hi ive got a problem,my bieceps wont grow.ive been working out hard for nearly 2 years now, im just 168 pounds,5ft 8inch tall. i can bar curl for 3sets of 8 at 90pounds and alt dumbell at 40 pounds. should i try to go heavier or go lighter and try get a better pump. my arms measure 14inch.any advise pleese.