VO2 max and longevity: why your fitness matters so much

VO2 max is your maximal oxygen uptake: the largest amount of oxygen your body can take in and use per minute at peak effort. It depends on the heart, lungs, blood and muscles working together, and is usually expressed in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min).

It is the most widely accepted measure of cardiorespiratory fitness, as a 2022 review in Sports Medicine points out. Studies also express fitness in METs, or metabolic equivalents: one MET is the oxygen uptake of a person sitting at rest, 3.5 mL/kg/min, and fitness is the number of METs reached at peak effort.

A VO2 max value only makes sense for a given age and sex. In the 2018 study described below, the cut-offs between “low” and “elite” fitness drop from one decade of age to the next and differ between women and men: each person is compared with people of the same age and sex.

One more MET, a lower risk

A 2009 meta-analysis published in JAMA pooled 33 observational studies of healthy adults, nearly 103,000 of them followed for mortality. Each additional MET of maximal capacity, which the authors equate to running about 1 km/h faster, was associated with a 13% lower risk of death from any cause and a 15% lower risk of coronary or cardiovascular events. People with low fitness had a 1.7 times higher risk of death than those with high fitness.

No upper limit observed

In 2018, a study published in JAMA Network Open analyzed 122,007 patients who had a treadmill exercise test at the Cleveland Clinic in the United States, with a median follow-up of 8.4 years. Each patient was ranked against people of the same age and sex, from “low” (the least fit quarter) to “elite” (above the 97.7th percentile).

After adjusting for other risk factors, the “low” group had about a five times higher risk of death than the “elite” group. The risk linked to reduced fitness was comparable to, or greater than, that of smoking, diabetes or coronary artery disease. Above all, the authors observed no upper limit: the fitter the group, the lower its mortality, and the “elite” group still did better than the “high” group, including in people over 70 and in people with high blood pressure.

A vital sign in its own right

These findings echo the 2016 scientific statement from the American Heart Association: low cardiorespiratory fitness is associated with a high risk of cardiovascular disease and death, it may predict mortality more strongly than smoking, high blood pressure, high cholesterol or type 2 diabetes, and adding it to traditional risk factors improves risk classification. Hence the AHA’s case for treating fitness as a “clinical vital sign” assessed in routine care.

An association, not a guarantee

These are observational studies. The authors of the 2018 study say so themselves: their data cannot tell whether high fitness lowers mortality or simply singles out people who were healthier to begin with. Patients referred for an exercise test are not representative of the general population either, and unmeasured factors such as socioeconomic status may play a part. What is solid is how consistently the association shows up from one study to the next; what is not is how many years any one person would gain by improving their fitness.

Three approaches coexist, from the most accurate to the most accessible.

The laboratory exercise test

The reference standard is a maximal exercise test performed in a laboratory with analysis of the air you breathe, known as cardiopulmonary exercise testing. It requires costly equipment and trained staff, which puts it out of reach unless there is a specific medical or sporting reason. If a longevity medicine clinic offers you one, ask what its result will actually change in your care.

Field tests

Standardized exercise tests done outside the lab, without going all the way to maximal effort, estimate VO2 max without gas analysis. According to the 2022 review, these indirect estimates are acceptable, at a fraction of the cost and effort.

Your watch’s estimate

Many watches display a VO2 max, calculated from heart rate, pace and your profile. The same review, a meta-analysis of 14 validation studies, found that estimates based on exercise sessions are clearly more reliable than those calculated at rest, which overestimate VO2 max. They are accurate on average across a group, but the error remains large for an individual: even with exercise-based estimates, the gap with the lab measurement could approach 10 mL/kg/min in either direction. Yet the authors note that gains of 1.75 to 3.5 mL/kg/min are already associated with a lower risk of death. Several brands that display a VO2 max still lacked scientific validation, according to the review.

In practice, read your watch’s number as a trend: same device, same conditions, over several months. For what else health wearables measure well and less well, our guide sorts it out.

With MyTwin for patients, data from your compatible watches and sensors sits alongside your reports and lab results in a single health digital twin: a trend can be followed over time and discussed with a healthcare professional.

This is what sets cardiorespiratory fitness apart from many other markers: it responds to training. A 2015 meta-analysis in Sports Medicine pooled 28 controlled studies in healthy adults aged 18 to 45. Compared with no exercise, continuous endurance training raised VO2 max by about 4.9 mL/kg/min and high-intensity interval training by about 5.5 mL/kg/min, over programs lasting at least two weeks. Interval training had a small extra edge, and gains were larger in people who started from lower fitness and in longer programs.

The WHO benchmarks

The World Health Organization’s 2020 guidelines recommend that adults do, every week:

• 150 to 300 minutes of moderate-intensity aerobic activity, or 75 to 150 minutes of vigorous-intensity activity, or a combination of both;
• muscle-strengthening activities involving all major muscle groups, on at least two days a week;
• from age 65, as part of that weekly activity, varied activities that train balance and strength on at least three days a week, to maintain functional capacity and prevent falls.

These figures are benchmarks, not a threshold below which nothing counts. According to the WHO fact sheet on physical activity, any amount of activity is better than none, and people who are insufficiently active have a 20 to 30% higher risk of death than people who are sufficiently active.

Before stepping up the intensity

According to the American College of Sports Medicine, exercise is safe for most people. Its pre-participation screening recommendations rest on three factors: how active you currently are, whether you have symptoms or known cardiovascular, metabolic or kidney disease, and how intense you plan to go. If you are inactive and aiming for hard efforts, if you live with a chronic condition, or if you notice chest discomfort, unusual breathlessness or feeling faint during exercise, talk to your doctor before you start. A preventive health check-up is a good opportunity to do so. If you have chest pain or feel unwell, call your local emergency number.

Cardiorespiratory fitness is not the only physical capacity linked to survival. The PURE study, published in The Lancet in 2015, measured grip strength in nearly 140,000 adults aged 35 to 70 across 17 countries, with a median follow-up of four years. Each 5 kg drop in grip strength was associated with a 16% higher risk of death from any cause, and grip strength predicted all-cause and cardiovascular mortality better than systolic blood pressure.

Again, this is an observed association, not proof that a firmer handshake makes you live longer. Grip strength is mostly a simple, inexpensive reflection of overall muscle health. It is one more reason not to skip the muscle-strengthening work the WHO recommends: endurance and strength complement each other.