What's your VO₂ max?

VO₂ max is how much oxygen your body can use at full effort. Higher cardiorespiratory fitness is linked to lower rates of heart disease and early death in large population studies — in the Norwegian HUNT study, each extra 3.5 mL/kg/min was associated with about 21% lower risk of cardiovascular death.

That's an association across populations, not a prediction about you. This test can't tell you anything about your health, and it isn't medical advice.

The good news is that it moves. Most people who train it deliberately for 12 weeks gain a few points, though some gain little — response varies a lot between individuals.

Field tests estimate; they don't measure. The Cooper test correlated about r = 0.90 with lab treadmill testing in its original study, and the Rockport walk about R = 0.88. A correlation describes how well an equation tracked a group — it does not tell you how close your own number is, which can be further off.

Where each test applies. The walk test was validated on adults aged 30–69 and is too easy to be useful if you are already fit; published guidance subtracts about 6 mL/kg/min for ages 18–24. Outside 30–69, treat a walk result as rough. Both tests depend on pacing and on going genuinely hard.

Comparisons only work against the same test. A Cooper result isn't comparable to a Rockport result, to a lab test, or to your watch's estimate. If you retest later, repeat the same test on the same route.

Intervals are the strongest single lever, and the weekly aerobic volume around them is what lets you repeat them. A common session is the Norwegian 4×4: after a 10-minute warm-up, four 4-minute efforts at 90–95% of max heart rate, each followed by 3 minutes easy.

Two hard sessions a week is plenty for most people, never on back-to-back days, with the rest of the week genuinely easy.

If you have not trained in a while, don’t start here. Build 2–4 weeks of easy aerobic work first, then begin with shorter efforts — three 3-minute intervals rather than four 4-minute ones.