(The hill needs to be long/high enough that it takes you 1:30 to 2:00 to get to the top.)

Take your pulse as soon as you're finished running.
Do this the old fashioned way: 15 seconds on the stopwatch; fingers on carotid artery; multiply number by 4.

Repeat above process two more times.
That will be your max heart rate.