Spend enough time with a group of endurance athletes - swimmers, cyclists, runners, cross-country skiers, or anyone who needs to sustain an aerobic effort - and sooner or later, someone is bound to bring up a way to measure fitness called VO 2 max. A high VO 2 max is tied to better health and increased longevity. And if you know your score, you can use it as a tool to help you exercise more efficiently. What is VO 2 max and what does it tell you? VO 2 max measures how much oxygen your body