> not the mass used.

Completely anecdotal, but when I was 18, in highschool, I trained in the gym in my hometown, supervised with a trainer, 12 reps per muscle group, very modest gains.

I move to university, start reading a fitness forum where people were saying do max 6 reps if you want big gains.

I also started supplementing with whey protein, and within 3 months the gains were spectacular, everybody noticed, I felt on fire, best time of my life, I miss so much how great I felt in my own body.

I've seen other colleagues and how they trained -- I can say there was 100% correlation that those people who were not training hard also did not have big gains. People who had enough breath left in them to chat in the gym simply did not gain as much as people I saw as training hard.

Also for me, the 6 reps to exhaustion felt completely different then 12 reps (again, to complete exhaustion) -- immediately after the training it felt amazing to be alive, the world became a comfortable place, my anxiety completely vanished, and in the night and morning after an intense training (especially the legs and back) the erections and libido boost were out of this world, something I never felt with the 12 reps regimen.

Anecdotally as someone who strength trained on a recreational basis the last 20 years (and run a marathon just to see if I could), nothing beats heavy lifting.

A Strong lifts 5x5 program build around squat, deadlifts, bench and shoulder press can always make me feel pumped for the day!