Matthew McConaughey got in shape for Magic Mike as he was terrified of seeing his "backside 40 foot tall".

The Hollywood star appears in the stripper movie alongside Channing Tatum and Alex Pettyfer. Matthew plays Dallas, the leader of a troupe of male dancers. When the actor took on the role he knew he'd had to flash some flesh, but as the date of shooting drew close he started to worry about what he'd taken on.

"Vanity, baby," he laughed to Access Hollywood, when asked about what motivated him to shape up. "You want to get a bunch of guys who are already in shape [and] make sure they get in peak shape, tell them that you're going to be in a stripping movie and then your backside is going to be 40 foot tall and wide in the centre of the screen. It'll get you to the gym and eating right for sure!"

The actor has become known for appearing topless in movies, which many of his friends including Matt Damon tease him about. He doesn't mind though and was glad to show off his rippling muscles in the new movie.

Magic Mike is loosely based on Channing's experiences as a male stripper and Matthew knew he had to pull something special out of the bag if he wanted to compete with Channing.

"I had to [take the shirt off]. I couldn't do this film and not do that. Channing's such a damn good hip-hop dancer, I knew I wasn't going to challenge him at dancing. This was different, though, man. This was more than taking off my shirt," he told Shortlist magazine. "You'll see, man. I've got an exceptional thong."