Some people tend to benefit greatly from pre-exhausting and see great gains from it. Others (like myself) do not really respond to it.
When I did it I did 8 weeks pre-exhausting and then a week off followed by another 8 weeks without the isolations. I did get some gains in strength but didnt make much in the way of mass gains with it.
And yes, I did leg extensions before squatting and proceeded to puke up afterwards, so it is intense if anything
