We know that the flash doesn't tire out, but he's still running. When other people run they tend to sweat, does the Flash do this? Has the comics ever show him sweating after any sort of run?
Which version of the Flash are you talking about?
In the comics from the 70s, I've only seen him sweat when it is really hot out (and he's not running), nervous, or when he's sick with a fever.
I seem to recall him sweating from over exertion but in the race with Superman, (when he is presumably going all out) he is not shown sweating.
It is probably too late to answer the question now, but I'd like to add a few shreds of evidence to the plate (from the TV series-The Flash and not the comics)
- S04-E15 "Enter Flashtime": One can see Barry sweating (heavily, I must say, and it was mainly because of heat emitted due to detonation of a nuke) when he comes to Iris, scared and 'tired', and thinking, that he can not save the city this time.
- S04-E10 "The Trials of The Flash": One can clearly notice Barry sweating while he is trying to contain the radiation being emitted by the fallout (Neil Borman).
I don't remember watching Flash sweating (or getting that very tired, in fact) in any of the previous seasons.