RPE stands for rate of perceived exertion. Basically you’re asking yourself; “how hard was the task”? We can use RPE in strength training, endurance training and how to measure how hard a workout was at the end of a session. In strength training specifically, we’re asking ourselves; “how hard was this set? RPE is rated from 1-10. 1 being no effort, 10 being maximum effort. For example: 1×5 @RPE10 means you’ve done a set of 5 repetitions at a maximal effort. The barspeed of the last rep is most likely extremely slow compared to your first rep. You could not have done any more repetitions after this set. 

The thought of “how many reps could I have done after the set”, is a good way to judge what RPE this set was. 1×5 @RPE9 was a hard set of 5 repetitions. Most likely you could have done 1 more rep if you had to. 1×5 @RPE8 was a tough set of 5 repetitions. If I really had to, I could have done 2 more repetitions (see image below).

Why do we use RPE?
Let’s start off with an example. Let’s say you’ve been traveling a lot the past couple of days and sleep has been minimal. You go to the gym after a flight one day, at a time you’re not used to training and you have to perform squats. Your program says that you have to do 3×6 with 80kg. You perform your last warm up set before you have to start your working set which is (i.e. 1×3 70kg). It’s moving extremely slow and you get nervous for your working set. It messes with your mind. But the program says you have to do 3×6 @80kg. You load the bar with 80kg and you start your set and you fail at 4 reps instead of the prescribed 6 reps. You’re starting to doubt yourself. “Am I starting to get weaker?”.

Say hello to RPE! RPE would not give you a prescribed load. Instead, it would be prescribed as 3×6 @RPE8. Meaning you’re going to do 3 sets of 6 repetitions with a weight that is heavy, but you still could have done 2 more repetitions after if you had to. So during your warmup sets you’re noticing that 70kg (instead of the planned 80kg) would be a weight that would lead to a set @RPE8, then you can take advantage of the situation (traveling + lack of sleep) and do your working sets @ 70kg instead of 80kgs. As long as you’re doing the total amount of reps and the perceived effort is correct, you’re applying the right training stimulus.

The same works the other way around. Let’s say you’re having an extremely good day and you were planning to do 3×6 @RPE8 with 80kg. You perform your first working set of 80kg and you’re noticing that it’s moving fast. i.e. RPE7, you can in this case add a little bit more weight compared to what you’ve planned for. This way you can take advantage of good days as well. 3×6 @RPE8 with 82,5kg for instance.

Does this mean that you shouldn’t plan your weight? Not necessarily, it’s actually good to plan your weights in advance and try to progress on a weekly basis. If your goal is to become stronger, it’s probably a good idea to add weight on a regular basis to a given lift. To give an example how a program is planned:

Week 1: Squat 3×6 @RPE8 Planned 80kg
Week 2: Squat 3×6 @RPE8 Planned 82,5kg
Week 3: Squat 3×6 @RPE8 Planned 85kg

Reality could be:

Week 1: Squat 3×6 @RPE7 Performed with 80kg
Week 2: Squat 3×6 @RPE8 Performed with 85kg
Week 3: Squat 3×6 @RPE8 Performed with 87,5kg

Or

Week 1: Squat 3×6 @RPE8.5 Performed with 80kg
Week 2: Squat 3×6 @RPE8 Performed with 75kg
Week 3: Squat 3×6 @RPE8 Performed with 82,5kg

Another reason why RPE is useful is beacause it’s important to train at a correct intensity. We’ve all seen our ‘gym colleagues’ doing the same thing over and over again. 3×10 with the 10kg dumbbell year in year out. Probably capable of doing 10 more reps if he/she had to. Not really struggling and wondering why he/she doesn’t really progress over time.
Training under RPE 6 is generally not that useful from a long term training perspective. If you would like to make progress in the long run (ie gaining/maintaining muscle/strength), it’s important to push our sets to something between RPE 6-9. Anything lower than an RPE6 would not generate enough stimulus and anything higher than an RPE9 could generate too much fatigue for not a lot of return on investment. Roughly knowing at what RPE you are training at will give you this knowledge to train at the right intensity.

How do we start using RPE?
As soon as possible is the easy answer. RPE has a learning curve and the sooner we start at using it, the better. The first step is to rate every set. Ask yourself: What RPE was that? How many sets do I have left in the tank? Could I have done more reps? Etc etc. The more we practice at using RPE, the better we get at it (sounds like rocket science, doesn’t it). Does it have to be perfect straight away? Absolutely not. Does it have to be perfect in general? Also no! At the end of the day, these are estimates. It’s another tool in your toolbox to monitor your overall fatigue levels and to help you choose your weights for the day. Does it matter if your set was an RPE9 instead of an RPE8? In the long run, not really. Does it matter if most of your sets are done at RPE4 instead of RPE8? It most likely does.

If you don’t know where to start, there are ways to find your estimated RPE. One way is using the RPE/Percentage table below. Note that because RPE fluctuates and percentages don’t, It’s probably a good thing to start conservative and treat these numbers as an estimate. For example if you have to do 5 reps @RPE8, according to the table below that equals to an estimate of 82% of your 1 rep max.
Another tip when estimating weights is that every RPE is more or less 5%. So when you have to do 5 reps @RPE7 then 5 reps @RPE8, then step between the two is more or less 5% weight.

References:

www.muscleandstrengthpyramids.com

Read more