As you exercise, you pick the number that most closely corresponds to your sensation of exertion, with the help of verbal cues such as "fairly light" and "somewhat hard" accompanying the numbers. While the common-sense nature of this approach appeals to many exercisers, others worry that its simplicity compromises accuracy.

Is perceived exertion a good way to monitor exercise intensity?

Many people use the Borg scale (also known as the Rating of Perceived Exertion, or RPE) to exercise at their target exercise intensities. Many don't even bother with the scale any more, but have just developed a sensation of what intensity "feels" right.

The ability to sense what intensity feels right is usually easier for experienced exercisers than for beginners. People new to exercise, returning after a period of inactivity or starting a new kind of exercise, may wish to monitor exercise intensity with both heart rate (HR) and RPE. Over time, you will find that HR and RPE often go together, and that eventually you'll be able to replicate your prescribed exercise intensity primarily with RPE, occasionally taking HR to be sure you're on target.

It's difficult to decide on a number.

Sometimes the more you think about something, the harder it is to decide! Ask yourself, "How hard am I working right now?" Your number should reflect your overall perception of exertion, integrating all of your physical sensations such as how hard you are breathing, muscle aches and pains, and how tired you feel. If you are responding in a group setting, try not to compare yourself to others, or give a number because you think it is the correct one. Try to give the number that most closely reflects how you really feel. Just do the best you can, and with practice you will find it easier to pick a number that tells how hard you are working.