It seem like no one trained rear delts back in the days...nor the 80ies...Arnold did not train the rear deltoid, its pretty obvious by looking at him...
I think that muscle became popular in the 90s...having a rear deltoid popping out from the side...
When did ham/glute development got popular? In the 90s aswell?
Bodybuilder nowday is fucking developed from head to to...not a singel muscle who isent there...