I strongly suspect that marathon runners always try to be very quick. (At least if they actually try to break a world record.) However, a very concrete example

I strongly suspect that marathon runners always try to be very quick. (At least if they actually try to break a world record.) However, a very concrete example would be bringing him water, as opposed to slowing down and grabbing it. Something that I can easily imagine brings 20 s, and therefore we still do not know, if a 2 h marathon is possible.