Hollywood studios are increasingly focusing on creating expensive action movies with less costly unknown actors. For some of these unknowns, it’s a chance to skyrocket into fame, but it’s not that easy:

Hollywood has gotten creative in its hunt for the next big action star. Producers have considered scouting high-school football games. Brett Norensberg, an agent at Gersh, decided to structure a significant part of his practice around recruiting mixed-martial-arts fighters, professional wrestlers and martial artists. His list includes a karate whiz named Leo Howard, the star of Disney XD’s “Kickin’ It.” “He’s just turning 16. He’s almost 6 feet tall, and he’s got an eight-pack. He’s a thicker Keanu Reeves. The sky’s the limit for him.”

These efforts, though, belie a truth about action heroes: Almost any actor, even some of Hollywood’s most scrawny, can be physically transformed for the part if he’s willing to put in the hard work. The studios know this, which is why any inexpensive unknown can be chosen. The cast for “300,” including a post-“Phantom of the Opera” Butler and the relative newcomer Fassbender, were put on a brutal program with Mark Twight, a trainer whose workouts incorporated medicine balls, kettlebells and rings to emphasize the athleticism of the Spartans.