Apple has a fitness feature that allowsApple Watchusers to track their cardio fitness levels through VO2 max measurements.
Before the release of watchOS 7.2 which arrived at the end of 2020, the Apple Watch could estimate higher levels of VO2 max, but only for outdoor walks, runs, or hikes.

Assuming your smartwatch is running watchOS 7.2 or later, Apple Watch can now determine your cardio fitness as you walk throughout the day though, so you don’t need to intensely exercise for it to take and analyse your cardio fitness level.
Apple Watch Series 8
The Apple Watch Series 8 has a great design, heaps of sensors, and more features than you’ll probably know what to do with. Its battery life isn’t the best on the smartwatch market, but fast charging makes it easy to charge daily and the fitness features are superb.
What is VO2 Max?
VO2 max, or maximal oxygen uptake, is the measurement of the maximum amount of oxygen a person can use during intense exercise. It’s basically a measurement used to determine the endurance of a person prior to - or during - the course of training, and it can be improved through physical activity.
Apple notifies Apple Watch users' when their cardio fitness levels are either high, above average, below average, or low (in comparison to other people in their same age/sex group). Before it will do that though, the “Cardio Fitness Level” feature needs to be set up in the Apple Health app oniPhone.
How to setup Cardio Fitness Level on Apple Watch
Here’s how to setup the Cardio Fitness Level feature on Apple Watch:
And that’s it!
Once setup, the Apple Watch will take cardio fitness measurements whether you’re on an outdoor run or a walk, and all the results will be pulled together and viewable inside the Apple Health app.
There are multiple factors that can lower cardio fitness levels, such as pregnancy and lung and heart conditions, but if your cardio fitness levels should dip low, and if notifications are enabled, the Apple Watch will send notifications with recommendations on how to improve it.
Want to know more?
The Apple Watch Series 6, Series 7,Series 8andWatch Ultraare all capable ofmonitoring blood oxygen levelstoo. Read our separate feature on how to get a reading if you have a Watch Series 6 or newer. We also have anApple Watch tips and tricks featurethat will give you details on all the features Apple Watch offers and how you go about finding them and setting them up.