Zac Efron is know for his lean muscular physique.
The 5'8" heartthrob usually weighs in around 145 pounds, but he gained over 18 pounds to play a Marine in the upcoming film "The Lucky One."
To put on the weight, Zac was put on a 3,500 calorie a day diet and underwent months of intense training, including working out five days a week (with lots of powerlifting) and drills in a full Marine kit.
"By the end of the movie I didn’t recognize myself," the actor told Men's Health. "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."
For more photos of Zac, Christian and other actors who dramatically changed their bodies for roles, click on the "Launch Gallery" button below.
"The Lucky One" opens in theaters this Friday, April 20.