Charlie Hunnam found filming for 'Pacific Rim' like being on an "elliptical machine".
The 33-year-old actor - who plays Raleigh Becket in the science fiction film - admits he found it physically challenging when he was shooting scenes in a pilot chamber - which was created by director Guillermo del Toro - where he and his co-stars would navigate the robots.
Speaking to The Hollywood Reporter, he said: "[My co-stars] had all been in there beforehand, and so I had heard all of the horror stories, and I thought, 'God, you know, these Hollywood actors, let me show you how a real man is going to handle this situation.
"And then I got in and I realised I had grossly underestimated the demand of this thing.
"It's like being on an elliptical machine for 14 hours a day, on hardest resistance, wearing a suit of armour that weighs 40 pounds."
The British star previously admitted that he has become good friends with the film's Mexican director - del Toro - who has vowed to include him in all of his upcoming English language films, including a lead role in his next flick, 'Crimson Peak'.
He said: "He's just a sweetheart to work with. He's a very, very, just kind and generous and collaborative man. I can't speak highly enough of him.
"He's certainly expressed an interest in me being in all of his English language films from now on. He said that to me at the end of the movie, 'Oh, you're in, my friend.' And I said, 'What do you mean?' He said, 'I'm going to put you in every English language film I ever make from now on.' "
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