WASHINGTON — Paul Ryan’s dogged commitment to fitness and healthy living can be traced to 1986 when, at age 16, he found his father dead of a heart attack in the family’s Janesville, Wis., home.

The elder Ryan had become the latest male relative to die prematurely and Ryan wanted to avoid a similar fate.

Today, the 42-year-old Wisconsin congressman boasts of body fat between just 6 and 8 percent. He shuns sweets — even on his birthday. He holds early-morning workouts for colleagues in the House gym, favoring a high-intensity routine called P90X.

He’s also determined to stick to his routine now that life is a little more hectic as Mitt Romney’s No. 2 on the GOP presidential ticket.

It’s now almost a given for high-profile politicians to be committed to physical fitness, given the nation’s obesity epidemic. George W. Bush, for instance, became an avid mountain biker after injuries forced him to give up running.

President Barack Obama works out with a personal trainer most days, and plays basketball and golf. Michelle Obama, who as first lady has worked to inject healthy living into the public consciousness, trains daily in the White House gym.

Romney exercises at his hotel gym almost daily, usually on a stationary bike or elliptical machine. He was an avid runner until a foot ailment sidelined him.

Ryan’s devotion to physical fitness, and the story behind it, has been in the spotlight since Romney introduced his running mate last weekend.

The elder Ryan was 55 when he died, making him the third generation of men in the family to die of a heart attack before age 60. Friends say the implications for the congressman, given that family history, were not lost on him.

“It’s always made him health-conscious. He watches what he eats. He works out all the time,” said House Majority Whip Kevin McCarthy, R-Calif. “It’s part of that therapy time for him too, time for himself.”

Ryan once was so into fitness that he became a personal trainer. After graduating from Ohio’s Miami University in 1992, he considered a sports career, with skiing — freestyle or mogul — as a possible choice.

But he chose Capitol Hill instead, working as a congressional aide before being elected to the House at age 28. He rose in the ranks of the Republican Party, eventually becoming chairman of the House Budget Committee — and, to hear friends tell it — chairman of the House gym.

McCarthy said he’ll sometimes see Ryan in the gym late at night, when most members of Congress have long since gone home, if he missed an earlier workout because of a morning talk-show appearance.

Ryan favors P90X, a high-energy workout routine on DVD that’s peddled on late-night infomercials.

Google searches for “Paul Ryan P90X” spiked more than 5,000 percent since he was introduced as Romney’s running mate on Aug. 11. “Shirtless” was the No. 2 search term associated with “Paul Ryan” in the 12 hours after word broke that Ryan was Romney’s choice. TMZ on Friday posted a picture of Ryan and his wife, Janna, in swimsuits, believed to be from a vacation several years ago.

The cross-training routine, which combines cardio, abdominal work, yoga and karate, has built quite a following in the small, members-only House gym. Ryan leads a daily, early-morning P90X session when Congress is in session, and members from both parties have joined him.  

Tony Horton, the fitness instructor who created and markets the program, has flown in from California about a half-dozen times to train in the House gym with Ryan and his colleagues. Horton said the uptick in interest in his program since the Ryan announcement has been astonishing.

Mrs. Obama also has used P90X, Horton said.

“When you see Michelle Obama on one side in the Obama administration, and then you see what Ryan’s doing, it gets a lot of people to wake up and make a serious change in their lives,” Horton said.

Perhaps it’s no coincidence that P90X has become the workout of choice for a man like Ryan. As the GOP’s budget guru and architect of its plan to trim spending, Ryan has a competing set of demands on his time, his attention and his mind.

“Not only does it help keep you physically fit, but mentally it helps out so much, especially in the job we’re in,” said former Rep. Bart Stupak, D-Mich., who took turns with Ryan leading the P90X sessions until he left Congress last year. “It’s a place you can get away from all the pressures of the job.”

Ryan’s schedule will become even more demanding in the coming weeks as he hops from state to state shaking hands, giving speeches and raising money. Candidates and their staffs frequently complain about the rigors of life on the campaign trail — little sleep, too much fast food and almost no time for personal luxuries like a good workout.

In his first week on the ticket, Ryan was seen working out in hotel fitness centers before dawn, following P90X workouts playing on his iPad. Romney’s campaign said he intends to keep that up unless the travel demands make it absolutely impossible.