I have been doing the rites for around one and a half year now. The fourth rite is really tough for me and I also feel a slight ache in my lower back. I connect the ache to the fourth and fifth rite, but as I feel that my back generally has become stronger, I'm not that worried about the ache.
I have a slight cerebral palsy in the left side of my body, socalled hemiplegia, and when I started doing the rites I could only do 4 repetitions of the fourth rite. After doing some Feldenkrais work I have worked it up to 21 repetitions, also of the fourth, but I still have to do about four pauses to make it.
Another problem is, that I can't keep my heals in the ground, when I'm doing the fifth rite.
With more Feldenkrais work my performance will probably go on improving.