Ben Affleck didn’t know it at the time, but he started preparing for the role of Batman in 2009. That’s when he decided to get ripped for the movie The Town. Partly because he would be playing an ex-hockey player who was fond of doing chinups with his shirt off, and partly because he was directing, he figured that being fitter would give him more energy on set. So he connected with Walter Norton Jr., a trainer who had worked with the Boston Celtics, Boston Bruins, and New England Revolution (and who also owned a gym in the Boston suburbs, the Institute of Performance & Fitness). Affleck and Norton were nearly the same age and had attended rival high schools in Beantown.

SEE ALSO: The Super-Jacked Batman Workout

The two hit it off, and Norton was impressed with Affleck’s work ethic and coachability. By the first day of shooting on The Town, the 6’4″ Affleck was a svelte 198 pounds, with 6.8% body fat. “He probably lost 12 pounds for The Town,” says Norton. “But he was stronger in every lift and physically bigger everywhere except his waist. He put on a ton of muscle and lost a lot of fat.” Affleck and Norton continued to train together for the next few years, through movies like Argo, which captured the Academy Award for Best Picture. Then in the summer of 2013, Warner Bros. announced that Affleck would be playing Batman in a Man of Steel sequel. The Internet had a conniption—one fanboy’s nine-minute temper tantrum earned about a million views on YouTube—and the dynamic duo of Affleck and Norton knew they needed to take their training up a notch—or six.

After consulting with Batman v Superman director Zack Snyder, they decided they didn’t want Affleck to look at all like he did in The Town. And they definitely didn’t want him to look like Christian Bale or Michael Keaton. They were thinking bigger. Much bigger. After all, if Batman (a human being with no actual superpowers) was going to stand a chance against an alien who can fly, freeze stuff, and turn back time, he was going to need major muscle. Like, comic-book muscle.

Batman

In fact, initially some within the studio even had the idea that Ben could transform himself into a young Arnold Schwarzenegger. “We got a good chuckle out of that,” says Norton. “You’re talking about maybe the best body of all time.” Eventually, more logical heads prevailed, and the target look for Affleck became an MMA heavyweight fighter.

“With Batman, we had to get a physically imposing, powerful look,” says Norton. “And that takes a lot of reps. You have to be in the weight room day after day after day, so it certainly was a process.”

For 15 months, Norton and Affleck trained anywhere from 90 minutes to 2½ hours a day, typically six days on and two days off. They trained through the filming of Gone Girl, when Affleck was often getting up at 4 a.m. to work out before a 14-hour day of shooting. (Gone Girl’s director, David Fincher, is known for being particularly demanding with actors, requiring long hours and dozens and dozens of takes.) But according to Norton, Affleck understood this was all part of the job. Rather than shying away from the process, he embraced and enjoyed it. “You’re not going to have a ton of success if you’re scared by the number on the clock, and he certainly is not,” says Norton. “He gets it done, and it doesn’t matter what time it is. We often worked out at 5 in the morning, or late at night.”

THE IDEA WAS TO AVOID SCULPTING A PHYSIQUE SIMILAR TO FORMER BATMANS CHRISTIAN BALE’S OR MICHAEL KEATON’S AND INSTEAD HAVE THE DARK KNIGHT POSSESS THE IMPOSING, POWERFUL LOOK OF AN MMA HEAVYWEIGHT.

Another challenge during Gone Girl: They couldn’t get Affleck too lean, as his character was supposed to look puffy and hungover. So they focused on establishing a good base of muscle, and when that movie wrapped, Norton had Affleck training twice a day to slowly peel off the fat. (“I would be curious to know,” says Affleck, “the sheer amount of mass I had to move over the course of training.”) When filming for Batman v Superman finally began in Detroit in 2014, Affleck worked out daily in a three-car garage converted into a gym, using a hybrid program that was equal parts bodybuilding exercises and functional movements.

“Because we knew we had to train for such a long period of time, you’ve got to be a little more joint-friendly,” says Norton. “But you’ve got to add muscle, so there was certainly an aesthetic muscle-building element to it. He got very good at chinups and pullups. He’s very good at inverted rows. He added a lot of weight to his glutes and his legs that he hadn’t had before. His calves got a lot bigger. Certainly he’s got a great frame.”

SEE ALSO: First Look: Ben Affleck Becomes Batman

Affleck’s size as the Dark Knight was a formidable 228 pounds, with a mere 7.9% body fat. And to make sure Affleck didn’t balloon to 250 pounds, he enlisted renowned nutritionist Rehan Jalali to design his diet. A typical day of eating: egg whites and oatmeal in the morning; salad, double protein, and vegetables at lunch; fish or chicken at dinner with brussels sprouts, cauliflower, or broccoli. “We were seeing that in our sleep,” notes Norton. “Rehan designed a great diet, and Ben followed it to the letter.”

All in all, Norton puts Affleck’s discipline in sticking with a nutrition plan and training regimen right up there with that of the best athletes he’s ever worked with—guys like basketball great Kevin Garnett and hockey legend Ray Bourque. Affleck understood that being a movie star isn’t always about red carpets and love scenes—it’s damn hard work.

“It’s funny, people always talk about how it’s easy for celebrities to get in shape because they have a support team,” says Norton. “But the work can be done only by you. Nobody else can do it for you. That’s the cool part about the iron game. It’s equal for everybody. You make a choice, you commit to your process, and you’ve gotta get it done day after day after day.”

