The simple theory behind Mark Cunningham's approach to fitness is to keep moving, preferably in the ocean, where bodysurfing the Banzai Pipeline is his religion.

But with a routine that could redefine cross training, the retired lifeguard also stays in shape with a mix of paddleboarding, swimming, snorkeling and even yard work. All are a means to an end: Cunningham can swim easily into barreling 12-foot waves at the dangerous North Shore break.

Better than that, perhaps, is that he can do that even though he's often the oldest guy out there.

"For a 53-year-old, I am feeling pretty fit," Cunningham says. "There are guys faster and stronger than me, but I am still playing the game, and I have lot of contemporaries who are not playing anymore."

Cunningham has been a fixture in the Hawai'i bodysurfing scene since 1976, consistently winning contests and catching some of the sport's most unforgiving waves. He was also a Honolulu lifeguard for 29 years, and bodysurfing helped keep him stay in shape.

In those years, Cunningham was a more disciplined athlete, running in the sand, paddleboarding or swimming nearly every day.

Retirement in 2005 brought a more relaxed pace - and 10 more pounds. Cunningham doesn't mind, saying he's "fat and happy."

The core of his routine remains bodysurfing.

During the winter, when the waves at Pipeline are at their best, Cunningham will be in the water five or six days a week. During the summer, when he says he's "a little choosier," Cunningham will bodysurf the popular South Shore breaks at Sandy Beach and Point Panic about three to five times a week.

This summer, he also entered a series of distance-swimming races on the North Shore as well as several paddleboard races, but never really to compete. It was all part of an eclectic routine.

"I really like to mix it up," Cunningham says. "And I love snorkeling, snooping around and looking for shells and treasures. And I love yard work, trimming hedges and putting that in the compost heap, and raking the yard."

But Cunningham's relaxed approach to fitness does have a serious side. He would likely be a shell of himself if not for a steadfast attention to a dietary restriction and his firm belief that it's good to have regular medical checkups. He offers himself as proof.

Cunningham suffers from gluten intolerance, a condition that went undiagnosed for the early part of his lifeguarding career and left him weak. He says he was literally wasting away.

"I was on a vegetarian diet, and I kind of overdosed on carbohydrates — pastas, bagels, what have you — and it set this condition off," he says. "Your intestinal lining disappears. Food goes through and you don't absorb it. I was lifeguarding and had no muscle, and I was running out of gas. I didn't think I was strong enough to protect the beach anymore."

The problem was diagnosed 16 years ago with the help of a new doctor. Beer, pizza and pasta were replaced by corn and rice, and his weight — too scrawny at 160 pounds — improved to 175 pounds. Cunningham felt strong, physically and mentally.

"I found a doctor I could trust and I was comfortable talking with, and that was so important to me, having a friend I could go man-to-man with," he says.

The goal of all this is as simple as it is selfish. Cunningham hopes to continue bodysurfing into his 70s, and maybe even into his 80s.

"I love being surrounded, immersed, embraced, being loved by the ocean," he says. "Instead of riding a wave, you are a part of it. You are more connected to the ocean, as opposed to floating on top of it. It is more sensual."