When U.S. Navy veteran Jack Cotter runs alongside his canine charge, Tucker, in championship American Kennel Club agility classes, he forgets about his aches and pains.

It’s a far cry from his former self, who was once slowed down by multiple spine and neck fractures, two hip replacements, a knee replacement due to degenerative arthritis, a heart attack and severe muscle cramps.

Jack Cotter is classified "100 percent permanently and totally disabled" by the Navy, but you'd never know it to see him win with his champion agility dog, Tucker.

In fact, he's classified as “100 percent permanently and totally disabled,” Cotter told TODAY. The 70-year-old served on submarines from 1964 to 1970 and says he got hurt badly twice. In 1968, a fellow crew member opened a hatch, and because of unequal pressure on the other side, a bullet of air “shot out” and “blew him straight up in the air,” he said.

The accident broke vertebrae in his upper back. A similar incident occurred the next year, fracturing his lower spine. Typical for Cotter, he didn’t really complain either time.

“In those days, if you weren’t bleeding, you weren’t hurt,” he said. Later, once discharged, he endured a spinal injury while playing football.

Agile — and not fragile

But that was then and this is now. For the past nine years, Cotter and Tucker have both been on a journey of transformation. Cotter looks, feels and thinks like a new man, and Tucker has grown from a cute, cuddly puppy to a champion competitor.

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“We go out there and do what we’re supposed to do, and we’re in our own world,” he said about competing in agility with Tucker. “I forget about whatever else is going on, and competing is all that matters. It’s an adrenaline rush that’s hard to describe, but it’s incredible.”

His 9-year-old champion wire fox terrier is the No. 1 AKC dog for 2016 in agility for his breed his breed — his fifth year to hold such an impressive title. He also just clinched his sixth Master Agility Champion title.

Jack Cotter and Tucker just clinched their sixth Master Agility Champion (MACH) title, bestowed here by Dan Butcher, AKC agility judge. Jack and Nancy Cotter

According to the AKC, agility is designed to demonstrate a dog's willingness to work with its handler in a variety of situations. It’s an athletic event that requires conditioning, concentration, training and teamwork from both participants — meaning the owner doesn’t just sit around and bark commands.

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Dog and handlers of different breeds in the same class negotiate an obstacle course, racing against the clock as spectators work themselves into a frenzy. Tucker jumps his height — 12 inches — measured at his withers, the ridge between his shoulder blades and the tallest point of his body.

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Tucker shows his championship stuff as he lands perfectly over an obstacle on the demanding agility course, thanks to training from Jack Cotter and OneMind Dogs.

Cotter described a recent dog show during which he was getting over the flu and “felt pretty bad." He said, "I was having a hard time concentrating until we stepped into the ring. Then it was like I just got a shot of something that made me feel really good.”

All in the family

Cotter has a ritual with Tucker that’s kind of like a good-luck charm, he said. “When we’re lining up at the start, I always bend over and tell him I love him and that we’re going to have fun. And we sure do! This isn’t work for me — it’s play.”

He actively practices the training philosophies of OneMind Dogs, an organization that teaches people how to understand and communicate with their dogs using nonverbal cues and body language. The curriculum is based on one of the founder's experiences with her own deaf dog.

At his home north of Oregon and near Spokane, Washington, he and his wife of 36 years, Nancy, are raising not only Tucker, but wire fox terriers Bella, age 4, and her son, Jake, who’s 2.

Jack Cotter's adorable canine charges line up for a photo op: Can you tell who's who? (Answer: From left, Bella, Tucker and Jake Jack Cotter

Now Cotter and Tucker do three practice runs twice a week, racing 150 yards around a course in under 40 seconds. Then he runs with the two younger dogs.

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Agility has been a lifesaver, Cotter said, as the two compete (and often win) a couple of times a month. “I could have never done this back in 2007," he said. "I was having a hard time walking 10 feet without my crutches, and I couldn’t bend over.”

