Fastest I’ve done a mile at was at 12mph, which is around 5 minutes, and that absolutely killed me. Can’t believe he ran faster than that for a whole marathon.
When our school gym got its brand new powered treadmill – this is 25yrs ago, it was a big thing then, OK?! – there quickly developed a range of competitions on it. Fastest km, mile, 5min mile target and so on.
There were quite a few people who could routinely put out close on 4-minute miles but amusingly, no-one could come close outdoors because of the obvious extra help a powered treadmill gives you.
Related to the above, I’m going with a very impressive achievement but not *technically* a marathon because of the various illegal kit and pacing. A sub-2hr marathon distance yes but it won’t be recognised as “a marathon” by IAAF.
Technicalities. Like me saying I can do a 4-min mile and then admitting it’s on a powered treadmill in an air conditioned gym.