Quick answer: VO2 max is the most oxygen your body can take in and use during hard exercise, and it is the standard measure of cardiorespiratory fitness. A 2024 overview covering more than 20.9 million observations found that adults with high fitness had roughly half the risk of death from any cause compared with adults with low fitness, and each small step up in fitness was linked with lower risk. Fitness is partly inherited, but the rest responds to regular aerobic activity at almost any age, which makes it one of the most useful longevity markers to know and follow over time.
Key takeaways
VO2 max is the most oxygen your body can take in and use during hard exercise, and it is the standard measure of cardiorespiratory fitness.
Very large studies have linked higher fitness with lower risk of death from any cause, and the benefit did not seem to level off at the top.
Fitness is partly inherited, but it can still be built at any age, which makes regular aerobic exercise a practical part of a longevity plan.
When people ask me which numbers say the most about how well they are aging, they usually expect me to name a blood test. Lab markers matter, and I write about them often, but one of the strongest signals in the research is not found in a blood sample at all. It is how well your heart, lungs, blood vessels, and muscles work together when you ask them to do something hard. Researchers call this cardiorespiratory fitness, and the most common way to express it is VO2 max.
What VO2 max actually measures
VO2 max is the highest rate at which your body can take in oxygen, deliver it through the bloodstream, and use it in working muscle. It is usually reported in milliliters of oxygen per kilogram of body weight per minute. Researchers also describe fitness in metabolic equivalents, or METs, where one MET equals 3.5 mL/kg/min, roughly the oxygen your body uses while sitting quietly. A higher number means your whole oxygen delivery system has more reserve capacity.
That system includes the pumping strength of the heart, the flexibility of the arteries, the amount of blood and hemoglobin available to carry oxygen, and the density of mitochondria inside muscle cells. Because mitochondrial decline is one of the hallmarks of aging, VO2 max gives an indirect window into how well this cellular machinery is holding up. My article on daily habits that support your mitochondria goes deeper into that side of the story.
What 20.9 million observations show
In 2024, a research team led by Justin Lang published an overview in the British Journal of Sports Medicine that pulled together 26 systematic reviews with meta-analyses, representing 199 separate cohort studies and more than 20.9 million observations of adults. When they compared people with high fitness with people with low fitness, the high-fitness group had a 53 percent lower risk of dying from any cause during follow-up. Each 1-MET higher level of fitness was associated with an 11 to 17 percent lower risk of death from any cause.
The associations went well beyond mortality. High fitness was linked with a 69 percent lower risk of developing heart failure compared with low fitness, and each additional MET was associated with an 18 percent lower risk. The authors also noted earlier research tying fitness to lower rates of type 2 diabetes, stroke, depression, and some cancers. They were careful to say that the certainty of the evidence ranged from very low to moderate, mainly because these are observational studies, and that women remain underrepresented in the research. Even with those limits, they concluded that fitness would be a valuable tool for sorting out risk in clinical practice. The free full text is here: Cardiorespiratory fitness is a strong and consistent predictor of morbidity and mortality among adults.
A 122,000-person study with no upper limit
A 2018 study from the Cleveland Clinic, published in JAMA Network Open, looked at 122,007 adults who completed a symptom-limited treadmill test between 1991 and 2014 and followed them for a median of 8.4 years. The researchers sorted each person into a fitness group based on how they compared with others of the same age and sex. After adjusting for other risk factors, people in the lowest fitness group had about five times the risk of death of the most fit group.
Two findings from this study stand out to me. First, being in the below-average fitness group rather than the above-average group carried a risk similar to smoking or having diabetes, and greater than having known coronary artery disease. Second, the authors found no upper limit to the benefit. The most fit group, people at least two standard deviations above the average for their age and sex, had the lowest risk of all, and that advantage over the high-fitness group was also present in people 70 and older and in people with high blood pressure. The free full text is here: Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing.
Fitness can still be built later in life
According to the Lang overview, nearly half of the difference in fitness between people is explained by genetics, and the rest is shaped mostly by habitual physical activity. The authors point out that brisk walking for about 150 minutes a week can produce large relative improvements in people who start out sedentary and unfit. This is what makes VO2 max different from a marker like lipoprotein(a), which I wrote about in my article on the inherited heart marker worth testing once. Fitness is a number you can move.
The Generation 100 study from Norway offers a useful look at what that can mean in older adults. Researchers randomly assigned 1,567 people aged 70 to 77 to one of three groups for five years. One group did two weekly sessions of high-intensity interval training, built around four 4-minute intervals at about 90 percent of peak heart rate after a 10-minute warm-up. A second group did two weekly 50-minute sessions at a steady moderate pace, and a third group was asked to follow the national physical activity guidelines on their own.
