Your zones aren't calibrated correctly. Zone 5 is only sustainable for a few minutes. It's not just 220 - age for max HR and applying the %'s.

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mtalantikite 8 hours ago | parent [-]

Yeah, I'm not totally sure how to fix that tbh and always have assumed it's just off. Open to suggestions though!

I use WorkOutDoors (with a Polar H10), and I've attempted the whole "do hill sprints" thing to calculate it, but I'm generally not far off from 220-age. When I put my resting heart rate into WorkOutDoors the zones get thrown even further off, so I don't even bother with that data point. I've kinda just shrugged it off and assume what is reading as Zone 5 is more like a high Zone 4.

I've considered doing a lactate threshold test, but honestly I just go running once a week to supplement my muay thai training, so it's not totally worth it to me.

	▲	rige 7 hours ago \| parent [-]
		There's a good journal article that compares different perspectives and measurements for zones, that might help (if you're interested in the science!): https://journals.humankinetics.com/view/journals/ijspp/aop/a... Threshold test might help you dial it in, and it doesn't have to be in a lab (though that would be most accurate) -- you could do a workout effort to estimate your max sustainable heart rate for an hour, then calculate zones based on that threshold HR (i.e. my Garmin calculates based on % LTHR, where zone2 ends up being 83-89% of LTHR). It's also not an exact science - it's a spectrum and shifts day to day depending on lots of conditions!