What is a good VO2 max? What the number means, by age and sex

Short answer

There is no single good VO2 max. The number only means something within your age and sex band — 40 ml/kg/min is above average for a 50-year-old man and unremarkable for a 25-year-old. The reference charts everyone quotes come from over 80,000 lab treadmill tests, and your watch is not running that test.

If your watch has told you your cardio fitness is "low" and you felt sick about it, that is not your fault and the number deserves less weight than it was given. It is an estimate produced from wrist data, shown against a chart built from something quite different.

Note: this article explains a fitness measurement and is not medical advice. A low estimate is not a diagnosis. Breathlessness that is new, worsening, or out of proportion to what you are doing needs a clinician rather than a training plan.

What VO2 max actually measures

The maximum amount of oxygen your body can take in and use during hard exercise, expressed in millilitres of oxygen per kilogram of body weight per minute — ml/kg/min.

Three systems have to work together for that oxygen to get where it is needed: lungs to bring it in, heart and blood to carry it, muscle to use it. VO2 max is a single number describing the ceiling of that whole chain, which is why it is treated as the headline measure of cardiorespiratory fitness rather than of any one organ.

The per-kilogram part matters and is often missed. Because body weight is in the denominator, losing weight raises the number without any change in the engine, and gaining weight lowers it. That is not cheating — carrying less mass genuinely costs less oxygen per kilometre — but it means a change in your number does not always mean a change in your fitness.

How it is properly measured: a maximal exercise test, usually on a treadmill, wearing a mask that analyses the gas you breathe out. You exercise until you cannot continue. That is where the reference numbers come from, and it is not what any wearable does.

What counts as good, by age and sex

The reference standards most widely used come from the Cooper Institute's Aerobics Center Longitudinal Study — more than 80,000 adults who completed maximal treadmill tests with direct gas analysis. They are published as percentile tables in ACSM's Guidelines for Exercise Testing and Prescription, broken down by sex and five-year age band.

The categories — poor, fair, average, good, excellent, superior — are always read inside one age-and-sex bracket. That single fact resolves most of the confusion around this metric.

Some anchor figures from those standards:

And roughly where "good" begins for men across the decades: about 46 in the twenties, 42 in the forties, 35 in the sixties.

Two patterns worth reading off this.

Women's thresholds sit about 10 to 15% below men's at every age. This is physiology — differences in haemoglobin, heart size and body composition — not a difference in effort or training, and comparing across sexes tells you nothing useful.

The bar drops with every decade. VO2 max declines with age in almost everyone, so a number that is merely average at 25 is genuinely good at 55. This is why a 50-year-old man at 40 ml/kg/min sits above the 75th percentile for his age while the same number in a 25-year-old is ordinary.

For the full percentile table by five-year band, the ACSM guidelines are the source — and they are worth looking at directly rather than through a blog's redrawn version, because the redrawn ones frequently drop the age bands.

Why your watch number is not the chart number

This is the mismatch that causes most of the distress, and it is not talked about enough.

The chart was built from maximal lab tests with gas analysis. A mask, a treadmill, exercise to exhaustion, actual oxygen measured.

Your watch estimates. It infers VO2 max from heart rate during exercise, pace or power, your age, sex and weight — using a model, without measuring oxygen at all. It works best when you do steady outdoor running or brisk walking with good GPS and heart rate data, and progressively worse the further your activity is from that.

Which means:

The absolute value is soft. Watch estimates tend to sit within a reasonable range of a lab test for many people and can be meaningfully off for others, particularly if your heart rate response is atypical, you are on beta-blockers, or your training is mostly cycling, swimming or lifting.

Comparing your watch number to a percentile chart mixes two measurements. You are reading an estimate against a table built from direct measurement, and the category you land in may not be the category a lab would give you.

The trend is still useful. If the same device, using the same model, shows your estimate rising over months, something real is probably improving. That comparison is internally consistent even when the absolute value is not accurate — the same logic that applies to Body Battery, wrist temperature and every other modelled number.

If your watch says your cardio fitness is low and you want to know whether that is true, the answer is a proper test, not a different app.

