Activity Exersise and Workout Minutes

The google-fu is strong with this one. I did some more searching and found this really helpful page that explains how you can work out what your watch thinks your heart rate should be to count as exercise https://macdailynews.com/2015/04/27/how-apple-watchs-activity-app-measures-exercise-time/

So in my case I never entered the exercise zone because my target rate is 139bpm (based on the age calculation). Sigh...

Your activity rings don’t measure the length of your workout, they measure the time you were doing exercise. Doing an indoor walk at a leisurely pace with the workout app will count as a workout, but you probably won’t get any exercise credit for it since you weren’t making your heart work. The exercise goal is based off the intensity of your workout, basically.

Exercise is based on elevating your heart rate. If while indoor walking your heart rate was probably only elevated the amount of time you were credited with exercise.

I have this question too, and the heart rate answer partially helps, but how elevated does heart rate need to be to register it as exercise. I just did 10 minutes on a rower (I know, what a beast!) and my heart rate went up to 132bpm, and was over 100 for all of it but only 1 minute registered on my exercise ring

According to apple support, for the activity ring to register your workout (for outdoor walk or exercise ring) you need to maintain a speed of approx 3.3 mph or faster,this is their definition of a "brisk walk".If you slow down or pause the watch will stop tracking your movement as exercise credit,it will still measure your steps and calories burnt but will not give you any credit towards the exercise ring or workout app.A brisk walk speed is different for everybody as the watch takes into account your age,sex,weight and heart rate which why it is important to calibrate the watch when you set it up from new,the idea being that you're being encouraged to put more effort in to walk faster and to get your heart beating faster, if you just walk at a slow pace then you are not going to improve your fitness or get all those award badges that we all seek.