Mark Wahlberg relies on his boxing obsession to get in shape for roles.

The 44-year-old actor has revealed how some intense method acting helped him slim down for his role in the crime thriller 'Broken City' and then bulk up to play the part of a body builder for 'Pain & Gain'.

Asked how he manages to transform his body shape so quickly, the Hollywood star told Men's Health magazine: ''A liquid diet, running, jumping rope.

''Mostly jumping rope. Jumping rope is for me a lot more fun than running the treadmill, or even running out in the open.

''It's more rhythmic. You can change the speeds. It's a great part of boxing training. And I'm obsessed with boxing.''

Mark starred as former professional boxer Micky Ward for the 2010 movie 'The Fighter', which also featured Christian Bale, and subsequently admitted to suffering a few injuries on the set of the film.

He revealed: ''I picked up a lot of nicks and bumps and bruises. I almost got my nose broken a couple of times. But nothing that would have stopped production.

''We basically lied to the insurance company and told them we weren't going to be hitting each other and then went in there and that's all we did.''