Usually that damn stubborn fat that you get from a high amount of estrogen if you don't use a anti-estrogen. My last cycle I had nolva on hand just incase for my bulking cycle, but didn't use it cause I'm not prone to gyno......I managed to pack on the extra fat pretty good!!!! I don't want to get a lot like I did last cycle, so I'm using arimidex again this time. I'll still gain a little fat, but not what I would if I didn't use an anti-e during a bulking cycle. There has been a long debate over the anti-e's hindering gains if ran during cycle, but there has been no clear cut truth to it as of yet. So I'll take my chances and sacrifice a few pounds of muscle to not gain a few pounds of bloat!!!