Washington free safety Ryan Clark takes frequent breaks during training camp to sit on his cooler and drink healthy beverages, some of the measure he takes to remain active in his mid-30s against players in their early 20s. (John McDonnell/The Washington Post) (John McDonnell/The Washington Post)

Most NFL rookies couldn’t survive three weeks of training camp without their PlayStation or Xbox.

Ryan Clark’s one essential is the blue cooler he brings to practice each morning and sets on the sideline, never far from view, so he can trot over at scheduled intervals for a sip from one of four bottles inside.

He drinks Amino Matrix, rich in essential acids that boost energy and hasten recovery, throughout the two-hour workouts. Another bottle contains Red 54, packed with antioxidants from beets, carrots, cabbage, blueberries, pomegranate and other superfoods. There’s potassium-rich coconut water for the halftime break and an extra bottle for any teammate who wants one. And he drinks a protein potion afterward.

The cooler, which Clark packs himself, is just one of the extra measures the safety takes, at age 34, to keep his starting spot in the NFL.

“It’s just about training and being focused on the job,” said Clark, whom the Redskins re-signed this offseason after eight seasons with Pittsburgh. “At my age, I can’t do exactly what 21- and 22-year-olds do for training because I have to last the whole season. So it’s an ever-evolving process, whether it be diet, weightlifting, running — whatever keeps me explosive, keeps me ready, keeps me able to play the game.”

For the most part, the Redskins’ roster has gotten younger under General Manager Bruce Allen. But this season, the team will lean heavily on 30-somethings at key skill positions — Clark at free safety; strong safety Brandon Meriweather, 30; cornerback DeAngelo Hall, 30; and its fourth wide receiver, 35-year-old Santana Moss, the longest-tenured Redskin.

Counting nose tackle Barry Cofield, 30, and recently acquired defensive end Jason Hatcher, 32, who’s on the mend from knee surgery, the defense has five projected starters who are 30 or older.

For all the focus on the third-year quarterback Robert Griffin III, the Redskins’ fortunes may well hinge on whether these NFL veterans can stay healthy and hold back the clock for one more season.

Clark and Moss, in particular, are leaving nothing to chance.

Extra measures

Clark spends most of his offseason working out in Scottsdale, Ariz., with trainer Ian Danney, who counts NFL linebackers Terrell Suggs and James Harrison among his clients.

Moss, entering his 14th year in the league, employs a staff to help keep him in game-shape virtually year-round. With help of a nutritionist and personal chef, he overhauled his diet three years ago, shedding nearly 20 pounds to get back to his optimum playing weight of 193. And he has kept the weight off by rigorously adhering to the principles he learned: abandoning his beloved junk food for lean meats, a heavy diet of vegetables and banning carbohydrates after 4 p.m.

Moss also has an Ashburn-based chiropractor, a masseuse and an Atlanta-based trainer on call to ensure his muscles and soft-tissue stay intact.

The Post Sports Live crew debates whether the Redskins new head coach is the opposite of their former head coach. (Post Sports Live/The Washington Post)

“You have to pay to play,” Moss said in an interview this week. “You have to spend the money on your body so you can always be tip-top.”

No one is kept on an NFL roster for sentimental reasons. The moment a player can’t perform, he’s replaced. Even when a player is having a Pro Bowl season, his team devotes the college draft and free agent signing period to bringing in challengers for his job.

These days, that jockeying starts Day 1 of training camp.

That’s a change from a decade or so ago, when many NFL players stopped working out once the season ended, letting their weight balloon and fitness slide as a reward for months of hard hits.

Today, the Redskins’ strength and conditioning staff sends each player home at season’s end with a detailed workout plan. It’s voluntary, but ignored at their peril.

“When they come back, we’re expecting them to be ready to go,” said Ray Wright, the team’s strength and conditioning coach. “We don’t have time in April for them to lose a bunch of weight and undo what they’ve done in three months.”

In Wright’s experience, players who report out of shape don’t last long.

“They won’t be your Ryan Clarks or your Santanas or your London Fletchers,” Wright said. “Ryan and Santana definitely are paying that price to continue to play as long as they can.”

It takes a village

A two-sport athlete much of his life, running track and playing football, the 5-foot-10 Moss was always diligent in the weight room. But after breaking his hand midway through the 2011 season and missing four games, his production lagged, dropping from 93 catches the previous year to 46. Though he looked fit outwardly, still hitting the weights hard, he felt winded on the field for the first time in his career.

“Ridiculous!” he says now.

So he phoned Wright and asked for help.

That led to Richard Ingraham, a Miami-based chef who cooked for the Miami Heat’s Dwyane Wade. Moss hired him that offseason. He started cycling. And he shed 20 pounds by spring workouts.

“If it weren’t for the people who are taking care of me today, I wouldn’t be here, still doing what I’m doing,” Moss said. “I don’t take for granted anything that I do in life because I know that nothing is promised to us. That’s why I take my job very seriously.”

The Redskins’ front office has also gotten serious about players’ nutrition. In the early years of Daniel Snyder’s ownership, players were fed fast-food and boxed lunches provided by Bojangles’ and Chicken Out.

Under Allen, the team has hired a registered dietician and chef and built an elaborate kitchen and dining hall at Redskins Park that prepares three meals daily for players and coaches.

It’s a boon for Moss, a fan of the pizza with whole-wheat crust.

“The only reason I didn’t eat as healthy as I should was because I was working out and training and on the go,” Moss said. “What makes you go eat nasty is when you have to go eat something that’s not prepared.”

Coach Jay Gruden is also doing what he can to extend his veterans’ careers, giving occasional days off to the 13 Redskins on the roster who are 29 and older.

Advantages to age

Because they’ve played in more NFL games than younger players and tend to watch more film, Moss and Clark see plays develop even before the ball is snapped. That anticipation helps compensate for anything age has taken away, Wright says.

And even though the Redskins are awash in speedy, talented wide receivers with DeSean Jackson and Andre Roberts joining Pierre Garcon, Gruden has singled out Moss as a player who “can do everything.”

“He is a veteran guy who has been through a lot of big games, played a lot of big games, caught a ton of balls, touchdowns, been there, done that,” Gruden said this week. “So he is a very valuable asset to this football team not only from an experience standpoint [but] from a leadership standpoint.”

Defensive coordinator Jim Haslett says much the same for Clark.

“Ryan is here for a number of different reasons: To help us win games, to help run the defense, to help grow the whole secondary,” Haslett said. “His presence has helped the whole offseason. And we’re going to expect that leadership from him.”

Clark, however, has been careful not to cast himself as anyone’s mentor.

“I look at all of us as brothers,” Clark said. “It’s not like I try to come in here and be anybody’s grandfather or father. What I try to do is be part of the group. And when you are part of a group, guys see the way you work. They see the way you pay attention to detail. They see how focused you are about each rep. As you do that, if they feel close to you, that’s when they ask questions.”

There are times Wright surveys the field and forgets how old Moss and Clark are. They seem to see the game so slowly, yet react so quickly that for a moment, the trainer who played football at Duke can’t recall for a split second how old they really are.

By Week 6, both will be 35, approaching an age that a generation ago was reserved for NFL punters, kickers and the most sturdy quarterbacks.

And the younger Redskins are taking note, even as they try to take their jobs.

They sidle up after meetings and pick their brains over lunch. “How can I do what you do?” they want to know. “How can I play at such a high level for so many years?”

It’s enough to make Wright believe that in a few years, the sidelines at Redskins training camp will be lined with 40 or 50 blue coolers.