How iOS 16 Cardio Fitness Alerts Work

In iOS 16, the Health app uses Apple Watch data to monitor your cardiovascular fitness, clinically measured as VO2 max, and sends targeted alerts if your levels decline into an unhealthy range. When your aerobic capacity falls into the "Low" classification for your age and sex, your device triggers a direct push notification warning you of increased long-term health risks. This article covers how these notifications are generated, how they appear on your devices, and how to manage the feature in the Health app.

How the Feature Measures Fitness

Cardio fitness levels are calculated automatically using your Apple Watch during outdoor walks, runs, or hikes. Sensors measure heart rate and movement to estimate your VO2 max—the maximum amount of oxygen your body can consume during exercise. The Health app categorizes these readings into four tiers based on data from the Fitness Registry and Importance of Exercise National Database (FRIEND): High, Above Average, Below Average, and Low.

The Alert Mechanism

Cardiovascular fitness notifications only trigger when your estimated VO2 max drops into the "Low" category.

  • The Initial Alert: When a recorded workout results in a "Low" classification, the paired Apple Watch and iPhone deliver a high-priority push notification stating that your cardio fitness is low.
  • Follow-Up Notifications: If your cardio fitness remains in the "Low" bracket, the system will not spam you after every workout. Instead, iOS 16 spaces out repeat notifications, alerting you once every four months to remind you of your status and encourage improvement.

What the Notification Displays

Tapping the notification opens the Cardio Fitness section in the iOS 16 Health app. Here, the interface provides:

  • Contextual Data: A graph showing your VO2 max trends over days, weeks, months, or years.
  • Health Context: Educational material explaining that low cardio fitness is associated with risks such as cardiovascular disease, type 2 diabetes, and premature mortality.
  • Contributing Factors: Information on variables that can lower your readings, such as age, pregnancy, or certain medications like beta-blockers.

How to Enable Cardio Fitness Notifications

To ensure you receive these notifications on iOS 16, enable them through the Health app:

  1. Open the Health app on your iPhone.
  2. Tap the Browse tab and select Heart.
  3. Tap Cardio Fitness, then scroll down to the Cardio Fitness Notifications section.
  4. Follow the on-screen prompts to confirm your age, sex, and medications, then turn notifications on.