The question is not that straightforward obviously, as it depends on the individual.
But my question is a bit different:
How can a natural lifter know (at a given recovery level, at a given frequency of training and with a given exercise selection) wether the volume he’s doing is too much, or, on the other hand if he’d better do more volume).
I’m an amateur bodybuilder, starting to self program according to my training preferences but, when i lay down my program I wonder wether the volume is spot on. Obviously you’re going to find it with trials and errors but even in that case i wouldn’t know what to track.