What VO2max is, and why it matters

What it measures

VO2max (maximal oxygen uptake) is the highest rate at which your body can take in oxygen and use it to make energy during hard exercise. It is usually written in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min), so people of different sizes can be compared. Higher is better.

What limits it is mostly delivery: how much oxygen-rich blood your heart and lungs can get to working muscle. When people train and their VO2max goes up, the main change is that the heart can pump more blood per minute at its maximum, rather than muscles pulling more oxygen out of each liter of blood¹.

Why it matters for performance

VO2max sets the upper limit for endurance. It is not the whole story, though. How efficiently you move (running economy) and how close to your VO2max you can work for a long time also decide how fast you go. The pace you can hold at your lactate threshold brings all three together, and it is the best single predictor of distance running performance¹. That is why good programs train both: a higher ceiling, and the ability to work close to it.

Why it matters for health

Fitness measured on a treadmill is one of the strongest predictors of how long people live. A meta-analysis of 33 studies and about 100,000 people found that each step up in fitness of one MET (roughly 3.5 ml/kg/min of VO2max) went with a 13% lower risk of death from any cause and a 15% lower risk of heart disease events².

A Cleveland Clinic study of 122,007 patients who did a treadmill test found that people in the lowest fitness group had about five times the risk of death over the follow-up period compared with the fittest group. Low fitness carried as much risk as smoking, diabetes or coronary artery disease, or more³.

It declines with age

VO2max falls throughout adult life. In a study that tested the same people repeatedly over about eight years, the decline was 3% to 6% per decade in people's 20s and 30s, and sped up to more than 20% per decade from their 70s⁴. Building it while you can, and keeping it, gives you more room before everyday activities start to feel hard.

How to find yours

The most accurate measurement is a lab test on a treadmill or bike while breathing into a mask. A simpler field estimate is the Cooper test: run as far as you can in 12 minutes. In its original study, the distance covered tracked closely with VO2max measured on a treadmill⁵. You can take the Cooper test here, with GPS or a lap counter, and save your results to see how they change. Our VO2max Engine program uses it in Week 1 and Week 8. Smartwatch numbers are estimates too; use them to watch the trend rather than the exact value.

How to raise it

Regular aerobic exercise raises VO2max, and harder interval work tends to raise it a little more⁶. As a floor, the American College of Sports Medicine recommends at least 150 minutes of moderate or 75 minutes of vigorous aerobic exercise a week for adults⁷. The next articles cover three ways to train it:

• Running to increase VO2max: intervals, easy running, and a sample week.
• Tabata intervals: what the original study did, and what most classes do.
• Kettlebell circuits: what the evidence does and does not support.