how to add Apple Watch as data source for cardio fitness

Hi peschafer,

As long as your Apple Watch is paired with your iPhone, it is a data source but it won’t show up as one. Adding a data source would be a 3rd party app that’s also tracking your workouts. See: Manage Health data on your iPhone, iPod touch, or Apple Watch - Apple Support

If you are having trouble with your cardio fitness levels on your Apple Watch, review "How Apple Watch estimates your cardio fitness levels" in Track your cardio fitness levels. From this article, you can check the following:

• As seen here, make sure you have an Apple Watch Series 3 or later.
• As the Apple Watch takes into account your age, sed, weight, height and medications, make sure your health profile is set up: Use the Health app on your iPhone or iPod touch.
• Make sure both devices are up to date.

Also note:

It can take at least 24 hours of wearing your Apple Watch, followed by several Outdoor Walk, Outdoor Run, or Hiking workouts* and passive measurements with your Apple Watch before you receive an initial estimate.

Take care.