VO2 max: what is it, and how do you improve it?

The short answer: you improve your VO2 max by combining two ingredients — a big base of easy endurance work (the famous zone 2) and short high-intensity intervals, such as 4 × 4 minutes. VO2 max is your maximum capacity to take in and use oxygen during hard exercise. The higher it is, the bigger your engine.

And it's not just about athletic performance: VO2 max is one of the best measurable predictors of longevity and health we know of. People with a high VO2 max live longer on average, and in better shape. It's one of the few metrics that's truly worth pushing up.

What is VO2 max, exactly?

Think of your body as a car. VO2 max is the size of the engine: the maximum flow of oxygen your lungs, heart and muscles can process at full load. It's measured in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min). As a rough order of magnitude, a sedentary adult sits around 30-35, a trained recreational athlete easily tops 45-50, and elite athletes approach 70-85.

Smartwatches give you an estimate based on your heart rate and your paces. It's imperfect as an absolute value, but useful for tracking your trend over several months — the only thing that really matters here.

How to improve VO2 max: the two levers

There's no shortcut: VO2 max is trained from both ends, and it's the combination that pays off.

• The aerobic base, at low intensity. The bulk of your volume, in zone 2. It expands your network of blood vessels, multiplies your mitochondria and improves your heart's ability to pump — the floor everything else rests on.
• High-intensity intervals. The best-documented protocol is the 4 × 4: 4 minutes at 90-95% of your max heart rate (you can only get out a few words), followed by 3 easy minutes, the whole thing repeated 4 times. In a 2007 Norwegian trial (40 moderately trained men, 8 weeks), it raised VO2 max by 7.2%, more than the same amount of work run at a moderate pace or at threshold.

One or two interval sessions a week, on top of a solid endurance base, are enough. Piling on intensity without a base is the surest way to plateau and burn out — hence the importance of sticking to a training frequency your recovery can handle.

Why is VO2 max such a strong predictor of health?

A high VO2 max isn't just an athlete's number: it shows that your heart, lungs and muscles work well together. It's a summary of the health of your whole cardiovascular system — the same system that protects you from the most common diseases. A 2009 meta-analysis (33 studies, 102,980 participants) puts numbers on what's at stake: each extra MET of capacity — the equivalent of running 1 km/h (about 0.6 mph) faster — is associated with 13% lower mortality, and low capacity with a 40% higher risk of death than intermediate capacity. That's no reason to obsess over it, but it explains why the American Heart Association has argued since 2016 for making it a clinical vital sign, just like blood pressure: it considers it potentially a stronger predictor of mortality than smoking or hypertension.

How long does it take to improve VO2 max?

Months, not weeks. A beginner can make clear gains in 8 to 12 weeks of consistent training; the fitter you are, the harder you have to work for each gain. It's a long game, but the progress is very real and it sticks as long as you keep training.

A word on how much room you have: part of your VO2 max is genetic, and so is your response to training. But everyone improves with structured training: in a 2017 study of 78 adults, the “non-responders” to 6 weeks of endurance training all improved once the dose was increased. Genetics set your starting point, not your ability to improve.

VO2 max and age: it declines, but stays trainable

VO2 max declines with age, and faster and faster: in the Baltimore Longitudinal Study of Aging (810 adults followed for nearly 8 years), the decline goes from 3 to 6% per decade between ages 20 and 40 to more than 20% per decade after 70, active people included. Training doesn't erase it, but it lets you start from higher up, and VO2 max can be improved at any age: in people over 60, a meta-analysis of 41 trials (2,102 participants) found an average gain of 16% with endurance training. An active person in their 60s can therefore have a higher capacity than a sedentary person in their 30s.

Key takeaways

• VO2 max = your maximum capacity to use oxygen, and one of the best predictors of longevity and fitness.
• You improve it by combining a zone 2 base with hard intervals (such as 4 × 4 minutes), over months.
• It declines with age, faster and faster, but stays trainable for life: training lets you start from higher up.