I'm not sure what possessed me, but today I felt the urge to try using 5 lb weights for some of the moves. For example, for the lower ab move where the legs swing up and down, I held 5 lb weights above my chest, that wasn't so bad. I also used the 5 pounders for the static lunge - arm row combo. I had a fleeting thought to use them for the military press with leg extensions, but I couldn't bring myself to do it.
The pendulum lunges are still the absolute hardest move for me. I also continue to have difficulty with the chair squat - "v" raise move. Both of these moves are even harder than the plank jacks, squat thrusts, and plank twists, all of which I can feel myself getting stronger as I continue to do them.