AppleWatch 4 not recording heart rate during training

Hey there, and welcome to Apple Support Communities, Freddy-AppleWatch!

From my understanding, your Apple Watch is not recording your heart rate properly while training. I’d be happy to take a look at this with you.

First, I’d recommend ensuring that you follow the steps under “For best results” within Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support

From there, Get the most accurate measurements using your Apple Watch - Apple Support has some additional steps that can help.  

Let me know the results, and kindest regards.

We appreciate the update, Freddy-AppleWatch!

We're glad to hear that it's working for you again. If you need additional assistance, please feel free to reach out to us here on Apple Support Communities.

Have a great day!