To gain muscles, go near maximum, if you go to low, go just gain resistance, burn energy (and even muscle mass if your carb intake is too low). I see people in gym doing those stupid long series all the time and I just laugh. Doing 100 times at 80% on a muscle just risks muscle tears once the muscle goes lactic from overused and loses its flexibility.
Once the muscle's tired, move on to another muscle.
There's a reason why people train twice a day instead of doing
very long training sessions. You need to give the muscle time
to recover.