cuz 1 time he felt like he wasnt good enough to play edward so he got depressed and didnt see anybody for 2 months strait (well except his trainer [of corse!]:[) so he just went to the gym for 5 hours a day! :)
Robert Pattinson:I think its because he has alot of free time. I mean he says in alot of interviews and magazines that he is a loner. So like Edward he has to do something to keep himself occupied.
Edward Cullen: He doesn't sleep so he has to do something to keep himself occupied. He already learned how to play the paino and he probably read every book they own. So, his only alternative is Weight lifting and keeping himself fit!
all the running he does and he has to work out to stay fit for the series because vampiros arent chubby plus the whole time hes alone he prob works out hes public shy and publicity shy so prob just goes to a private gym and works out thats what i would do if i were him and ud prob have to know the owner to work out there id go to 1