Why VO2 max falls with age — and how much is avoidable

The decline is real, and the usual framing hides something useful.

Roughly 10% per decade is the figure commonly quoted for untrained adults from around the thirties onwards, accelerating somewhat later in life. That happens through several mechanisms at once: maximum heart rate falls with age, the heart's stroke volume declines, muscle mass reduces, and the small blood vessels and mitochondria in muscle become less efficient.

But a large share of that is disuse rather than ageing. People who keep training hard lose the number much more slowly, and the gap between a trained and untrained 60-year-old is far larger than the gap between a trained 30-year-old and a trained 60-year-old. Maximum heart rate does fall regardless of what you do — that part is not negotiable — but most of the rest responds to what you ask of it.

Which is why the age-banded chart is the honest way to read this. The alternative, comparing yourself to your own twenties, is both discouraging and uninformative. What matters is where you sit among people your age, and whether the direction is up or down.

The practical version: a decline that tracks the expected slope is ordinary. A decline noticeably steeper than that, without a change in training, is the one worth asking about — and it is also the one a wearable trend can plausibly show you, since it is a comparison against your own past rather than against a table.

Does VO2 max actually matter?

More than most fitness metrics, and this is where the evidence is genuinely strong rather than merely suggestive.

The largest study of its kind followed 122,007 adults who underwent exercise treadmill testing, with a median follow-up of 8.4 years and 13,637 deaths across 1.1 million person-years. Cardiorespiratory fitness was inversely associated with long-term mortality, and the association held across age, sex, body mass index and existing illness.

The size of the association: roughly 13 to 15% lower mortality risk per 1-MET improvement, where 1 MET is about 3.5 ml/kg/min. And notably, the researchers found no point at which the benefit stopped — the fittest group had the best survival, with no observed ceiling.

Two honest caveats about what that does and does not show.

This is association, not proof of cause. People with higher fitness differ in many ways from people with lower fitness, and a treadmill-tested population is not a random sample of everyone.

But the size and consistency are unusual. The relationship appears across large cohorts, in different populations, and the dose-response shape is what you would expect if it were causal. It is among the more robust findings in preventive cardiology, which is why VO2 max is taken seriously as a health marker and not just an athletic one.

The practical translation is modest and worth keeping: moving from the bottom category towards the middle is where most of the benefit lives. The gain from "low" to "below average" is larger than the gain from "excellent" to "superior."

Why two people with the same number are not equally fit

The single figure hides three quite different things, and knowing which one is yours changes what to do about it.

The heart's side. How much blood is pumped per beat and per minute. This is the part most people picture, and it is the part that responds to sustained hard aerobic work over months.

The delivery side. Haemoglobin carrying the oxygen, and the density of small vessels feeding the muscle. Anaemia lowers VO2 max directly for reasons that have nothing to do with training, which is one of the more common non-fitness explanations for a disappointing number.

The muscle's side. Mitochondrial density and the enzymes that use the oxygen once it arrives. This is where a great deal of trained adaptation actually lives, and it is largely invisible from outside.

Two consequences worth carrying.

The same number can have different fixes. A sedentary person and someone with untreated iron deficiency can land on the same value; training helps the first and does almost nothing for the second until the iron is addressed.

And the number does not describe your limits. VO2 max is a ceiling. What you can actually do depends much more on how much of that ceiling you can hold for an hour — which is trainable, improves long after VO2 max plateaus, and is why people keep getting faster with a flat number.

What a low reading actually means

Not a verdict, and worth unpacking before you act on it.

It might be accurate and expected. Low cardiorespiratory fitness is common, it responds to training, and it is the most changeable item on most people's health list.

It might be a measurement artefact. Not enough qualifying workouts, mostly indoor or non-running activity, poor heart rate contact, a wrist device on a loose band, or an activity type the model handles badly.

It might be medication. Beta-blockers cap heart rate, which breaks the assumption the estimate is built on. Several other drugs affect heart rate response. The watch does not know you take them.

It might be something worth checking. Persistent unexplained low fitness, particularly if it has fallen noticeably without a change in training, has medical explanations — anaemia, thyroid problems, lung disease, heart conditions, long COVID. This is the one case where the number is a reason to make an appointment rather than a training plan.

