VO2 max explained: what the number means and how to improve it

VO2 max is the most oxygen your body can take in and use during hard exercise, usually given in millilitres per kilogram of body weight per minute. It is one of the best single measures of aerobic fitness, and it can be estimated reasonably well without a laboratory. The VO2 max calculator gives three field estimates; this guide explains what the number means, how good those estimates are and what actually moves it.

What VO2 max measures

When you exercise harder, your muscles need more oxygen, so your heart pumps faster, your breathing deepens and your muscles extract more oxygen from the blood. At some point oxygen use stops rising even as the effort increases: that ceiling is your VO2 max. It depends on how much blood your heart can pump, how much oxygen your blood can carry, and how well your muscles use it. Because it is divided by body weight, two people with the same heart and lungs will have different VO2 max values if they weigh different amounts.

VO2 max also connects to METs, the unit used for exercise intensity: one MET is set at 3.5 ml/kg/min, so a VO2 max of 35 means you can briefly work at about 10 times your resting rate.

Typical values

Figures vary with age, sex and training, but rough reference points are:

• average untrained healthy men: about 35 to 40 ml/kg/min;
• average untrained healthy women: about 27 to 31 ml/kg/min;
• elite distance runners: up to about 85 for men and 77 for women, with some elite cross-country skiers and cyclists above 90.

Women's values average lower partly because of differences in body composition and blood haemoglobin, not effort. VO2 max also declines gradually with age, which is why fitness charts are split into age bands. Compare yourself with people of your own age and sex, or better, with your own earlier results.

How it is measured and estimated

The direct measurement is a laboratory exercise test on a treadmill or bike while wearing a mask that analyses your breath, continued until exhaustion. Field tests estimate it from simpler measurements, and the calculator offers three:

• The Cooper test: run as far as you can in 12 minutes. The estimate is (metres covered minus 504.9) divided by 44.73, so 2,400 m gives about 42.
• The Rockport walking test: walk one mile as fast as you can, then note your time and heart rate at the finish. It also uses age, sex and weight, and suits people for whom a hard run is not appropriate.
• The resting heart rate ratio from Uth and colleagues: maximum heart rate divided by resting heart rate, multiplied by 15.3.

Smartwatches estimate VO2 max from heart rate and pace data during runs, using their own proprietary models.

How accurate the estimates are

Field estimates can easily be 10 percent or more away from a lab result. The Cooper test depends on pacing a 12-minute effort well, and on running economy, which varies between people. The Rockport test assumes an all-out walk. The heart rate ratio method was developed in well-trained men aged 21 to 51 and works best with a measured maximum heart rate; with the age-based estimate the calculator uses by default, 208 minus 0.7 times age, the error can be large, and later research suggests the 15.3 factor overestimates for many untrained people. The value of any of these tests is in repeating the same one under similar conditions and watching the trend. Resting heart rate: what is normal, how to measure it and why it changes covers how to take the resting reading properly.

How to improve it

VO2 max responds to training, particularly in people starting from a low base, though how much it improves varies widely between individuals and genetics set much of the ceiling. The mainstream approach combines:

• Regular aerobic volume: mostly easy running, cycling, swimming or brisk walking several times a week.
• Hard intervals once or twice a week, such as three to five minutes at a hard effort with equal recovery, which push the heart close to its maximum. The interval timer handles the timing.
• Losing excess body fat, which raises the per-kilogram figure even if the heart is unchanged.

The heart rate zones calculator shows the zones for easy and hard work, and Heart rate zones explained: how they're calculated and what each one trains explains how to use them. Check with a doctor before an all-out test or hard intervals if you have a heart condition, symptoms such as chest pain, or have been inactive for a long time.

Why it matters for health

Cardiorespiratory fitness is strongly linked to long-term health. Large observational studies find that people with higher fitness have lower rates of cardiovascular disease and death from all causes, and in 2016 the American Heart Association recommended that fitness be assessed routinely as a clinical vital sign. These studies show association rather than proof that raising one number causes the benefit, but they support the same advice either way: regular activity that makes you breathe hard does more than most single health habits. VO2 max is not the whole picture for racing, though; running economy and how long you can hold a high fraction of your maximum matter too, which is why actual race results, used by the race time predictor, are often a better guide to performance.