I actually think for very runnable (i.e. smooth dirt and not much climbing/hills/mountains) 50-100-milers that a road marathon PR correlates very very well to ultra distance running performances. I mean its all just the sport of distance running. If one can run a good fast marathon than someone has some good endurance and efficiency already. You're too stuck up on the distance when it is the nature of the course (profile, climbing, trail type) that I think matters the most. Kilian will only do "real mountain races" for example. It could be a VK or 100-miles but he focuses on legit mountain races purely. When you throw in powerhiking up grades over 15-20% and thousands of feet of vertical (not to mention technical trails) the game can change from relative PRs on the roads and track. Variable Running Economy determines muscle cramps from sheer failure as well as a lot of nutritional /hydration woes. Adverse weather can change the game even more. That being said a 50-miler is generally going to run a lot differently than a 100-miler. With longer events/longer durations you simply have more variables that can go exponentially wrong. Limiting factors could be sheer muscle failure (think quads blowing out), but then also dehydration and/or glycogen depletion. Compound that with possible stomach /GI issues/overheating/hypothermia. Yeah in 100-milers I would generally worry about the 2:25-2:35 marathon runner types almost more than the sub 2:15 marathon guy. Just like in a road marathon do you worry more about the sub 3:50 1500m runner or the guy that only ran a 4:03 1500m but has also gone sub 29:20 for 10km? It really depends on the course profile though.
joecrunner wrote:
I specifically mentioned sub ultra distance, aka under 31 miles. But for clarity let's say any event that would take an elite runner 3 or more hours to finish.
I definitely think for 100's and 50 milers, short distance prs are practically irrelevant.