Their stories are impressive: a 14-year-old girl finishing a marathon in Antarctica. A pair of pre-teen sisters competing in a 13-mile national trail-running competition. A 15-year-old running in the U.S. Half Marathon Championships.
As the popularity of marathons spills over to teenagers and pre-teens, doctors, parents and race officials are wondering how young is too young to run extended distances.
For the Dick's Sporting Goods Pittsburgh Marathon, runners must be 18 to register. The minimum age for the half marathon is 16, and it is 14 for the marathon relay. Those ages are in accordance with recommendations from the International Marathon Medical Directors Association.
"There's a misconception that children and adolescents are just smaller adults, and that's just not the case," said Aaron Mares, a sports medicine physician at the UPMC Center for Sports Medicine and executive medical advisor for the Pittsburgh Marathon. "They way they handle stress is different from both physical and mental perspectives."
Children and teenagers don't dissipate heat as well as adults, said Dr. Mares, and their bodies lack the compensatory mechanisms to cool down as effectively. They also are more susceptible to overuse injuries, he said, and there are concerns about the long-term effects of running on their cartilage and growth plates.
He also worries about the psychological state of youth runners.
"You have kids who are into running and, whether they push themselves or other people push them, they get emotionally burned out," he said. "The point is that maybe not only on a physical level but on a psychological level, it might not be appropriate."
The Pittsburgh Marathon has a mechanism for children who are younger than the age minimums to apply for a waiver. Prospective runners need to submit an email detailing the reasons they believe they are qualified to participate.
A few runners under 18 are running the marathon this year, and several ran last year, said Kelsey Jackson, public relations manager for the Pittsburgh Marathon.
Ron Roth, medical director of the marathon, said he usually will allow 17-year-olds within a couple months of their 18th birthday to run, but would be very reluctant to allow a 15-year-old to run.
For runners who are 16 or young 17-year-olds, Dr. Roth said the criteria considered are age, previous endurance running experience, whether they are running with a family member or coach, or for a charity, and health history.
The Pittsburgh Marathon also includes a Kids Marathon Saturday -- a 1.2-mile "fun run" recommended for children in kindergarten through sixth grade.
While many marathons follow the recommendations of the International Marathon Medical Directors Association, other marathons set different age limits -- or no limits at all. The Los Angeles Marathon has no age minimum, for example, and the Houston Marathon requires that runners be at least 12.
Spurred by the increasing popularity of marathons -- the number of finishers has increased from 353,000 in 2000 to 518,000 in 2011, according to Running USA -- the American Academy of Pediatrics examined the topic in 2007. The AAP determined that young athletes should not be barred from running marathons as long as there is proper training and supervision.
"Ultimately, there is no reason to disallow participation of a young athlete in a properly run marathon as long as the athlete enjoys the activity and is asymptomatic," said their report.
The group noted that the running distance should not increase by more than 10 percent from week to week, weather conditions should be carefully monitored and athletes should have at least one day off per week.
Ron Colland, who has coached track at Hempfield High School, never has had an athlete who wanted to run a marathon in high school. And, for the most part, he thinks that's the way it should be.
"It's an awful lot of pounding on the legs," he said. "I would encourage them to wait awhile, after they are out of high school or college."
Colland said that the maximum distance that one of his athletes will run is about 10 miles during a long cross-country practice.
"That would be about the limit," he said. "Just the idea of 26 miles -- it's very difficult to stay focused for that amount of time."
That said, there might be high school athletes who would be ready. "I would probably discourage 99.9 percent of kids from trying to do something like that, but there might be one of those exceptional individuals."
Anya Sostek: email@example.com and 412-263-1308.