Running is widely known to be just as much of a mental sport as it is physical, and for two runners competing in the Oklahoma City Memorial Half Marathon Sunday, that theory rings true. Cameron Clapp, 30, and Seth Alexander, 20, are each bilateral amputees, meaning they are missing both legs from above the knee.

For Clapp, who was 15 when he was hit by a freight train near his California home, severing both his legs and his right arm, Oklahoma City will be his fourth marathon but likely the most meaningful. Clapp will be running with Alexander, who lost his legs in a car accident at age 16. The two formed a bond over their love of running, which had provided them with a freedom they haven’t felt since their injuries.

“Before the accident, my twin brother and me were the fastest kids in our school,” Clapp told FoxNews.com. “We loved running, and we excelled in sports. Going into high school I was more of a ‘skater-surfer California dude,’ and then after the accident, I was turned into an amputee multiple-sports athlete.”

Alexander has a similar story, as he was being scouted in his home state of Missouri to play baseball at college, and had a love for basketball before his accident in 2011. During his month-long hospitalization, he isolated himself from sports, abandoning what once made him happy as he underwent 13 surgeries to recover.

“It was very difficult for me. Being 16 years old, I was a junior in high school,” Alexander told FoxNews.com. “I went from being this kid that was into basketball and baseball— I had college scouts looking at me for baseball— and it was really hard to accept that my active life was pretty much out the window, or at least I thought.”

Although their accidents occurred 10 years apart, Clapp and Alexander wound up at The Hanger Clinic in Oklahoma City, Oklahoma. While the clinic has more than 750 offices around the country, the Oklahoma City location specializes in bilateral above-the-knee patient care. Both men were fitted with their prosthetics at the clinic and regularly return for the Hanger Clinic Bilateral Bootcamp Workshop, which is where they first connected in 2012.

“The months leading up to boot camp was a really hard time for me,” Alexander said. “At bootcamp I got to experience running for the first time since my accident. It was very scary, very hard, but at the same time it was very liberating. I felt like nothing could stop me.”

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Alexander then attended the Endeavor Games at University of Central Oklahoma to run the 100-meter spring and the 200-meter sprint. He spent a week preparing among other athletes, which happened to include Clapp, who pushed him like nobody had before.

“The track was a pivotal point in my recovery process because there was a moment where I was on a straightaway, and my leg buckled and I fell down,” Alexander said. “I got a nice road rash on my arm and I broke down, and Cameron sat down and said basically that things aren’t easy but they get easier, and they get better the more you do it, and the more you push yourself to the limits.

“Ever since then, I’ve had this little fire inside of me, this little spark of motivation and drive that makes myself push myself every day to do a little bit more. That’s what got me back into sports,” Alexander added.

Clapp and Alexander kept in touch despite living in separate states, and they reunited at the bootcamp each year. This year, Capp had heard a few friends talking about running the Oklahoma City Memorial Half Marathon and told Alexander about it while out on a 3-mile run. They both agreed to make participating in the race their 2016 goal.

“The closer we get to that day, the more excited that I get and the harder I push myself,” Clapp said.

That includes making sure their prosthetics are prepared for longer-distance running, and their bodies are prepared for the strain. They both use a knee system and a running foot, as neither has an actual knee joint. They have other interchangeable prosthetics they can use for walking, driving, swimming or other extracurricular activities.

“At first, we learned to run without a knee— you just put on a straight running foot to get the feel of it because the design of the running foot is very dynamic,” Clapp said. “Once you get the feel for it, depending on your preference, you get a knee. Seth and I both have carbon fiber running feet with the knee system [attached to it].”

The marathon has a deeper meaning for them than it may other runners, as they chose the city specifically to show gratitude and appreciation toward their medical teams at the Hanger Clinic. Both say that without the clinic’s technologies, competing in the marathon wouldn’t be possible.

“I’m incredibly grateful and I’m thankful to my team,” Clapp said, “because with the ComfortFlex Socket made by Hanger Clinic there’s no way I would be able to have the quality of life I have today as an independent hundred percent full-time on prosthetics.

“I’m not just doing everyday living activities,” he added. “I’ve gone beyond that in being able to run half marathons, and that has given me so many valuable experiences that have been rewarding. I don’t know any other way to try to give back.”

Alexander echoed Clapp’s sentiments, saying that running the race will also be a way for them to show others that there’s more to life than a “TV screen and living in your comfort zone.”

“Seth and I are a two-man team determined to be triumphant in the face of adversity,” Clapp said, “to live our lives to the fullest, to have some good times and a good experience. I’m for sure this will be a great memory that we will be very proud of.”