Ways the pelvis can move:
Side to side - Alternating sitz bone weight from left to right
Bob Jesselson – weight is on left sitz bone when bow is at the tip (press right foot into the floor)
Selma Gocken – weight is on right sitz bone when bow is at the tip (lift your right foot to feel this)
Both Bob Jesselson and Selma Gocken talk about alternating weight from right to left sides of the pelvis. The amazing thing is that their advice is completely in reverse! This doesn't mean that one is wrong and the other is correct. Try both and see which advantages each one gives. The aim is to move in a way that allows you to be balanced and free.
Alternating sides of pelvis (forward to behind you)
This direction of movement is probably already happening when you walk or do the exercise above. If you exaggerate it, it will look and feel like the way a runway model walks, which translates when sitting, to the knees alternating forward and back.
The entire spine can go from flexion to extension
Your spine can be curved as if you are slumping (the top of the pelvis is tilted back) and forehead is dropped down. Alternately, the spine extends when you arch your back and head and chin are up. Slightly flexing or extending the spine in this way can give you more sound (your body weight is helping you) or a lighter sound (taking the weight out). Don't over do either!
Forming a sideways C Curve
To feel this, sit with only one buttock on your chair and the other one falling off the side of the chair. Do it on the other side of your chair to feel the opposite sideways C curve. Of course these are extreme movements but it is yet another way our amazing spinal column and pelvis can help us play the cello!