Now we're ready to see why Billy trains harder than Sally—that is, why a 20-mile week that includes three 5K races represents a greater workload than a 35-mile week consisting entirely of easy running. Let's say that each of Billy's 5K races takes him 20 minutes to complete. The appropriate RPE for a 5K race is 9. So the total session RPE for the three races is (60 x 9) = 540. Now let's say that the remaining 11.7 miles in Billy's week are run at a pace of 9 minutes per mile. So the total RPE for these easy miles is (11.7 x 9 x 2) = 210.6. The total session RPE for the entire week, then, is 750.6.
Now let's look at Sally's training. Let's say that she completes 20 miles out of her 35 total weekly miles at 9 minutes per mile and an RPE of 2 and the other 15 miles at 8:30 per mile and an RPE of 3. In that case, the session RPE for the slower miles is (20 x 9 x 2) = 360, the session RPE for the slightly faster but still easy miles is (15 x 8.5 x 3) = 382.5, and the total session RPE for the week is 742.5. So Billy is training slightly harder than Sally even though he's running 43 percent less.
Once you've got the hang of it, tracking session RPE can help you in a variety of ways. For example, you can use it to create a training plan in which the workload (and not necessarily the mileage) increases gradually, as it always should, except in recovery weeks. It also can be used to ensure that your recovery weeks truly are recovery weeks. You may even use this type of monitoring to determine the maximum weekly session RPE your body is currently able to handle, so you can respect that ceiling and avoid overtraining.
Don't let a little bit of multiplication frighten you. Tracking session RPE isn't much harder than tracking miles, and it is far more useful.
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