TRAILER: Zac Efron Beefs Up For 'The Lucky One'

Zac Efron, 24, is about to set young hearts aflutter in his new role as Logan Thibault in The Lucky One, adapted from the Nicholas Sparks (The Notebook) novel and directed by Scott Hicks (Shine).

In The Lucky One, Efron plays a U.S. Marine Sergeant who returns from Iraq to search for a mysterious woman whose photograph kept him going during the war. The generally slim Efron put on 25 pounds for the role, turning to a personal trainer to get him in Marine shape — the same personal trainer who got Efron's ex-girlfriend Vanessa Hudgens' biceps pumping in 2010's Sucker Punch.

According to Efron, the training consisted of "just trying different techniques and methods and working with a guy who met who trained Vanessa during Sucker Punch," reports ComingSoon.net. Efron, who was originally made famous by Disney's High School Musical, which costarred Hudgens, calls bulking up "one of the only concrete things that you can do to feel differently about a character. I didn't feel like a Marine. I didn't have the posture. I didn't feel like I had the presence, and that was just one thing for me that I could do to really up that change."

Efron's bulging muscles still haven't altered his stubborn denial of his heartthrob status, however. "I don't think I am a heartthrob," Efron said during an interview with CBS Sunday Morning, reports Us Weekly. "I hate [that word]. I hate it. It follows you around, but you don't deserve it. It's like, 'Why?'"

So how does Efron think of himself, if not as a heartthrob? "I'm just me," he said. "I'm just Zac."

See Efron be "just Zac" — plus 25 pounds of solid muscle — in The Lucky One, hitting theaters April 20.

Watch a trailer here: