To the Limit: Ultramarathoner Dean Karnazes

To most people, a marathon sounds like an epic physical challenge, a draining test of one's conditioning, such as the 26.2-mile Boston Marathon. Then there are athletes like Dean Karnazes, who has run for 262 miles straight.

Karnazes competes in ultramarathons, grueling endurance challenges that only a select few athletes take on. A prime example is the Badwater Ultramarathon in Death Valley National Park, a race held in the desert -- in July -- every year since 1987. In 2004, Karnazes won, running 135 miles in 120-degree heat in 27 hours, 22 minutes.

There have been other feats, other races, from a race traversing Mont Blanc in the Alps to a sub-zero marathon to reach the South Pole. He has surfed huge waves and ridden bicycles farther in 24 hours than many will ride in a year.

For all his titles and achievements, Karnazes, who lives in San Francisco, says he's not done: He's planning to run 300 miles straight in the fall.

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