Jeremy Allen White got a lot of attention—and his fair share of internet thirst—earlier this year when he , the result of his in A24's . But in order to get into fighting shape, the actor had to switch up his usual fitness regiment.

"I didn't know what I was doing," the star of admitted to Jimmy Kimmel this week. "I knew I had to eat more, so I ate more. I knew I had to lift heavy things, so I lifted heavy things. And I knew that you should try to stay away from [cardio]. I like to run, I like to do jump rope in my everyday life, that makes me feel good, these guys didn't do a lot of that stuff.

His transformation was made all the more challenging, he added, by the fact that he was starring in the movie opposite Zac Efron, who got into perhaps the most muscular state of his career to play .

"He looks incredible, it's really something... I think he could beat anybody up," White joked. "I didn't want to stand near him during the movie, which was a problem, because we play brothers, and we need to stand close to one another."

In addition to building his wrestler's body prior to filming, White also found that performing his character's stunts in the ring to be a physically arduous process, thanks in part to the authenticity of the set.

"In the real professional wrestling, the plywood and the springs are right there, there's very little cushion, there's metal cable with very little cable," he explained. "And I was like, we're making a movie, do we need to be doing it this way? We could use a little extra cushion... and they're like, no, no, this is how it's done, and I was like, alright."