I've been doing weight lifting for 3 months, during the period, I've gained about 15 lbs of (mostly muscle, I believe...hopefully) weight, chest increased from 91cm to 98cm, shoulders grew 3cm as well (allow some minor discrepencies due to pumped and resting stage). The problem is my arms are not growing even though I split up my time pretty evenly between muscle groups, and I AM stressing my biceps pretty hard (it's not saying much, since I am skinny to begin with, and my biceps got stressed easily. but that should be the winning formula, right?), I'm yet to see any solid progress compares to chest and shoulders, right now my arm is at a puny 33cm (around 12 inch?) when flexed. what I've been doing is simple dumbell curls, 3 or 4 sets or decreasing number of reps and increasing weights, but very effective in getting my biceps exhausted. (same thing with triceps, and they are even weaker) I tried to search for answer on the web, some say tall people with relatively longer muscle fibers in arms are just harder to work with, period. now, I am 6'3, but I wear size R suits (33 sleeve length shirts), it's my legs that are relatively longer. even assuming the case that my arms are long (which they aren't), still I see those 6-foot-and-above NBA players with solid arms, something is definitely missing. please help me, what am I doing wrong?