This looks like a fascinating book - Born to Run by Christopher McDougall. Where are these guys in the Olympics?...
From NPR's review:
Born to Run is like those dreams many of us have, which start simply and end in the land of the bizarre. In this case, the simple question of why most American runners suffer injuries despite expensive sneakers brings Christopher McDougall to the unforgiving terrain of Mexico's Copper Canyons, home to an indigenous population of ultra-runners, the Tarahumara Indians.
They call themselves the Raramuri, or the 'Running People.' They never suffer illness. Eating a diet of ground corn, mouse meat and homemade alcohol—and sleeping no regular hours—the Tarahumara men and woman somehow pack the endurance to run cliff-side races topping one hundred miles and sometimes lasting two days. Their economic system of bartering and pre-Aztec language are an anthropological mystery, but local legend leaking from the canyons has it that men can chase a deer until exhaustion renders the beast an easy kill.
McDougall recounts his quest to understand these near superhuman ultra-runners with adrenaline-pumped writing, humor and a distinct voice. Pulling you with him through sun-crisped canyons, plopping you into the path of sweat-less super athletes, and crushing your faith in Nike, he never lets go from his impassioned mantra that humans were born to run. "Way before we were scratching pictures on caves or beating rhythms on hollow trees," he writes, "we were perfecting the art of combining our breath and mind and muscles into fluid self-propulsion over wild terrain."