Kenya's Marathon Runners

Article on how Kenya produces the best marathon runners.
In the history of the marathon, 17 US citizens have run a marathon in under 2:10.
This year 70 runners from Kenya have broken 2:10.
Article goes on to explore if there is a genetic factor involved.
In the end, they determine it is one's endurance of pain as the differentiating factor. When they are teenagers, the Kalenjin undergo a whole series of tests before they enter adulthood. The majority entail enuring high degrees of pain. Their developed ability to tolerate pain makes them able to endure the hardships associated with long distance running. A Kenyan man and woman each won the New York City marathon this weekend.

http://www.npr.org/blogs/parallels/2013/11/01/241895965/how-one-kenyan-tribe-produces-the-worlds-best-runners