Zac Efron was initially worried about the "striking" physical difference between himself and his newest film character.
The 24-year-old star plays U.S. Marine Logan Thibault in upcoming drama The Lucky One. Zac worked alongside military professionals to prepare for the role, which saw him beef up considerably.
The Hollywood hunk says working out to achieve his new physique was hard work.
"First and foremost, I wanted to spend as much time around Marines and the troops as possible. I was able to go to Camp Pendleton early on with [director] Scott Hicks and just hang out with them, see what it was like," he told Collider.com.
"There were striking differences between the way that they were and I was. I was able to look at that early on, and then physically, there was a lot to be done. The hardest part about this was the physical transformation."
Zac has continued with some elements of the physical training beyond filming. The star has joked that it's by no means on the level it was during shooting though.
"I mean, the principles I learned, absolutely. I carry them with me and I still try to apply them, on a lot less rigorous agenda," he smiled.
Zac has previously spoken about his dramatic transformation.
"The amount of food I had to eat to put on weight is, for anyone, intense," he said.
"No dude it's so impractical [to stay that size]. It doesn't feel good in life to walk around like that. I mean I was wearing different size clothes and it was easier to lie down than move around. I felt like a slob just sitting around and just eating and eating.
"It was harder to breathe even. I was like, 'Am I wheezing?'"