In article 19, it is stated that, if you can do 10–15 repetitions of bench extensions with extra weight of 1/3 of your body weight, then your back should be strong enough for more intense hip flexor exercises—lying leg raises without weights. Also, it is stated that when you begin to get in shape, you can do squats without weights. The time to add weights is when you are permitted to perform good mornings (1 set of 500 unweighted sit-ups), which occurs prior to the 1/3 body weight extension mark.
In the DVD, it is stated that before you may perform the "leg exercises" you must be able to do 3 sets of the 1/3 body weight bench extensions. Does that 3 set rule apply also to Article 19? Also, are we to assume that even if we cannot perform 3 sets of such bench extensions, we may still perform squats and lunges WITHOUT WEIGHTS?