switch tuesdays workout for wednesdays... then just start the cycle over again on friday... adjust volume so u can progress in weight, reps, sets, TUT, or whatever it is that u beleive in progressing on... that way you will start to hit muscles 2x every 4 days or so...
im sure you dont just dilly dally in the past w your arms, so thinking somehow you will "concentrate" on them and they will grow 2"s and the rest of your body will stay tha same, i just dont see happening... your whole body will grow as one and if your back chest overpower ur arms, well, they still probably will when ur 15lbs heavier in my experiences.... i see it this way bc i figure that everyone trains balls 2 da wallz on every muscle anyways, so how much MORE can you concentrate on?
my delts, calves, and bis hav been my weakest points since i started at 160lbs... they are defientley bigger now but still in the same proportions no matter how much ive "concentrated" on them... i know they are my weak points and go 110% on them, but they will never somehow surpass my genetic "good parts" that i train 110% as hard as possible as well...