As for the old pros, it is an interesting topic because it delves into the concept of "muscle memory" which is still being explored and understood but from the latest research it would appear that if say Arnold went on a cycle of dbol, yes he would swole up and gain muscle.. Then he stops cold turkey. What happens? Understandably be ends up losing quite a bit of the gains made, or you would assume at least but this was also a time period of really high protein I takes so maybe it helped attenuate some of the loss. But what's interesting, well to me at least, is the physiologic aftermath from the cycle. Research would suggest that during his cycle structurally changes were made in his muscles, namely myonuclei, would remain post cycle. Meaning, it would be easier for him to gain muscle even after that cycle. It's still a new topic that is emerging and being explored but it does have some interesting implications, especially since "muscle memory" has always thought to be a neural/motor control type cause for it but now we have some evidence suggesting there might be a physiological role at play here