My wife and I both have Apple 3 watches. When we go on a walk together, my watch will show 15 of 30 minutes exercise and hers will show 3 of 30. Why the difference? any help appreciated.

Also, who is in better shape? For moving the excercise circle your heart rate has to be at about 75% of max heart rate. Your pace may be too slow for her.

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.

My wife and I walk together at a brisk walking pace and our exercise minutes are identical.

You can calculate your maximum heart rate by subtracting your age from 220.