I mean a average human can run at his full speed for 15 to 20 mins before getting tired. Trained athletes can go on running for much more time without tiring out.
Do Superheroes like Quicksilver or Flash ever get tired due to excessive running?
According to Marvel's previously posted bio, Quicksilver did have limited endurance prior to his new Terrigen Crystal-based powers.
Quicksilver possessed superhuman speed, and could travel on foot at speeds exceeding the speed of sound for hundreds of miles before tiring;
Since getting his new powerset, he still has limited endurance.
His molecular speed that he generates displaces him out of the mainstream time/space so that he is able to propel himself into the future. He can leap from thirty seconds to up to twelve days, and remain for several minutes to several hours before being recalled to his present time once his body tires, or he can return at will before his time is up.
Sometimes called "enhanced endurance", Superhuman Endurance is a term used to describe the ability of some characters to never get tired. Their bodies metabolize at a rate that far exceeds normal humans allowing them to continue in their task for an incredible amount of time.
I can find no reference to the comics versions of The Flash becoming fatigued.
The exception, however, seems to be the current live-action version, who does become fatigued at times. It can be noted, however, that this version of Barry Allen is still in training and has been increasing his maximum speed and endurance through the course of the show.
Why do we get tired on running:
Now Speedsters like QuickSilver, & The Flash have heightened metabolism & regenerative abilities. Reference Indicates this.
Now considering their abilities, let us look again at our reasons for fatigue.