So just as a headsup, i have also heard of people using “hard start” style FTP intervals, as a way of getting some glycolis / lactate production going, on the theory that it helps stimulate the body to build up the required plumbing to shuttle and buffer (I think the theory is that the presence of this extra lactate while you’re working hard but also long will induce your body to make those transporters that take it out of muscles where there’s too much and into muscles that can use and force it into the Krebs cycle).
This could conceivably be an easier way of dipping a toe before doing true over-unders. If it works, maybe it makes them easier for people.