I like to use lactate threshold, but don't want to fly somewhere to get the lab workup or buy a meter and stop every few minutes to measure. So I go by breathing, testing myself on my rollers to find VT1 and VT2. Lactate threshold should be just a couple beats below VT2, and VT1 is the break between slow and deep breathing and more rapid and deep breathing. So I put my guess at LT into the TrainingPeaks calculator to see zones. Then I modify the Z2-3 junction according to my VT1 HR. I never used MHR, which doesn't seem to have a whole lot to do with one's lactate levels. Maybe it does statistically but not so much individually. Zones are really all about lactate levels. The three-zone system is even simpler with the upper and lower breakpoint of Z2 being VT1 and VT2 absent actual lactate testing.
I find that training will modify the location of these breakpoints, so I modify my zones from time to time as seems appropriate..
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