I'll take a stab at this. It is a well known fact arabs usually have great shoulders and shit arms most of the time. Gh15 has said this before.
my theory genetics aside...they dont use enough anabolics with their test.
Let us take deca for example, it's no secret that nandrolone is the best steroid ever made for getting big arms yet having a small body. Look at pumping iron. you see guys in there with legit 19 inch lean arms yet they look like a norma guy in clothes. (compared to today's guys anyways)..but ask yourself how much have the arms really progress since then with the mega doses of test?
Notice how well your shoulders respond to high doses of test even without any additional anabolics. even on 1000mg-1250mg test you will really love the way you delts look. On this dosage of test, the shoulders may very well look like they belong to a superheavyweight competitor despite your shitty ass arms being 17-18 inches . the shoulders just love tesosterone. However, deca will never give you that swole look that high doses of test gives. Stand sideways to the mirror on high doses of test and notice the pecs starts very high up..then turn straight ahead and see your delts round outwards even when your standing relaxed. Your naturally a narrow guy yet you look like god gave you a new set of clavicles. You dont believe me? Ask Phil Heath...the day Jay told him to use an amp of norma every day with breakfast was the day Phil stopped kicking his dog and beating his wife cursing god every day at his pathetic structure:) This is the power of high doses of testosterone! Not 500mg. Not one 750mg shot of enanthate a week. You need that amp in you every 48 hours.. amp every 24 hours is big boy territory but I haven't gone that high yet.