The Post’s Adam Kilgore discusses how much he expects the offseason acquisitions of starting pitcher Doug Fister and outfielder Nate McLouth to impact the Nationals in 2014. (Post Sports Live/The Washington Post)

Jayson Werth holds tight to an idea about hitting. His close friend Raul Ibanez, the ageless outfielder now playing for the Los Angeles Angels, once told him, “If you can hit, you can do anything.” Werth found it irrefutable, a simple edict spun from perfect logic.

“Because it doesn’t work both ways,” Werth said. “Just because you can do something else doesn’t mean you can hit. If you can hit, you can do anything. Because it’s the hardest thing to do. There’s nothing harder. I can bake a cake. I could figure out a way to do algorithms. But a guy that knows how to do algorithms could never hit. It’s literally the hardest thing to do. If you can do the hardest thing, you can do anything else.”

For Werth, hitting is a ceaseless pursuit that fascinates and frustrates. Werth has swung a bat for 30-some years and taken 4,464 plate appearances in 11 major-league seasons. And still, hitting remains a fluid endeavor. It requires maintenance and vigilance over a career. It saps physical strength and mental energy over a season.

“There’s nothing harder in the galaxy,” he said.

And for that, Werth loves it.

After a disappointing season last year, the Nationals have made some big changes, but Thomas Boswell thinks the newfound maturity of the players will keep them from repeating last year's mistakes. (Whitney Leaming/The Washington Post)

Two months shy of 35 years old, Werth is entering a phase when players historically decline, and he’s also coming off perhaps the best offensive season of his career. Despite missing a month because of an injury — another challenge he finds ever-shifting — Werth blasted 25 homers and posted career highs in batting average (.318) and slugging (.532) to go with a .398 on-base percentage.

Four seasons remain on the seven-year, $126 million contract Werth signed in December 2010, and the Washington Nationals need him to continue producing in the middle of their lineup. Werth showed last year he could be the rare player who sustains success into his middle and late 30s.

He thrived, in part, because he embraces the unique technical challenge hitting presents. A basketball player’s jumper or a linebacker’s tackling form change seldom, if at all. Any hitter’s swing is a work in progress. Despite his success, Werth has never stopped tinkering with his form or adjusting — and re-adjusting — to pitchers.

“I mean, it never ends,” Werth said. He makes the struggle sound almost like a poker game.

“It’s better than poker,” Werth said. “I play poker. I know poker. This is way better.”

One afternoon last week, as the Nationals played the New York Yankees at Space Coast Stadium, Werth walked to the plate for his first at-bat. He dug into the box and held his hands close to his body, at a level even with his chest.

In his second at-bat, Werth moved the position of his hands, a subtle but noticeable change. Werth held them further away from his body and higher, about 10 inches in front of his ear.

“To get them up is like, ugh,” Werth said. “It’s like a chore. It’s definitely a more complicated swing.”

Werth has been grappling with that chore for years. At the start of the 2009 season, Werth batted with his hands extended and held high, as he had for most of his career. During the middle of the year, he moved them down. He clobbered 36 home runs and led the Philadelphia Phillies back to the World Series.

Werth tinkered with his hand placement over his first two years in Washington, but he always kept them in the same general area. Last year, he noticed how Bryce Harper held his hands at the plate, and it reminded him of his old self. He saw a picture of himself with his pre-2009 stance and decided he wanted to try it again.

“I think I can do more damage with them up,” Werth said. “It’s a commitment.”

And that covers only the hands. Maintaining the rest of swing — stride, rotation, moving hips and shoulders in concert — takes as much thought and work. Once that is in place, an army of scouts, coaches and pitchers start to pinpoint every exploitable weakness.

“As you adjust to the game, the game adjusts to you,” Werth said. “So then you have to adjust to the game. And then the game will adjust to you. It just never stops.”

Werth’s willingness and ability to tinker may not determine the length of his career. “I think that seven-year deal probably had more to do with my longevity,” he said. But it may help explain why he has persisted at a high level, and it may provide the Nationals hope he can continue into his late 30s.

“I took some jujitsu classes for a while in my life,” Werth said. “My Brazilian instructor would say, ‘For every counter, there’s a counter. And a counter. And a counter. And a counter.’ I was like, ‘Oh, it’s like hitting. This is great!’ I really got it.”

The daily toll requires an equal measure of preparation. Taking care of his body, Werth said, “is everything.” Knowing how much the season will chip away at his body, Werth tries to pack weight on in the winter. He believes it helps not only the physical demands, but also the mental.

Werth tinkers, too, with his offseason regimen, finding new ideas and circling back to old ones. He studies the individual way his muscles work, trying to balance the strength in complementary groups: He wants his quadriceps, for example, to be precisely as strong as his hamstring. He has found he is most susceptible to groin injuries, so he is careful not to strengthen it so much it can be torn easily.

“It’s like you become a kinesiologist in a sense,” Werth said.

Werth settled this offseason on heavy, Olympic-style weightlifting. He lifts as much weight as he can once or twice, trying to mimic the explosive, quick actions on a baseball field. He has tried exercises such as yoga, but he found it not quite right.

“I’m more of a meathead body-builder,” Werth said. “There’s a place for that stuff. I’ve done it in the past. I just didn’t get the feeling I was looking for. I didn’t like that stretched feeling. When you go to swing, it’s violent. It’s everything you got. Some guys have that nice, easy, sweet swing. Mine’s like more of a chop down a tree. That’s kind of how I train: one rep as hard and as fast as you can move.”

Werth is ready to start another season, another year of countering pitchers and tweaking his swing. Few players sustain excellence into their mid-30s, but Werth thinks he can be the exception. After all, he can hit, can’t he?