When Mark Colbert walked through the door into ICOR boxing gym three years ago, coach Emily Klinefelter thought he would come to practice a handful of times and then quit.

The then-55-year-old Colbert had other thoughts. He started because he wanted to occupy his free time but never thought his career would turn out the way it did.

And three years later, his career all but over, he owns a championship belt in the 165-pound Masters division from the Ringside World Championships Tournament — an event that draws boxers from all over North America. But that title isn’t the most important thing for Colbert.

“No one will know how good it feels to get your youth back,” Colbert said. “I don’t know how to put it in words; I can’t sit here and tell you. It’s priceless.”

Finding that fountain of youth wasn’t easy for Colbert. His weight was a problem, his age was a problem, and his wife was a problem. He said the first time he came home with his face beat up, she wanted him to quit. That wasn’t enough for him to stop, and neither was his coach.

Colbert said the coaching staff put him through drills that no one else in the gym had to partake in. It wasn’t just that he had never boxed before and was terrible — the staff was also worried about the well-being of the club.

“I was a liability,” Colbert said. “It was like, ‘We need him out of here quick. Get him out of here, we don’t want the ambulance coming down here and picking up a 55-year-old man and taking him to the hospital.’ ”

Klinefelter’s thoughts were along those lines, but in addition to the sense of worry, she had trouble taking him seriously. She didn’t think he’d ever step in the ring competitively, let alone win an international tournament.

“I just thought he was some goofy guy who would probably be gone in a month,” said Klinefelter, who amassed more than 90 career wins before a severe brain injury caused her to retire in 2011.

She was wrong. He kept training, and the weight began to fall off. His footwork, which he said was one of his biggest issues, began to improve. He had naturally heavy punches, which weren’t an advantage until the technique came along.

Klinefelter began to warm up to him, and he became popular around the gym, offering encouragement or just keeping the mood light with his upbeat personality.

That, coupled with his tremendous improvement, led his coaches to believe that he was ready to fight. He took second in his first Ringside World Championship Tournament in 2012 and won a year later — the pinnacle of his successful, short, career.

That championship fight was Colbert’s final bout, for a combination of reasons. His wife doesn’t want him to fight anymore, he’s not getting any younger, and perhaps the biggest, he can’t find an opponent.

Klinefelter said there aren’t any other Masters boxers in the state of Iowa that Colbert is eligible to square off with. Boxers must be within 10 years of each other in age and 10 pounds to battle.

That lack of competition may be frustrating for the 58-year-old and the rest of the people in his gym, but that hasn’t changed the way he works and helps at ICOR.

“He might know that ‘OK, there are very few people that are going to fight me out there,’ ” ICOR gym manger Clif Johnson said. “But he trains like he has a million fights lined up … It’s not like ‘I’ve got a fight, now I’m really going to train hard.’ Or, ‘I don’t have to fight, I’m just going to sit around and talk with the guys.’

“No, he’s training every day, no matter what, like his fight is next week.”

Only time will tell if his most valuable contribution to the club is going to come as a product of that ethic. But at least for now, as Colbert wraps up his career, it certainly is.

That attitude that Johnson spoke about is rubbing off on the rest of the boxers who train in the Iowa City gym. Whether it’s keeping the mood light or pushing his training partner, it’s tough to deny how much Colbert means to ICOR.

“He’s one of the life components of that gym,” said Bryan Johnson, an Iowa sophomore who trains at ICOR. “He truly invests himself … that’s the best way to describe him — invested.”

Unfortunately for Bryan Johnson and his teammates and coaches, they’ll soon have to do without Colbert. The club will honor Colbert at its exhibition on Saturday. It should be a victory lap for the man who transformed himself and transformed his training place in the process.

“I’ve had to do it all my life,” Colbert said. “I came in a liability, and I’m leaving an asset.”