VO2max: the indicator with the strongest link to mortality

VO2max is the maximum volume of oxygen the body can consume per minute during maximal exertion. Of all the metrics used in biohacking, this one has the strongest link to life expectancy in observational data. And it is also the most frequently misunderstood in terms of what that link actually means.

What the largest cohort showed

A retrospective study by the Cleveland Clinic included 122,007 patients referred for a treadmill stress test between 1991 and 2014. The median follow-up was 8.4 years, during which 13,637 people died.

Participants were divided into five fitness groups adjusted for age and sex. Mortality was inversely proportional to fitness: compared to the elite group, the adjusted hazard ratio for the lowest-performing group was 5.04. For comparison, in the same model, coronary artery disease had a ratio of 1.29, smoking 1.41, and diabetes 1.40.

The authors found no upper limit to the benefit: even between the "high" and "elite" groups, a difference remained (0.77). Study in JAMA Network Open.

Why the number is so high

This is where the main trap lies. This is a cohort observation, not a trial. People with low fitness are, to a significant extent, people who already have underlying issues: undiagnosed disease limiting exertion, consequences of past illness, or a lower general level of functioning. Reverse causality is particularly plausible here: disease reduces fitness before it manifests as a diagnosis.

Therefore, the correct phrasing is "low cardiorespiratory fitness is associated with higher mortality," not "endurance training reduces mortality fivefold." The latter statement does not follow from these data.

The American Heart Association, in a separate statement, proposed considering cardiorespiratory fitness as a clinical vital sign alongside blood pressure and pulse—precisely because of the strength of its association with outcomes. Statement in Circulation.

How VO2max is measured and estimated

True measurement is ergospirometry: a mask, analysis of exhaled air, and a stepwise increasing load until exhaustion. Everything else is an estimate based on indirect indicators.

• Stress test without gas analysis. Fitness is expressed in metabolic equivalents based on the speed and incline achieved. This is how it was measured in the Cleveland cohort.
• Field tests. The Cooper test, shuttle run, or step tests—formulas tied to the result.
• Watches and trackers. A model that correlates running pace with heart rate and outputs a number. The error of individual estimation is several milliliters per kilogram per minute, and it systematically depends on how accurately the device measures heart rate and how typical your maximum heart rate is.

The same limitation applies to any wrist-based calculated metrics—more details in the article on fitness trackers and calorie expenditure.

What the number changes and what it does not

VO2max is composed of the heart's ability to pump blood, hemoglobin levels, and the muscles' ability to extract oxygen. The heritability of the baseline level and the capacity for improvement is high: people with the same training program respond differently, and part of this difference is genetic.

From this comes a practical implication for interpretation: comparing your number to someone else's tells you less than comparing it to your own past. On how to distinguish a real shift from noise in your own measurements, see the article on self-experimentation.

Where certainty ends

It is known that fitness is strongly associated with mortality in large cohorts. It is known that training increases fitness. It has not been verified by a randomized trial on mortality: that increasing fitness in a specific individual reduces their risk to the same extent predicted by the observational curve. Such a trial would require tens of thousands of people and decades, and it does not exist.

This is exactly the gap in which a significant portion of "longevity protocols" lives—see the article on biohacking in general.

Count it from a photo

Frequently asked questions

What is VO2max?

The maximum volume of oxygen the body can consume per minute during maximal exertion. It is typically expressed in milliliters per kilogram of body weight per minute.

How strong is the link between VO2max and mortality?

In a cohort of 122,007 people, the adjusted hazard ratio for death in the lowest fitness group compared to the elite group was 5.04. In the same model, coronary heart disease had a ratio of 1.29, smoking 1.41, and diabetes 1.40.

Does this mean that exercise reduces mortality by five times?

No. These are observational data, where illness may reduce fitness before a diagnosis becomes apparent. They indicate an association, not the magnitude of the effect of training.

Do watches accurately measure VO2max?

Watches provide an estimate based on a model that correlates pace and heart rate, rather than a direct measurement. True measurement is ergospirometry using a mask and analysis of exhaled air during a graded exercise test.

Why do people with identical training regimens have different VO2max levels?

The metric is determined by heart function, hemoglobin levels, and the ability of muscles to extract oxygen. Both the baseline level and the magnitude of improvement in response to the same program are heavily dependent on genetics.

Read next

• Zone 2: where the trend for slow cardio came from and what comparisons have shown — Zone 2 is an intensity at which you can speak in full sentences and blood lactate levels barely rise.
• How many calories are burned during a workout: running, cycling, swimming, gym — An hour of running at a moderate pace for a 70 kg person is about 550–700 kcal, cycling at a leisurely pace is 350–450, swimming is 400–600, and strength training is 200–350.
• Why a sedentary lifestyle is harmful — Sedentary work affects health not because a person doesn't exercise enough, but because they barely move during the other fifteen hours of the day.

This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.

Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.