Chris Hemsworth in awe of co-star's abs

Chris Hemsworth is not lacking muscles, but the Australian known worldwide as Marvel beefcake Thor was in awe of one of his co-stars in the new Afghanistan war film 12 Strong.

"Did he show you?" Hemsworth excitedly asks when the topic of Trevante Rhodes' abdominal muscles pops up during a recent interview in Los Angeles.

No, Rhodes, a former Louisiana high school football and sprint star, Calvin Klein underwear model and member of last year's best picture Oscar winner Moonlight cast, kept his shirt on during an earlier interview.

It wasn't the case when Rhodes worked out with Hemsworth and the rest of the 12 Strong cast at a gym near the war film's New Mexico set.

"We were all kind of in the gym training together and one day we were standing there and I said 'What the f...?'" Hemsworth recalled.

"Trevante has his shirt off getting changed and I was like, 'Can I touch that?'

"I poked him in the stomach and said, 'What the hell is that?'

"He is one of the fittest humans I have ever met."

Hemsworth, Rhodes, Oscar nominee Michael Shannon and Michael Pena star in the film about the US Army's Special Forces' covert incursion into Afghanistan just days after the September 11 attacks in the US.

The elite forces were dropped into remote northern Afghanistan and forced to ride horses to complete an operation against al-Qaeda and the Taliban.

Hemsworth was in awe of the special forces soldiers who assisted the actors on the set.

He struggled to imagine what it was like for the soldiers to leave their families and conduct operations including the one recounted in 12 Strong.

"Just last week I was leaving and I had been home for 10 days and I said to my daughter, 'OK, see you later' and she was like, 'You just got back. You have already been at work'," Hemsworth said.

"It breaks my heart every time she, or my boys, say that, but I'm going off to a safe movie set or press tour.

"To walk out the door not knowing how long you are going for, not knowing if you are going to be coming back and what you're walking into, I don't think there could be any tougher job."

Hemsworth, his Spanish actress wife Elsa Pataky, and their six-year-old daughter India Rose and three-year-old twin boys Sasha and Tristan live in Byron Bay.

The scene in 12 Strong where Hemsworth's character says goodbye to his wife does have some reality to it, with Pataky playing his wife.

It also gave the couple a quick break from their kids, who stayed in Los Angeles with their grandparents when Pataky dropped into Albuquerque to shoot the scene.

"We had a little working holiday in Albuquerque," Hemsworth smiled.

Rhodes says he was also impressed with Hemsworth's physique and workouts, which turned into competitions.

"It was like being back in high school and college playing football with your buddies in the gym," Rhodes said.

"It was competition on all levels."

The rest of the male cast were not so impressed.

Geoff Stults said he could not compete in the gym, particularly while watching Rhodes spend an hour each day working on his abs alone.

"I would watch what he did and then Thor would show up with his trainer and his hammer," Stults sighed.

12 Strong opens in Australia on Thursday.

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