I. Introduction

You’ve always known that exercise is good for you, with wide-ranging benefits not just for how you look but also your health, longevity, performance, mood, and quality of life. But you might be surprised by just how good exercise is for you. In fact, a growing body of research demonstrates that your level of fitness does a better job predicting how long you will live than any other modifiable variable that we know of. Yes, you read that right. Your level of fitness is a stronger predictor of mortality than many other...