Nationals pitcher Rafael Soriano at his home emerging from his hyperbaric chamber which he believes has kept him injury-free for four years. (Bill O'Leary/The Washington Post)

After 13 seasons and more than 9,800 pitches in the major leagues, Washington Nationals closer Rafael Soriano has earned the right to be one of the last players to get to the stadium. But long before he reaches Nationals Park before a home game, Soriano has been preparing his body for another day of work.

In the basement of his rented house in Chevy Chase, Soriano begins a typical day of a night game with a workout, followed by a massage. He then zips himself into a cylinder called a hyperbaric chamber, pulls on a breathing mask and spends the next 90 minutes or so resting in an oxygen-rich environment.

At about 71 / 2 feet by 4 feet, the chamber is not for the claustrophobic. Once the air pumps are activated via a remote control, the urethane chamber inflates and stiffens like a rock. The Food and Drug Administration has approved hyperbaric chambers for certain medical uses, including treating decompression sickness among deep sea divers. While opinions differ on their efficacy for athletic recovery, Soriano is a believer.

“I’ve seen the results because I don’t feel as tired or worn out when I use it,” Soriano said. “. . . It gets the toxins out of your body and helps you with breathing, your blood. It helps.”

The chamber has been part of the enigmatic 34-year-old pitcher’s fitness commitment since he first investigated it in 2012. Few arms can withstand the irregular and taxing nature of the bullpen as long as Soriano has. Since 2009, only one closer, Jonathan Papelbon, has more saves than Soriano’s 181.

The Post Sports Live crew assesses the Nationals at the midway point of the season, and look at which players need to lead the team down the stretch to a potential National League East crown. (Post Sports Live/The Washington Post)

“That’s what separates the veteran player to the successful player to the guy whose career doesn’t really amount to making the money a veteran player ends up making,” said Nationals right fielder Jayson Werth, who, at 35, is the oldest player on the team. “That’s the way it’s set up. I’d say nine times out of 10, that’s all about longevity and being able to stay injury-free or being able to maintain through injuries and play with injuries. That’s the difference.”

Soriano was introduced to the hyperbaric chamber when he was with the Atlanta Braves from 2007 to 2009. Teammate John Smoltz, an eight-time all-star and 1996 NL Cy Young Award winner, swore by the device and even slept in it. But Soriano thought little of it until 2012, when he was 32 and closing for the New York Yankees.

His close friend Jose Veras, a fellow Dominican who pitched for the Milwaukee Brewers that season, used a hyperbaric chamber and told Soriano to talk to Raul Ibanez . Ibanez, now 42 and in his 19th major league season, was also with the Yankees that year and explained to Soriano how the machine helped with recovery by providing oxygen-rich air. Soriano checked with his doctor, who suggested it could help him with his mild asthma. He purchased one for $20,000 and has used it ever since as part of his fitness routine.

“When I was younger, I didn’t train like this,” Soriano said in Spanish. “I do more now. I have more to take care of. Because of that, I’ve got to work harder. Back then, I didn’t know how to take care of my body.”

When he is at home, Soriano uses the hyperbaric chamber after some exercising. In his basement, he has a treadmill and stationary bicycle he bought when he moved to Washington. He uses them based on how he feels. He lifts weights mostly in the offseason, and when he does, he avoids lifting with his upper body to avoid any damage to his arms and shoulder. During the season, he uses elastic bands for his upper body and arms and skips weights altogether.

“I can’t have my body feeling sore or tired,” he said. “With the elastic bands, I can do that daily and be okay.”

In his basement, Soriano also has a massage and chiropractic table. For the past five years, he has employed a Dominican massage therapist who lives nearby. Following his massage, it’s time to get into the chamber.

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During a recent session before a night home game, Soriano spent an hour and 40 minutes inside the device, texting family and friends and watching a DVD of a Telemundo telenovela called “El Señor de los Cielos” (“The Lord of the Skies”). Once he was ready to exit the machine, an assistant turned a knob to release the air pressure. After the chamber slowly deflated, Soriano unzipped the opening and hopped out.

The first time he used the machine, Soriano said it felt like he was in an airplane, his ears popping. He has grown accustomed to the feeling and now finds the time relaxing. Sometimes after games in which he has pitched or after a heavy workload, he gets in the chamber again when he returns home.

“Sometimes you just feel exhausted,” Soriano said. “I get in the machine and get a massage and feel good.”

Many professional athletes have employed hyperbaric chambers to varying degrees. Colorado Rockies all-star shortstop Troy Tulowitzki, record-setting Olympic swimmer Michael Phelps and San Francisco 49ers Frank Gore and Michael Crabtree have been known to rely on the devices. Werth used one in 2005 to help with recovery from an injured wrist but hasn’t since. Paul Pierce, who recently signed with the Washington Wizards, used a portable one at home and during long trips when he played with the Boston Celtics. Some Washington Redskins players have, too, to help recovery.

“It really helps with relaxation while you’re oxygenating your body,” Ibanez said. “The recovery is the biggest thing. Late in the season is where it starts showing up. And it pays dividends at the end of the season. This game is all about recovery. If you feel good, then you’ll be able to continue to perform. [Soriano] deserves all the credit though. He listened to me, took it to heart and did it. That requires a discipline and will to succeed. That’s why he’s such an elite closer.”

Soriano’s stellar season is also the product of improved command. He is striking out batters at a higher rate (8.5 per nine innings) than last season, and opponents’ batting average against him (.164) is at its lowest in four years. His slider, which was hit hard last season, is a strikeout pitch again.

“I’m calmer and fixed my breaking ball,” he said. “I took that and put it together with all the good that happened in 2012 and last year. I left the bad stuff to the side and pushed on. I threw more breaking balls for strikes more consistently.”

Soriano is careful about his fitness routine but allows some leeway in his diet.

“I eat my Dominican food,” he said. “Chicken, beef, whatever. I eat it whenever. No problem.”

This season could be Soriano’s final one in Washington. The Nationals hold a $14 million team option for 2015, half of which is deferred. The option vests if Soriano finishes 120 games between 2013 and 2014, but he isn’t on pace to trigger it. Soriano likes the Nationals but worries little about his future.

“That’s a decision for the bosses, my agent and what he understands is best for me,” he said. “I come here every day and try to do the best that I can and help the team win. I don’t think about stuff beyond that.”

After Soriano finished his recent session in the chamber, he ate a hearty lunch and took a shower. Around 2:45 p.m., he left for Nationals Park, his body and well-traveled right arm prepared and ready for another day of work.