(Image Credit: ABC News)

When more than 38,000 competitors set off Sunday at the Chicago marathon, few of them likely had a more incredible journey to the start line than Ben Maenza.

Maenza, a Marine lance corporal, lost both his legs two years ago when they were blown off by a bomb in Afghanistan, weeks after his deployment there had begun.

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But instead of losing his competitive nature, Maenza was fueled by his injuries. Using a hand bike, he has now competed in multiple marathons and even ridden across the country from Florida to California.

"People think you can't do stuff like that without your legs, so being out there and proving that you can and making it happen, it's really gratifying," Maenza, 24, said in a phone interview from his hometown of Nashville, Tenn.

That motivation to succeed on his bike came at a crucial time for Maenza.

After leaving Afghanistan, he spent a year and a half in rehabilitation at the Walter Reed Medical Center outside of Washington, D.C. It was there that he started talking to Achilles International, a group that helps athletes with disabilities.

"It was exactly what I needed at that point in my recovery," he said. "I was at a crossroads. They came in and gave me a way to get a sense of accomplishment. It gives you something to work towards, the knowledge that you are capable and you can do it."

"I never really was a runner or a cyclist before, but when Achilles approached me and asked me to do it, it kind of lit a fire in me and, quite frankly, I'm pretty good at it."

During his races, Maenza feeds off the crowds, mentioning the motivation he gets from seeing fans waving U.S. flags.

"When people cheer for you, I get goose bumps," he said. "It's overwhelming."

Maenza had to overcome some equipment problems Sunday in Chicago, but he still managed to finish the marathon in an hour and 48 minutes.

"Obviously, I was a little slower than I intended, but I've got a good excuse, my wheel was broken," he said. "Now I'm going to continue to train harder and push to the limit. I can use it as motivation for my next race."

"Plus," he added, "some of my teammates did very well. So I've got something to work towards since I can't let them beat me."

Indeed, Maenza's biggest accomplishment last week did not come on the racecourse but rather in the classroom. Before he left Nashville for Chicago, the college student took a test. When he returned to class today, he learned his grade: an A.

"I was pretty stoked," he said.

That is because Maenza's main goal now is not an athletic one, but an academic one. He hopes to earn a college degree, and do it with a 3.0 GPA to boot.

"As silly as it may sound, the only thing that's intimidated me is school. I am terrified of it," he said. "People think you're a Marine, you're tough. But I'm a human being, you know? I'm just a normal guy, just missing my legs. That's it."