Your annual physical probably checks your blood pressure, cholesterol and blood sugar. It almost certainly doesn’t measure the number that, in large studies, predicts your risk of dying better than any of them: your cardiorespiratory fitness, usually measured as VO₂ max.
What VO₂ max is
VO₂ max is the most oxygen your body can take in and use during hard exercise. It’s measured in millilitres of oxygen per kilogram of body weight per minute. It reflects your heart, lungs, blood and muscles working together, which is why it says so much about your health overall.
What the research shows
- A study of 122,007 patients who took treadmill tests at the Cleveland Clinic followed them for an average of 8.4 years. The least fit patients had about five times the risk of death of the fittest. Low fitness carried as much risk as smoking, diabetes or coronary artery disease, or more. The study found no upper limit: the fittest group did better than the merely fit (Mandsager et al., 2018).
- A review of 33 studies found that each 1-MET increase in fitness was linked to about 13% lower risk of death from any cause, and 15% lower risk of cardiovascular events (Kodama et al., 2009). One MET is roughly the effort of sitting quietly, so it’s a small step.
- In 2016 the American Heart Association recommended that doctors treat cardiorespiratory fitness as a clinical vital sign (Ross et al., 2016).
How to know yours
- Lab test: a treadmill or bike test with a mask that measures your breathing. It’s the most accurate, and it’s available at some sports-medicine clinics.
- Field tests: walking or running tests, such as how far you can cover in 12 minutes, give a reasonable estimate.
- Your watch: many fitness watches estimate VO₂ max from heart rate and pace. It’s useful for spotting a trend over months, less so for one exact number.
How to raise it
The good news is that fitness responds to training at any age.
- Build a base. Most of your weekly cardio should be at a pace where you can still talk in full sentences: brisk walking, cycling, easy running.
- Add hard intervals once or twice a week. For example, 4 rounds of 4 minutes hard, with 3 minutes easy between. In trials, intervals like these improved VO₂ max more than moderate exercise alone did (Helgerud et al., 2007).
- Be consistent for months. The gains come from weeks of training, not one heroic session.
If you’re starting from very little, walking more, and more briskly, is the intervention. The biggest drop in risk in these studies comes from moving out of the least-fit group.
This article is general information, not medical advice. Talk to your doctor before starting hard exercise, especially if you have heart disease or symptoms like chest pain or breathlessness.
Sources
- Mandsager K, et al. Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Netw Open. 2018;1(6):e183605.
- Kodama S, et al. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024–2035.
- Ross R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign. Circulation. 2016;134(24):e653–e699.
- Helgerud J, et al. Aerobic high-intensity intervals improve VO₂max more than moderate training. Med Sci Sports Exerc. 2007;39(4):665–671.
