Cardio fitness notifications are available today on Apple Watch

 Apple Watch can monitor and classify cardio fitness, a strong predictor of overall health

A low cardio fitness classification is displayed in the Health app on iPhone 12 while a low cardio fitness notification is displayed on Apple Watch Series 6.

Apple Watch users can now view how their cardio fitness level is classified based on their age group and sex in the Health app on iPhone, and receive a notification if it falls within the low range.

With iOS 14.3 and watchOS 7.2, Apple Watch users can view their cardio fitness level in the Health app on iPhone, and receive a notification on Apple Watch if it falls within the low range. Breakthrough technology released in watchOS 7 allows Apple Watch to easily measure low cardio fitness, and today cardio fitness notifications empower users to be more active for dramatic long-term health benefits.

Cardiorespiratory fitness, as measured by VO2 max, is the maximum amount of oxygen the body can use during exercise, and it can be increased through physical activity. Apple Watch already estimates average and higher levels of VO2 max during vigorous outdoor walks, runs, or hikes, which many runners and other athletes monitor to improve performance.

Now, with watchOS 7, Apple Watch uses multiple sensors, including the optical heart sensor, GPS, and the accelerometer, to estimate lower levels, too. This is significant because direct measurement of VO2 max typically requires a rigorous clinical test with specialized equipment that is not readily accessible to most people. watchOS 7 also allows Apple Watch to take cardio fitness measurements as users walk throughout the day, whether or not they are tracking a workout. With this innovation, Apple Watch is better able to measure VO2 max for users with low cardio fitness, who may not complete high-intensity workouts. 

https://www.apple.com/newsroom/2020/12/cardio-fitness-notifications-are-available-today-on-apple-watch/