Since he doesn't fatigue, can he actually tire?

 During the Avengers training when he doing a  training battle against the Avengers themselves Ironman, Thor,  Giantman, Wasp.  After they finally caught him Tony stated quit making them look bad as Tony implied they were all sucking wind.
 
Also during secret wars Black Panther passed out to due fatigue and heat exhaustion before Steve.
 
Steve also out fatigued the Rhino himself and once the Rhino fatigued he KO'ed him with a jump kick to his nose in volume 3 IIRC.  Steve lungs capacity could even breath the thin air better then the Rhino.  Peak of human "potential" indeed.

Have we ever seen him tire?

Whoa I swear Thor has better stamina than Captain america?

@Kyzuko said:

Have we ever seen him tire?

I think we have but it varies from writer to writer. I once remember Logan calling him the energizer bunny of the spandex kind....LOL

I don't think he can tire, but if he can, it takes a helluva lot of stuff to tire him

So how does he get himself to sleep then?

I do believe he can eventually exhaust himself, but like mentioned above it would take a lot to do so. I know that recently in the Marvel Now! series while trying to stop the Green Skull Cap mentions that he had been going weeks without break. Though whether or not this meant he hadn't slept during this time is unclear, but I assume that because his body is at peek physical form he can still exhaust himself like anyone else and does need to rest, he is simply able to push his body for longer periods than the normal is able to. But ultimately he would eventually need to rest his body, even Super-Soldiers need sleep. :P

@war_killer:

Yeah pretty much agree with you.

Also I think, at least in the comics, there is a difference between being tired and being fatigued, he does get tired and needs to sleep, but he can go for hours, at least, at maximum exertion before needing to stop and let his batteries recharge, so to speak.

I always thought his whole deal was that he has essentially limitless endurance. I guess I never thought about him sleeping, and how often he even needs it. Very interesting question, I assume he can last weeks without sleep if need be, and the need for sleep is the only thing that would make him get fatigued, as in he would never "need to take a breather" or something.

@nightcrawler358:

There have been times where Cap has actually been exhausted and stated so. Granted it was back in the 60's-70's, but he missed a shield throw and actually said it was because he was tired.

Ask agent 13 she knows :)

Interesting to note, but Captain America Reborn actually has Cap say 'I'm a man who can't feel fatigue'.....odd?

Considering Thor is a practically immortal Asgardian God, I find it quite reasonable that his stamina would be greater than Cap's/the peak of human potential.

@war_killer: @krauser99: @kyzuko:

IMO... if he can be considered superhuman in any way its his stamina because the SSS is constantly rejuvenating him so its very hard for him to get tired. It says in his profile he can work at peak capacity for about an hour before fatigue STARTS to impair him.