Dog walks man

That year, he had to be pushed in a wheelchair to watch his son play basketball in a tournament. “I was devastated and embarrassed and I thought, ‘I have to figure a way for this never to happen again,’” he said.

Cotter had been forced to quit work because of his disability, and “he was depressed and couldn’t get around,” Nancy Cotter told TODAY. That same year, a couple who were friends of theirs invited them to meet a dog they'd rescued and that dog was Tucker. He was just over 3 months old.

“Tucker came running to us and jumped into Jack’s arms, love at first sight,” Nancy Cotter said. The couple gave the dog to the Cotters, and so began Jack's profound transformation. He started one step at a time, taking Tucker for walks to the end of the driveway.

Cotter has come a long way from using a wheelchair to partnering with a champion agility dog.

“He’d pull me a few steps more, and then more, and pretty soon we were walking a long way,” Jack Cotter said. When he took Tucker to obedience classes, he saw owners and dogs practicing agility. He thought that looked pretty fun and decided to dive in head first.

“Other people said Jack would never do it due to his poor physical condition, but don’t say ‘you can’t’ to Jack,” his wife said.

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“It didn’t take very long for me to get hooked on it,” Cotter said. Soon he had greater aspirations and was told to seek out local champion agility trainer Barb Davis, winner of nine national championships, and a competitor on the AKC USA World Team.

"Good boy!" Jack Cotter tells his champion agility dog, Tucker, after the two finish another stellar training session. Jack and Nancy Cotter

They said he couldn’t

She remembers Cotter’s potbelly and his struggles to run alongside Tucker in the beginning. “I told Jack his ability to laugh and keep it fun for his dog was his strength, even when Tucker was dog was running all around the arena, out of control,” Davis told TODAY.

Jack Cotter used to wear a size XXL shirt, but thanks to Tucker, shown here as a young dog, he's turned his life and health around. Jack and Nancy Cotter

“Jack developed a great passion for agility, and started losing weight and working out, to be the best teammate he could for his cocky little partner,” she said. “He worked hard on what I was teaching and he would say, ‘I will have that down by next week,’ and he often did. He was one of my favorites to work with because he did his homework.”

Davis said Cotter does everything he can to make sure he can compete at top form, and to ensure his other two dogs are healthy and strong. He even makes them healthy, homemade dog treats.

“Agility has been a godsend for Jack, and he is the epitome of giving it all you’ve got,” Davis said. “You’ve just gotta’ love him.”

Physical activity saves lives

Cotter credits Tucker and their agility training for making him fitter, stronger, more motivated, happier and even less forgetful — his memory is better — all testimony to what medical research has reported for decades about the many benefits of physical activity.

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“Every day I work with the dogs, I figure I’m adding another week to my life,” he said. He’s even ready for the Pacific Northwest’s shorter winter days and won’t let them impact training. “I’ve already made arrangements with a local hotel to bring the dogs and run up the stairs inside. I throw a ball and they go after it.”

It's one more accolade for Cotter and Tucker at the UKI Master Championship last April, shown here with Tuulia Liuhto, left, and Timo Liuhto of OneMind Dogs. Jack and Nancy Cotter

While the rest of us are wondering what to buy for holiday gifts, Cotter and Tucker are hard at work prepping for the AKC Agility International in Orlando, Florida, Dec. 16 – 18. Davis will meet the pair there, and she and Cotter have high hopes Tucker will rate high with the judges.

It’s about more than winning for Cotter, however. Agility has given him a new life, and he wishes that for anyone who’s looking for goals and purpose, and more reasons to live a great life.

Tucker shows us that even champion agility dogs need a bath sometimes, but water doesn't dampen his winning spirit! Jack and Nancy Cotter

“Maybe one or two people will look at what we’ve done and think, ‘I can do that,’" he said. "If so, it’s just another reason this has been so worth it."