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During a Sept. 30 appearance on The Tonight Show Starring Jimmy Fallon, Dwayne Johnson opened up about the body transformation he underwent to portray Mark Kerr in The Smashing Machine
The actor said that he had to gain around 30 lbs. for the movie, but that he had to do it in a very specific way to emulate the wrestler’s muscles
“You know how you have some actors, and they’re our friends, and they say, ‘Hey, I have to put on weight. I went to McDonald’s every day,’ ” Johnson said, noting he could not emulate them
Dwayne Johnson is famous for his muscular physique, but he had to get even bigger to play Mark Kerr in The Smashing Machine.
The 53-year-old actor brings the wrestler to life in the biopic, which hits theaters on Friday, Oct. 3.
While promoting the film with a Tuesday, Sept. 30 appearance on The Tonight Show Starring Jimmy Fallon, Johnson opened up about transforming his body to bring Kerr to life, saying that he gained roughly 30 lbs. of muscle at the urging of director and writer Benny Safdie.
Recalling a conversation with Safdie, Johnson said he was told, “‘Hey D.J., I don’t know how to tell you this, and I don’t know if you’ve ever heard this…’ He goes, ‘You’re going to have to get bigger.’ “
And I went, “‘Okay, here we go.’ “
Johnson noted that he had to put on the weight in a very specific way to emulate Kerr’s massive and muscular body. That meant that he couldn’t just gain weight by eating fried food like some stars have in the past.
A24
Dwayne Johnson in ‘The Smashing Machine’
“You know how you have some actors, and they’re our friends, and they say, ‘Hey, I have to put on weight. I went to McDonald’s every day,’ ” he said to host Jimmy Fallon, adding, “Mark Kerr had just this quality of muscle. Like fast-twitch quality muscle because he was a wrestler. And I had to still put on this weight, still be able to move like an MMA fighter, and it was about 30 pounds.”
Speaking about Kerr, he said that his silhouette was impressive due to his profession.
“Being a wrestler, always going in for the double-leg takedowns and lifting guys up, he had these massive shoulders. His neck was huge, his chest, his quads. It was a lot,” Johnson admitted.
For him, it wasn’t just muscle that he put on. The Moana star also used “about 22 prosthetics,” which were applied by Kazu Hiro. “We had a physical transformation and certainly an emotional transformation and a vocal transformation, too,” he told Fallon.
Johnson previously addressed his body transformation during an August 2025 press conference for the film.
“It was very specific training because if you think about it, Mark, as an amateur wrestler, there’s movements that he would do constantly all day that would just build certain fast-twitch muscles,” he said, per E! News. “You know, I’m in my fifth level of life. [But] when Benny Safdie says, ‘Hey, I need you to … ,’ [I go], ‘Okay, I’ll try it.’ ”
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Dwayne Johnson in ‘The Smashing Machine’
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This isn’t the first time that Johnson has undergone a dramatic regimen to get ready for filming. He did the same while gearing up to play the titular antihero in 2022’s Black Adam.
“My goal was to bring in the best physique of my career,” he told Men’s Health in a November 2022 interview. “When you have that suit on, every detail shows. Man, it was constant work, constant tweaking, tweaking, tweaking for months.”
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Dwayne Johnson in ‘The Smashing Machine’
After debuting a slimmer physique at the 2025 Venice International Film Festival, he revealed that the latest body transformation was for his role in Lizard Music, another collaboration with Safdie.
“This is me slimmed down,” he said during an “In Conversation With…” series at the 2025 Toronto International Film Festival on Sept. 8. “In the process of slimming down. I still have a long ways to go.”
Johnson shares the screen in The Smashing Machine with Emily Blunt, who plays Kerr’s ex-wife Dawn Staples. The movie hits theaters on Friday, Oct. 3.
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