work out 4 times a week? arms are still really skinny

[Hursty]

I know in the gaining mass book it says to keep it to 3 times a week, but i was wondering if I can add a 4th day for forearms, biceps, triceps and abs, seeing how biceps triceps and abs heal faster then most muscles, and I never really get a good work out for my forearms. I thought in the book it said it was alright but, I can't find it so i figured I would ask. Also if I do this should I take a post carb drink?