Dwayne “The Rock” Johnson has revealed the physical transformation required for his role as UFC legend Mark Kerr in the upcoming film The Smashing Machine. In an interview, Johnson explained how he gained over 30 pounds of what he called a “different kind of muscle” to authentically portray the mixed martial arts pioneer.
“Believe it or not, I already came to the party a fairly big boy,” Johnson said, recalling a conversation with director Benny Safdie. “When I talked to Benny, he said, ‘I don’t know how to say this, but I need you to get bigger. Puffier, but just—’ and I said, ‘I think I know what you’re saying.'”
Johnson noted that Kerr had a body type that was difficult to replicate. “When you look at pictures of Mark Kerr back in his prime, his silhouette was just crazy. It was like not human,” he explained, describing the MMA star’s massive shoulders, narrow waist, and powerful legs.
The transformation went beyond adding size. “This is the kind of muscle that you have to put on that has real fast twitch fibers to it, which is a different kind of muscle,” Johnson told CBS. He bulked to between 280 and 290 pounds while working to maintain speed and agility for the fight scenes.
Johnson also trained with MMA coaches and fighters to prepare, despite his wrestling background. “MMA is a completely different world and it’s a completely different animal for the men and the women who do it,” he said.
The physical work was paired with a demanding prosthetic process, requiring three to four hours daily. “The prosthetic transformation was the thing that allowed me to really transform and become Mark Kerr,” Johnson explained, saying the mirror work helped him embody the character.
To capture Kerr’s demeanor, Johnson worked with dialect coach Liz Himlstein to reproduce his soft-spoken voice. “He’s this walking contradiction of a man who’s a giant but he’s so soft and he’s so tender and he’s so softspoken,” Johnson said.
The role marks a shift for Johnson, who has spent most of his career in blockbuster action films. He admitted that this project pushed him into more difficult dramatic work, saying he wanted to “rip himself open” artistically.
Kerr’s life story—marked by both professional success and struggles with addiction—required Johnson to tap into his own traumatic experiences. The performance earned a 15-minute standing ovation at the Venice Film Festival, confirming the impact of his decision to take on the role.
For Johnson, the transformation was as much emotional as physical, signaling a new phase in his career and his willingness to take risks for authenticity in storytelling.
