VO2 max is the amount of oxygen your body can use when you exercise your hardest. It shows how fit your heart and lungs are. It is measured in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min), and a higher number means better aerobic fitness.
Where your number comes from
A true VO2 max is measured in a lab, with a mask, on a treadmill or bike, to exhaustion. Apple Watch estimates it instead, from your pace and heart rate during outdoor walks, runs and hikes, and saves the estimate in Apple Health.
Kiiro shows those Apple Health values directly. It does not replace them with its own.
How to read it
- Look at the trend over months, not a single reading. One value can be off; the direction rarely is.
- Expect it to move slowly. A steady rise over a training block means the work is paying off.
- Compare yourself with yourself. Values differ with age and sex, and Kiiro tells you where yours sits for your age group.
More: Why is my VO2 max not updating on Apple Watch? and Why is my VO2 max lower on Apple Watch than on Garmin?
Related terms
- Resting heart rate: Resting heart rate is the number of times your heart beats in one minute when you are calm and not moving. A lower value usually means a fitter heart.
- HRV (heart rate variability): HRV is the small changes in time between each heartbeat. It shows how well your body can handle stress and recover.
- Zone 2: Zone 2 is easy aerobic effort, the pace at which you can still hold a conversation. In a five-zone model it is 60 to 70% of your maximum heart rate.
