This is an excerpt from the chapter in Once A Runner by John L. Parker Jr., where the main character, Cassidy is starting a third "set" of 20 X 400m @ 62-63 sec. Basically 15 miles worth of running at 4:08-4:12 pace - a little unbelievable - but, sometimes you have to push reality a little to get at a deeper truth.
"He began the melancholy ritual as night was falling. After the first five he was running by the soft glow of a huge clear moon. Cassidy thought, Bruce thinks of everything.
Then he sought out the mental neutrality that is the refuge the contained wan comfort of the runner. He grooved his mind upon the thin platinum rail of his task, a line that stretched out in front of him and disappeared into the gloom, further than he could contemplate all at once, even if he had the desire to, which he did not. When his trance broke and a word or phrase popped into his mind, his dizzy mind played with it like a seal with a beach ball, in a disturbing, gibberishly mad way, the way your mind acts in the druggy twilight before sleep. In a very controlled, abstract way, he knew how much he was suffering; the slightest break in this concentration allowed self-pity to well up in him instantly.
He was, in a manner of speaking, accustomed to this distress in the same manner that a boxer is "accustomed" to being struck; but the familiarity of experience in no way lessens the blow or mitigates its physiological effects. It merely provides the competitor a backdrop against which his current travail may be played, gives him a certain serenity in the face of otherwise overwhelming stimuli, allows dispassionate insight where otherwise there would be only a rush of panic. In a hail of killing blows, the fighter's quiet center of logic, schooled in brutality, will be calmly theorizing: We are hurt pretty badly. If we do not cover up and take up the slack we will soon be unconscious.
Not that this quiet center of logic fears unconsciousness (indeed, how welcome it might seem at times), but it knows that one can't win while unconscious. Likewise, no highly trained runner slacks off because he fears pain, but because the quiet center of logic says he will win nothing if he runs himself to a standstill.
All of this availed Cassidy not at all. His deeply ingrained conditioning and his mahogany-hard legs merely allowed him to push himself that much more. He had the mental ability to literally run himself right into the ground like Sambo's tiger. He knew that Denton expected him to do exactly that, and, just as each repetition made the next seem more impossible, he knew that without question he would do it. There was no refuge in injury, his body could not be injured in this way. There was no refuge in mercy, there was nothing to forgive, no one to issue dispensation. And at last he saw: There was no refuge in cowardice, because he was not afraid. There was no alternative, it just had to be done."