For most people running one marathon is a daunting prospect but research scientist Leslie Miller belongs to group of runners who have completed 100 or more marathons, many of them just for the fun of it.

"It's my hobby," said Miller, from Seattle, Washington who has been running for about 10 years and averages one marathon a month. "I just get out and run almost every day."

Although she is only 32 years old, Miller has completed 160 marathons so far. Her only goal now is to keep running.

"It would change my life if I had to stop," she said.

Road runners and couch potatoes alike can draw inspiration from Miller and others like her who have completed the ancient 26.2-mile race 100 times or more.

"I was struck by just how happy everyone was," said Malcolm Anderson, who interviewed over 120 such runners for "The Messengers," his new book on the subject.

"This was what they were so passionate about doing," said Anderson, a New Zealander living in Canada, adding that often they began with nothing but a desire to change their health.

"Many started out by not wanting to run or not liking to run," Anderson said.

He found that runners who completed 100-plus races ranged in age from mid-20's to 80's, but as a group they tended to be goal-driven, patient, resilient, and social.

"They have a strong comfort level for taking on adversity," he said. "But it's primarily about doing something with other people, seeing new places and sharing."

He said when the race is run they'll sit down for coffee or beer and never mention their times.

Tom Holland, an exercise physiologist based in Darien, Connecticut, who has run over 70 marathons, said many 100-marathoners are late bloomers.

"You would also be surprised at how many started running much later in life," said Holland, author of "The Marathon Method," a 16-week training program for the race.

He said it's not uncommon to encounter a 55-year-old veteran of 110 marathons who started to run at 50.

"You would be really surprised at how many of these people are actually overweight," said Holland. "They don't run fast, just far, and often."

Holland, who strongly urges all runners to cross train, rest and recover, said for some, running is a necessity.

"It gives them a purpose, a goal, and a way to quiet their minds. They are much better people because of running."

Young or old, fat or thin, these veterans of 100 marathons have delivered their message to Anderson.

"I keep getting told I should get 100," said the 50-year-old. "I've run about 42, and I've got a few more in my sights."

This year, Anderson said, he'll run about 10 or 12.

"I'll get there eventually," he said. "I don't want to get too grandiose."