kmaclam wrote: .........because you & I and a kilo of crack couldn't pull this workout off even as a relay team.
As someone else pointed out, the difficulty of the workout depends entirely on the pace. When I run up mountains, I know that the pace depends entirely on the grade, and I adjust so that the effort is where I want it to be. For Bersagel, the belt is presumably moving very, very slowly, but at a level that keeps her intensity where she wants it for a 2.5 hour run.
Of course, it could be a typo. But to me, 2.5 hours at 10% grade is no more or less plausible that 2.5 hours on the flat. It all depends on how fast you're going. (Unless you think she couldn't even keep moving for 2.5 hours at that grade, in which case I think you're seriously underestimating her fitness.)