Superman Henry Cavill

Meanwhile, on the other side of the “v,” the Brit playing Superman was working equally hard in the gym. To get himself ready for the film, Henry Cavill reteamed with Mark Twight, the supremely meticulous strength coach and co-owner of Gym Jones in Salt Lake City, UT, who had helped Cavill add 20 pounds of muscle for Man of Steel (and who had served as lead fitness trainer on Snyder’s groundbreaking 300). Not only had Cavill already been through the body-transformation process before, but he also had a couple of other advantages over Affleck. For one, he’s more than 10 years younger. (Cavill will turn 33 in May.) And for another, he’s not out directing big-budget movies in his spare time.

SEE ALSO: The Super-Jacked Superman Workout

He is, however, a very in-demand actor. So Twight came back into the picture while Cavill was busy shooting The Man from U.N.C.L.E. in the U.K. in August 2013. Just like Norton and Affleck during Gone Girl, Twight couldn’t alter Cavill’s size too much at first. Instead, he worked on establishing a great foundation and bringing up Cavill’s level of conditioning and strength. When that movie wrapped near the end of 2013, Twight and Cavill had a couple of free months before shooting was to begin on Batman v Superman.

To give you an idea of his commitment to the project, Cavill spent his Christmas holiday in Salt Lake City at the gym—eating a lot, sleeping a lot (usually nine hours a night), and training a lot. The target body type this time around was similar to what it was for the first film, only larger. (So it goes with sequels.) Cavill came to Twight early on and said, “Look, I want to be bigger and stronger.” It was music to Twight’s ears—and probably Snyder’s as well.

Cavell and Affleck Talk Training

Transforming their bodies into believable physical representations of the Man of Steel and the Caped Crusader involved super efforts from the film’s dynamic duo.

Superman-2-rainHenry Cavill: “I remember many moments when I wanted to quit. Not the training altogether, but every time a session goes from not hard to hard, the negotiation starts in your head. Part of you is making excuses to quit. Another part of you is arguing against those excuses. If you don’t want to quit, you’re probably not working hard enough.”

Ben Affleck: “We knew going in that the preparation involved would be demanding. If the audience was going to believe I stood a fighting chance taking on a superhero, I was going to have to physically match the size and power Henry [Cavill] had dauntingly established in Man of Steel.”

“In [Man of Steel], Henry didn’t have another superhero to be next to, apart from General Zod,” says Twight. “In this one, because he was going to be next to Batman a lot, the general consensus was that he needed to be a little bit bigger.”

Naturally, this meant Cavill was encouraged to eat more. During The Man from U.N.C.L.E., Cavill kept his calories under control. But during the break before Batman v Superman, his body possessed, in the words of Twight, “a lot of desire for super compensation.” And Twight let him…compensate. Translation: Seconds and thirds were had.

SEE ALSO: How Henry Cavill Got Superhero-Shredded

“His diet was in the 5,000-calories-a-day range, which is typical for anyone of his size in the gaining phase,” says Twight. “He still ate relatively clean, but he loved it because he had a lot of latitude.”

They paired this nutrition plan with grueling two-hour workouts in the gym. Pretty soon, Cavill’s measurables rose. “Six months into Batman v Superman,” says Twight, “his numbers were through the roof.” His deadlift neared 500 pounds. He was front-squatting 335 pounds. He did a lot of shoulder work, because there’s never been a superhero who didn’t have broad shoulders and a narrow waist. With Twight’s assistant, Michael Blevins, Cavill even spent time doing gymnastics work, like tumbles and handstands.

CAVILL TOPPED OUT AT 220 POUNDS AND GAINED AN EXTRA 12 POUNDS OF MUSCLE COMPARED WITH THE SHAPE HE WAS IN FOR MAN OF STEEL. HIS DEADLIFT NEARED 500 POUNDS, AND HE FRONT- SQUATTED 335.

“We hit a lot of PRs compared with [training for the first movie],” says Twight. “And some of that, too, was not only improved physical ability but also the psychological changes of being confident enough to go after a heavier weight. You know, he was willing to take a little bit more of an aggressive attitude to the weight. And he was so much more physically capable on this one.”

The result was impressive. On Man of Steel, Cavill got up to 199.8 pounds and was cut down to 190 pounds for shooting. On Batman v Superman, Cavill topped out at 220 pounds and was walking around at 202 pounds, with 7 or 8% body fat. Which means he gained an extra 12 pounds of muscle compared with his shape for the first movie—when he was already rather big. As for whether there was a friendly rivalry between the two actors to see who could lift the most or look the best, both Norton and Twight say not really. “It’s normal guy behavior to think, ‘I want to be bigger, I want to look better,’ ” says Twight. “And so certainly that kind of thing would come up. But comparing numbers, it’s just not feasible for a variety of reasons.”

Wonderwoman

But Twight had other things on his mind at that point anyway. Because in addition to prepping Cavill, he was also tasked with getting the film’s jaw-dropping starlet, Israeli model and actress Gal Gadot, in fighting shape to play Wonder Woman. Twight calls this nine-month process—including three months with her, one on one, in Tel Aviv— “challenging and immensely satisfying.” One of the primary challenges: convincing the slender 5’10” Gadot that it was OK to add a significant amount of weight. Twight says it required her to make a transformation in self-image and body image.

SEE ALSO: The Wonder Woman Workout

“Anytime you present someone with a really radical change, it’s hard to get them to buy in 100% to the idea,” says Twight. “So we took it in incremental steps. We went from a model to a high jumper, in terms of an athletic look. And then once she was comfortable with that, then we’d go a little bit further.”

Interestingly, the key to Gadot’s transformation was the same as the one for Cavill and Affleck: training and eating right every day, for months and months at a time. “The real thing is consistency,” says Twight. “It just has to be something that you are paying attention to all day, every day. And the training itself isn’t enough unless other behavior changes. So, yeah, everybody loves to put on the size, but what makes Henry look like Superman is the fact that he is very lean also. So every muscle that he built, you can see. And that’s the hard part to maintain.”