Pain at the sacrum sometimes comes from chronic contraction of the deepest, narrowest-in spinal muscles.
The leg movement seen locates and aims into the most sore position felt at the low-back/waist, the working position.
Once you find the working position, you lift your hands, elbows and head 1/4" and side-bend to the same side as the lifted leg position so that the bend locates the same sensation at the waist as does the leg position. Both actions converge at the same sore place.
The movement is straight up and straight down to complete relaxation.
This movement substitutes for the similar movement found in Lesson 1 of Disproving the Myth of Aging | Click here for the entire program.