At last a book that explains in great detail just what 'core strength' really is. It goes into great detail about the structure of the outer and inner layers of muscle that support your back and abdomen and then offers lots of useful information about exercises. Most importantly, it explains which exercises to concentrate on if you have had any back problems and which exercises are likely to cause more problems. I've completely changed my approach to abdominal and back exercise after reading this book and the improvement in both abdominal strength and reduction in back problems has been dramatic. Worth every penny.