User-specified (Custom) Heart Rate / Zone

Question

I have a pixel watch 2.
I am trying to do Maffetone heart rate zone training, which is well known in the running community, and requires staying at a particular heart rate (as close as possible) during a run.  There is a formula for this target heart rate, that is very specific to the user activity and injury history so it cannot be built into the pixel watch.  Thus the user must be allowed to define it - not the watch.  
Currently the watch auto-defines all heart rate zones, based on the configured max heart rate (220 bpm default, or user configured). Unfortunately this amount of configurability is insufficient for the Maffetone training use case.
I would like to stay at 121 bpm when running. So I'd like to define a custom zone from 117-125 bpm.  I'd like the watch to notify me if I'm below or above that target zone.
I think this question may be appropriate for the fitbit user community forum, but you must own a fitbit exercise tracker, not a pixel watch, to post to the fitbit user community forum.

Rieko Cohn · Accepted Answer

To add to Alistair's reply, the Pixel Watch is considered a "Fitbit device" since the Fitbit is the default fitness/exercise tracker app. 
Since there isn't a specific Pixel Watch device forum, it's recommended to use the Android app forum, see the link that Alistair provided.

Alistair Watson · Accepted Answer

Hi, @Matt, you do not need a Fitbit device to post in the Fitbit forum, I suggest you check out Fitbit Android App. Your PW2 has the Fitbit app and you should pair it with the App on your phone. In the "Today" screen>Heart tile>three dots in the top right>Heart settings>Heart Rate zones>set max HR Check out How to set up high & low HR notifications. I suspect this might not be what you are looking for but it does describe the flexability available.
I hope this helps.
Cheers