VO2 Max and Cardiorespiratory Fitness, Explained

The single measurement that predicts lifespan better than blood pressure, cholesterol, or smoking status. What it is, what the ranges mean by age, how watches estimate it, and how to raise it.

If a clinic could measure only one thing to predict how long a person would live, the best candidate is not blood pressure, cholesterol, or weight. It is cardiorespiratory fitness, and the standard measure of it is VO2 max: the maximum volume of oxygen the body can use per minute during hard exercise, expressed in milliliters per kilogram of body weight per minute.

In a 2018 study of more than 120,000 patients who had undergone treadmill testing at the Cleveland Clinic, the least fit fifth had a death rate about five times that of the most fit, a larger gap than for smoking, diabetes, or coronary disease. The relationship had no upper limit; the very fittest did better than the merely fit. The American Heart Association has since called for fitness to be treated as a vital sign.

What it measures

VO2 max integrates the whole oxygen delivery chain: how much air the lungs move, how much blood the heart pumps per beat, how much oxygen the blood carries, and how well the muscles extract and use it. A weakness anywhere lowers the number. That is why it predicts so broadly. Heart disease, lung disease, anemia, deconditioning, and obesity all show up in it.

The ranges

Values are in ml/kg/min. These are rough population figures for untrained to moderately active adults; athletes sit well above them.

Age	Men, average	Men, good	Women, average	Women, good
20 to 29	40 to 45	over 50	33 to 37	over 42
30 to 39	37 to 42	over 47	31 to 35	over 40
40 to 49	34 to 39	over 44	28 to 32	over 37
50 to 59	31 to 36	over 41	25 to 29	over 34
60 to 69	28 to 33	over 37	23 to 26	over 31

The number falls about 10 percent per decade in sedentary adults, roughly half that in people who keep training. The cutoff that matters most for health is at the bottom: values below about 18 for men and 15 for women are associated with difficulty in daily activities and a sharp rise in risk. Moving out of the lowest fifth for your age and sex, the "unfit" category, is where most of the mortality benefit sits. Going from unfit to average is worth more than going from average to excellent.

How it is measured

The gold standard is a treadmill or bike test in a lab, breathing through a mask that measures oxygen in and carbon dioxide out, ramping effort until exhaustion. It takes about 15 minutes and is available at sports science labs, some hospitals, and cardiology clinics.

Watches estimate it. Garmin, Apple, and others use the relationship between heart rate and pace or power during outdoor runs and walks, with an assumed maximum heart rate. Their estimates correlate reasonably with lab values, typically within about 10 percent for most people, and are worse for those with unusual maximum heart rates, on beta blockers, or who mostly train indoors. The estimate is most useful as a trend on the same device, not as an absolute figure.

Without a device, a 12 minute run or walk test gives a serviceable estimate: cover as much distance as you can in 12 minutes on a flat course. VO2 max is approximately (distance in meters minus 505) divided by 45. A 2,400 meter effort works out to about 42.

Resting heart rate tracks the same underlying fitness and is much easier to watch daily. See resting heart rate explained.

How to raise it

VO2 max responds to aerobic training, and specifically to time spent at a heart rate above about 70 percent of maximum. Two approaches work and the best programs combine them.

Volume at moderate effort. Steady work at a talking pace, 150 to 300 minutes a week, builds the heart's stroke volume and the muscles' capacity to use oxygen. This is where beginners should start; see how to start running from zero. Brisk walking counts for people beginning from a low base.

Intervals at hard effort. Once a base exists, bouts of 3 to 5 minutes at an effort where you can say only a few words, separated by equal recovery, repeated four times, once or twice a week. Trials of this format show VO2 max gains of 10 to 15 percent in eight to twelve weeks in untrained adults, more than steady training alone over the same period. Shorter intervals of 30 seconds to a minute also work and are easier for people with joint limitations.

Gains come fastest in the least fit, which is the group that needs them most. A 50 year old who moves from 28 to 35 has, in risk terms, taken about a decade off.

When to check first

Adults with known heart disease, chest pain with exertion, or uncontrolled blood pressure should see a clinician before starting hard intervals. For everyone else, the advice is to build the moderate base first, then add intensity. The same rule about progression that applies to running applies here: fitness improves in weeks, tendons in months.

Why Ribbon Checkup covers it

Most health numbers describe a risk. This one describes a capacity, and it is one of the few that can be changed substantially by the person who owns it, at any age, with no prescription. It belongs in a home health log next to blood pressure and weight, and for most adults it is the number with the most room to move.

By the Ribbon Health Press editorial team. Reviewed against current clinical guidelines at publication. Report an error: editors@ribboncheckup.org. See our editorial policy.