Zac Efron on and in Men's Health (May 2012) talks about bulking up for The Lucky One:

"You get this strange sense of power as those weights increase. By the end of the movie I didn't recognize 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."

Good for him, though I'm not sure building a better body is quite the same as tearing one down (as Bale and others have done for roles).

More hi-res Zac after the jump...