Originally Posted by
Carbonfiberboy
The boundary between zones 3 and 4 is ill-defined and somewhat arbitrary. Zone 3 is an area where you tire yourself but aren't going hard enough to get a good training effect.
Andrew Coggan and countless others would disagree with you on that. Working that boundary between zone 3 and 4 (upper z3, lower z4) gives you one of the greatest bang for the buck workouts you can get, and once that's repeatable and sustainable for quite a while. It's generally called "sweetspot" training and is generally around 88-95% of FTP.
I consistently put more time in that zone during the winter months than all the others when I'm only getting in 7-8 hours a week.
Gives an excellent training effect. Same for just straight-line z3. 60-90 min steady in z3 is a very nice workout.