Zac Efron underwent extreme body transformation for Iron Claw

Zac Efron has revealed the muscle he had to gain for his role in the wrestling movie Iron Claw.

Fans have been left shocked by the transformation of the High School Musical star for the new role, which is a marked difference from how he had previously looked.

Gone is the fresh-faced basketball player turned singer, replaced by a muscle-bound hunk for the upcoming wrestling movie.

Efron has showed off his muscular figure ahead of Iron Claw's release on December 22.

He revealed that he would work out multiple times a day, and gained a whopping 15lbs of muscle for the role.

Speaking to Variety, he said: "It was a singular focus for month and your life goes out the window during prep. That necessity to be perfect... became an obsession."

There's no denying the incredible athleticism of wrestlers, whose occupation manages to sit somewhere between acting, martial arts, and gymnastics.

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Efron also revealed how he managed to get in shape for the part.

He said: "I was able to incorporate old-school body-building and Olympic lifting, and really achieved that specific look of pro wrestlers."

Not only that, but Efron revealed that physically changing his body also helped him to get in the headspace of his character for the role.

He said: "It was an unforeseen ally. Having all that weight on, you don't feel normal.

"And the delayed-onset muscle soreness was through the roof."

He added: "During preparation, it's one thing to manage that — you don't have to be super social. I found myself withdrawing quite a bit."

But Efron also admitted that he had to rein in his perfectionist streak for the role, saying that he had to remind himself that 'life is way too short'.

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He added: "We're supposed to be having fun. I have to remind myself that this should be fun above all else.

"If being a perfectionist is going to be the thorn in my side from this point on, it's like, life is way too short."

Efron paid tribute to the late Matthew Perry during the ceremony to unveil his star on the Hollywood Walk of fame.

Paying tribute to his 17 Again co-star He said: "It's very important to reach out to friends and foster relationships where you can talk and share stories.

"I hold the time we shared together really dear,

"I've been thinking about him a lot, every day."