VO2 max: what it is and how to improve it

VO2 max is among the best-known measures in endurance training, but also among the most confusing. In this article, we explain in plain language what this number actually measures, why genetics sets a ceiling on how much you can raise it and how sensible training can still help you improve.

What VO2 max actually tells you

The textbook definition is the maximum volume of oxygen your body can take up, in milliliters per kilogram of body weight per minute — abbreviated as ml/kg/min. This is the amount of oxygen your body can take up when your heart and lungs are working at their limit.

Many definitions online describe it as the amount of oxygen a person “can use”. That wording is misleading. It can easily suggest that the problem lies in the cells — as though the blood delivers enough oxygen to their doorstep, but the cells simply cannot take it in.

In reality, it is the other way around. Your lungs draw in more air than you will ever need. Your muscle cells use oxygen as soon as it arrives. The bottleneck lies between them — in the transport capacity of your blood and heart. At a given stroke volume and heart rate, your heart can only pump a certain amount of blood, and that is what limits how much oxygen reaches your muscles each second.

The simple truth is that VO2 max does not show how well your cells take up oxygen, but how much oxygen your blood can carry from your lungs to your cells. That is precisely why it is described as an oxygen uptake ceiling — the limit comes from transport capacity, not the cells’ appetite for oxygen.

What limits VO2 max

The first limiting factor is genetics. The size of your heart, the thickness of your left ventricular wall, the amount of hemoglobin in your blood and the density of the capillary network in your muscles are all largely inherited. Estimates of heritability vary between studies: they usually range from 30 to 60 percent, with some experts suggesting as much as 80 percent.

What does that mean in practice? If your current value is, for example, 45 ml/kg/min, good, consistent training might get you to 54 ml/kg/min. That is slightly above average for a healthy adult. It will not take you to the top of world sport — Lance Armstrong once recorded 84 ml/kg/min, while Norwegian cross-country skier Bjørn Dæhlie recorded 96 ml/kg/min. Even so, the improvement realistically available to you is already substantial.

The second limiting factor is age. After the age of 25–30, VO2 max gradually begins to decline without training. Training can slow that decline considerably and, in some cases, reverse it. In Estonia, it is not unusual for a 50-year-old recreational runner to record better values than many sedentary people in their 20s.

The third factor is sex and body build. Women have a lower average value — not because they are “worse”, but because hemoglobin levels and cardiac stroke volume differ physiologically. Men and women show the same percentage improvement in response to training.

How to improve VO2 max

The classic formula still works: 3–5 workouts a week, lasting at least 20 minutes without a break, at 65–85% of your maximum heart rate. This is the range that increases the size of your heart and makes your capillary network denser.

Interval training builds on that foundation. Short, hard efforts — for example, 4 × 4 minutes at a hard pace, with 3 minutes of easy effort between them — force your heart to beat at a rate you would never reach on an easy run. Finnish and Norwegian coaches have used this format for decades, and the results speak for themselves.

Here is what to do each week:

• A long, steady session 1–2 times a week (at 60–70% of maximum heart rate), lasting 60–120 minutes. This lays the foundation for fat burning, growth in blood volume and vessel capacity, and mental endurance.
• Tempo training at your anaerobic threshold (around 80–85% of maximum heart rate) 1–2 times a week, for 20–40 minutes continuously or broken into intervals.
• 1 really hard interval workout a week — these are the efforts that count when it comes to raising your VO2 max ceiling.
• 1–2 days a week of complete rest or gentle activity to aid recovery. Without rest, you will not improve, however motivated you are.

Training experience makes a difference: beginners see the fastest increase in their first 6–12 months, sometimes gaining 15–20%. After that, each additional percentage point takes more work. For an elite athlete, the difference between peak season and the period between seasons may be just a couple of percent — but that small margin is what decides the finishing order.

Anaerobic threshold — just as important as VO2 max

VO2 max alone will not win you a race. Dr. Stephen Seiler has illustrated it this way: a high value is like an invitation to the grand ball. Having an invitation on paper does not mean you will actually make it onto the floor and dance with the most beautiful woman. For that, you need another measure — your anaerobic threshold.

Your anaerobic threshold is the intensity at which your body starts producing more lactate than it can clear. Above that point, the pace starts to “burn”, and before long you have to slow down, whether you want to or not.

An untrained person reaches their anaerobic threshold at just 60% of their maximal oxygen uptake. This means that even with a high theoretical ceiling, much of that capacity goes unused. Effective training can shift the threshold to 70–80%, while elite endurance athletes can reach close to 85%.

What does this mean in practice? If you feel you have no more room to improve your VO2 max, it often makes more sense to focus on how much of that capacity you can actually use while running or cycling. Raising your anaerobic threshold often does more for your race results than chasing those last few ml/kg/min.

Another important detail: your anaerobic threshold is specific to your sport. A cyclist’s anaerobic threshold on the bike does not transfer directly to running. If your goal is to improve your half-marathon time, cycling training alone will not be enough — you need to run. There will certainly be some carryover, but it will never be complete.

How VO2 max is measured

The most accurate measurements are taken in a sports laboratory using a breathing mask and gas analyzer, either on a treadmill or a cycle ergometer. Several sports medicine centers and university exercise physiology laboratories in Tallinn and Tartu offer this test. Including preparation and recovery, the test takes about 1 hour and costs about as much as a mid-range smartphone.

Estimates from heart rate watches (Garmin, Polar, Apple Watch) have become fairly reliable. They do not measure VO2 max directly, but calculate it from your heart rate, pace and submaximal exercise. They are perfectly adequate for tracking trends and comparing your fitness over the years. There is little point in taking the watch’s absolute value too seriously — a laboratory test may give a result 5–10 units higher or lower.

FAQ

What is a good VO2 max?

Typical adult men have a VO2 max of 35–45 ml/kg/min, while women typically fall within 30–38 ml/kg/min. Recreational endurance athletes often reach 50–60, and well-trained club athletes reach 60–70. Above 70, you are entering semi-elite territory, where athletes compete for podium places at the Estonian championships.

How quickly does VO2 max improve?

Beginners can see the first changes after 4–6 weeks. A 10–15% increase over 6 months is entirely realistic with consistent training. Progress slows after that, and training quality starts to matter more than volume.

Can you trust your heart rate watch’s estimate?

For tracking trends, definitely. If the number on your watch rises by a few units over several months, that is a fairly accurate reflection of your actual fitness. Treat the absolute figure with caution — a laboratory test will often give a different number, but the watch and laboratory trends usually move in the same direction.

Translated by: Janar Rückenberg

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