Worth noting some of the changes being made to VO2 intervals by Chad, over on this thread - especially on sustained power build with workouts like Shortoff +4 and Monadnock +4.
General trend is an increase in recovery interval duration, as the conclusion from data seems to be that 3 minutes isn’t enough to recover from 3 minutes @ 120%. Which I can attest from previous attempts at Shortoff +4 was damn close to impossible.