VO2 Max Explained: What It Is and How to Improve It

VO2 max is the maximum amount of oxygen your body can take in and use during intense exercise. It is one of the best single measures of cardiorespiratory fitness. Higher values are associated with better endurance performance and, in large studies, with lower risk of death from many causes.

How It Is Measured

The most accurate measurement uses a lab test on a treadmill or bike, with a mask analysing your breathing as exercise gets progressively harder. Fitness watches estimate VO2 max from heart rate and pace data. Those estimates can be useful for tracking trends but may be off for individuals.

It is usually expressed in millilitres of oxygen per kilogram of body weight per minute (ml/kg/min).

What Affects It

• Genetics: a significant part of VO2 max and how much it responds to training is inherited.
• Age: it gradually declines with age, but training slows that decline substantially.
• Training: both endurance volume and high-intensity work improve it.
• Body composition: because it is expressed per kilogram, losing fat can raise the number.

How to Improve It

• Build an aerobic base: regular easy cardio — two to four sessions per week — raises VO2 max, especially in untrained people.
• Add high-intensity intervals: efforts at around 90 to 95 percent of maximum heart rate are particularly effective. A classic example is 4 rounds of 4 minutes hard with 3 minutes of easy recovery.
• Be consistent: improvements come over weeks and months of regular training.

How Fast It Changes

Untrained people often see meaningful improvements within two to three months of consistent training. Already fit people improve more slowly. Fitness drops relatively quickly when you stop, so consistency matters.

Beyond the Number

VO2 max is a useful marker, but not the whole picture. Strength, muscle mass, mobility and how you feel day to day matter too. Use it as one tool among many. For a lower-intensity approach to aerobic fitness, read zone 2 cardio explained.