Some of Hollywood's biggest male stars really put in the work in 2017, whether it was for work or just because they simply decided to get fit(ter).

And to be fair, while a number of these actors and celebrities were already in pretty good shape—looking at you, Chris Hemsworth, Mark Wahlberg, and Jason Momoa—those guys got even more shredded for roles in films like Thor: Ragnarok, Transformers: The Last Knight, and Justice League.

But 2017 wasn’t all about superheroes gaining more muscle. Jonah Hill completely transformed his physique, dropping the 40lbs he gained for 2016’s War Dogs as he transformed himself into a lean, mean, boxing workout machine. Christian Bale, no stranger to body transformations, did one again, but instead of gaining muscle he added pounds of flab for his next movie role. (That's not exactly what we'd consider aspirational, but it is extreme.)

Take some inspiration from these celebrities into 2018 as you try and hit your fitness goals.

Here are the 15 most incredibly extreme celebrity body transformations of 2017.