great question.
Address VO2 max, I started this season's BASE periods doing 1-2 WO's per week where i did increasingly longer intervals @ vo2 max wattage, eventually building up to about 12' @ 110% in 2' intervals.
This way when I started my 4x4's @ 115%, it was quite easy as I was already familiar with that type of effort.
I typically do 4'-4:20 VO2 intervals just because that's the length of my most convenient hill. I typically do 4-5 reps and try and push the power up a bit each successive workout.
As I'm coming out of a peak period, I'm going to be doing some more 2' intervals @ VO2max power just to feel the effort level needed. 6 weeks out from my second peak I'll start bringing the 4x4's back into the fold.
-L