Earlier quoted context omitted.
"One thing that stuck out with me is that they only hiked for 8 hours/day. That seems like a light day! compared to these races," Really. Carrying a 20kg pack for eight hours over rough terrain is less strenuous than bike riding? Do this for over 500 miles? Ever done this before? Hike on foot with 20kg packs on consecutive days? Make camp, make food, rest, break camp. Everything on your back. This is a lot more stren…
Over the same distance sure, but have you ever raced mountain bikes? The broken terrain thing applies as well. And the increased efficiency just translates into more speed and distance. You might think descending 10k feet on a bicycle is cake compared to hiking, but packing that elevation drop into a tiny fraction of the time leads is actually a fairly intense upper body workout.
No. I think the OP was referring to road racing. One question, "do you carry the bikes uphill?"