Friel, lactate-threshold heart-rate zones

Joe Friel’s practitioner framework that anchors training zones to lactate-threshold heart rate, estimated from the average heart rate of the final 20 minutes of a 30-minute solo time-trial, rather than to maximal heart rate. Because the anchor is the threshold, the zone boundaries differ from percentage-of-maximum schemes. A widely used coaching convention, not a trial-validated model. Limited (practitioner source).