I use RPE to judge how hard I am working out all the time. There are several ways to measure your output including V02 max (oxygen uptake by your cells) and Heart Rate. Both rise as the intensity of your workout increases. But my favorite way to measure intensity is using the RPE scale. It's easy and requires absolutely no equipment. RPE is basically how hard you "feel" like you are working. It is a scale from 1-6, 1 being not working hard at all and 6 being working as hard as you can. I have broken down the scale with descriptions of how you should be feeling. I refer to this scale a lot when I design workouts.
Rate of Perceived Exertion (RPE)
- Lying Down: you can do this forever, you will never get tired. Your breathing is slow and shallow, you can talk, scream, sing, and laugh.
- Walking at a slow pace: you can do this for a really long time without getting tired. Your breathing is still pretty slow and shallow, you can talk, scream, sing, and laugh, although with not quite as much ease as at level 0.
- Walking briskly: you can keep this up without getting tired for longer than an hour. Your breathing is picking up a bit, you can hold a conversation but screaming or singing becomes more difficult.
- Jogging: you can keep this up for at least thirty minutes. Your breathing is becoming more labored. You can talk but only short sentences before you start to get out of breath. You can no longer scream, sing, or laugh without becoming exausted.
- Running: you can keep this up for five to ten minutes. Your breathing is labored. You can say one word answers (yes, no, maybe), but that is it. You cannot hold a conversation.
- Sprinting: you can't keep this up longer than thirty seconds to a minute. You are having a very hard time breathing. You cannot talk at all because all your focus is one trying to get as much oxygen as possible.