Runner to take on 50 marathons in 50 days?

This fall, the 43-year-old long distance runner will tackle one marathon a day for 50 consecutive days, running a total 1,310 miles (2,108.2 km) in 50 days. And for each 26.2-mile (42.2 km) race, Dean Karnazes and his family of four will travel to a different U.S. state. Karnazes insists he's not crazy. He just loves to run. A lot.

Arguably the world's best-known ultramarathoner, Karnazes has already run 350 miles (563.3 km) in one stretch, run a marathon in the South Pole, and raced across the California desert in the middle of the summer.

With this fall's challenge, however, Karnazes said on Tuesday he is going a step further in testing the human body's limits. "I'm curious to see what the limits of human endurance are," he said in an interview. "I still haven't found them."

To train, Karnazes said he logs anywhere from 80 to 175 miles (128.7 km to 281.6 km) of running a week around his home in San Francisco. He has also picked up the pace of his racing schedule in the last five months, averaging about two marathons a month in addition to a range of ultramarathons, or distances longer than 26.2 miles. This week, he'll tackle a 100-mile (160.9 km) race in Colorado.

"It's almost like designing an engine that can go 200 miles (322 km) an hour for a 100-mile(161-km)-an-hour race," Karnazes said of his aggressive training regimen, adding that he averages about four hours of sleep a night so that running does not get in the way of spending time with his two children, Nicholas, 8, and Alexandria, 11. Article here.