ENTER RESTING HEART RATE

On my Epix I can change/enter it in the user settings.

... more precisely (though varying from model to model), it is typically in Device Settings » your device » User Profile » Heart Rate & Power Zones » Heart Rate » Resting HR » Use Average » OFF » Set Custom

Which watch exactly? Best asking on the forum for your respective watch model, since the menus may vary depending on that.

trux said:

it is typically in Device Settings » your device » User Profile » Heart Rate & Power Zones » Heart Rate » Resting HR » Use Average » OFF » Set Custom

In my experience, like toddsdn said, this affects the resting HR used for HR zone calculations (when applicable - e.g. zones based on HRR%). It does not affect fitness age calculation [*]

For example, I've had that option set to Set Custom > 50 bpm forever. But if I look at my fitness age page in Connect, the card for Resting HR says "maintain 45 bpm", which happens to be equal to my 4-week average for *measured* resting HR (in Health Stats > Heart Rate). 

In short, I don't think you can manually enter resting HR for the purposes of fitness age or any other feature that looks at resting HR measurements.

[*] It does seem like *Edge* devices gained this feature 2 years ago.

https://forums.garmin.com/sports-fitness/cycling/f/edge-1040-series/351943/new-edge-1040-series-version-19-19-now-available 

> Enabled manual setting of Resting Heart Rate to enable Fitness Age calculations on Garmin Connect.

This especially makes sense in light of complaints from Edge users who don't own a Garmin watch - obviously they only record HR data during activities, and therefore have the same resting HR problem as OP.

Referring to that update, someone said they couldn't find the new option:

https://forums.garmin.com/sports-fitness/cycling/f/edge-1040-series/352114/how-to-enabled-manual-setting-of-resting-heart-rate-to-enable-fitness-age-calculations-on-garmin-connect  

I am also unaware of such on option on watches (other than the option already mentioned, which does not appear to affect fitness age calculations.)

My best (educated guess) is that the only workaround for Garmin watches is to wear the watch more often (especially while you sleep, as Garmin recommends).

Oh, didn't know there would be differences between watches for a common thing like fitness age.  I will look at the Garmin Forerunner 245 forum.

flowstate said:

In my experience, like toddsdn said, this affects the resting HR used for HR zone calculations (when applicable - e.g. zones based on HRR%). It does not affect fitness age calculation [*]

My experience with several different Instinct models differs. Fitness age shows exactly the Resting HR that I have set manually. Perhaps you did not notice any difference after changing the RHR value, because Fitness age uses the 7 days average, so you may need to wait up to a week, before you see exactly the value you have set.

I was hoping not to have to use the 7 day average and wear my watch all the time.  Just want to only wear the watch while doing an activity and just type in my RHR to be used in the fitness calculation.  Looking like thats a  no go for the Forerunner 245.

toddsdn said:

I was hoping not to have to use the 7 day average and wear my watch all the time. 

If you set up the RHR manually, after 7 days, the 7days average will be equal to the value you've set up manually 

However, setting the RHR value manually makes the Fitness Age useless, because one if its most important metrics is no more measured. You can as well write your desired fitness age on a sheet of paper and look at it instead.

On another note, looks like Garmin recently add a link below your vo2max reading saying see your fitness age whereas before is just said it right under the vo2max reading only with percentile.  I am 61, vo2max 44 and it used to always say my fitness age was in the 20's.  Now that its using 132bpm is says my fitness age is 62!!!  I love it.