At 15 you're just entering the beginning stages of puberty... of course you haven't been able to pack on muscle mass... I don't get why all these 14 year old and 15 year old guys are so eager to look like hulk when you haven't had the physical changes which allow for it yet. Also, you should wait until you are about 18 before lifting super heavy so you don't stunt your growth. Those other 15 year olds that you think look big and buff, well they will also stay 5'6" the rest of their life from lifting too heavy too young. Do yourself a favor and wait. I waited until I was 18 and packed on a lot muscle because I was at the prime age to begin lifting.

Agree with you Spawn, when you're that young your metabolism is insanely active. So it's too hard to retain much of your weight, you don't start holding weight until you're in your twenties.

Hasnt had significant growth?? Hes effing 12 ft 4! Come on now, hes not getting bigger. Then again, you are 18 ft tall evidently so probably not good at math if you cant put it in the system right.

I just finished the shortcut to size 12 week program and honestly i am satisfied with my results but not ecstatic. I completed this program to the fullest extent but i honestly believed it was going to pack on more lean muscle. But overall cant complain.