What is perceived exertion?

Perceived Exertion is a scale used to describe the difficulty or physical effort involved in certain activities. Given the practical difficulties in monitoring heart rate, perceived exertion provides a scale for people on the street to use to gauge the intensity of their exercise. For example, the suggested intensity for aerobic exercise allows you to maintain a conversation, but not sing a song. This is easy to use without equipment, and is a fair measure of respiratory activity.