Meet Dean Karnazes, a man who can run 350 miles without stopping.

The 53-year-old distance runner has no trouble running a marathon. In fact, he can do them back-to-back while hardly breaking a sweat.

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"To run that far and that long is a super-human feat," Nicole Marie Pinto, an exercise physiologist at the University of California San Francisco Medical Center, told Inside Edition.

His endurance is credited to his body's ability to flush lactic acid from his system. As we exercise, lactic acid builds up, causing muscle cramps and fatigue.

"I don't care how fast I go," he told IE. "I care about how far I go."

He has the ability to run marathons two at time.

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He sets out at 2 a.m. to run his first 26.2-mile jaunt. When he finishes, he joins another 5,000 runners for a marathon in Monterey, California.

He's barely sweating when finishes mile 52.4. "Just got warmed up," he says. "Still feel fresh.

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