Magnus Carlsen, the two-time world chess champion, believes the fitter the body, the sharper the mind.

The Norway-born Mr. Carlsen, 25, has been playing chess since he was 8. At 13, he was one of the youngest people ever to be awarded the title of grandmaster, the highest level of chess mastery; in 2013, he won his first world championship. He is set to defend his world title at the World Chess Championship, playing a series of matches against challenger Sergey Karjakin in New York City through November 30.

Many parents will be sorry to learn that Mr. Carlsen keeps his mind focused by playing videogames. He gives his memory a workout by practicing chess blindfolded. At the Sohn Investment Conference in 2015, he defeated three challengers in simultaneous timed blindfold matches, to raise money for pediatric cancer research and treatment.

Magnus Carlsen, three-time World Chess Champion, on a visit to the Liberty Science Center, in Jersey City, N.J., in September. Photo: Paul Zimmerman/Getty Images

Read More Physical Fitness Leads to Mental Fitness

With regular matches at Mr. Carlsen’s level easily lasting five hours or more, and conceivably as long as three weeks at a stretch, physical stamina, as well as mental stamina, is needed. Mr. Carlsen says he believes a healthy diet and physical training are crucial for a chess master to remain at peak, just as they are for other types of athletes. “I get bored very easily, so I don’t do well in the gym,” Mr. Carlsen says. “Luckily for me, I have a real love of sport.”

While prodigies often set aside every other hobby to focus on one talent, Mr. Carlsen says he always made time for soccer. “No sport challenges your endurance like soccer, both mentally and physically,” he says. He still plays on a local recreational team in Norway called Lokomotiv Oslo.

From the Archive World Chess Champion Magnus Carlsen gave a thoughtful interview about his life in chess...and then beat WSJ’s Jonathan Zalman in about 30 seconds. (Originally published 6/26/14)

In soccer games, as in chess matches, “games are lost or won in the final hours due to mistakes caused by fatigue,” says Mr. Carlsen, who is known as a chess player who makes very few errors while often causing opponents to do so.

When he is in his best physical shape, Mr. Carlsen says, he is able to sleep and relax between chess matches. He also practices yoga. He has three sisters who also practice yoga, and a yoga teacher is the head of his game-development company, Play Magnus. “I find that the routine of yoga helps me calm my mind so I can focus on strategies,” he says.

In 2013, Mr. Carlsen started training with Peter Heine Nielsen, a Lithuania-based chess coach. The two discuss mental and physical training routines by email and phone. “My goal is to get Magnus in the best mental and physical state possible leading up to big tournaments,” Mr. Nielson says. “Diet, rest and exercise are a big part of that. He also needs to have fun to keep the pressure off.”

Magnus Carlsen, right, the top-ranked chess player in the world, played a former world champion, India’s Viswanathan Anand, at the World Chess Championship in 2014. Photo: Artur Lebedev/Associated Press

The Workout

When Mr. Carlsen is on the road for a tournament, he depends on his workouts to help him relieve tension and relax. He might run intervals on the treadmill at a hotel gym, adjusting the incline and intensity for 30 to 60 minutes. “Running is a time where I can go through game strategies,” he says.

After he gets his heart rate up, he winds down with a series of stretches, or he will flow through yoga sequences for 20 minutes. “Much of my core work comes from yoga,” he says. “I’m not the type to go to the gym and run through reps and sets of exercise. I need something more fluid and fun.” If he can find a hot yoga studio, he’ll attend a class.

He says he likes the challenge and focus of yoga, but still prefers the competitiveness of soccer, basketball or tennis. If he has a rest day between matches, he sometimes gathers team members for a low-key pickup game of basketball or soccer. “Hard physical training, especially in a competitive setting, takes a lot of energy, so during tournaments we keep the training at a level light,” says Mr. Heine. “Never more than an hour or two of soccer or basketball.”

Magnus Carlsen played some recreational soccer at the Tata Steel Chess Tournament in Wijk aan Zee, the Netherlands. Photo: Fred Jonny

At home in Oslo, Mr. Carlsen goes to a 90-minute hot yoga class two to three times a week. He plays defense on his local soccer team but says he prefers to attack when playing casually with friends. He trains with his team one to two times a week for an hour and usually has one game a week. During Norway’s long winters, he goes cross-country skiing and hiking on weekends.

Whenever he has time to kill, such as when traveling or waiting in line at a store, he uses the opportunity to play games on his phone. “I have a team of grandmasters that create interesting chess-related games,” he says. Lately, he has been playing a text-based, multiplayer role-playing game called Avalon. It is played in real time, so players are constantly thinking about the next move. “It’s a mythological environment where you can create your own character and move through over 20,000 locations over 19 continents,” Mr. Carlsen says. “It’s easy to get caught up and play for hours.”

The Diet

Mr. Carlsen eats a mostly vegetarian diet. For breakfast, he makes a superfood smoothie with ingredients like açaí berry and hemp milk, or he’ll have a fresh pressed green juice, with ginger and lemon. Lunch is a salad topped with avocado, walnuts or pumpkin seeds. He likes Asian flavors and often makes a vegetable stir fry over brown rice for dinner. During tournaments he focuses on getting enough protein to maintain his energy over long time periods. He relies on plant proteins like beans, nuts, seeds or hemp protein and drinks water throughout the tournament.

On days off from chess, Magnus Carlsen plays basketball to unwind. Photo: Tarjei. J. Svendsen

Cost & Gear

He spends $30 a month on soccer dues. He likes soccer cleats made by Warrior. “I like to keep things simple and wear whatever is in my closet. I’m not overly picky about the brands I wear to work out.”

Playlist

“I listen to a lot of rock music when I run, but my playlist is very diversified. One thing all of my music has in common is that it’s upbeat and keeps my momentum up.” His fight song is by gangsta rapper Lil Jon, with a title that can’t be printed in a family newspaper.

Corrections & Amplifications:

Magnus Carlsen, the World ​Chess Champion​since 2013, is the two-time champion. An earlier version of this article incorrectly referred to him as the three-time world champion. (Nov. 16, 2016)

Write to Jen Murphy at workout@wsj.com