@solokwa I recently came across the same type of research that I did not know about. 6-8 sets / muscle group per session. And 10-20 sets per week for a muscle group.
Before I found this research, a typical chest day for me would consist of 4-5 sets of bench, followed by 3-4 sets of DB press, and another 3-4 sets of flys. 10-13 sets in total.
Since finding this research out, a typical chest day for me now is 2-3 sets of a horizontal press, 2-3 sets of a fly and 1 set of BW pushups to failure. So about 7 sets in total.
The quality of my workouts have gone up so much more since switching to this lower volume. I have pushed myself like never before. One thing that ive really took note of is my leg extensions. I would normally do 3-4 sets of 100-120 pounds for 12 reps. Now im doing 2 sets after squats, and last night I was able to do 180 pounds for 18 reps, that was to complete failure.
The lower volume just allows me to really push myself to that 0-3 RIR range a lot better. I notice now that before I would predetermine a number of reps (say 12) and I would just hit that number and wait for another set. Even if i had 4+ RIR.