When Lutheran High School South senior Gus Gross was a freshman, he made a promise to himself: he would complete an Ironman by the time he graduated high school.

The Ironman is an intense, long-distance triathlon that spans a total of 140.6 miles. Racers start with the swim portion, which lasts 2.4 miles, before moving to the biking portion, which lasts a vast 112 miles. The triathlon wraps up with a full 26.2-mile marathon run.

On April 18, Gus successfully completed the race in 13 hours and 38 minutes. He was among the youngest racers to compete.

“It’s probably something I’ll never experience ever again,” Gus said. “I’m not sure I’ll ever get to do something that great again.”

It was a goal that took four years to come true. To prepare for his Ironman, Gus took it one step at a time. He ran a half-marathon in his freshman year, a full marathon in his sophomore year and a half-Ironman in his junior year. When the time came to sign up for the real thing, Gus was ready.

“It was a super cool goal for me,” Gus said. “A year ago, registration opened up. I took the chance to sign up early and force myself to start training for it. … I just plunged myself into it.”

Gus says he did six workouts a week to train for the race. This regimen included a long bike ride on Saturday and a long run on Sunday; throughout the week, he would do one long swim. For his other three workouts, he would do shorter bike rides, runs or recovery workouts. In the end, he spent five months training for his Ironman.

Gus’s father, Paul Gross, was his coach. Eight years ago, Paul began running triathlons, and Gus would attend the races to watch and support his father. Eventually, Paul encouraged his son to join the middle school cross country team. When Gus was in seventh or eighth grade, Paul ran his first full Ironman.

“It was super inspirational to me,” Gus said. “I watched him through the whole race, and I was there when he finished. I thought it was a cool experience. Ever since he did it, I’ve wanted to try something like that.”

On the day of the race, Gus woke up at 4 a.m. for the Ironman. Around 7 a.m., the starting gun went off, and Gus went into the water.

The swimming portion of the race took Gus through a lake, which eventually entered a canal. He says this part was physically the easiest, and he finished the swim in 1 hour and 51 minutes.

After Gus was out of the water, he hopped on his bike and took off, riding from downtown streets to a long stretch of toll road. He completed the biking portion in 6 hours and 11 minutes. Gus says he “ended up crushing” this stretch, partially thanks to a cool rain that fell during those hours.

“A third of the bike was in the rain, which actually made it really nice,” Gus said. “Better than the sun and the heat.”

Then came what Gus believed to be the toughest part of the race: a full marathon.

“Starting out on the run was definitely pretty rough,” Gus said. “If you’ve done triathlons before, you know that the way your legs feel after the bike is just a super unique feeling. That’s for the first five miles. But you get into the hang of it after that.”

Gus says the race started to get “really difficult” around mile 16 of the marathon. While the clouds and coolness helped, he still had to walk and stop a few times throughout the run.

“For the last two or three miles, I was just imagining crossing that finish line and I pushed through the pain,” Gus said. “I ran the whole last three miles without stopping. That finish experience was super awesome.”