While recording an activity, why does the heart icon move and what does it indicate?

When you are recording an activity and viewing your heart rate, you can look at this bar to see which PAI intensity zone you are currently in. The heart icon will appear when your heart rate is high enough to earn PAI points. As your heart rate increases, you will progress from Low, to Moderate, to the High intensity zone. The higher the intensity, the quicker you will earn PAI points.

For example, a 45-minute workout at Low intensity may earn only 2 PAI points, while the same duration at High intensity could earn you 50 PAI points.