Spiderman After the Apocalypse

Correlation does not imply causation. Maybe the excessive running tricks the body into panic mode thinking the lifespan will shorten and accellerates reproduction ability to counter act? That's just a silly theory but there are so many factors to correlate to. Who feels the need to run marathon anyway? The ones with high testosterone, "jocks", or just people with long ring fingers?

That should be ' ring finger longer than index finger ' folks.
http://en.wikipedia.org/wiki/Digit_ratio

Long distance runners have more air movement around their scrotum, cooling the testicles. Excessive heat in the testicles is correlated with lower sperm viability and motility.

The Kenyan Kalenjin people are a large percentage of the record breakers within long distance runners, partly due to their body form which has evolved from living in a hot climate and developing a method by which to cool it. Another portion is cultural, which is being less frequently exercised. Traditionally, both men and women underwent rites of passage which includes crawling nearly naked through stinging nettles, having the shins beat upon, being circumcised with a sharp pointed stick, and running everywhere. Reproductive preferences side with those who have undergone the rituals with those who had not being seen as "not quite a man/woman."