VO2max is the maximum rate at which your body can take in, transport and use oxygen during intense exercise. It is usually expressed relative to body mass as milliliters of oxygen per kilogram per minute: ml/kg/min.

In simple terms, it describes the size of one part of your aerobic engine. A high VO2max is clearly useful in endurance sport. All else being equal, a larger aerobic capacity gives an athlete more potential to produce energy aerobically.

But runners are never equal in all the other things that determine performance.

A useful way of thinking about endurance performance is as the interaction of several qualities.

This is why VO2max matters physiologically but is not a ranking system for runners. Two athletes can have the same measured VO2max and produce very different race performances because one may be more economical, sustain a greater proportion of VO2max, or retain those qualities better as fatigue accumulates.

The size of the engine matters. So does what you can do with it.

This is where much of the confusion starts. The number displayed on your watch looks like the physiological measurement described above, so it is very easy to assume VO2max has actually been measured.

It hasn't.

A laboratory VO2max test measures respiratory gases during a maximal exercise test. A running watch cannot measure oxygen consumption. It estimates VO2max from things it can observe, particularly the relationship between running speed and heart rate, combined with the manufacturer's algorithm.

That estimate can still be useful, particularly as a long-term trend, but individual error can be meaningful. Anything that changes the relationship between pace and heart rate can potentially affect what the algorithm sees: heat, fatigue, terrain, hydration, illness, cardiac drift, heart-rate measurement error and changes in running economy.

That also means the estimate partly reflects how efficiently you produce running speed at the intensities and in the conditions the watch observes. It cannot fully separate aerobic capacity from everything else affecting the pace-to-heart-rate relationship.

A watch therefore gives us an estimate of VO2max, not VO2max itself.

These three numbers may look related, but they answer different questions.

The distinction matters. The laboratory measures one physiological characteristic. The watch tries to estimate that characteristic. The race result tells us what happened when the entire system had to perform.

A 2021 study by Anders Aandstad compared 3000 m performance with directly measured treadmill VO2max in 259 adults. The relationship was strong enough to produce prediction equations linking average 3000 m speed with measured VO2max.

Why is 3000 m interesting? It is long enough for aerobic capacity to matter enormously, but short enough that fueling and long-duration durability contribute relatively little. It is still not a purely aerobic event: a meaningful anaerobic contribution remains, which is one reason some runners can outperform what their VO2max alone might suggest.

You still have to turn that aerobic capacity into running speed through economy, threshold, pacing and the ability to tolerate the effort.

That makes the 3000 m useful here. It sits somewhere between the laboratory and the road: not a replacement for measuring VO2max, but a simple way of asking how effectively a runner is converting aerobic capacity into performance.

There is an important limitation. The Aandstad study contained 229 men and only 30 women, and the sex-specific regression equations were different. I don't think that is strong enough evidence to turn those differences into a general claim about how men and women convert VO2max into running speed.

For our purposes, a broad span is more useful and more honest than separate male and female predictions.

Do not use this table backwards as a VO2max calculator.

The ranges below are deliberately broad. They use the published regression equations simply to give some context for the VO2max values associated with different 3000 m performances.

The highest directly measured VO2max in the study was 68.7 ml/kg/min in the men and 52.2 in the women. The fastest male 3000 m was 10:08 and the fastest female performance was 12:22.

Once we move toward 9-minute 3000 m performances, we are therefore moving to the edge of, or beyond, the population from which the equations were derived. Treat the fast end of the table as context rather than a validated conversion.

This is the part I find most useful as a coach.

Suppose your watch says your VO2max is 50. The interesting question is not whether the "correct" value should really be 49, 50 or 51. A better question is whether your running performance broadly makes sense alongside that estimate.

If it does, fine. If it doesn't, the mismatch gives us something useful to investigate.

Perhaps the watch estimate is distorted. Perhaps running economy is limiting performance. Perhaps the athlete has a relatively large aerobic engine but has not yet developed the threshold capacity needed to use enough of it. Perhaps they are simply under-trained for the distance, the 3000 m was badly paced, or the conditions were poor.

Or perhaps something genuinely interesting is happening in the relationship between physiology and performance.

The point is not that the 3000 m is a better VO2max test. It answers a different question: what can the whole runner currently produce?

The direction of the mismatch can also give us a clue about where to look.

Watch VO2max high, 3000 m relatively slow: perhaps the athlete is not yet converting aerobic capacity into performance particularly well. Threshold development, economy at higher speeds, speed endurance, pacing and simple familiarity with racing hard are all possible explanations.

Watch VO2max low, 3000 m relatively fast: perhaps the runner is unusually economical, has a useful anaerobic contribution over 3000 m, or regularly trains in conditions that make the pace-to-heart-rate relationship look worse to the watch, such as heat or hills.

Neither diagnosis is automatic. The value is that the mismatch gives us somewhere to start looking.

There is a substantial inherited component to aerobic capacity. Research including the HERITAGE Family Study has shown that both baseline VO2max and the response to a standardized endurance-training program cluster within families. In HERITAGE, the heritability of the VO2max training response was estimated at around 47%.

That does not mean that 47% of your personal VO2max is genetic and the remaining 53% is available to train. Heritability is a population statistic.

The practical message is simpler: people start from different places, and they do not all respond to the same training by the same amount. VO2max is therefore neither destiny nor a completely malleable fitness score. It can improve, sometimes substantially, but both the starting point and the response to training vary between individuals.

Which is another reason not to turn a single VO2max number into a judgment about the athlete.

Notice it, but don't chase it.

A sustained trend can be useful supporting information, particularly when it agrees with what is happening in training and performance. A movement of one or two points over a few runs is not something I would change training around.

In the Norwegian Singles Project, VO2max is not one of our anchors. We are much more interested in your actual running performance, whether you can execute the sessions at the intended pace and effort, how pace, heart rate and perceived effort relate to one another, and whether those relationships improve over time.

If the watch VO2max rises as well, that is interesting. It is not the objective.

Performance first. What can you actually run? A 3000 m or 5 km result is an observed performance, not an algorithmic estimate.

Watch VO2max second. Use it as another piece of information and perhaps as a long-term trend, not as an objective score.

Use the gap. If the estimate and the performance do not seem to agree, that creates a useful coaching question rather than a problem.

Measure it if VO2max itself matters. If we genuinely need to know your physiological VO2max, the appropriate tool is a laboratory test.

VO2max is interesting and it matters, but it is still only one part of endurance performance. Your watch is trying to estimate that one part of the machinery. Your running tells us what the whole system can currently produce.

Aandstad A. Estimation of maximal oxygen uptake from the 3000 m run in adult men and women. Journal of Sports Sciences. 2021.

Bouchard C et al. Familial aggregation of VO2max response to exercise training: results from the HERITAGE Family Study. Journal of Applied Physiology. 1999.

Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. Journal of Physiology. 2008.

Maunder E, Seiler S, Mildenhall MJ, Kilding AE, Plews DJ. The importance of 'durability' in the physiological profiling of endurance athletes. Sports Medicine. 2021.

Systematic review and meta-analysis literature on wearable VO2max estimation generally supports reasonable group-level validity while showing potentially meaningful individual-level error.