Hi
To credit progress towards the daily Exercise goal, the Activity app aims to identify activity that equals or exceeds the intensity of a brisk walk. This requirement applies both during general daily wear and when recording workouts via the Workout app.
The definition of a brisk walk depends on your personal information. To check that this is accurate (and to update it over time):
On your iPhone, in the Watch app, go to: My Watch (tab) > Health > Edit - tap and adjust items, then tap on Done.
If you have not yet done so, it may also help to update your iPhone and Apple Watch to the latest software (starting with your iPhone). After updating from earlier software versions, some users reported seeing increases in the proportion of their activity that was credited as Exercise.
During general daily wear and when using the Workout app to record Indoor Walk, Indoor Run and certain outdoor workouts when the iPhone is not taken along, the Activity app and Workout app rely on arm motion (measured by the accelerometer) to track movement for the purpose of estimating results including Exercise credit, distance and pace.
For the best results, allow the arm on which you are wearing your watch to swing naturally as you move around and, where relevant, during workouts. If the iPhone is also taken along during outdoor workouts (with Location Services and Bluetooth enabled), the watch can also access GPS data to help inform estimations.
Calibrating your watch can improve the accuracy of estimations made by the apps by teaching your watch how your arm movements relate to your stride lengths at different speeds when walking and/or running. It does this by comparing data from the accelerometer with GPS (Location Services) data from your iPhone. Instructions for calibrating your watch are available via the link below. The article also includes instructions for resetting any existing calibration data and starting the process afresh. For the best results, calibrate for at least 20 minutes at each of the speeds at which you typically run and/or walk.
Also ensure that you wear your watch snugly on the top of your wrist during workouts. Apple suggests that you consider tightening your watch band before workouts and loosening it again afterwards.
If you would prefer to receive Exercise credit for workouts regardless of their intensity levels, track them via the Workout app using Other as the activity type. This will credit one minute of Exercise for each full minute of the workout. Active calories will be estimated at a rate equivalent to a brisk walk or based on data recorded by the heart rate sensor, whichever is higher.
More information:
Use the Activity app on your Apple Watch - Apple Support
Use the Workout app on your Apple Watch - Apple Support
Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support