Question for you Lyle..
When describing the setup you wrote "Basically, lie on your back with knees about 90 degrees and feet hip width. Put a belt around your thighs so that when you push out into it, your knees are over your toes."
What did you mean by knees over your toes? From looking at the pictures it appears the knees are applying constant pressure outward, hips are moving upward, and knee placement is actually slightly behind the ankle, not forward and over the toes, which would be quite an uncomfortable position.