After an injury-riddled college career, Chris Kwiatkowski was the top American finisher at the 2013 Army Ten Miler, when he ran a personal-best 48:17. Above, he trains for Sunday’s 2015 race. (Jonathan Newton/The Washington Post)

The scar on Chris Kwiatkowski’s left arm spans nearly eight inches from his wrist to more than halfway up his forearm. Kwiatkowski laughs when he talks about it now — about how he fell after getting tangled up with another runner in just his second collegiate track meet for Oregon and about how he knew his arm was broken when he tried to push himself off the ground.

“My whole family was there,” he said. “I wasn’t laughing then, but now I look back, it’s kind of funny in a sad way.”

A highly recruited runner out of high school, Kwiatkowski suffered multiple running-related injuries — two fibular fractures, two femoral neck fractures and one sacral stress fracture — in addition to his broken arm during five years with the Ducks, derailing what was once a promising collegiate career. Each injury would take about eight weeks to heal.

“I was always trying to play catch up,” he said. “I wasn’t doing it right. Any athlete, you got to put your own program together under the system.”

Since graduating in 2012, Kwiatkowski, 26, has managed to stay healthy and is motivated to reach unfulfilled goals as an elite post-collegiate runner. A successful road racer, Kwiatkowski, an Arlington resident, will be a contender and one of about 35,000 registered runners lining up Sunday morning near the Pentagon for the 31st annual Army Ten Miler. The event, which benefits the U.S. Army’s Morale, Welfare and Recreation programs, was Kwiatkowski’s first road race when he moved to the District in 2012 and is the site of one of his best performances.

Chris Kwiatkowski coaches cross-country at American University and runs professionally under the Pacers/New Balance banner. (Jonathan Newton/The Washington Post)

“That was an exciting moment for me,” Kwiatkowski said of running a personal-best 48 minutes 17 seconds at the 2013 Army Ten Miler, where he was the top American finisher in fourth place. “It’s an awesome race.”

Several times a week, Kwiatkowski, an assistant coach for cross-country and track and field at American University, trains with the Eagles’ runners. He runs 15 miles a day on average and is sponsored by the Pacers/New Balance professional running team.

On a recent workout, Kwiatkowski led a pack of the team’s strongest runners on several loops around a field in Bethesda. With a seemingly effortless stride, Kwiatkowski was among the first to finish each mile repeat and ended the five-mile workout with a 4:35 mile.

“He’s just a late bloomer,” American Head Coach Matt Centrowitz said. “Certain guys, physically and mentally, they just [need] a lot more confidence, certain things to go on in their makeup. He’s that kind of guy.”

Like many long-distance runners, Kwiatkowski grew up playing soccer. As a midfielder, he would get his share of running, but it wasn’t until his freshman year of high school in Bellingham, Wash., that Kwiatkowski ran competitively. And after competing in club soccer and cross-country in the fall for two seasons, he quickly realized his future was in running.

“Honestly, I was too small to play soccer,” the 5-foot-9 Kwiatkowski said. “And I fell in love with running from the get-go. . . . I just liked the feeling.”

Kwiatkowski won the 3,200-meter state title as a senior in 9:05.88 and was recruited by several top collegiate programs. He narrowed his choices to Washington, Portland and Oregon before choosing the Ducks, home of several legendary American distance runners. It was there that he met his current coach’s son, Matthew Centrowitz, a five-time All-Met from Broadneck High who is one of the biggest stars in the sport.

Centrowitz and Kwiatkowski bonded over a mutual interest in video games and their favorite movie, “Superbad.” The two remain best friends and talk nightly through Xbox Live. It’s a friendship some have found odd because of their vastly different personalities.

“It is funny how opposite we really are,” the younger Centrowitz said. “I think we just got along so well because, you know, I can be pretty hotheaded and brash, and he’s kind of leveled me out.”

Centrowitz, 25, plans to be in town for the next week and a half to visit family and celebrate his birthday, giving him the chance to watch Kwiatkowski run at the Army Ten Miler. A silver medalist in the 1,500 meters at the world championships in 2013, Centrowitz set personal bests in the 800 meters (1:44.62), 1,500 meters (3:30.40) and 1,000 meters (2:17.00) this season.

It is Centrowitz’s confidence that has inspired Kwiatkowski the most.

“Everything he does now, nothing surprises me,” Kwiatkowski said. “I definitely feed off a lot of his stuff, not necessary watching the races or seeing the results but just talking to him, hearing his confidence. It manifests itself in me.”

Kwiatkowski qualified for next year’s U.S. Olympic marathon trials after running a 1:04:43 at the Philadelphia Half Marathon in November. But Kwiatkowski, who has never competed in a marathon before, also is hoping to qualify for the Olympic trials in the 10,000 meters — his preferred event.

A strong performance at the Army Ten Miler will help set the stage for next season and put his injury-riddled college career further in the past and out of his mind.

“I’ve been healthy for three years and haven’t missed a day,” Kwiatkowski said. “I’m excited to see what I can do. I’m just really excited to compete and just build on each race that I can.”