Be very very careful of body building! For piano, you need speed and agility, but not really strength. As others have noted, you may be trying to do too much of the work with your forearms. In fact, overall, you may be working too hard! It really doesn't take that much strength, even fortissimo (some instruments do -- some tracker organs, never mind carillon! -- but not piano).
Remember, in louder passages particularly, it isn't how hard you hit the key, but how fast.