How to stop the "fitness app"?

Hello, I just tried using the " Fitness" , it looks like a good tool for running, but I find it just keeps working all the time in the background even after I close it from the " Recent Task" or tap on the " Pause" , the green light keeps flashing at the back of the watch , I also restrict the background battery usage for this app from settings, nothing worked

then I have to restart the watch to really stop this " Fitness" app,