¿Qué es el VO₂ máximo?
VO2 max is the maximum rate at which your body can take in oxygen, move it to your working muscles, and use it to produce energy. It is reported in millilitres of oxygen per kilogram of body weight per minute, which is why it is written as a number that means nothing in isolation.
The important word is maximum. VO2 max is a ceiling — not a speed, not a time, not a performance. It describes the size of your aerobic engine, and says nothing about how much of that engine you can hold open for an hour.
What the number actually describes
Getting oxygen from the air into a muscle fibre is a chain, and VO2 max is limited by its narrowest link:
- Your lungs move air in and transfer oxygen into the blood.
- Your heart pumps that blood. How much it shifts per beat is the biggest determinant for most people, and one of the most trainable links in the chain.
- Your blood carries oxygen on haemoglobin, so its carrying capacity caps delivery.
- Your muscles extract that oxygen and use it in their mitochondria. Endurance training increases both the capillaries supplying them and the mitochondria inside them.
Because body weight sits in the denominator, the figure also moves when your weight does, with no change to your heart, lungs or muscles at all.
What VO2 max does not tell you
This is the section most explainers skip, and it is the most useful thing on this page.
Two athletes with the same VO2 max can finish a long race many minutes apart. Not seconds. Minutes. The reason is simple once you see it: almost no endurance event is run at your ceiling. A race longer than a few minutes is run at some sustainable fraction of it, and that fraction varies enormously between people who share a ceiling.
So the ceiling is one input among several, and rarely the one that separates athletes of similar standard.
| Quality | What it governs | Does VO2 max capture it? |
|---|---|---|
| Aerobic ceiling | The absolute upper limit of your oxygen use | Yes. This is exactly what it measures |
| Lactate threshold | The fraction of that ceiling you can hold in a steady state, and therefore your sustainable race pace | No. Two athletes with the same ceiling can have very different thresholds beneath it |
| Economy | How much oxygen you need for a given pace. Better economy means a faster pace at the same cost | No. A less efficient runner needs more of their ceiling to hold the same speed |
| Durability | Whether your threshold and economy still hold up late in a long event | No. A resistance-to-fatigue quality, invisible to a maximal test |
| Fuelling and pacing | Whether you arrive with anything left, and whether you spent your effort evenly | No. The most common reasons a well-trained athlete has a bad race |
Four of the five things that decide a race are not in the number. That is not an argument for ignoring VO2 max, but it is an argument against using it as your progress tracker — the fuller version of that case is in why lactate threshold beats VO2 max for performance gains.
Why it flattens out
VO2 max responds well to training from a low base. Consistent aerobic work produces real gains in the first months, which is why beginners see the number climb and find it motivating.
Then it flattens. In a well-trained endurance athlete it sits close to a plateau, and further improvement in performance comes from the other four rows of that table. Which produces a frustrating, completely normal outcome: you can take minutes off a race time over a season while your VO2 max stays where it was. The number has not failed. It is correctly reporting a quantity that did not change.
Your lactate threshold does change over that same season, on a timescale of weeks, which is what makes it the more useful thing to train against.
A lab measurement and a watch estimate are not the same number
These two share a name and should not share your confidence.
A laboratory test measures the gas you breathe. You wear a mask connected to an analyser, run or ride a protocol that gets harder until you cannot continue, and the equipment compares the oxygen going in with the carbon dioxide coming out. The result is a measurement of your actual oxygen consumption, with a technician watching the criteria that confirm a genuine maximum.
A watch estimate measures nothing of the kind. It infers. Because how fast you move at a given heart rate says something about your aerobic capacity, a sports watch collects pace-and-heart-rate pairs from your runs, extrapolates towards your pace at maximum effort, and converts that into an oxygen figure. Clever and useful — but it inherits every error in its inputs, above all a wrong stored maximum heart rate. It also needs the right kind of run to work from, so plenty of your training produces no estimate at all.
The practical consequences:
- As a trend for one person under consistent conditions, an estimate is reasonable. That is the use it is fit for.
- As an absolute value, hold it loosely. It is an inference from two variables, and a lab test is the only thing that measured you.
- For comparing yourself with other people, it is close to worthless. You would be comparing two calculations built on different settings, different sensors and different terrain, not two athletes.
If your watch's figure is moving in a direction that makes no sense, the cause is almost always a data problem rather than a fitness one. How Garmin's VO2 max estimate works and why it drifts covers the specific causes there, and how heart rate zones are anchored explains why a wrong maximum propagates so widely.
One safety note: a true VO2 max protocol is an all-out effort to exhaustion, and it is supervised for a reason. This is not medical advice. If you have any cardiac history, any symptoms during exercise, or you are returning from illness, speak to a doctor before maximal testing of any kind.
Frequently asked questions
What is a good VO2 max?
Good compared with what — because the raw figure is meaningless without a reference. The useful comparison is against population norms for your age and sex, since values typically differ between men and women at the same training standard and decline with age in almost everyone. A figure that is unremarkable at twenty-five can be excellent at fifty-five.
Is VO2 max the best measure of fitness?
It is the best single measure of your aerobic ceiling, and a poor measure of endurance performance. Among athletes of similar standard, race results track the sustainable fraction of that ceiling — threshold, economy and durability — far more closely than they track the ceiling itself.
Can you improve your VO2 max?
Yes, and substantially so if you are starting from a low base, through consistent aerobic training plus harder work near the top of your aerobic range. The gains slow considerably once you are well trained, at which point performance improves through threshold and economy instead.
Is the VO2 max on my watch accurate?
Treat it as a trend, not a measurement. It is estimated from the relationship between your pace and your heart rate rather than measured from your breath, so it is only as good as its inputs — a wrong maximum heart rate, a bad heart rate trace, hills, heat or a treadmill will all distort it.
Does VO2 max decline with age?
Generally yes, in almost everyone, which is why it is graded against age norms rather than read in absolute terms. Continued endurance training slows the decline, so a trained older athlete can hold a value well above the norm for their age group.
Do I need a VO2 max test?
Only if you want to know your ceiling. For deciding what to actually do in training, a lactate threshold test is the more useful purchase, because it returns a pace and a heart rate you can train at rather than a ceiling you never visit.
Train the fraction, not the ceiling
A ceiling you cannot race at is interesting; the share of it you can hold is what decides your finish time. Lactate Training builds and adapts your plan around zones anchored to your lactate threshold rather than an estimate, using the Garmin and Strava activities you already record.