It’s not that Marc Scarbrough has developed gills or petitioned the Ironman governing body to allow him to use a snorkel during this year’s competition.

But the Lawrence-based internal-medicine doctor and part-time triathlete actually has turned his least favorite part of the competitions — the swim — into the element he enjoys the most.

“The first time I put my face in water, I had a panic attack,” Scarbrough said. “It’s dark, there’s no line. What’s down there that’s gonna get me, a killer catfish or something?”

But it wasn’t just the fear of the unknown that had Scarbrough squeamish.

“It’s not just swimming in the lake,” he added. “There’s 200 people thrashing around trying to get ahead of you. The whole thing’s just very intense.”

Used to be intense, that is. Today, with a handful of triathlons already under his belt, the swim is Scarbrough’s favorite part, the part that is the most relaxing. It’s not just the feel of his body gliding through the water or the low-impact nature of the swim — compared with the pounding that comes during the running portion of the event — that make Scarbrough sing. It’s the fact that, once upon a time, he was unable to do it.

“It’s very gratifying to have gone from being terrified to put my face in cloudy water to feeling calm when I’m in the water,” he said.

On June 14, Scarbrough and hundreds more will put that theory of calm to the test in the biggest way when they compete in the Ironman Kansas 70.3, a world-class, 70.3-mile run, bike and swim that invades Lawrence for the second year in a row.

Scarbrough did not compete in the event a year ago, but he was there — in the medical tent, doing his best to help some of the sport’s biggest names recover from the intense strain they put on their bodies to finish the race in under four hours.

“Being in the medical tent was really exciting because I got to see stud pros come through after they had finished the race,” Scarbrough said.

This year, he’ll be among them, although he doesn’t anticipate finishing quite as fast.

“Can you imagine, you play baseball, and then all of sudden you’re in the same competition with the Royals? Or you’re a golfer and you’re playing with Tiger Woods,” he added.

The 37 year-old doctor has been involved with athletics throughout his life but only recently picked up running as a way to keep his body in top shape. A knee injury that kept him off the running trails inspired him to try cycling, and before he knew it he had thrown swimming into the mix and had become a bona fide triathlete.

“Golf was kind of my big sport in high school,” he said. “You’re bullet-proof when you’re in your 20s, and you feel like you can do anything and eat anything. As you get older, you get less energetic, and you see yourself in a different place than you’re used to. I started running a few years ago and loved it, but there was always something bigger, longer, farther. This is sort of the next step.”

Initially, Scarbrough got into triathlons after being nudged by his buddies, several of whom had made the transition from marathons and other races to the three-sport extravaganza.

Although they knew they’d be adding a competitor when they encouraged him to sign up, his friends said they believed Scarbrough would be a natural.

“Marc is an incredible athlete, and when he really has time to train his body to compete, he’s very good,” said Jon King, a fellow competitor and longtime friend and training partner.

Today, in addition to being someone Scarbrough can prepare with, King represents that one man the Goddard High graduate can keep his sights on during the heat of battle.

“If I could catch King, if I could get stronger in the bike and catch him, that would be fantastic,” Scarbrough said.

At the most recent triathlon, the two men competed in a couple of weeks ago in Kansas City, King finished ahead of Scarbrough by about 10 minutes. True to his newfound form, however, the one area where Scarbrough outdid his friend was the swim, where he finished six minutes ahead of King.

It’s as much the competition with others as it is the competition within himself — bettering his own times, watching his skills improve in each segment, each time — that has driven Scarbrough to take the plunge and compete in this year’s Ironman Kansas.

“You do, you get addicted,” he said. “The competition, being in the moment, where you’re kind of nervous before the gun goes off and then the gun goes off and you’re in the fray, and you have to tell yourself to calm down because the adrenaline is going to be great for like two minutes, and then it’ll kill you … all of that is just fantastic.”

In addition to preparing his body for the biggest race of his life, Scarbrough also has been preparing his house, which he shares with wife Kim and three children, for company. Professional triathlete Kim Loeffler will be staying with the Scarbroughs when she’s in town to compete, and that, along with all of the other elements that make competing such a thrill, just adds to Scarbrough’s excitement.

“You’re doing something that’s good for you, it’s fun, and you have all your friends there. It’s just a blast,” he said. “If I can just get through this week at work, then the fun begins.”