I just finished this book. It provides a pretty good analysis of what happens to the 50+ athlete and how to minimize what is inevitably a loss of endurance and power. To put it succinctly, if you want to stay fit and competitive you have to keep strength training in the program and you have to incorporate intervals that are going to hurt. Long slow distance just isn't going to do and for that natter neither will those high endurance efforts. It really does take those shorter but high end zone 5 efforts to stay fit.