Do not write the dog paddle as a stroke for small children. At 52, Dean Jarvis, an above-knee amputee, uses basic swimming technique to record over 20 miles per week in the pool.

“I don’t go up and down the tracks like Michael Phelps,” says the Maryville, Tennessee-based insurance agent. “But it was a way for me to lose weight and improve my cardio form.”

Mr Jarvis lost his left leg below the knee, as well as the use of his left hamstring, at age 19 after contracting bone cancer. The former high school athlete, now cancer-free, struggled to find ways to stay competitive and keep those extra pounds off. In his late forties, he began competing in ParaLong Drive competitions, where success is measured by how far you hit a golf ball. But that didn’t provide enough cardio. The stress of his nearly 265-pound frame on his prosthesis put too much pressure on the top of his leg.

Realizing he needed to find a low impact cardio exercise, he embraced long distance swimming. “I never dreamed that I would be a swimmer,” he says. “My original prosthesis contained a computer chip, so I avoided being near water at all costs.”

Mr. Jarvis had not swam since childhood and began to familiarize himself with the water again using the dog paddle. The technique focuses on capturing underwater and pulling arm strokes and resembles the actions a dog uses while swimming.