I have had the same issue with smaller arms in comparison to everything else. Lately I am hitting bis and tris every 4th day and carbing up pwo with igf/60mcg pwo and 10ius slin/10gr creat/glut 20 minutes later followed by the normal post slin nutrition. Eating clean until the slin clears and then mega carbs for about 24 hours following. Then back to regular diet until the next arm workout. My training split is lifting everyother day so it goes mon-arms, wed-chest/bk/sh, fri-arms, sun-legs, tues-arms, thurs-ch/bk/sh etc. It has worked in the past and is working now. On the ch bk sh Legs i don't go to intense. Just about 5 sets for each and 10 for legs and my carbs are about 200/day until the arm day were I carb up. My theory is that low carb days up until arm day allows my bi and tris to utilize the igf, slin, creatine and carbs for growth. Also the following 24hours for recovery. Keep in mind I am not growing in ch, bk, sh, and legs but I don't really want to. This is temporary until the arms are symmetrical. I am of course on aas as well. It works for me. You may want to give it a try. I am sure it will work with just food too if you did not use igf and slin. The synergy for me with these compounds and mega calories work well. And for syntherol....my advise is to leave it alone. I have tried it a couple times with the recommended protocol. It actually did nerve damage to my left bicep. It did recover but it looks a liitle flat compared to the right! But that's just me