The results are worth describing accurately. Overall, the two supervised exercise groups combined did not have lower mortality than the guideline group, which may partly reflect how healthy and active the participants already were and the fact that many people in the guideline group chose to do intervals on their own. The interval group had the lowest death rate, about 1.7 percentage points lower than the guideline group, although that difference did not reach statistical significance. After five years, the interval group’s peak oxygen uptake was 0.7 mL/kg/min higher than both other groups, and the interval group also reported better physical and mental quality of life. Perhaps most encouraging, the researchers had expected peak oxygen uptake to fall by at least 3.5 mL/kg/min with age over those five years, and none of the three groups showed that decline. The free full text is here: Effect of exercise training for five years on all cause mortality in older adults: the Generation 100 study.
How VO2 max is measured
The most accurate measurement comes from a cardiopulmonary exercise test, in which you walk or run on a treadmill or ride a stationary bike while wearing a mask that analyzes the oxygen and carbon dioxide in your breath. Many sports medicine clinics, cardiology practices, and performance labs offer this test. A standard exercise stress test, like the one used in the Cleveland Clinic study, estimates fitness in METs from how long you last and how hard the final stage was.
Many fitness watches now estimate VO2 max from heart rate and pace during walks or runs. These numbers are less precise than a lab test, but they can still be useful for watching your own trend over months, as long as you use the same device and similar conditions. I find that seeing the trend is often more motivating than any single reading. If you have heart disease, chest symptoms, or have been inactive for a long time, it is wise to talk with your clinician before doing any maximal fitness test or starting hard intervals.
How fitness fits with the rest of your longevity plan
Cardiorespiratory fitness is one piece of a broader picture of physical capacity. Muscle strength tells you something different, which is why I also pay attention to grip strength as a longevity biomarker and encourage regular strength training. Everyday movement matters too, and my article on daily movement for longevity covers the benefits that come from simply moving more throughout the day.
Fitness also tends to travel with the cardiovascular markers I look at on lab work, including blood pressure, blood sugar, and lipids. My guide to heart health discusses those connections, and my article on epigenetic clocks and the pace of aging explains another way researchers try to measure how quickly the body is aging. When I review functional lab testing with someone, I like to know how their fitness compares, because a lab panel and a fitness measure together tell a fuller story than either one alone.
Curious how your fitness and your labs fit together?
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Questions to bring to your clinician
These questions can help you get the most out of your next visit.
What would be a realistic way for me to start building my aerobic fitness?
What would be a gentle starting point for aerobic training, given where I am right now?
Is there anything in my health history that would make aerobic training need extra care?
How would we know that aerobic training is helping me, and when should we check in?
Frequently asked questions
Is the VO2 max on my fitness watch accurate?
Watch estimates are calculated from heart rate and movement data rather than measured directly from your breath, so they can be off by a meaningful amount for any one person. They are most useful for following your own trend over time with the same device. A cardiopulmonary exercise test remains the most precise option if you want a true baseline.
How much does one MET of fitness matter?
One MET equals 3.5 mL/kg/min of oxygen use. In the 2024 overview by Lang and colleagues, each 1-MET higher level of fitness was associated with an 11 to 17 percent lower risk of death from any cause. Researchers often use a 1-MET change as the smallest difference that is meaningful in exercise studies.
Is it too late to improve fitness after age 70?
The research suggests it is not. In the Generation 100 study, adults who started between ages 70 and 77 held their fitness steady over five years instead of losing the amount researchers expected, and the group doing intervals gained a small amount compared with the other groups. Anyone starting a new exercise routine later in life should check with their own clinician first, especially when heart disease or other health conditions are present.
Sources
- Lang et al. Cardiorespiratory fitness is a strong and consistent predictor of morbidity and mortality among adults: an overview of meta-analyses representing over 20.9 million observations from 199 unique cohort studies. British Journal of Sports Medicine. 2024. Free full text on PubMed Central.
- Mandsager et al. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Network Open. 2018. Free full text on PubMed Central.
- Stensvold et al. Effect of exercise training for five years on all cause mortality in older adults: the Generation 100 study, randomised controlled trial. The BMJ. 2020. Free full text on PubMed Central.
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting a new exercise program, supplement, or significant change in diet or medications, especially if you are pregnant, nursing, or managing a health condition.
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