ET looks into how action stars get so big so fast in preparing for roles. While some go to the gym, others may be going to the doctor.
"I've never touched a steroid or hormone or magic pill in my life, so I wouldn't know anything about that," Joe Manganiello told ET. "I hear rumors, but I don't judge people who have. That's their life experience."
Chris Evans' life experience has been similar to Joe's.
"You're just lifting a lot of weights and eating a lot of protein," Chris said. "It's pretty boring to be honest. It's not as glamourous as you think it is."
Dwayne "The Rock" Johnson practically lives in the gym while he's training for a role.
"You're in the vortex. You're training hard," Dwayne said. "It's six to eight months of prep."
For others, Hollywood's dirty secret is anabolic steroids.
"They will flat out say I need to bulk up," Dr. Andre Berger said. "I have a role or I have a concert coming up and I need to get myself in better shape quickly. In other words, most of it is about not wanting to go through the hard work."
Charlie Sheen is one of the only stars who have admitted to taking steroids. The Golden Globe winner says that he used performance-enhancing drugs to prepare for the 1989 classic Major League.
"I only did them for like two months to put some speed in my fastball and that was it," Charlie told ET. "I got into a few bar fights but who cares? Nobody cared back then." Watch the video for more.