A difference wrote:
There is a difference between doing a ton of volume and getting faster. AT dude didn’t get faster after those big weeks. He got more slow endurance.
Walmsley didn’t get faster after those big weeks either.
This was a 20ish hour race not a 41 day race. Supremely fit AT dude wouldnt have faired too well at UTMB with that volume of training either.
I'd guess that the AT guy is not overtrained at this point though, and probably would have fared decently at UTMB. The overall winning time is 12+ minutes a mile with a lot of climbing and descending which he was super adapted to. Obviously running is necessary for the runnable parts to keep up, but I think he would have done reasonably/exceptionally well for a non-pro runner if he had raced UTMB soon after his AT record.
What I've seen in super hikers, including a couple I know, is that they can get fitter as they go, putting in the largest days at the end if things go well. There is a similar, pretty well-known effect of this fitness improvement in dogs at the long distance sled dog races.