"I almost felt like I was a professional athlete," Charlie Hunnam tells people of his titular role in King Arthur: Legend of the Sword

It turns out that portraying a buff biker isn’t the only role that’s gotten Charlie Hunnam into great shape.

The Sons of Anarchy alum says he never realized how fit he’d become playing another character — King Arthur — but the actor tells PEOPLE his role in the upcoming King Arthur: Legend of the Sword got him in elite physical shape.

“There was just an enormous amount of fighting. Some of the sequences would take five or six days to shoot, so every day, 14 hours a day fighting,” Hunnam, 36, said while attending CinemaCon on Wednesday. “The fitness level that I achieved during the course of that, I almost felt like I was a professional athlete, on that level.”

CinemaCon 2017 - Warner Bros. Pictures Presentation
Credit: Michael Tran/FilmMagic

The actor said he weighed 180 pounds during filming, but he had to continue going to the gym after clocking in a day on the set in order to keep his muscle, since the sword fighting was very cardio intensive.

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“Imagine sword fighting, which is particularly physical, especially how we were doing it because the technique that [Director Guy Ritchie] wanted to use was doing different speeds for the fight sequences,” he said.

Credit: Tim Walker/VMAG

Hunnam said he had to learn not only his sword fighting sequences, but also those of the other actors because everything was filmed separately to allow the filmmakers to play with the swordplay speeds.

KING ARTHUR: LEGEND OF THE SWORD, Charlie Hunnam, 2017. ©Warner Bros. Pictures/courtesy Everett
Credit: Warner Bros

“I’d had to put an enormous amount of force into it and then an equal amount of force to stop it, to play as though there was resistance when there was none, which was incredibly physically demanding to keep doing that over and over and over and over for 12 hours a day,” he said.

Credit: Marc Hom/EW

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Although he might have wanted to hit the spa after his long days of filming, Hunnam instead opted for the gym.

“I had to keep training,” he said. “I’d go the gym after work no matter what, so it wasn’t an enormous amount of salt baths or anything going on.”