Cardio Fitness + Widgets allows you to track your cardio fitness on your home and lock screen

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.

VO2 readings from your Apple Watch, those manually logged in the Health app or a third party app will be automatically available in the app, home screen and lock screen widgets.