Signs it was time:
- Frequent aches and pains, despite good technique
- Anxiety-inducing loads "having" to be used to progress in the weight x reps sense
- Gains in fullness & roundness not reflecting gains in strength, even in bodybuilding rep ranges
- Poor ratio of muscle-to-fat gain in a surplus, even while progressing in strength
- Coming close to a ceiling on strength...this one has some wiggle room, since you can technically keep adding load and / or reps...but you'll get to a point where you're using as much or more weight than guys who are bigger than you with similar frames.
Probably above all of those is the realization that, no, strength progressions are not the only way to add new muscle - that goes for both new contractile proteins and gains in sarcoplasm, fullness, whatever you want to call it. I think that the stronger you get, the more this is true. When you're only hack squatting 4-5pps for 8-10 reps using a normal ROM and rep tempo, 1-2pps with a fancy tempo, set / rep schemes, intensifiers, etc.
might be a waste of time. But when you're handling impressive loads on every movement, scaling things back 20-50% and getting creative is still going to have you handling significant weights in a productive way.
As an aside, I'm extremely glad I've taken a paradigm shift in my training - much of which just involved listening to my wife (phenomenal physical therapist and coach, @danilamartinadpt). Had I just kept hammering away at progressive overload, I'd have probably assumed I likewise had to keep ramping up food and gear - neither of which is really going to improve my look when I'm already taking the "standard" SHW ~2g AAS + 10iu GH and eating 5-6k calories per day in the off-season. I really think we'll see more healthy huge guys if more of us look at training - BIG changes in training - as the variable that can move the needle (pun not intended, lol).
Another edit / aside - more volume in terms of work sets isn't necessarily the answer. It's often a part of this process, but for example I'm still doing 6-8 hard sets for quads per week, spread across leg press, hack, and leg extension. The change is in how I'm executing those sets, along with the use of different intensifiers from what I was using before. With other body parts, the total number of sets definitely is increasing. Just depends on where the needs are.