Jeremy Allen White Says Iron Claw Cast Experienced 'Trauma Bonding' While Training for Movie (Exclusive)

Jeremy Allen White and his onscreen brothers got close fast while making the new sports drama The Iron Claw.

The actor stars alongside Zac Efron, Jeremy Allen White, Harris Dickinson and Stanley Simons as the legendary Von Erich brothers, who made history in the world of pro wrestling in the early 1980s. Before filming got underway in Baton Rouge, the four trained in the ring for months to prep for the movie.

"I do feel like it was some sort of trauma bonding that happened," White, 32, tells PEOPLE in this week's issue. "We were all insecure and nervous about learning this new thing. And we were comfortable letting each other know how overwhelmed we were at the beginning."

Adds Dickinson, 27: "The wrestling brought us close quite quickly because you're forced to engage in very trust-based stuff. Obviously there's no skirting around the niceties and stuff, so I think that was an acceleration of familiarity."

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Another thing that drew them together? Their "tiny" wardrobes.

"We definitely had to put vanity aside and get used to inhabiting these clothes," Efron, 36, says of first trying on "these tiny spandex sort of things," as Dickinson describes the wrestling garments.

"Those were the early days of meeting each other as well," Dickinson says. "And we were full-body shaved by our wonderful makeup department."

Adds White: "I felt very vulnerable all the time. The wardrobe was so important to the men at the time. You had to commit... or else."

The actors ate thousands of calories a day and trained for months to play Kevin Von Erich (Efron), Kerry Von Erich (White) and David Von Erich (Dickinson), sibling wrestling champions who deal with familial struggles and try to live up to the expectations of their father, famed wrestler Fritz Von Erich (Holt McCallany).

Kevin is the only surviving Von Erich brother, a group that also includes Mike Von Erich, played by Simons, and Chris Von Erich, who is not depicted in the film.

The retired professional wrestler, now 66, appeared at the world premiere in Dallas in November alongside the cast, where he told PEOPLE that Efron "had a tough job" in stepping into his shoes.

"It's not easy to be me. I wrestled seven years World Class, but then I wrestled 22 years," Kevin said. "That's a whole lot to cram into a movie, but he was able to do it ... he's a real star. They all are."

For more on The Iron Claw, pick up this week's issue of PEOPLE, on newsstands now.

The Iron Claw is in theaters Dec. 22