Originally Posted by
Carbonfiberboy
Why do you think that 80% of MHR is an interesting number? That's about the top of Friel's Z2. I should hope you could sustain that for over an hour. I've averaged an 80% HR on 3 hour group rides. For most people, Z5 starts at 89%-92% of MHR. However that may be, only testing can tell you your lactate threshold which is the beginning of Z5.
Information about a common LTHR field test can be found here:
CTS Field Test: Why two 8-minute efforts instead of one 20-minute effort? - CTS
I believe you are incorrect about what the literature says about Z5 interval limits.
The HR training guide I read calls "zone 4" the 80% to 90% zone.
It calls "zone 5" 90-100%
Should I be able to average "Zone 5" for over an hour and never get below "Zone 4" from mile 2 to mile 22?
EDIT: Ziel's LTHR formula also put me in "Zone 5" as an average for the whole ride. (162-172)