07/20/2012 04:16 pm ET Updated Jul 21, 2012

Joseph Gordon-Levitt, Other Celebrities Who Have Gotten Buff

His recent GQ cover has made it clear: Joseph Gordon-Levitt is kinda jacked. The 31-year-old former "Third Rock from the Sun" kid has grown up to be a bona fide action star, debuting bulging biceps in the much-anticipated Christopher Nolan flick "Dark Knight Rises," which opens in theaters Friday, July 20.

But Gordon-Levitt isn't the only male celebrity to have undergone a transformation, onscreen and off. Check out our gallery of male stars who have gone from lean to mean, including Christian Bale, Mickey Rourke, Zac Efron and more.