Skeletal structure has much to do with this. My arms seem to change with my body weight. My wrists are only six inches(very small bone structure) yet I have 18 inch biceps(cold, flexed) when I weigh about 175-180 with about 10-12 percent body fat, when I cut up and drop to 165-170, and about 6-8 percent body fat my arms get proportionally smaller17 to 17 and a half cold and flexed. I am not out of proportion either. MY arms are probably my best body part, but they certainly dont overpower anything else. Look at bone structure too guys.