June 12, 2026
5 zones or 7? Making sense of Joe Friel's heart-rate model — and how intervals.icu uses it
Joe Friel's heart-rate zones are built on LTHR, not max HR or FTP. Here's why the same model is shown as 5 zones in some apps and 7 in others, how it differs from Coggan's 7 power zones, and how intervals.icu sets it up.