Zone 4 : Lactate threshold
LoadIntense training zone around the lactate threshold (about 90-105% FTP), where lactate production begins to outpace clearance.
Zone 4 corresponds to an effort intensity around the lactate threshold : the point at which lactate production exceeds the body's ability to clear it. In cycling, this is typically 90-105% of FTP; in running, it is roughly threshold pace. Zone 4 sessions last 20-40 minutes continuously, or break into 8-15 minute intervals. It is the most specific training zone for improving threshold power or pace.
In TriPaced:
In TriPaced, Zone 4 sessions appear in BUILD and PEAK phases : typically 'threshold pace' or 'threshold intervals' of 3×12 min. The plan avoids Zone 4 in recovery weeks and never stacks two threshold sessions within 72 hours.