Cardio Fitness Score is a more user-friendly name for VO2 Max, a universal and established metric of fitness based on how much oxygen your body can transfer to your blood.
How to Check Your Cardio Fitness (VO2 Max) on an Apple Watch
Which Apple Watch Models Can Check VO2 Max?
The Apple Watch has lagged behind sports watches (like Garmins) in how it displayed your cardio fitness. With the watchOS 7.2 update, which was released on December 14, 2020, the Apple Watch can now track your VO2 max.
The Watch has actually been able to do this for a while, but it’s been a hidden option tucked away in the Health and Fitness apps. However, with the update, it’s now front and center. You can see how you stack up against other people your age, and you can get notifications if your cardiovascular fitness is low.