Every other 3-day cycle, the 2nd day is supposed to be 5x5 vo2 intervals I believe.
BTW, I have a general training question. I think there was a thread where it was discussed, but I cannot find it anymore.
Nx20 min are developing LT,
Nx5 min are developing VO2max
What are 40/20 developing and why a triathlete would want them?
I find 5 min to be a bit long for what I want to use my VO2 fitness for. I'm not a high level bike racer, so most road races your "hard" efforts are going to be probably less than 5min.
I tend to use 3min. Two sets of 3x3min at 1:1 work/rest ratio. 6 minutes rest between sets. Pick a power you can do all the reps/sets at. Last two reps on last set you might grind to a stop, that's ok.
If you really want some "snap", do some 1:1 efforts at 1min each. Couple sets of 5 reps. You've picked the right power level when you can complete the sets but are still "puffing" hard breathing and are about to start another rep.
You're basically maximizing the time you spend anaerobic the best possible way.
I find 5 min is way too long to either spend "building" into the anaerobic state, or, is way way too difficult to choose power you get there quick and "stay" there for the duration.
Peak/fades are good too, but a bit brutal. Basically overcook it on purpose and keep reducing the power so that the pedals keep turning over until time is up. Over 2 min you may go something like 450w, 425, 400, 375, 350, 325, 300, 275. 15 seconds each, 2min total.
None of this is anything I'd say is "truth". It's just what I've found online, tried, and works for me and am expressing what it feels like for me to do a rep, or a set.