Heart rate during workouts

My apple watch USED to display my heart rate during outdoor walks and workouts, but now it doesn't. I've gone to the phone/workout/workout view/<name of exercise>, and heart rate is greyed out. How do I get it to un-grey and display again?

I have done all these things. Neither Heart Rate or Workout will track heart rate for a whole exercise period. It has been waiting 10 minutes or more to start tracking. Tonight I was only able to get one data point in 25 minutes. If workout is not running, I have a continuous record of heart rate.

On your iPhone, go to Settings/Privacy/Motion & Fitness and check that both Fitness Tracking and Health are On.

Open your iPhone’s Watch app and go to General and make sure that Workout Power Saving Mode is Off.

Next, go to Privacy and check that both Heart Rate and Fitness Tracking are both On.

Finally, go to Passcode and check that Wrist Detection is On.

If any of these settings are incorrect, they will prevent your watch from reading your heart rate during a workout. Set them correctly, and test your watch again.

On the phone watch app;

Tap on workout/workout view/name of your workout and you can change what you see on the screen during the workout here.