Starting position:
Sit up tall with hips abducted so legs are wide.
Assistant / therapist manually moves the lumbar spine and torso into flexion while you extend the knee. Then the assistant / therapist manually moves the lumbar spine and torso into extension while you bend the knee. Try to keep the other joints still. Alternate between these two positions.
The technique should be painless.
The movements should only be taken to the point where the patient begins to feel something.