here's how it goes.
we all have a natural limit to grow muscle and an enhanced limit.
everyone who is using AAS with the intent of gaining size is heading for polumboism in a sense. when you hit your enhance limit but continue to try and get bigger is when you get it.
as everyone knows not everyone can get as big as pros no matter the drugs or training. so what does a body like that look like if you keep trying to make it bigger anyway?
it looks like something along the line of derrick anthony's later stage before he got sick. he hit his e-limit but tried to keep forcing the body to get bigger. if he had pro genes, at that point his body, instead of melting, would have continued to grow and polumboism wouldn't have developed.
so the theory suggests that when you see a pro showing signs of polumboism it's because he's is still trying to gain even more mass, and where you see a pro avoiding it, it's because they either haven't reached their e-limit or are not trying to get bigger but just maintain where they are, like say a dexter jackson. if you look at him over the years his body hasn't changed all that much, it doesn't seem like he's been one of those "i always gotta get bigger" type, always shooting for more. so maybe that's why he's lasted where so many others have melted away.