Chris Hemsworth had to have his 'Thor' costume altered because he'd bulked up too much.

The actor takes on the role of the action hero in the big-screen adaptation of the iconic Marvel comic book but admits he went a bit too far with his weight gain.

He said: "I got the part and immediately started looking at the comic books, and the guy is 500 pounds or something and looks like Schwarzenegger. And I thought, 'OK, I'm not gonna get to that.' But I have to get bigger.

"The filmmakers kept saying 'Yeah, get as big as you can, as big as you can.' And then I came back right before Christmas, just before we started the movie, and had a final sort of camera test and put the costume on and within a couple of minutes, my hands started going numb," he recalled. "And everyone was like, 'Yeah, that's not cool.' And I started getting pins and needles and you'd touch the skin and the blood wouldn't return to that area so quick. And I thought, 'OK, it doesn't fit.' "

The costume had to be changed and director Kenneth Branagh told him to "pull back" on his intense workouts and now Chris is looking forward to the highly-anticipated film being released in May.

He told the Los Angeles Times: "It's the normal sort of anxiety that you want it to succeed and do well."