"Move. Your. Body," says Jen O'Brien, a 31-year-old bike messenger in Boston, one city notorious for its frigid temperatures and crazy drivers. "You need to put up with things like frozen wet feet for nine hours at a time and windburn on your face—but it's fun." In college, her roommate was a messenger, but Jen was overweight and didn't think she could ever do the job. "I couldn’t run two blocks to save my life," she says.
Photo: © 2009 Jupiterimages Corporation