Heart Rate: You can use a strap that goes around your chest or a watch with a built-in heart rate monitor to get real-time heart rate data.
Perceived Effort: Rating of Perceived Effort (RPE) is often a tool used in studies with a numerical rating scale based on how hard you think you’re working.
Pace: Simply put, a pace range that you should be running in.
Heart Rate: You can figure out your Max Heart Rate by performing a MHR test. Then you can break this down into zones. And then different runs may be prescribed a HR range. For example a recovery run may be zone 1 and 2.
Perceived Effort: This is harder to put a number on if you don’t have the chart in front of you. With my athletes, I typically recommend they do the vast majority of their training at “an easy conversational pace” where they could read poetry or converse with a friend in a decently normal way.
Pace: Typically this is like Heart Rate and you use a personal record (such as a 5k time) to create suggested pace ranges. For example, and easy pace may be 1.2-1.4 X your 5k race pace. Or you may do tempo runs at 95% half marathon pace.
Various reasons. Heart Rate and Pace ranges are nice suggestions when you need a broad range to stay in, such as for easy runs.
Paces are helpful when you need to hit goal splits for a key workout.
Effort is nice during easy runs since it requires no electronics. Effort is also helpful when it is more difficult to maintain a prescribed pace or heart rate, like on the trail, hilly terrain, or over snow.