Heart rate zones - how many % for eacg zone?

1/Leave them at the Garmin defaults
2/I use LTHR and use the default percentages
3/Your MaxHR for running is far higher than the bike, which is far higher than the swim.

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3/Your MaxHR for running is far higher that the bike, which is far higher than the swim.

Also, your experience levels and muscular adaptation to each of those sports may be different.

Also, your experience levels and muscular adaptation to each of those sports may be different.

Indeed, the fact that elite cyclists tend to have cycling HR zones similar to their running ones, while less experienced cyclists have a bigger gap between them tends to support this idea.

Hello.
2. Do you use LTHR or resting heart rate as a base and what's the difference between them when setting zones?

I would say that basing your HR zones on the LTHR is more precise than the other two, RHR and maxHR.

RHR is based on a generic formula and estimations, and maxHR is also based on generic convention of % of HR but they can be different in each person, for example, my zone 5 actually starts at 93% of maxHR and not 90% of maxHR.

While the LTHR is actually by definition the value that separates zone 4 and 5, the two most important zones when training, so its better to base your zones on that mark than on the other more generic impersional marks.

Not to mention if you use HRmax= 220- age formula for the maxHR zones since the formula is 100% useless and not based on science at all (it was taken from a study of just ten non randomized individuals many decades ago and it just stuck into mainstream without being questioned), and it can be easily off by as much as +/-15bpm especially for people over 30yoa. In my case its off by as much as 16bpm.

This is actually a good read about equations for estimating HRmax. In reality, you should only be setting your zones based on known values, not estimates. It does not matter which you use as long as the values you input have been derived from measured tests.

The width of the zones will largely depend on whose methodology you choose to use. Pick one and see how it works for you.

Great read, thanks!
Bottom line, don't use any formulas for maxHR, even the one they report as most accurate (though still unacceptable) gives me the exact same result as the 220-age formula, 16bpm off my maxHR. Just simply do a maxHR test on your own, or a stress test, to determine it.

The calculated HRmax from this site - https://www.ntnu.edu/cerg/hrmax - was surprisingly close to my known HRmax (61y, 167cm, 78kg).

And that site doesn't give a fig about anything but your age. They quote the used formula further down on the page:

'The HRmax Calculator is based on this formula: "211 - 0.64*age"'

Do the math. In another thread fawning over that calculator ( https://forums.garmin.com/forum/into-sports/running/forerunner-935-aa/1399061-always-unproductive?p=1399601#post1399601 ) you state "my true max is 176". Plugging an age of 61 into the formula above gives 171,96 - using the webpage adding weight and hight says 173.

Claiming your height as 1 cm and weight 1 kg still gives 173...

I'm 58 - 187 cm and 76 kg at the moment, not that it matters - and their formula would place me at 173,88 (page shows 175). The silly '220-age' says 162.

Well, measured (with HRM strap) my HRmax was 186 five years ago as a neophyte runner. Almost fainted/vomited at that time and vowed never to lose such an amount of control again. I've actually reached 186 once this year (on a steep slope) at the end of a long run where I really pushed the last km. But since my aerobic conditioning is good, it merely felt exhausting. Still, forced to slow down I quit the run a few minutes after - having reached my Training Effect goal.

My true max probably lies a few beats above 186 bpm, but for my modest purposes this registered number is sufficient.

Formulated HRmax calculations <-- Just say NO!

Thanks for all the comments but....
I'm not interested in establishing my max hr but in % for specific zones :)
There are so many options/formulas and I can't decide which one I shoukd choose :)

Well, you need to establish first your HRmax if you are going to use HRmax or HRR method for determining heart zones, you can't use any age related formulas to determine your HRmax since they are completely unreliable. Otherwise use your LTHR estimate from your Fenix5 for the zones, which is what I would recommend.