VO₂ Max Explained: What It Is, Why It Matters & How to Improve It

Your VO₂ max is the single best number you have for how well your body moves oxygen. It predicts long term health more strongly than your cholesterol, your blood pressure or your weight, and unlike your age it is something you can change.

Most people arrive here wanting one thing first: is my number any good. So that is where we start.

What counts as a good VO₂ max

VO₂ max is measured in millilitres of oxygen per kilogram of body weight per minute, written as mL/kg/min. A "good" score is always relative to your age and sex, because both change the expected range substantially.

The tables below come from the Fitness Registry and the Importance of Exercise National Database, known as FRIEND. It is the reference standard used by the American College of Sports Medicine, built from 16,278 treadmill tests across 34 laboratories. The numbers are percentiles, so the 50th column is the median for that age and sex, and the 90th column is the score you would need to sit in the top ten percent.

VO₂ max percentiles for men (mL/kg/min)

VO₂ max percentiles for women (mL/kg/min)

Source: Kaminsky et al., Mayo Clinic Proceedings, 2022. Treadmill values. Cycle testing produces lower numbers for the same person, typically by ten to twenty percent, so compare like with like.

How to read your own number

Find your age row, then your sex, then see which columns your score falls between. A 42 year old woman at 30.0 is sitting on the 70th percentile, which means she is fitter than roughly seven in ten women her age. The same score in a 27 year old woman would place her below the median.

That relativity is the point. Chasing an absolute number you read somewhere is how people end up discouraged by a score that is actually strong for them, or complacent about one that is not.

What VO₂ max actually measures

Oxygen has to travel a long way to do anything useful. You breathe it in, your lungs move it into your blood, your heart pumps that blood out, your vessels deliver it, and your working muscles pull it out and burn it for fuel. VO₂ max is the ceiling on that whole chain, measured at the point where working harder stops producing more oxygen uptake.

For most people the limiting step is the heart, specifically how much blood it can push out per beat. That is why endurance training works: a heart that has been asked to move a lot of blood, repeatedly, gets better at moving blood. Your muscles adapt too, building more capillaries and more mitochondria, but the central pump does most of the heavy lifting on the way up.

This also explains why VO₂ max is expressed per kilogram. Oxygen delivery is shared across whatever mass you are carrying, so two people with identical hearts will score differently if one is heavier.

Why the number matters beyond performance

If VO₂ max only told you how fast you could run, it would be a niche metric for endurance athletes. What has changed the conversation is how strongly it tracks with long term mortality.

The largest study on this followed 122,007 adults who underwent treadmill testing at the Cleveland Clinic, with a median follow up of 8.4 years. After adjusting for age, sex, body mass index, existing heart disease, diabetes, smoking and medication use, the people in the lowest fitness group had roughly five times the risk of death during follow up compared with the elite group.

The comparison that tends to land hardest is with the risk factors people already take seriously. In that same analysis, being in the below average fitness band rather than the above average band carried a hazard ratio of 1.41. Smoking carried 1.41. Diabetes carried 1.40. Coronary artery disease carried 1.29.

Two things are worth saying plainly about that. This is observational data, so it shows association rather than proof that raising your VO₂ max causes you to live longer. And fitness is partly inherited, so some of the gap reflects genetics rather than training. What the researchers did find, across the full range, was no upper limit at which further fitness stopped being associated with benefit.

What happens to VO₂ max as you age

In the FRIEND data, median VO₂ max falls by about 13.5 percent per decade, which works out at roughly 4 mL/kg/min every ten years. A man at the median drops from 46.5 in his twenties to 29.2 in his fifties.

The slope is real, but it is not fixed. A large part of the population decline is not ageing itself, it is the activity that quietly disappears between your twenties and your fifties. Look across the tables again: a 55 year old man at the 90th percentile scores 43.4, which is higher than the median 30 year old. Training does not stop the decline, but it can move you up a band or two, and a band is worth more than a decade.

How VO₂ max is measured, and how far to trust your watch

The reference method is a graded exercise test with a mask, where the air you breathe out is analysed directly. You run or cycle at increasing intensity until you cannot continue. It is accurate, it takes about an hour, and it usually costs somewhere between one hundred and three hundred dollars in Australia.

Everything else is an estimate. Your Apple Watch, Garmin, WHOOP or Fitbit infers VO₂ max from the relationship between your heart rate and your pace during outdoor activity, then fits that to a model.

Those estimates are useful, but they are not the same thing, and it is worth knowing the size of the gap. A 2025 validation study compared Apple Watch estimates against laboratory measurement in thirty participants. The watch underestimated VO₂ max by an average of 6.07 mL/kg/min, with a mean absolute percentage error of 13.3 percent. The limits of agreement ran from 6.11 below to 18.26 above, meaning individual readings varied considerably in both directions.

The practical read: treat the absolute number from your watch as approximate, and treat the trend as meaningful. If your estimate climbs from 38 to 42 over four months of consistent training, the direction is real information even if neither figure would survive a lab test. What you should not do is compare your watch estimate against a friend's lab result, or against the tables above, and draw firm conclusions.

A field test you can do without equipment

The Cooper test is the simplest option. Warm up, then cover as much distance as you can in twelve minutes on a flat course, and record the distance in metres. Your estimate is that distance minus 504.9, divided by 44.73.

Someone covering 2,400 metres lands on 42.4 mL/kg/min. It is still an estimate, and it depends heavily on pacing and motivation, but repeated on the same course a few months apart it will tell you whether you are moving.

