Actors like Hugh Jackman have to be able to get bigger for certain roles. They have personal trainers and nutritionist to help them achieve their goals and they dedicate themselves to packing on muscle and learning their script and the character they have to play.
Looking here at pics of Hugh reveal just what kind of metamorphosis he went through to get big for his role as Wolverine in the movie X- Men
Arms to big arms.
Skin and bones to ripped muscle.
Its hard to find any recent pics of Hugh with his shirt off or not wearing long sleeves. I guess he shrank back down.