I know this is a great workout, but I dont think it is out of this world for top notch marathoners.
My coach ran in the 80s and 90s, his PRs were 1:02 for the half and 2:13 for the marathon and he has told me a few times of a workout he did, 20 x 1k all at around 2:55 with 50 seconds break.
I do not see Walmsley running under 2:12, however, I do hope I wrong as I like the guy.
I would imagine the altitude is the impressive part of this workout....right?
It was done at 3000 feet, so the altitude is negligible. Maybe 1 second per mile or so.