Apple Running App.

If the display is not remaining awake for as long as it should do, the following steps may help:

If you have not yet done so, update your iPhone and Apple Watch to the latest software, starting with your iPhone:

• Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support
• Update the software on your Apple Watch - Apple Support

Restart both your iPhone and your watch:

• Close the Watch app on your iPhone:
  • Double-click the Home button, then swipe up on the app preview to close it.
• Turn both devices off together, then restart your iPhone first:
  • Restart your iPhone, iPad, or iPod touch - Apple Support
  • Restart your Apple Watch - Apple Support

Unpair and re-pair your watch:

• The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app. Choose to Restore from Backup during set up. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
• Unpair your Apple Watch and iPhone - Apple Support
• Set up your Apple Watch - Apple Support

Hi

It is not possible to keep the display permanently awake when recording a workout other than by interacting with it.

When waking the screen by raising your wrist (with that setting enabled), the screen will stay awake for a few seconds without further interaction.

The display can also be configured to remain awake without ongoing interaction for up to either 15 or 70 seconds. This option applies when the screen is tapped on to wake it from sleep or when it is tapped on after being woken by raising your wrist.

To set your preferred wake duration when tapping the screen:

On your iPhone, in the Watch app, go to: My Watch (tab) > General > Wake Screen - under On Tap, select Wake for 15 or 70 Seconds.

Regardless of the chosen setting and of how the screen is woken, it is normal for the screen to sleep again if you lower your wrist before it is due to sleep automatically.