re: Lengthened partials

I will stick to the stretch then. So last set of an exercise go to absolute failure, then stretch? Or is failure not recommended prior to the stretch?

I agree about sticking to full ROM. But I do see a benefit do doing extra lengthened partials after you can't complete any more full rom. Especially one movements where the main muscle you are targeting is most active in the lengthened position, yet lockout is where its hardest. Things like side laterals, rows, chins, bench for example. If you could do 4 more half sets of bench at the bottom, since your triceps are tired it seems like you are leaving gains on chest if you don't finish with partials. What do you think on that? I haven't seen any studies talking about this.

I would say it varies widely based on a lot of factors and is controversial. You can grow on 1 set 3x/week with progressive overload but more is better, though you hit a point of diminishing returns pretty quickly due to fatigue and time constraints. You need to be able to recover from the volume. If you’re trying to train every body part equally probably 6-15 sets per week per muscle is a reasonable target. Exercise selection makes a big difference too, with heavy compound lifts causing more fatigue, making less total sets more optimal, whereas you can do more volume on isolation exercises and those that use shortened muscle lengths. If you wanted to target a body part (women with glutes, men with arms/shoulders), you can do more for that muscle but would want a lot of that volume to be isolation exercises

Yes