VO2 Max by Age: What Is a Good Number?

A watch shows you a number called VO2 max, or cardio fitness, and then says nothing useful about it. People arrive at a search box holding that number and one question: is it bad?

Here is what it is, what the bands actually are, and how much of it is yours to change.

What VO2 max measures#

VO2 max is the most oxygen your body can take in and use in a minute of all-out effort, divided by your body weight. The units are millilitres of oxygen per kilogram of body weight per minute, written ml/kg/min.

Three things set it. Your lungs have to move the oxygen in. Your heart has to pump it around, which is mostly about how much blood leaves the heart with each beat. Your muscles have to pull it out of the blood and burn it, which depends on how many small blood vessels and how much mitochondria they contain.

Of those three, the lungs are almost never the limit in a healthy person. The ceiling is the heart and the muscle, which is why VO2 max is really a measure of your cardiovascular system rather than your breathing.

It is a capacity, not a symptom. A low number does not mean you are ill. It means that if you had to run up two flights of stairs carrying a suitcase, you would be closer to your limit than someone with a higher one.

Why anyone cares about it#

Fitness is one of the strongest single predictors of dying early that has been measured. In large studies that put people on a treadmill and then follow them for decades, the lowest-fitness group dies at a much higher rate than everyone else, from all causes and not only from heart disease.

The shape of that relationship is the part worth knowing. The step from the bottom fifth to the next fifth up is bigger than every step after it combined. Going from unfit to moderately fit buys most of the benefit. Going from good to elite adds very little on top.

That matters because it changes the target. The goal is not to chase an impressive number. It is to not be in the bottom group.

The bands, by age and sex#

These are directional bands, rounded from published population norms. Different charts and laboratories place the boundaries a point or two apart, so read a number near a boundary as sitting in both bands.

Men, ml/kg/min

Women, ml/kg/min

Women sit six to eight points below men at the same age, mostly because of body composition and blood haemoglobin, not effort or training.

In METs, if your report uses those#

Exercise reports from a hospital treadmill test often give METs rather than ml/kg/min. One MET is 3.5 ml/kg/min, so divide by 3.5 to convert.

How much your watch really knows#

No consumer watch measures oxygen use. A real test needs a mask, a treadmill or bike, and a gas analyser.

What a watch does is simpler and cleverer than it sounds. It knows your pace from GPS and your heart rate from the wrist, and it knows that fitter people move faster at any given heart rate. Feed enough of those pairs into a model with your age, sex and weight, and you get an estimate.

That estimate behaves in predictable ways:

Read the trend, not the reading. A number that moves from 34 to 37 over four months on the same watch, the same routes and the same weather is real information. A number that changes by two points between Tuesday and Thursday is not.

What actually raises it#

Three things move VO2 max, in this order of reliability.

More easy aerobic minutes. The unglamorous base. Most of the adaptation that raises VO2 max, more blood plasma, more capillaries around the muscle, more mitochondria, comes from accumulated time at a pace where you could still hold a conversation. The public guidance of 150 minutes a week of moderate activity is roughly the dose where this starts to show.

One harder session a week. Intervals raise the ceiling in a way that easy work alone does not: four to six efforts of two to four minutes, hard enough that talking is broken, with equal easy recovery between them. One such session a week on top of the base is enough for most people. Two is the point of diminishing returns for anyone who is not an athlete.

Losing excess fat. VO2 max is divided by weight, so the number rises as weight falls even if nothing about the heart changed. This is real in the sense that everything does get easier, and misleading in the sense that it is not new cardiovascular fitness.

What does not raise it: supplements, breathing gadgets, altitude tents used casually, and sitting in a sauna. Heat and altitude do produce adaptations under structured protocols in trained athletes, which is a long way from a weekly sauna visit.

What I get asked most#

The question is almost always some version of "my watch says 32, should I be worried?"

Usually the answer is no, and the more useful question is what it was six months ago. A 32 that used to be 28 is a person doing well. A 32 that used to be 40 is a person whose life changed, and the change is normally an injury, a new job with a commute, a new baby, or a stretch of illness. None of those need a doctor. They need the base rebuilt.

The version that does need a doctor is different, and it comes with a symptom rather than a number: breathlessness that arrived over weeks, on effort that used to be fine. That is not a fitness question. A number falling in step with a life that got busier is ordinary. A number falling while nothing else changed, in someone who feels short of breath, is worth a conversation.

At work#

Physically demanding work does not reliably build VO2 max, which surprises people who are on their feet all day. The pattern that raises fitness is sustained effort at a decent intensity. The pattern of most manual work is short bursts, static holding and long low-level activity, often with a load. People finish tired without having trained.

Shift work makes it worse in two ways. Short sleep blunts training adaptation, so the same sessions produce less. And the hours make regular sessions hard to hold, which matters more than the sessions being perfect.

For anyone on rotating shifts, the version that survives contact with a real roster is short and frequent: twenty minutes, three or four times a week, at whatever hour is actually free, rather than an hour-long plan that collapses in week two.

When the number is a medical question#

A low VO2 max on its own is a fitness finding. It becomes a medical question when it arrives with something else:

• Breathlessness at rest, or on mild effort that used to be easy
• Chest pain, tightness or pressure with exertion
• Swelling in both ankles, or waking breathless at night
• Fainting or near-fainting with exercise
• A resting heart rate that has risen and stayed risen

Those are reasons to be examined rather than to train harder. In a clinic the question would not be your watch number; it would be your heart, your haemoglobin, your thyroid and your lungs, in roughly that order.

The bottom line#

VO2 max is a good measure of something that matters, reported to you by a device that can only estimate it. Use the bands to find out whether you are in the bottom group, because that is the group with everything to gain, and then ignore the exact figure. The way out of the bottom group is ordinary: more easy aerobic minutes most weeks, one harder session, and enough sleep to absorb both. The number will follow, and so will the thing the number is standing in for.