Originally Posted by
grolby
Friel is a good source for LTHR based training zones, there are other good sources. To elaborate on TMonk just a little bit, max HR is a poor basis for zones because the relationship between it and LTHR is highly variable in the population, the relationship between LTHR and training zones is much more reliable.
And even with LTHR I find that it is constantly changing over the course of several months.I have to keep an eye on it and adjust zones frequently. HR fluctuation, oh the woes of no power.