Audiences have come to expect pumped up pecs and perfect abs from their action stars, but a buff bod takes a lot of work. We've put together a gallery of some of our favorite action stars and what they had to do to get into shape.

Photo by Niko Tavernise/Fox SearchlightFor "The Wrestler," Mickey Rourke trained for seven and a half months, eating six or seven meals a day. The result: 27 pounds of tanned muscle.

Photo by Kobal Collection, WireImageUnlike most of the people on this list, Arnold Schwarzenegger didn't have a problem bulking up for the role. By the time he was cast in Conan the Barbarian, he had already won the Mr. Olympia title -- body building's greatest honor -- several times over. Instead, Ahnold had to slim down for the part. His pumped up arms and chest were too big to properly wield a sword.

Photo by TriStar, Everett CollectionLinda Hamilton was a brand-new mom before training for her role as Sarah Connor in "Terminator 2." All that baby weight soon evaporated, however, under a grueling 13-week regime of weightlifting, aerobics, and eating a lot of chicken.

Photo by TriStar Pictures, Everett CollectionSly Stallone got his famous battle-ready physique for Rambo: First Blood Part II in a mere six weeks training along side former Olympic weight lifter Franco Columbu. Of course, they were six exceptionally intense weeks.

Photo by Warner Bros. PicturesGerard Butler endured a brutal eight week training regime to get those killer abs in "300."

Photo by Warner Brothers Pictures, Everett CollectionIn order to look as fit as one of those Greek statues, Brad Pitt trained for six months for his role as Achilles in "Troy."

Photo by Hollywood Pics/Kobal, WireImageDemi Moore, along with co-star Viggo Mortensen, actually did endure the Navy SEAL's famously harsh training for her part as Jordan O'Neil in "G.I. Jane."

Photo by Columbia/Kobal Collection, WireImageWill Smith gained 35 pounds of pugilist muscle to match Muhammad's weight in "Ali."

Photo by Warner Bros. Pictures, Everett CollectionComing off "The Machinist," where he lost 63 pounds for a part, Christian Bale gained 100 pounds of muscle to play the Caped Crusader in "Batman Begins."

Photo by Universal Pictures, Everett CollectionFor his role as Max Cady in "Cape Fear," Robert De Niro trained for months, bringing his body fat down to a mere 3%.

Photo by Kimberley French/Summit EntertainmentThere were rumors that fan-favorite Taylor Lautner wouldn't be back to play Jacob Black in "New Moon." But the studio suits gave him the green light after he agreed to hit the gym and get ripped.