And it might be that you are unfit and can change it. Which is the most common answer, and the most actionable.

How to raise it

The short version: you have to go hard sometimes. VO2 max responds to intensity in a way it does not respond to volume alone.

Intervals at high intensity are the most efficient stimulus — repeated hard efforts of a few minutes with recovery between. This is the part most people skip, and it is the part that moves the number.

A base of easy aerobic work underneath it. Intensity without volume stalls, and volume is also where most of the cardiovascular benefit accumulates.

Consistency over months. Meaningful change takes weeks to months, and the first improvements come fastest to the least fit — which is encouraging if you are starting low.

Body composition affects the number through the per-kilogram denominator, which means weight change moves it without the engine changing. Worth knowing so you interpret a jump correctly.

And a caveat that matters more than it sounds: if you have a condition where exertion provokes a delayed worsening — ME/CFS, long COVID with post-exertional malaise — none of the above applies to you, and high-intensity intervals are actively harmful. Improving VO2 max is not a universal goal, and chasing this number is the wrong objective in energy-limiting conditions.

Where VO2 max is the wrong thing to look at

It has become the fashionable number, which means it now gets applied to situations it does not fit.

If exertion makes you worse a day or two later. In ME/CFS and long COVID with post-exertional malaise, the whole logic of pushing to a maximum is inverted. A VO2 max estimate in that context is not a target to raise — and the two-day exercise testing used in research on that condition exists precisely because performance drops on the second day. Chasing this number there causes harm.

If you are training for something specific. VO2 max is a ceiling, not a predictor of performance. Two runners with the same value can be minutes apart over ten kilometres, because what fills the gap is how much of that ceiling you can sustain — the threshold — plus economy and pacing. Athletes past the beginner stage usually stop gaining much VO2 max and keep improving anyway.

If your device barely has the data. Two indoor cycling sessions a month is not enough for the model, and the number it shows you is closer to a guess than an estimate. Low confidence looks identical to a low value on the screen.

If you are recovering from illness or heavily sleep-deprived. The estimate reflects your current state, and a transient dip is not a change in fitness.

And if the number has become a source of anxiety. That happens with this metric more than most, because it has been marketed as a longevity score. It is one marker among several, it is estimated rather than measured, and checking it weekly tells you nothing that checking it quarterly would not.

How to bring this up with your doctor

Bring the trend and the context, not a single reading. "My estimated VO2 max has fallen from around 38 to around 30 over eight months without a change in my training" is a useful sentence. "My watch says 30" is not.

Say it is a wearable estimate. Being upfront that this is a modelled number, not a lab test, makes the conversation more productive rather than less.

Mention your medication list, beta-blockers especially, because they change what the estimate means.

Pair it with symptoms. Breathlessness climbing stairs, needing to stop where you did not before, fatigue out of proportion. The symptoms are what a clinician can act on; the number is supporting evidence.

Ask about a proper test if it matters. A cardiopulmonary exercise test measures rather than estimates, and it is the right answer when the question is clinical rather than curious.

And take new or worsening breathlessness seriously regardless of what any device says. That symptom has a differential that includes things worth finding early.

How Welltory helps — and what it cannot do

The limit first. Welltory does not measure VO2 max and does not run a cardiopulmonary exercise test. Nothing on a wrist does — every consumer VO2 max figure, ours or anyone's, is a model output rather than a measurement of oxygen.

What it does is work with the signals that sit underneath cardiorespiratory fitness and change sooner than it does. Resting heart rate, heart rate variability and how quickly your heart rate falls after exercise all respond to training within weeks, while a VO2 max estimate moves slowly and noisily. Read against your own months of history, they tell you whether the training is landing well before the headline number does.

Two honest caveats, the same as everywhere in this category. These signals are non-specific — they shift with illness, alcohol, heat and poor sleep as readily as with fitness, so a change says something is different rather than what. And none of it diagnoses anything: Welltory is a general wellness product with no regulatory clearance.

A record of how your body is responding, not a score for how fit you are.

How we made it

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Data analysis by Jane Smorodnikova, co-founder of Welltory and the person who built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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