I got an email from Intervals.icu after my most recent race that I have an updated threshold of 175. When I plug this into garmin for my zones it’s much higher than basing it off of max heartrate. I would just choose one but they are far enough apart that I have to imagine heartrate threshold wouldn’t always keep me in zone 2 power
If you’re basing max HR on 220-age I’d go with the Intervals.icu threshold estimate. My theoretical max is way off… but estimated threshold compares pretty well to sitting at FTP. I don’t think the correlation between HR and power is good for Zone2, but I don’t really watch it and I know that my HR goes up pretty quickly, so I usually choose to train to power zone rather than HR.
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My max is based on what garmin has picked up over rides/workouts. Probably not my real max.
Power is tough where I live and I like to do endurance rides on my mtb (no power meter) so ai use heartrate. If I had a power meter it probably wouldn’t help much anyway given the trails are not the type to be able
To sustain power easily.
If you go on intervals.icu Settings / Ride / Heart Rate Settings, there you see “Threshold HR” field. Clicking on it shows link to webpage from where it gets guidance detecting this value.
Whether you want to use this value or cycling MaxHR for setting heart rate zones is different story. For example, Joe Friel’s provided HR zones work with his training plans intensity distribution but you may want different zones if following Garmin provided plans that are based on HR.
I myself use [guesstimated] LT1 HR instead for Z2 and power for Z3+ intervals.
That’s my fault I should have been more specific. I plug it into garmin just to have the data for Z2 on my rides to make sure I’m Within the acceptable range. I don’t use any of their plans.
Following the Threshold instead of max would most likely put me in zone 2 power anyway since I’m usually pretty low on HR when following power.
I just though such a huge variance may make a difference to endurance training. I’ll always take the higher heartrate so I have more wiggle room and make the ride less boring for sure
Indeed, I wrongly assumed you want ride at lowest HR cap for Z2 that still gives you adaptations. But you instead want to get highest HR cap for fun but does not overburden you? Sorry, don’t have good answer for that. I imagine it be might be trial-and-error approach to find it for you personally 
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Worth sense-checking that ride against your “normal” riding conditions. For instance, I got a big bump in Threshold HR (that I didn’t accept) after a workout I did during a heatwave. I didn’t think that proposed number was representative. Fatigue, hydration status, caffeine and illness will all play into the mix too.
Yea this was a mtb race and I was on a hardtail
And definitely “underbiked” for the terrain. Pretty technical. So my average for the whole ride was 177 with a max of 186. This makes it a maybe not so ordinary ride but the fact that I was able to sustain it still makes it relevant or maybe not?
Well yes in a way. I was just saying if the lower numbers are what I should follow the. So be it but if going off of hr max or threshold the greedy part of me would choose the one that would give me a bit higher zone
This actually was point of my first response: there are different methods calculating HR zones but learning your actual LT1 HR gives you more benefits long term. Riding below it gives you freedom to push volume very high without overburdening your central nervous system.
Couple years ago when got my first power meter, I always rode at highest Z2 (IF 0.7+) but lost motivation every 8-9 weeks due overreaching. Now with HR cap, no such problem any more, can ride whole outdoor season 14-24h/week (with 1-2 intense days per week).
But of course, if you are time-crunched, then it makes sense to push fun factor higher with intensity 