The hypothsis of this book is that testosterone - or rather the declining effective levels of it we experience, is the key factor in causing us to lose energy, vitality and sexual desire as we age. Its a very interesting argument that most men will relate to once they get past 40 - and therefore with out doubt of great interest to many. The book is readable and informative. The author, an MD specialising in testosterone therapy marshals clinical research and anecdotal evidence to support his argument. As well as describing how declining testosterone negatively effects us, he also goes on to say exactly what we can do about it, and what we should discuss with our doctors (not that these things affect me - I read it for a friend of course! ). The good news is that there is a lot that we can do. Want to be bonking at 90? This book will tell you how. Definately a compulsive read for men who take an interest in their own health and want to live their lives with the energy and drive of their 20s and 30s.