Brandon Kintzler is “not afraid to show his frustrations or opinions over anything,” Max Scherzer said. That includes his teammates’ workouts. (Jonathan Newton/The Washington Post)

The Washington Nationals clubhouse was nearly empty Sunday morning, save for a few players sprawled on red chairs before the game, as Erick Fedde stood in front of Brandon Kintzler’s locker, perched as if he were on the pitching rubber.

Over and over, he practiced his delivery, from standing on his back leg to following through as if throwing a ball straight into Anthony Rendon’s locker a few yards away. Each time, Kintzler would observe his form, point to something, then see what Fedde had to say. Over and over, they would repeat the process, a budding pitcher and his volunteer pitching coach working on drive and mechanics.

Bright stars and loud personalities pack the Nationals clubhouse, which is loaded with more familiar names and faces than Kintzler’s. But subtly, the 33-year-old reliever has emerged as a valued piece of the chemistry puzzle, a veteran as eager to share his thoughts as his teammates are to hear them — if not occasionally more eager than they are.

In the Nationals clubhouse, where Shawn Kelley creates T-shirts as fast as his teammates create memories worth immortalizing, influence can be measured by whether one’s face ends up printed on 100 percent cotton. Kintzler’s likeness was on dark gray T-shirts within weeks of his arrival at last year’s deadline, a picture of him sprinkling salt. To a man, his teammates call him “salty,” a nod to his willingness to express critical opinions.

“He’s all salt,” Max Scherzer said with a smirk. “He’s filling my J-Dub [Jayson Werth] void. He’s not afraid to show his frustrations or opinions over anything.”

Kintzler has opinions about many things and an uncommon willingness to share them, two qualities that do not often combine to form a beloved teammate. For example, most players offering unsolicited critiques to ultracompetitive three-time Cy Young Award winners such as Scherzer would not find their advice particularly well-received. But when asked about Kintzler’s suggestions, Scherzer sighed.

“He makes some good points,” Scherzer said. “There’s some things I think he’s opened my eyes to that I think I can add into my program. He’s on to something.”

For a man as calculated as Scherzer to concede that, especially to a teammate as new to him as Kintzler, speaks to the credibility of the reliever’s criticism. Kintzler can be bold with his ideas because he has spent months researching and implementing them. He has had arm trouble and underwent surgery for a torn tendon in his left knee after the 2014 season. He didn’t recover well. He didn’t reestablish himself until he joined the Minnesota Twins in 2016.

Then, last year in spring training, Kintzler started feeling symptoms of patellar tendinitis in his other knee. Twins trainers worked on him, but he didn’t improve. He took pain medication to mask the pain but couldn’t eradicate it.

“I was like, nope, I don’t want to do this again. So I need to figure out exactly why this happened,” Kintzler said. He started mining the Internet for answers and came across a teaser video from a self-help fitness company started by the founder of one of the earliest CrossFit Gyms in San Francisco. He signed up, paying the monthly fee for a subscription to its videos.

“Then I started watching all the patella tendinitis videos, trying to find what was the cause,” Kintzler said. “And it all started with the feet and ankles.”

Slowly but surely, Kintzler started amassing enough information to address his own tendinitis trouble, then establish a maintenance routine to prevent it from recurring. Through the videos, he learned about the importance of big toe mobility — in simplest terms, the ability to move one’s big toe separate from the others — and its effect on the gluteal muscles so many pitchers use to generate power.

He began putting a lacrosse ball under his big toe to increase its mobility, to make sure he engaged his feet — and by extension, the larger muscles of his legs — more effectively. Even as he pitches now, Kintzler thinks about pushing off his big toe until the last possible moment.

“Obviously everything works from the ground up. So when I had a knee injury, my ankles and my feet were extremely tight,” Kintzler said. “If they don’t absorb the impact, the impact goes upstream. It goes up to your hips. I learned a lot about it, so I spread it around the clubhouse when I can.”

When Sean Doolittle started feeling tendinitis in his knee last year, Kintzler passed along advice.

“Now [Doolittle]’s getting supple,” said Kintzler, who has a hat from the fitness company in his locker and wore its gear around often enough that teammates started asking him about it. Joe Ross always had what he described as “bad feet,” so when Kintzler arrived with suggestions about toe mobility, he listened. Now he wears toe spacers in his cleats and when he trains.

“It puts them in the right spot so you use your ankle correctly, and my balance gets a lot better,” Ross said. “I’m trying to get to the point where I don’t need them.”

Stephen Strasburg, who has spoken extensively about the kinetic chain and the lessons he’s learned the hard way about how leg injuries can affect his arm, spoke to Kintzler about the program, too.

“It’s great to be able to acquire some knowledge from him like that, about how your body works — if I’m feeling tight there, this is probably why, and how I can treat it,” Strasburg said. “. . . I’m more along the lines of, hey, if it’s not going to hurt me, I’m going to try it.”

Strasburg did go on a 34-inning scoreless streak shortly after Kintzler’s arrival last season. Then again, as evidenced by the kinetic chain, causation can be complicated.

Sammy Solis joked that he sometimes has to tell Kintzler to “stay over there” during workouts. Manager Dave Martinez called the veteran “a quiet instigator.” But for all the jokes about his “salt,” and all the teasing about his many opinions, Scherzer and many other Nationals texted Kintzler when he was deciding where to sign this winter, pleading with him to return. Now Kintzler and Scherzer are throwing partners, playing daily games of catch that would probably be a pitching student’s delight — if they were at all suitable for public consumption.

“We’re not afraid to say, ‘Hey, that was a dog crap slider,’ or ‘What were you thinking here?’ ” Scherzer said. “That’s how we are. We’d rather just have each other lay it on the line. We aren’t sensitive.”

Scherzer is helping Kintzler improve his slider. Kintzler is helping Scherzer improve . . . well, Scherzer is too secretive to say. But few baseball minds can challenge Scherzer’s enough to penetrate it. No suggestions earn genuine consideration without careful vetting. Kintzler, impromptu pitching coach, unheralded workout guru, has passed his stringent test.