Intensity is hard term to define, it depends on your own perceptions, thus being rather subjective. When you are performing any kind of aerobic activities, an exercise intensity correlates with how hard the activity feels to you. Another way of reflecting the intensity of your workout is your heart rate.
The Rate of Perceived Exertion (RPE) is one of the ways to measure exercise intensity for you. It uses a scale from 1 to 10, 1 meaning rest and 10 being the maximal exertion and it allows you to rate your physical and mental state while performing an exercise. An RPE between 5 and 7 is advised, meaning that during your workout, you are ranging between “somewhat
hard” and “hard.”