VO2 max (cardio fitness)

VO2 max is the most oxygen your body can use during hard exercise, in millilitres per kilogram per minute. It's one of the best single measures of aerobic fitness, and it tends to fall with age unless you train.

Where Soma gets it

Apple Watch estimates it during outdoor walks, runs and hikes, when your heart rate rises enough. Apple calls it Cardio Fitness. Garmin, Polar and others estimate it too. A lab test on a treadmill is the only direct measure.

Getting a reading

• Walk briskly, run or hike outdoors for 20 minutes or more, with GPS, on fairly flat ground.
• Start the workout on your watch.
• Keep your age, sex, height and weight up to date in the Health app.

How to read it

Watch the trend over months more than the number on a given day. Regular cardio, especially some easy Zone 2 work and some harder efforts, moves it up.

It shows in Longevity > Body, at the top and under Fitness.