As shredded as some of your favorite actors are, not all celebrities get into great shape for the love of fitness. Some of the most incredible and extreme celebrity transformations came out of necessity: A major role in a superhero film or action movie comes along and requires the actor to completely transform their physique and acquire six-pack abs, massive muscles, and beyond.

Even some actors you always picture as ripped may have started out as skinny or overweight. Think about Christian Bale before he played Batman: The actor gained over 100 pounds to turn into the Caped Crusader after previously cutting more than 60 pounds for a previous role. Bale has transformed his physique multiple times over his career, including when he played Patrick Bateman in American Psycho. Later on, Bale’s Dark Kight Rises co-star Tom Hardy, himself a skinny guy earlier in his career, stacked on layers of muscle to play the villain Bane, a physical force who nearly killed the Dark Knight.

There are even more extreme examples of celebrity transformations, like when Chris Hemsworth trained with Navy SEAL Duffy Gaver to turn into Thor, the God of Thunder, for his Marvel movies. One of the best examples out there is Chris Pratt, who broke out as the overweight, schlubby Andy Dwyer on the TV show Parks and Recreation before getting extremely cut for movies like Zero Dark Thirty, Moneyball, and the epic Guardians of the Galaxy, which saw him add plenty of muscle to play hero Peter Quill, a.k.a. Star-Lord.

If you’re wondering just how these stars got it done and what it took to make it happen, we compiled the workouts, tips, and trainers that these guys used. Here are eight incredible celebrity transformations that show just how dedicated actors can be for the sake of their craft.

Chris  Hemsworth

Chris Hemsworth's God-Like Thor Workout

Chisel out the Avenger's physique with the official routine from his trainer for the Marvel films.

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