What is VO2max and how important is it for living longer?

Your VO2max, the measure of how well your heart, lungs and muscles work together during exercise, is probably the most informative health measurement you can take. A review of dozens of large studies (more than 20 million participants) found that people with high fitness have roughly half the risk of premature death compared with people with low fitness, and each step up in fitness is associated with about an 11 to 17 percent lower risk. That is a much stronger association than for most other measurements.

What the number means in practice: a threshold that repeatedly appears in research is around 8 MET (a moderate exercise intensity, comparable to brisk walking). People who are well above that do considerably better; people who are well below it have more reason to pay attention to it. The most reliable measurement is an exercise test at a sports medicine or cardiology outpatient clinic, where your VO2max is measured directly. A good fitness tracker or a walk or run test over a fixed distance gives a rough estimate, which is sufficient to see how you compare with peers your age and to track your progress.

The good news lies in the nature of this measure: fitness is largely trainable, and improvement genuinely translates into lower risk. It is therefore not a result that says something definitive about your future, but a compass that shows where you stand right now and whether you are moving in the right direction. A single measurement is a snapshot; anyone who wants to monitor it seriously is better off looking at the trend over a year or two than focusing on any single number.