"An extraordinary 2006 article from The New York Times profiles ultra-endurance cyclist Jure Robič who apparently regularly loses his sanity during his races - literally becoming psychotic as he pushes himself to the limit.
The craziness is methodical, however, and Robic and his crew know its pattern by heart. Around Day 2 of a typical weeklong race, his speech goes staccato. By Day 3, he is belligerent and sometimes paranoid. His short-term memory vanishes, and he weeps uncontrollably. The last days are marked by hallucinations: bears, wolves and aliens prowl the roadside; asphalt cracks rearrange themselves into coded messages. Occasionally, Robic leaps from his bike to square off with shadowy figures that turn out to be mailboxes. In a 2004 race, he turned to see himself pursued by a howling band of black-bearded men on horseback...
In a consideration of Robic, three facts are clear: he is nearly indefatigable, he is occasionally nuts, and the first two facts are somehow connected. The question is, How? Does he lose sanity because he pushes himself too far, or does he push himself too far because he loses sanity? Robic is the latest and perhaps most intriguing embodiment of the old questions: What happens when the human body is pushed to the limits of its endurance? Where does the breaking point lie? And what happens when you cross the line?
It's a wonderfully written article that touches on the man himself, the physiology of fatigue and the psychological strain of intense athletic feats."
In a gearpunk/Cthulhu fiction version of this, you'd have a feedback loop where he pedals himself to an insane state that gives him additional endurance to pedal himself beyond the nightmare Rasputin Cavalry and physically into Hell itself, where as long as he pedals fast enough, nothing can catch him. It can be a version of the Eurydice/Orpheus story, where Robic is the only one able to pass beyond the nightmares and retrieve his (or someone's) true love from hell, as long as he never stops to regain his breath or look to closely at the asphalt-crack messages that spell out forbidden eldritch knowledge that would keep him from ever being sane again. Of course, you'd have to keep the ending of the original, so let's just say there won't be a sequel.