VO2 max is the maximum amount of oxygen your body can take in and use during intense exercise. It is usually expressed in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min), and it is one of the most widely used measures of cardiorespiratory fitness.
What Does VO2 Max Measure?
Using oxygen takes teamwork. Your lungs bring air in, your heart and blood vessels deliver oxygen to your muscles, and your muscles use it to produce energy. VO2 max reflects how well that whole chain works together at peak effort, which is why it says so much about overall fitness.
How Is VO2 Max Tested?
The most accurate way is a graded exercise test with breath analysis. You wear a mask connected to a metabolic analyzer while exercising on a treadmill or bike. The intensity increases every minute, and the analyzer measures the oxygen you use with every breath until you reach your peak.
Smartwatches and fitness apps estimate VO2 max from heart rate and pace. Estimates are useful for spotting trends, but a breath-based test measures it directly, and also shows your fuel use, breathing pattern and personal training zones.
What Affects Your VO2 Max?
- Training: the factor you can change most
- Age: VO2 max tends to decline gradually with age, and staying active slows that decline
- Genetics: some people start higher or respond faster to training
- Sex and body composition: which is why results are compared with age- and sex-matched norms
- Altitude, sleep and recovery: all affect how you perform on test day
Can You Improve VO2 Max?
Yes. VO2 max is trainable at any age. A mix of steady aerobic work in the right zones and well-dosed high-intensity intervals is the core of most programs. Breathing efficiency and respiratory muscle strength play a supporting role, especially near your limits.
The key is knowing what is holding you back. Two people with the same VO2 max can be limited by different things, which is why the full breakdown from a test matters more than the single number.
Why It Matters Beyond Sport
VO2 max is not only for athletes. Large studies have linked higher cardiorespiratory fitness with better long-term health outcomes. Read more in VO2 Max and Longevity: What the Research Says.
This article is for general education and is not medical advice. Talk to your physician before starting a new exercise program or testing.
Know Your Numbers
A Metabolic & Respiratory Health Assessment measures your VO2 max, resting metabolism and breathing in one visit.