The fitness of the marathon runner is extraordinary, and it therefore demands extraordinary things from the person who possesses it. Can you take a body that is brimming with strength and ride it delicately to utter exhaustion? Can you turn its strength against itself, use that strength surgically and witheringly to destroy that self-same body? You have to be singularly mad to perform such a task. The sane try to preserve themselves. The mad destroy themselves. It is not sane to reach for total exhaustion, but it's what singularity demands.
And so, the week before a marathon, one gives oneself the task of becoming quite mad.
http://thelogicoflongdistance.blogspot.com/2010/10/anticipation.html