ABC News

Marine who lost both legs is running 31 marathons in 31 days to raise money for wounded veterans

"Running is a different beast than biking, Jones said, explaining that his muscles ache, there are skin abrasions on his body, and there's "a dull ache in the background" throughout running. "The biggest challenge is the repetitive stress every day for such a long period of time. It will add up eventually," said Jones. But the pain won't deter him in his mission. "I am doing it for a purpose. The purpose is a lot more important than me being comfortable," added Jones."