Thanks for sharing as that is a great read. In setting zones for HR I always find it frustrating that Andy Coggan’s zone 2 is much lower (115-140) versus Joe Friel’s zone 2 (135-150) based on my LT HR. This is always in the back of my mind when doing zone 2 rides. I also follow my power numbers but basically have come to the conclusion that my HR in the 130-140 range is low zone 2 for me and 140-150 is high zone 2. This seems to align with feel and power numbers as well…although I have been riding lately with low tempo power numbers and my HR staying in the middle of zone 2.
Based on that summary the zone 2 calculation based on Lactate HR and Max HR seem to align correctly for me and is closer to Joe Friel’s numbers.
i have the same, andy coggan zone 2 is up unti l153 for me. Joel Friel up to 163. How it actually feels? In between. Like 160 exactly feels like my upper limit zone 2. Past 160 breathing becomes a bit more laboured and its not “talking easily” anymore. So while I mostly go by power numbers… on a long endurance ride I keep in mind not to push beyond 160hr for too long.
Very nice! All in one place.
This is interesting because it doesn’t seem to include the most commonly used definition of z2 at all (and the one where “z2”) came from.
That is, where z2 is determined as a percent of FTP.
Very few cyclists IRL have any idea where their LT1 is, and it is not easily measured with useful precision outside of a lab. So definitions based off this will not be useful to the majority of cyclists and coaches.
In addition, there can be large variation between z2 defined off a percent of FTP, and z2 defined as lower than LT1.
To be a bit pedantic, VT1/2 and LT1/2 also often occur at slightly different places from each other - IOW VT1 is not exactly at LT1 (though the difference is probably meaningless).
I’ll probably stick with my personal definition of z2 still as “an intensity I can do for at least an hour or two without incurring so much fatigue that I won’t be able to do threshold intervals the next day.” Or “the intensity I can comfortably ride 160-200km at without dying from fatigue.” 
It’s the relative lack of fatigue from “z2” riding that guides how it’s used in my training, not the intensity of it.