Three simple, yet cryptic, stickers adorn the back window of Mathew Mixon’s truck.

In the lower left corner is a plain, black-and-white oval that reads “26.2.” On the right side are two others, stacked atop each other, with “70.3” prominently displayed.

They’re trophies for, respectively, completing a full marathon and a half-distance Ironman triathlon. Like a fighter pilot signifying his victories, Mixon proudly displays each with a well-earned sense of accomplishment, and he’s eager to add another to his cluttered collection.

This week, Mixon will head to Cozumel, Mexico, and on Sunday will attempt his first full-distance Ironman triathlon. The race encompasses a 2.4-mile open water swim, a 112-mile bicycle ride and a full 26.2-mile marathon. It’s one of the most grueling endurance tests in sports and one Mixon is looking forward to passing.

“I’ve thought about the tag. That’s a big deal. Those two (half-Ironman) stickers might come off and get replaced,” Mixon said. “It’s a pride thing. But it’s for yourself. It’s not to get credit or publicity, it’s a personal accomplishment. It’s a badge to remind you that when things get tough, you have to endure. That’s what the whole symbol stands for.”

Mixon isn’t the only Vicksburg resident who has strived to gain Ironman status this fall. A group of four local triathletes — Ryan Lumbley, Branan Southerland, Dale Cordes and Jim Cole — completed the Ironman Florida in Panama City on Nov. 2.

Mixon was unable to go to Florida with that group because of a schedule conflict, but often trains with them. Members of the group also have teamed up for relay triathlons, in which each member takes a leg of the race.

“We train together probably 80 percent of the time. Without the group of guys we have in Vicksburg, it would’ve been way harder to do,” Mixon said. “They had already earned Ironman status before they went to Florida. They just had to clear the paperwork.”

Mixon, 30, has been building toward the Ironman distance for several years. He swam in college at Delta State, ran the Rock and Roll Marathon in New Orleans in March and did half-Ironman triathlons in Augusta, Ga., and Miami in 2010 and 2011.

His training regimen for Cozumel began in earnest in late spring. For the past 20 weeks, he’s invested roughly 20 hours per week to get his body in peak condition. His preparation has included several 100-mile bike rides, 20-mile runs and 3-mile swims, along with dozens of shorter workouts — all for an effort that can be derailed by a single cramp, flat tire or ill-timed stomach ache.

“This is a natural progression,” Mixon said. “In my world, it’s like my Mount Everest. It’s very unpredictable. You never know what conditions you’re going to get or how your body’s going to respond.”

Making it to the end of the race requires not just training and a bit of luck, but also strategy. To replenish the thousands of calories he’ll burn, Mixon plans to ingest up to 4,000 calories of energy drinks, gels and food during it.

His fueling plan is to take in between 250 and 300 calories per hour for the duration of the 13-hour-plus race.

“It’s really four sports — swim, bike, run and nutrition,” Mixon said.

Mixon has also tried to strategize for the weather. His final stretch of training has come on 30-degree mornings in Mississippi. The triathlon is expected to be run in temperatures approaching 80 degrees, which can quickly sap an athlete’s strength.

Mixon said he’s run more on a treadmill and switched pools to work out in warmer conditions.

That the bulk of his training came in the dog days of summer also will help, he said.

“Hopefully those hot Mississippi summers will pay off,” he said with a smile.

Winning is not on Mixon’s agenda Sunday.

The winners of Ironman Cozumel will cross the finish line in a little over 8 hours. If everything goes according to plan, Mixon hopes to do it in fewer than 14.

What Sunday is about is testing his limits.

Accomplishing a goal. Surviving.

And, at the end, getting a 4-inch wide sticker that’ll stand taller than any other trophy he’s ever won.

“I only have one goal, and that’s to step across the line before it says 17 hours,” Mixon said, referring to the time limit triathletes face to complete the race. “Realistically, I’d like to go 13:30. The ultimate goal is to cross the finish line. I can’t get caught up in the numbers.”