It was written by a former piano technician who became a physical therapist - there are a lot of bum shoulders and knees, etc. in that business. The material is based on volumes of research done by a couple of doctors back in the 60's, one of whom was one of JFK's doctors. The basic principle it espouses is that over 80% of pain originates in the muscles. It's a terrific resource for managing or solving your pain with simple massage techniques.