Having done a bit of cycling and running for years without any stretching I had become very inflexible, leading to problems with my lower back. I've tried many stretching and sports injury books (mostly more modern than this one) and usually ended up making my back worse by following the suggested stretches. Most books seem to assume that you are very flexible to start with!
This book is very different. The focus is on getting in positions where you are able to stretch muscles in isolation (without risking damage to over-tight muscles elsewhere) and also there is a huge variety which you can use depending on how flexible you are to start with. There is no downside really except the descriptions are incredibly detailed so the first time you do a stretch you have to keep refering to the book to read what you're supposed to do next. The first time you try a full routine allow a couple of hours!