About cardio fitness
Cardio fitness is a measurement of your VO2 max, which is the maximum amount of oxygen your body can consume during exercise. Your cardio fitness level is a strong indicator of your overall physical health and a predictor of your long-term health. Your Apple Watch gives you a cardio fitness estimate by measuring how hard your heart is working during an outdoor walk, run, or hike.
If your cardio fitness levels are low for your age and sex, you'll receive a notification. If your cardio fitness levels continue to remain low, you'll receive additional notifications.
Most people can improve their VO2 max by increasing the intensity and frequency of their cardiovascular exercise. Certain conditions or medications that limit your heart rate might cause an overestimation of your VO2 max.
View your cardio fitness data
- Open the Health app on your iPhone, then tap Browse.
- Tap Heart, then tap Cardio Fitness.
- Tap D, W, or Y to view your average for the Day, Week, or Year.
- Tap Show All Cardio Fitness Levels.
- Tap a cardio fitness level to compare your results to other levels based on your age and sex.
You can also tap the "i" icon to view the average cardio fitness levels for all ages for Female, Male, or All.
How Apple Watch estimates your cardio fitness levels
Apple Watch Series 3 or later can record an estimate of your VO2 max using the heart and motion sensors during an outdoor walk, run, or hike. It can also estimate your VO2 max if you start an outdoor walk, run, or hike in the Workout app. Apple Watch supports a VO2 max range of 14-60 mL/kg/min that is validated for users 20 years or older.
To estimate your cardio fitness level, your Apple Watch also takes into account your:
- Medications that might affect your heart rate
It can take at least 24 hours of wearing your Apple Watch, followed by several workouts* and passive measurements with your Apple Watch before you receive an initial estimate.
If the Health app detects that your previous cardio fitness estimates could be more accurate, you'll have the option to update your data. In Cardio Fitness, tap Update under Update Your Data. After you update, the Cardio Fitness Data Updated notification shows you the results of the update and how your estimates changed.
* Push workouts are not supported.