27,000 people are signed up for the Honolulu Marathon Sunday.
Among the competitors are 230 kids and teenagers.
"How early is too early to run a marathon? That's actually the million dollar question," Dr. Rachel Coel, medical director of sports medicine at the Queen's Medical Center said.
Dr. Coel has reservations when it comes to kids testing their endurance. The Honolulu Marathon allows kids as young as 7 to sign up.
She says that might not be for everyone.
"These are bodies that aren't mature yet; the skeleton is still young and still developing. While it's growing, it could be susceptible to injuries from the pounding and overuse of the 26 miles, and more importantly, over all the training leading to the 26 miles. But there's other theories showing that there is really, truly no harm," Coel said.
One of the rules of the race: kids have to run alongside an adult or guardian. To find out if your kid is marathon ready, Coel suggests taking a close look at their motivation.
"Whose goal is this? Is this the child's goal or is this mom and dad's goal, a coaches goal? If it's the child's goal then really, that's a key component," Coel said.
Another key component, the pain factor.
"The idea there being. If it hurts you to be doing gymnastics, soccer or running for 26 miles, then we need to step back and look at if there's an injury we need to be treating. If you're repeatedly being injured, maybe this isn't the sport for you," Coel said.
While bodies mature and develop at different ages, Coel says 16 is usually a safe bet to start prepping for a marathon. Proper sleep, nutrition and training are critical to preventing injuries.
"I think bodies were made to be in motion and I really encourage that. Whether it's running, hiking, biking surfing, we need to find that activity that inspires somebody," Coel said.