It's probably a self-limiting event. After ATP-CP power is gone it depends on acid-producing glycolysis which puts a wall at around 40 seconds. The faster you go, the faster you produce acid so that you tie up even earlier.
That's why there's nobody that can get out in 20.5 and bring it back around in +2. The fastest 400 runners get out in 21.xx on mainly efficiency. Through years of rote they learn to float. Every tenth faster requires so much extra power, for various reasons, that it doesn't work at 20 second pace.
I've never seen a coherent theory about how the body "clears lactate" or "buffers" acid or otherwise deals with rigging, and I think there's no such thing. Whatever you call how the body handles acidosis, I think there's a solid ceiling to it that all elites have long since reached, and their gains are a matter of finding ways to produce less acid in the first place. Which is much harder to do at 20 point than 21 point. All those people who think Bolt could do sub 43 are wrong, he'd have trouble getting to sub 44.