Zac Efron didn't recognise himself after putting on 18lbs of muscle for his new movie.

The 24-year-old actor bulked up to play a war veteran in 'The Lucky One' and admitted he was impressed with his own willpower.

He told Men's Health magazine: "By the end of the movie I didn't recognise myself. You hear about guys like Christian Bale who dive into it and are really able to transform. I've always wondered if I had the willpower to actually do it. And I'll always have pride around the sense that I can."

Although the 'High School Musical' actor claims he doesn't have any special talents, he thinks his willingness to work hard plays has played a huge part in his successful career.

Zac added: "I could pick up almost anything. If you put it in front of me, I could always find a way to tackle it. [While training for 'The Lucky One'] I'd get this strange sense of power as those weights increased. I was never a natural at anything, but I could always outwork everybody."