Z6 : Zone 6: anaerobic capacity
LoadVery short efforts (1-5 min) above 150% of FTP, where oxygen delivery can't keep up.
Above Z5 (VO2max), you enter anaerobic capacity: glycogen burns without oxygen, lactate climbs fast. Efforts last rarely beyond 3-5 minutes before forced stop. In long-distance triathlon, Z6 is almost never prescribed : but understanding it helps avoid the trap of going out too hard on the bike.
In TriPaced:
In TriPaced, Z6 doesn't appear in any standard IM or 70.3 plan. If a session shows 'Z6', it's a warning flag: the prescribed intensity is likely too high or you entered a FTP that is too low.