One of the biggest mistakes that people make when bulking up in the off-season is gaining too much bodyweight. I've seen people add 40-50 lbs of pure bodyweight; pounds which later have to be shed in order to display any muscularity (muscle detail). My philosophy for off-season bodybuilding has always been "quality over quantity". There are many other mistakes that I see people make in the off-season and my friend IFBB Figure Pro Pauline Nordin has done a fantastic job at summing these up in her article "Stay Lean in the Off-Season; Pauline Nordin's Bodybuilding Advice For The Off-Season". By following the advice on this article, you will get better results from your off-season efforts and you will have a much easier time dieting when you decide to get real lean, as you won't have that much weight to lose.