How to actually improve it

This is where most advice goes vague. The useful research here is a 2007 trial that put 40 moderately trained men through eight weeks of running, three sessions a week, with four different protocols and total work equated between them.

Source: Helgerud et al., Medicine & Science in Sports & Exercise, 2007.

The result that surprises people is the top two rows. Moderate continuous running, for the same total work, produced no significant change in VO₂ max over eight weeks. Time spent close to your ceiling is what raises your ceiling.

A few caveats before you throw out your easy runs. This was one study in moderately trained men over eight weeks. Easy aerobic work builds the base that lets you tolerate hard intervals, supports recovery, and carries its own health benefits. And if you are starting from a low base, almost anything will raise your VO₂ max at first, because the limiting factor is simply that your heart has not been asked to do much.

What a week might look like

For someone training three to four times a week and wanting to move their number:

• One session of 4 x 4 minute intervals at an effort you could hold for about five minutes if forced, with three minutes easy between. Warm up properly first, it takes longer than you think to reach that intensity safely.

• One shorter interval session, either 15/15s or 30/30s, which delivers similar stimulus with less accumulated fatigue.

• One or two easy aerobic sessions where you can hold a conversation. This is the volume that makes the hard days repeatable.

• Strength work stays in the week. It does not raise VO₂ max directly, but it protects the joints doing the running.

Give it eight to twelve weeks before you judge it. Meaningful change in this metric is measured in months, and a watch estimate that jumps three points in a fortnight is noise rather than adaptation.

Why two people doing the same program get different results

Response to endurance training varies widely between individuals, and a meaningful share of that variance is genetic. Some people gain very little from a program that transforms someone else. That is not a discipline problem and it is not a reason to stop, but it is a reason to measure your own trend rather than compare yourself to whoever posted their numbers online.

Where your own data comes in

A VO₂ max estimate on its own is a number on a screen. What makes it useful is context: whether you are recovered enough to do the interval session today, whether your sleep supported the work you did yesterday, whether the trend over three months is moving.

hlth. coach reads your wearable, health and body composition data daily and adapts your training, nutrition and recovery around what your body is actually doing. If your recovery is down, the hard session moves. If the trend is flat, the program changes. That is the difference between tracking a number and training on it.

The short version

• VO₂ max is your ceiling for oxygen use, in mL/kg/min, and it is only meaningful against your own age and sex.

• Use the FRIEND percentile tables above rather than a single "good" number.

• Low fitness carries a mortality association comparable to smoking or diabetes in the largest study to date, though this is association rather than proof of cause.

• Median VO₂ max falls about 13.5 percent per decade, and training moves you up the bands rather than stopping the slope.

• Your watch underestimates by around 6 mL/kg/min on average. Trust the trend, not the digit.

• Intervals near your ceiling raise your ceiling. Moderate continuous work, on its own, did not.

Common questions

What is a good VO₂ max?

There is no single good score. VO₂ max is only meaningful against your own age and sex. Using the FRIEND reference standards, the median for a man in his forties is 35.3 mL/kg/min and for a woman in her forties 25.7. Anything at or above the 70th percentile for your age and sex is strong.

What is a good VO₂ max by age?

It falls steadily. Median values for men run from 46.5 mL/kg/min in the twenties to 20.6 in the seventies. For women, 36.6 down to 17.2. The full percentile tables for both sexes are in the charts above, so you can place your own number rather than compare against a single figure.

How much does VO₂ max decline with age?

About 13.5 percent per decade in the FRIEND data, which works out at roughly 4 mL/kg/min every ten years. Training does not stop the decline, but it moves you up the percentile bands. A 55 year old man at the 90th percentile scores higher than the median 30 year old.

Is the VO₂ max on my watch accurate?

Treat it as approximate. A 2025 validation study found Apple Watch underestimated VO₂ max by an average of 6.07 mL/kg/min, with a mean absolute percentage error of 13.3 percent. The trend over months is useful information. The individual number is not precise enough to compare against a lab result.

How do I improve my VO₂ max?

Time spent near your ceiling is what raises your ceiling. In an eight week trial, 4 by 4 minute intervals at 90 to 95 percent of maximum heart rate raised VO₂ max by 7.2 percent and 15/15 intervals by 5.5 percent, while moderate continuous running at matched total work produced no significant change.

How long does it take to improve VO₂ max?

Give it eight to twelve weeks before you judge a program. Meaningful change in this metric is measured in months. A watch estimate that jumps three points in a fortnight is noise rather than adaptation.

Sources

• Kaminsky LA, Arena R, Myers J, et al. Updated Reference Standards for Cardiorespiratory Fitness Measured with Cardiopulmonary Exercise Testing: Data from the Fitness Registry and the Importance of Exercise National Database (FRIEND). Mayo Clinic Proceedings, 2022;97(2):285 to 293.

• Mandsager K, Harb S, Cremer P, Phelan D, Nissen SE, Jaber W. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Network Open, 2018;1(6):e183605.

• Helgerud J, Høydal K, Wang E, et al. Aerobic High-Intensity Intervals Improve VO₂max More Than Moderate Training. Medicine & Science in Sports & Exercise, 2007;39(4):665 to 671.

• Lambe R, O'Grady B, Baldwin M, Doherty C. Investigating the accuracy of Apple Watch VO₂ max measurements: A validation study. PLoS One, 2025;20(5):e0323741.

This article is general information, not medical advice. If you have a heart condition, or you have been inactive for a long time, speak to your doctor before starting high intensity interval training.