Well extreme fatigue like you feel after you've done one of those workouts but it never going away fully. I was big into the Mentzer Jones Nautilus stuff years ago. I dreaded those workouts, but also loved them too.
Yeah I was mental back then. When I got done with one of those torture sessions I felt like I was hit by a truck, OK maybe more than one truck. This feeling never fully went away. Some days felt better than others, but for the most part just tired and I was in my teens and 20's back then so I should not have felt that way.
Each day I do the Adonis 100.
I train one bodypart a day and do 3-4 exercises 4 sets each and once I finish with that, I go to the first exercise I did and start with a little more weight than I did on my first set and the goal is to get to 100 reps, no matter how many sets it takes. The weight is heavy enough to where I can just get 10-13 reps.
If I have to drop the weight a bit during the Adonis 100, I do it once I reach 25 reps.
I did it for squats today, after going very heavy, and I don`t think I have ever had a more difficult workout.