Jennifer Frighetto is not a marathoner, but it is not for lack of trying. Had she crossed the finish line at this year’s race in Chicago, it would have been her first successful attempt at the 26.2-mile distance. But just as at the 2008 and 2009 Chicago Marathons, Frighetto was unable to finish because of injury.

Frighetto, a self-described former couch potato, said that since she first decided to run a marathon in late 2006, she has seen doctors for a stress fracture in her foot, plantar fasciitis and iliotibial band syndrome. The activity that promised to make her healthier was actually increasing the frequency of her doctor visits, a fact that makes amateur athletes like her a problematic group of people for health insurance companies to insure. And as more and more people become marathoners  the 2011 Boston Marathon sold out in eight hours  distance runners are becoming a hard group to ignore.

“Insurance companies love runners because they’re healthy people,” said Nathan Nicholas, the president of Nicholas Hill Group, a Colorado-based insurance brokerage firm that works with USA Triathlon. “Many of them are younger and have disposable incomes. They’re a great demographic.”

But, he added, because they train so hard, they have injuries and accidents that can sometimes make them difficult to insure.