How Chris Hemsworth's superhero body kept the '12 Strong' cast in fighting shape

Still, there's a special kind of pressure that comes from working out alongside Chris Hemsworth on the set of 12 Strong every day.

“Well number one, fucking Thor shows up on set. I mean really it is Thor,” Stults said when asked about his routine for preparing for the film. “I mean, I’m 6’3’’ and he’s bigger than me.”

Hitting the gym with a superhero wasn't the only thing new to Stults. “I was playing a real person and that's not something that I had done before,” he told Men’s Health about his role as Sean Coffers, a member of an actual elite Special Forces team sent to fight the Taliban in Afghanistan just days after 9/11.

At the time, their mission was classified, meaning they came home to no recognition. That was, until 2009, when author Doug Stanton published the book Horse Soldiers, finally revealing their story to the world. The special forces troops were not only the first to volunteer to head to the Middle East, but when they arrived, they had to drop their regular transportation plans and instead ride on horseback.

“I never, ever heard about this. I couldn’t believe when I read it, that you had these modern American soldiers riding into battle, alongside these Afghan soldiers, and then on horseback — it was so ‘Lawrence of Arabia,’ ” Nicolai Fuglsig, the film’s director, told Army Times.

Stults had to put his physicality to the test, because the real men who went to Afghanistan hours after the deadliest terror attack in U.S. history were willing to do just about anything to get the job done. That included riding into battle on horseback and traversing some of the most treacherous land passes on Earth.

“We had to do things like learn to ride a horse and learn to shoot guns and look like we knew what the hell we were doing while portraying bad ass American heroes who really put their lives on the line,” Stults explained.

The film, which premiered on Friday, also stars the aforementioned Hemsworth, who plays Capt. Mitch Nelson, commander of Operational Detachment Alpha 595. The 12 main cast members — including Hemsworth, Trevante Rhodes, Michael Shannon and Michael Pena — used each other as motivation to get as strong as possible.

“We owed it to ourselves, we owed it to these characters,” Stults said. “As guys, as civilians portraying soldiers, we worked out.”

That workout included plenty of time at the gym, but also a lot of time learning to ride horses, which is far more physically demanding than one would expect. Just take a look at this workout inspired by the Mongol Warriors, who often fought on horseback and had to have extreme endurance and both enviable lower-body strength to ride for hours and upper-body strength to wield heavy weapons in battle. It'll give you just a taste of what the entire 12 Strong crew had to do to really be prepared.

Beyond the group workout sessions, Stults said the crew came together like a true band of brothers after the sun went down on set each day in Albuquerque, New Mexico.

“We were all grungy and dirty and nobody nobody was really doing hair and makeup,” Stults said. “It was like a locker room, and you know back in my locker room playing sports, we’d challenge each other. When you’ve got guys like Chris Hemsworth and Trevante, I felt like, ‘I gotta do more sit-ups.’”

Stults also reaped the benefits of his co-star’s impeccable eating habits on set, too. “Hemsworth was in between Thor and Avengers, and he was trying to maintain the same look," Stults said. "So he had food prepared and delivered to set. And he would get full all the time, so any time he’d get food delivered I’d just show up."

The guys often turned to cast mate Kenny Sheard, who was a Navy SEAL before becoming an actor, for advice on acting the part — everything from the correct way to hold a gun to ensuring their uniforms were on right.

“We’d really defer to him a lot,” Stults said.

When asked what he enjoyed most about making the film, Stults pointed back to all of his cast mates for making it easy to come to work every day.

“I've been lucky enough to work a lot with a lot of great people but when the main guy, that person on top on the call sheet, the star of the project is a good person," Stults said, adding, “I wouldn’t say it to his face because I make fun of him too much, but Chris Hemsworth is as good as they get.”