We know our cholesterol. We know our blood pressure. Increasingly, there is another number worth knowing, and unlike your age, it is one you may be able to meaningfully change.
It is called VO₂ max, and while the term sounds like something reserved for Olympic training centers, it is becoming increasingly relevant to anyone interested in staying energetic, capable and healthy for decades to come.
VO₂ max is a measure of aerobic capacity: the maximum amount of oxygen your body can take in, transport and use during intense exercise. The “V” refers to volume, O₂ is oxygen, and “max” means maximum. It is commonly expressed as milliliters of oxygen used per kilogram of body weight per minute.
Think of it as a measure of your body’s oxygen-delivery system. Your lungs bring oxygen in. Your heart and blood vessels transport it. Your muscles extract and use it to produce energy. How well those systems work together is central to cardiorespiratory fitness, or CRF, the broader measure of your ability to sustain physical activity.
And that makes this far more interesting than a bragging right for runners.
The American Heart Association has argued that cardiorespiratory fitness is important enough to be considered a clinical vital sign, noting that it provides information about health risk beyond traditional factors. Higher cardiorespiratory fitness is strongly associated with lower cardiovascular and all-cause mortality.
One striking study published in JAMA Network Open examined more than 122,000 adults who underwent exercise treadmill testing. Higher cardiorespiratory fitness was associated with progressively lower long-term mortality, with no observed upper limit of benefit.
Another study, published in the Journal of the American College of Cardiology, followed more than 4,000 apparently healthy men and women for an average of 24 years. Cardiorespiratory fitness was measured directly through cardiopulmonary exercise testing, and greater fitness was associated with lower risk of death from all causes, cardiovascular disease and cancer.
The encouraging part? You do not need to become an endurance athlete to benefit.
In fact, the American Heart Association notes that more than half of the reduction in all-cause mortality associated with increasing fitness occurred between the least-fit group and the next fitness category. In other words, moving from low fitness to somewhat fitter may matter enormously.
So how do you improve it?
Start by moving with more intention. Brisk walking, hiking, cycling, swimming and running can all challenge the cardiovascular system. Build a foundation of regular aerobic exercise, then occasionally ask your body to work harder.
Intervals can help. Depending on your fitness level, that might mean alternating several minutes of brisk walking with short uphill efforts, or incorporating harder intervals into cycling, swimming or running. The objective is not to make every workout punishing. It is to progressively challenge the heart, lungs and muscles, then allow them to recover.
And that distinction matters, particularly for women accustomed to believing that exercise only “counts” when it leaves them exhausted. Fitness is built through challenge and recovery. Consistency matters more than theatrics.
VO₂ max can be measured most precisely during a cardiopulmonary exercise test, while many fitness devices provide estimates. Either way, the goal is not to collect another number to obsess over.
It is to build a body with a larger capacity for living.
Because perhaps the most compelling thing VO₂ max can tell us is not how fast we can run.
It is how much engine we have for everything else.