VO2 max is the most oxygen the body can use during hard exercise, and it reflects cardio fitness. In a 2018 study of more than 122,000 adults, lower fitness was linked with a higher risk of death. Fitness can improve at any age, usually through a mix of steady and interval training.
VO2 max used to be a number for endurance athletes. It now shows up on smartwatches and in longevity conversations, usually with a bold claim attached. The research behind it is solid, and it is also easy to overstate.
What VO2 max is, in plain English
VO2 max is the maximum amount of oxygen the body can take in and use during all-out exercise. It is reported in milliliters of oxygen per kilogram of body weight per minute.
It depends on the whole delivery chain: the lungs bringing oxygen in, the heart pumping it out, the blood carrying it, and the muscles using it. That is why researchers treat it as a summary measure of cardiorespiratory fitness.
A lab measures it directly with a mask during a hard treadmill or bike test. A watch estimates it from heart rate and pace. Watch estimates are useful for tracking a trend over months, but the absolute number can be off.
What the 2018 study found
Researchers at the Cleveland Clinic followed 122,007 adults who had a treadmill stress test between 1991 and 2014. They grouped people by fitness level for their age and sex, then tracked deaths from any cause over a median of about eight years. The results were published in JAMA Network Open.
Three findings stood out:
- Higher fitness was linked with lower risk of death at every step up the scale.
- There was no upper limit where more fitness stopped being linked with benefit.
- The risk linked with low fitness was comparable to or greater than the risk linked with coronary artery disease, smoking or diabetes.
This fits earlier work. A 2009 meta-analysis in JAMA of 33 studies found that each 1-MET step up in fitness, roughly the difference between walking a little faster on the treadmill, was associated with a 13% lower risk of death from any cause. In 2016 the American Heart Association published a scientific statement arguing that fitness should be treated as a clinical vital sign.
Why it matters more after 40
Cardio fitness tends to fall with age, and the decline is faster in people who are inactive. The practical effect is a shrinking reserve. Carrying groceries upstairs or hiking with family takes a larger share of a smaller maximum.
The encouraging part is that fitness responds to training at any age. Adults who start from a low base often see the largest relative improvements.
How training raises VO2 max
Studies point to two kinds of work, and most programs use both.
Steady, easy aerobic work. Often called zone 2, this is effort where a conversation is still possible: brisk walking, easy cycling, a relaxed jog. It builds the aerobic base and is easy to recover from. Our guide to zone 2 cardio over 40 explains how to find that effort level.
Short, hard intervals. A 2007 trial in Medicine & Science in Sports & Exercise compared four training styles matched for total work. The group doing four 4-minute intervals at 90 to 95 percent of maximum heart rate, with 3 minutes of easy movement between them, improved VO2 max by about 7 percent in eight weeks. The steady-pace groups did not improve it significantly. The participants were healthy young men, so the exact numbers may not carry over to other groups.
A common weekly structure in the research and in coaching looks like this:
- Two to three easy sessions of 30 to 45 minutes
- One interval session, such as 4 minutes hard and 3 minutes easy, repeated four times
- At least one full rest day
People new to exercise usually build the easy sessions for several weeks before adding intervals. Shorter efforts, such as 1 minute hard and 2 minutes easy, are a common way in.
Who should check with a clinician first
High-intensity exercise is demanding. Guidelines advise a medical check before starting vigorous training for people who have heart disease, diabetes or kidney disease, who have symptoms such as chest discomfort, unusual breathlessness or dizziness with exertion, or who have been inactive for a long time.
Chest pain, fainting or severe shortness of breath during exercise needs urgent medical attention, not a training adjustment.
The takeaway
VO2 max is one of the better-studied markers of long-term health, and it is one that training can change. It is still a single number. Blood pressure, lipids, blood sugar, strength, sleep and not smoking matter too, and a clinician can help put them together.
DirectCare AI connects adults with US-licensed clinicians who can review health history and bloodwork as part of that wider picture.
This article is educational and is not medical advice. Talk with a licensed clinician before starting a new exercise program.
References
- Mandsager K, Harb S, Cremer P, et al. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open. 2018;1(6):e183605. Source
- Kodama S, Saito K, Tanaka 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. Source
- Ross R, Blair SN, Arena R, et al. Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association. Circulation. 2016;134(24):e653-e699. Source
- Helgerud J, Hoydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc. 2007;39(4):665-671. Source
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