Hollywood's Buff Boys!

Credit: Everett Collection; Marvel Studios; Ray Tamarra/Getty Images

Scrawny to brawny!

It's not uncommon for actors to beef up for certain movie roles.

Chris Evans packed on 20 lbs. of muscle for the tile role in Captain America: The First Avenger, and Hugh Jackman began eating a 6,000 calorie a day diet to bulk up for X-Men Origins: Wolverine.

Gerard Butler took getting into shape for 300 seriously, spending four months transforming his body into a warrior's physique. He told Men's Health: "I've seen so many actors play these kinds of roles, and you see all this equipment on either a big belly or skinny little arms."