Workout Sessions displays and analyzes your Workouts. The Workout Sessions app cannot track workouts itself but gets your workout information from the Health App. To be able to display them the app needs access to your Health data stored on your iPhone.
You can use following ways to track your workouts to have them shown in the Workout Sessions app.
Using your Apple Watch
The easiest way to track your workouts is using the Workout app on your Apple Watch. Just complete a workout and it will be available in the Workout Sessions app. It might take some time for the data to be transfered from the Apple Watch to your iPhone but don’t worry it will be available in the Workout Sessions app eventually. If you have Notifications enabled, we even tell you when there is something new in the app to see.
Using Apps that support the Health App
Most of the workout apps you can find in the AppStore support the Health App, which means they store the fitness data securely in the Health App on your iPhone.
Here a small list of Apps that Support the Health App but you can always search for HealthKit on the AppStore to find thousands of Apps.