If your Apple Watch shows a message that says "No Movement Detected," it usually means the Watch did not receive a strong GPS signal while your activity was being recorded. When an activity ends without GPS data, the app may mistakenly conclude no movement occurred.
Strava relies on GPS data to process your activity. Without this information, an activity can have trouble syncing to our server. You may still see some data from the Watch's pedometer during your activity, since Apple's Activity app uses the Watch's accelerometer to record data even when GPS has not yet acquired a fix.
How to Fix It
Wait until you're outdoors to open the Strava Watch app, then wait about a minute before you start an activity. This gives the Watch time to collect a stronger GPS signal and helps prevent this issue from happening again.
Uninstall and reinstall the Strava app on both your iPhone and Apple Watch:
Use the Watch app on your iPhone to force-uninstall the Strava Watch app. Note that it may take some time for the app to fully uninstall from the Watch face.
Confirm the app has been uninstalled from the Watch.
Uninstall the Strava app from your iPhone.
Force close all apps on your iPhone.
Restart your Watch and iPhone.
Download and install the Strava app on your iPhone.
Confirm you are logged into the Strava app.
Confirm the Strava app has been installed on your Apple Watch.
Unlock your iPhone and open the Strava Apple Watch app.
Watch for and approve the prompts on both devices.