Did you have imbalances after working through the tests in the book or any nagging aches and pains? My lower back usually feels tight when I squat. The problems is probably lack of strength and flexibility in certain muscles.
Also, my 5th and 6th cervical vertebrae have fused together do to years of butting helmets, not on purpose, during my football days. I wonder if something like this will help balance me out a little? My back has always been weak.