Cardiorespiratory Fitness: Why VO2 Max Is the Ultimate Longevity Marker

If doctors could only measure one thing to predict how long you'll live, a good case could be made for cardiorespiratory fitness. It's not as famous as cholesterol or blood pressure, but study after study shows it's one of the most powerful health markers we have.

What VO2 max actually is

VO2 max is the maximum amount of oxygen your body can take in, deliver and use during hard exercise. It's usually expressed in millilitres of oxygen per kilogram of body weight per minute (ml/kg/min). A higher number means your heart, lungs, blood vessels and muscles are working well together.

Think of it as the size of your engine. A bigger engine makes everyday tasks — climbing stairs, carrying shopping, chasing a bus — feel easier, because they use a smaller share of your total capacity.

Why it predicts longevity so well

A large 2018 study from the Cleveland Clinic followed more than 120,000 adults who had completed treadmill tests. People in the lowest fitness group had a much higher risk of death than those in the highest group. The researchers noted that poor fitness carried a risk comparable to, or greater than, well-known risk factors such as smoking and diabetes. Importantly, they found no upper limit: the fittest people had the lowest death rates.

Higher fitness is linked with lower rates of heart disease, stroke, type 2 diabetes, some cancers and dementia. It also reflects many other healthy systems at once, which is why it works as a kind of summary score for the body.

How VO2 max changes with age

Without training, VO2 max typically declines by around 10% per decade after the age of 30, and the decline can speed up in later life. Part of this is unavoidable: maximum heart rate falls with age. But a large share is due to inactivity and loss of muscle — things we can influence.

Well-trained older adults often have the fitness of inactive people decades younger. In that sense, VO2 max is a very real measure of "fitness age."

How to measure it

• Lab test: The gold standard is a graded exercise test on a treadmill or bike while wearing a mask that analyses your breath.
• Wearables: Many smartwatches estimate VO2 max from heart rate and pace during outdoor walks or runs. They aren't perfectly accurate, but they're useful for tracking trends over time.
• Field tests: Simple tests, such as how far you can walk or run in 12 minutes (the Cooper test), give a rough estimate.

How to improve it

The good news: VO2 max responds to training at any age, and the biggest gains go to people starting from a low base.

• Build a base with easy cardio. Brisk walking, cycling, swimming or jogging at a pace where you can still talk. Aim for at least 150 minutes a week.
• Add some intervals. Once or twice a week, include short bursts of harder effort. A popular approach is four rounds of four minutes hard, followed by three minutes easy.
• Be consistent. Fitness gains fade within weeks if you stop. Regular, moderate training beats occasional heroic efforts.
• Keep your muscles strong. Strength training supports the muscles that use oxygen and helps you keep moving as you age.
• Lose excess weight gradually if needed, since VO2 max is measured relative to body weight.

If you have heart disease or other health conditions, check with your doctor before starting high-intensity training.

Key takeaways

• VO2 max measures how efficiently your body uses oxygen during exercise.
• Low fitness is one of the strongest predictors of early death — on par with smoking.
• VO2 max declines with age, but training can slow that decline dramatically.
• Steady cardio plus a little interval training is the most effective way to raise it.