Keelan Glass trotted across the finish line at Sunday’s Showdown Half Marathon in Dallas two hours and 46 minutes after the race began — a respectable time for any burgeoning runner, and good enough to merit fifth place for Keelan. But the 6-year-old was just happy to finish. Crossing the finish line solidified her record as the youngest person ever to complete a half marathon.

For every accolade heaped onto Keelan, her parents have received just as much finger-wagging. Running 13.1 miles is taxing for anybody; for a 6-year-old, it could prove downright dangerous. Advocates of the sport say the activity is natural, that humans were designed to run, evidenced by the numerous tribes for whom eating dinner means chasing and killing that dinner. What about a first-grader? Surely her growing bones aren’t cut out for two hours and 46 minutes of pavement pounding. Science may not be so sure.

Keelan, at least, was having a blast. Her mom, Tracy Glass, ran beside her the whole way and checked in every couple of miles.

"We got to mile six and I said, 'How do you feel?' and she said 'Great. Let's run to eight.' And I said OK," Tracy told KTXS News. "We ran to eight and when we got there, I said, 'How are you feeling?' and she said, 'Great, we can go to mile 10.' So we just kept going at her pace and on her time schedule."

According to her mother, Keelan’s record is only apparent to the people around her. The implications of setting a world record as the youngest half marathon finisher haven’t settled yet — or if they have, they’re eclipsed by the success of raising nearly $3,000 raised for a pro-life group at her local pregnancy resources center.

“That's the thing,” Tracy said. “She doesn't really even understand how amazing it is.”

The same could be said about the physicality of running a half marathon. One of the hallmarks of a child’s spirit is her unwillingness to give up. Adults fret and worry at the first sign of blood, while kids roll around in mud and fall down and scrape their knees and bonk their head, all without complaint or contest. Sure, there may the occasional teary eye, but children seldom assign the same limits to their abilities as their elders.

This winning attitude is what allowed Keelan to finish her race. It’s also what has doctors worried. When children don’t acknowledge their physical limitations, parents must do it for them. Keelan, whose goal is to run a full marathon by the time she’s 10, has all the makings of a determined athlete — watchful doctors aren’t so sure.

"I think they're asking for trouble," Dallas-area pediatrician William Moore told The Dallas Morning News. "There's a lot of potential for bad things and not a lot of potential for exceptionally good things to happen."

Marathon organizers typically set at least some form of an age restriction for their entrants. Usually, that age is 18. Sometimes it’s 17, or even 14. Sometimes, there are no age minimums: a parent needs only to give consent. The International Marathon Medical Directors Association advises teenagers to blow out the candles on their 18th birthday cake before signing up for a race.

“Risk factors unique to the growing child are numerous,” according to an IMMDA advisory statement. “It is well known that stress fractures, a distinct overuse injury, are a function of the number of repetitions and amount of applied force per repetition.”

In pure numbers, Keelan’s feet will strike the ground more times over the course of a race — of any distance — than older runners, whose legs are longer and can therefore take longer strides. “Immature articular cartilage is more susceptible to shear force than adult cartilage and predisposes children to osteochondritis dissecans,” an overuse injury where the thin layer of cartilage and bone around the knee detaches from the end of the bone. “For the safety of young runners, it is imperative that the training program and its progression be followed closely and monitored carefully.”

Keelan’s parents say they consulted with an orthopedist prior to letting their daughter run the half marathon. Tracy has yet to fully decide whether letting Keelan run a full marathon at age 10 is the right decision. For now, she’s happy that her record-breaking daughter accomplished what she set out to do, even if she doesn’t fully understand the true reach of her achievement.

“I love the fact that she does it for a bigger reason,” Tracy said. “It's fun for her and it's about running but she wanted to use her skills for something different and people saw that. They were asking her about her shirt and the announcer told her whole story. I don’t think she realizes what a big impact she has on people.”