Another less scientific yet helpful way to gauge exercise intensity is the Borg scale for Rating of Perceived Exertion, more commonly known as RPE. The key word here is perceived because you are using your own sense of your body to gauge how hard you are working. Therefore, this is a subjective measure of how hard you are exercising. The Borg scale goes from 6 to 19.

Amazingly, Borg found that if you add a zero to the number of your perceived exertion, you would very often be working at that heart rate. So, for example, if you feel as if you're working at level 14, chances are your heart rate is somewhere around 140.

The Pros of RPE

Despite the RPE's unscientific qualities, research has found that the scale corresponds consistently to the heart rate that a person experiences during exercise. For example, you are most likely to achieve the cardiorespiratory training effect at intensity levels that are “somewhat hard” to “hard” and these intensities correspond almost exactly to a rating of 12 to 15 on the scale.

Using Perception Properly

The con to the RPE is that it is, as mentioned, not scientific, and therefore inexact. But whatever your health, exercise level, or activity, your sense of intensity needs to be consistent. The Rate of Perceived Exertion scale uses your own sense of intensity to allow you to judge how hard you are working, but how hard is hard? You need to honestly evaluate how hard you are working, so here are some guidelines on how hard “hard” is (and how easy “easy” can be).

The first few numbers on the scale use the word “light,” which means your heart is not pumping harder than it usually does when you walk around your house. “Somewhat hard” refers to the awareness that you are beginning to move with a specific intensity. You could keep going for a while and you aren't stressed, but you notice the movement. “Hard” is intense, and an activity level that could not be continued indefinitely. As it gets more intense, i.e., you're using the word “very,” you would be less likely to be able to keep moving at that level for any length of time.

Don't think about these specific words too deeply. The fact is, you know when you're working or not working. If you don't know, if you really can't feel how hard your body is working, then here are some questions to ask yourself, and the intensity levels your answers may correspond to.

To use RPE, all you need to do is ask yourself periodically throughout your workout is: “How hard am I working?” Then answer honestly using the scale. If you find yourself not working hard enough, pick up your pace. If you're working too hard, slow down. It's that easy.