Bradley Cooper’s preparations to portray Chris Kyle in “American Sniper” began in the dining room and the weight room: To take on the role of a 230-pound Navy SEAL sniper, Cooper would have to pack on muscle — and a lot of it.

“I had to get to the point where I believed I was him,” Cooper told Men’s Health. “At 185 pounds, it would’ve been a joke. His size was such a part of who he was.”

But Cooper’s work to ready himself for the role — for which he ultimately earned an Oscar nomination — wasn’t about simply adding extra lean muscle; Kyle, he said, “wasn’t ripped. He wasn’t sinewy. He was just a bear.”

The transformation had to be completed quickly, in about three months’ time, before filming began. “It was a heavily regulated regimen,” Cooper told the Navy Times. “I had a goal of 30 pounds of muscle. Not bodybuilding, but to be like Chris. He was a very big, thick, strong man.”

That regimen required waking up at 5 a.m., working out for five hours and consuming about 6,000 calories a day, Cooper told the Navy Times.

The actor began training after he wrapped up filming on another movie; for that role, he was told not to lift anything heavier than a kayak paddle. “He came to me with back and shoulder problems,” his trainer, Jason Walsh, told Men’s Health. “He had some major, major imbalances.”

First, Walsh had Cooper do “corrective movements” and performed exercises such as dead lifts and squats “to build a foundation solid enough to hold the extra mass,” according to Men’s Health. Cooper would then do more traditional exercises to build out muscle.

Walsh also said he developed exercises so that Cooper could move about in his new and bigger body as if it had been his all along. But the trainer said the most difficult part was the eating: “We had to force-feed him,” Walsh recalled.

Cooper told Men’s Health that the diet “was a real shock to my body. If it’s pizza and cake, that’s one thing. Putting 6,000 calories a day in your body gets old quick.”

Aside from eating five meals a day, Cooper consumed energy bars and pre- and post-workout supplement drinks known as Plazma (product listing: “Brutal Workout Formula for Enhanced Growth & Recovery”). “Without that kind of caloric intake and the ability to recover, he probably wouldn’t have made it,” Walsh told Men’s Health. “His body just absorbed everything I threw at it.”

Walsh told muscle site T-Nation that Cooper “never missed a workout.”

“He showed a kind of dedication to his training that we seldom see with actors,” said Walsh, whose company, Rise Nation, is known for helping actors from Jessica Biel to Jennifer Garner prepare for roles. “This kind of intense training is unfamiliar to the Hollywood crowd. These weren’t smoke and mirrors workouts. He trained like a strength athlete in the morning, then he came in again in the afternoon and trained to build muscle.”

According to T-Nation, Cooper gained 39 pounds and maintained “roughly the same percent body fat. By the end of the program, he was performing rack pulls with 425 pounds for 10 reps.”

In the latest trailer for "American Sniper," directed by Clint Eastwood and based on the autobiography of the name, Bradley Cooper plays U.S. Navy SEAL sniper Chris Kyle, who is said to have had the most confirmed kills in U.S. military history. Kyle struggled with PTSD and was killed at a gun range by a fellow veteran in February 2013. The film opens Dec. 25. (Warner Bros. UK)

Beyond matching Kyle’s physicality, Cooper also had to work on getting the sniper’s mannerisms and personality right. One thing he learned for the film: When he looks through his rifle’s scope, he sniffs, much as Kyle did. “It’d be almost like a tell in poker,” Kyle’s widow, Taya, told the Dallas Morning News. “In a stressful situation, Chris would do that.”

Chris Kyle was killed at a shooting range in 2013.

Cooper received rifle training on the weekends with Kevin Lacz, a Navy SEAL sniper who had served alongside Kyle, according to People magazine.

“He actually proved himself to be really good,” writer-producer Jason Hall told People of Cooper’s gun skills. “The second day, in the morning, he went out there and was consistently hitting 800-yard targets the size of a teacup. So he took to it pretty quickly.”

Getting Kyle’s Texas accent just right also required four hours a day of dialect work. “I had so much access to Chris, based on interviews he’d done and video. Hours and hours of him talking,” Cooper told the Navy Times. “I had this huge document that I put on my iPhone and my iPad and I just had it on constantly. I had earbuds on that whole time, just listening to his voice, repeating what he would say.”

Cooper also focused on the small details.

Walsh told T-Nation that Chris Kyle’s picture often graced the gym’s wall during workouts to the Navy SEAL’s own playlist, which included Metallica and Toby Keith. The songs were provided by Taya Kyle, according to the Dallas Morning News, which added that Taya played in integral role in helping Cooper prepare:

Kyle didn’t want them to make a caricature out of her husband. “I didn’t want them to stereotype him — the stereotypical cowboy or the stereotypical SEAL,” she said.
Cooper reassured her. “He just said, ‘You don’t have to. We’re getting everything we need just by being here.’”
For two days, the three of them sat around and talked. She showed them his baseball caps, cowboy boots and the clothes still hanging in the closet.
Cooper played with her children in the backyard and rolled on the ground with her dogs. “It felt like I had a couple of friends over,” she said. “They were very respectful, kind and warm.”

Taya recalled watching the film for the first time: “Initially I was so focused on Chris and making sure that it honored him, but I just lost myself,” she told the Military Times. “It was so Chris. It wasn’t Bradley on the screen. It was Chris.”