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Lance Armstrong Tackles "Heartbreak Hill"

Lance Armstrong is at it again.

Although the seven-time Tour de France winner has retired from professional cycling, he doesn't take a break when it comes to taking on another physical challenge. He keeps the 'cycle' going.

Armstrong was among the sea of 25,000 male and female runners at the 112th annual Boston Marathon, a 26-mile and 385-yard trek that is known as the one of the most physically challenging marathons in the U.S. with its infamous "Heartbreak Hill" that makes or breaks most runners' time.

Photos: Lance Armstrong
Armstrong won the Tour de France seven times on the strength of his work in the mountains. When he started preparing for Boston, some race veterans told him the hills weren't as difficult as their reputation made them out to be.

"They were wrong," said Armstrong, who finished 496th in 2:50:58. "They are harder, and they do come at a difficult time in the race."

Today marks Armstrong's third marathon since he retired from professional cycling and his first time running the Boston Marathon.

He qualified for Boston with a 2:46:43 finish at last year's New York City Marathon. The qualifying time for Armstrong's age group is 3 hours, 15 minutes, according to CBS affiliate, WBZ-TV.

Photos: 2008 Boston Marathon
Armstrong, who won the 1993 World Cycling Championship before being diagnosed with an aggressive form of testicular cancer in 1996, has become an internationally recognized sports icon and a cancer survivor on a crusade for a cure.

Armstrong's recovery has been a miracle, considering his cancer spread to his lungs and brain. He then went on to win seven straight Tour de France titles from 1999 to 2005.

He ran his first marathon a year later, finishing New York in 2:59:36, WBZ-TV reported.

Armstrong isn't running just for fun, he is raising money for the Lance Armstrong Foundation, LIVESTRONG, which focuses on cancer prevention, access to screening and care, empowering cancer survivors, and an investment in research.

The Lance Armstrong Foundation, LIVESTRONG, which many supporters can be seen wearing its signature yellow wristbands, has 50 runners in the Boston Marathon, who hope to raise $250,000.

"I'm excited to be here," Armstrong told WBZ's Steve Burton before the race. "If I broke 3 hours I'd be happy. I'm not in perfect shape, but the point is to get out here and enjoy it and really be part of the atmosphere and the ambiance of this great marathon."

By Melissa Castellanos