I know this should be a no-brainer. “RPE 10 is nothing left, RPE 9 is one left, RPE 8 is two left” etc. But, I complicate things 
On a press or deadlift, “weight up” is the first part of the movement and as I reach the end of an RPE 9+ set, I cannot even move the weight up without using good form. So it’s easy to know when I’ve hit a true RPE 9+. No questions there.
But on a bench or squat, it gets fudgier. “Down” is the first part of the movement and as I reach the end of an RPE 9+ set, I’m recruiting some different muscles (let’s say) on the way back up, and my form might suffer a little bit, but the rep is do-able, so yeah I can keep going for another couple reps. And then I’m not sure if I did the set right.
Let’s take “Squat to RPE 9” as an example.
A. Does it mean, squat to the point where I have “one left in the tank” under 100% perfect form? (imagine Rip is there, trying to embarass me with his yelling)
B. Or does it mean, squat a little further, to the point where I have “one left in the tank” before I’d have to drop the weight for truly not being able to move it? Thus getting another 2 reps, say, before I call the RPE as done.
A or B?
What is perfect form and how much do you think your form REALLY deviates in either of these scenarios?
Continuing the squat example: at the end of a RPE 9+ set, my lower back wants to round at the bottom of the last rep, giving a little rockiness to the upward lift (as hips & spine struggle to hold their proper relationship).
In the bench, the analogue would be to lift (or arch) the back too much, on that last rep.
That may answer the question. In hitting RPE 6/7/8. I should see no loss of form. If I get to a rep where form decays, it would be time to stop; thus I must have hit a 9-or-more.
My confusion is because I always feel that I could still grind out another “bad” rep or two; so should I label the whole set as a 9, as a 10, or as a mistake?
Maybe this question can’t be answered without video.
I’m not sure that you answered my question about what is perfect form?
For example, your back is flexing during 100% of your squat reps. Your form also varies for each rep, even at very light intensities. I also think it unlikely that no form changes at RPE 8, but do at RPE 9.
In any case, I don’t think you should be taking into consideration your technique’s efficiency for rating RPE, but rather were you able to adhere to the performance standard for the lift, e.g. depth, keeping your butt on the bench, not hitching, etc. and, when using RPE as a proxy for reps in reserve, should be used as such. In other words, how many reps could you have done while adhering to the same standard.
Perfect form - Apologies, I had taken your question as rhetorical, like “who can even define perfect form?” - and indeed, though expert (you) might, I cannot.
I hear you saying that I should have in mind a reasonable minimum standard of form, and then RPE / RiR is, how many more could I have done at that standard.
Continuing the squat example: I can feel subjectively (sorry, my present gym setup has no mirrors, is outdoors for covid) when 1. I got to a good depth, 2. I came up with knees, hips and back moving in a visually pleasing alignment, and 3. my back stayed strong. Number 3 feels like a good “uprightness” to my back, although I know that’s the wrong word because the back does get angled, a bit flexed, etc.
Likewise, I can feel subjectively when 1. I didn’t quite reach depth, 2. I came up with hips lurching because 3. my back flexed or hunched too much, and it was an ugly struggle to get up.
So today I was aiming for an RPE 9 set (of 6 reps) and maybe pushing the weight number. On the last rep, the above bad stuff happened. I stopped there. I could have ground out (but didn’t) one more “bad” rep. RPE-wise: was that set a 9, a 10, or a mistake / Jeff wtf are you doing?
I don’t know if the above stuff is “bad”, though there may be opportunities for performance improvement with some of these via cueing, programming adjustments, etc., but I don’t think they should routinely influence your RPE/RIR rating.
I’d also question what you mean about visually pleasing and back “staying strong”, but I think I’ve answered your question at this point.
OK here’s what I’m getting: while we always want good-or-improving form, that last “bad” (my word) rep or two at the end is tolerable and the answer to my question would be that I did an RPE 9 set.
If I misunderstood, please lmk. Otherwise thanks!
Do we always want “good” or “improving” form? What does this actually mean, as I’m not sure I agree.
In order to really put a bow on this, my thoughts are that acceptable technique allows a person to fulfill the predetermined points of performance of the exercise, e.g. ROM, velocity, tempo, etc. There is likely room to improve efficiency of movement to improve performance, but this also likely resolves over time as an individual becomes more trained, e.g. self organization. There are exceptions here, particularly as significantly different movement strategies are adopted, e.g. a conventional puller switching to sumo.
In any case, RPE can be used for a number of different subjective metrics. In this case, you are using it as a proxy for repetitions in reserve. Each rep has a standard that you need to meet for it to “count” as “good.” In this context, I would use RPE to rate how many reps I could do to this standard. I would not try to include other aspects of technique, in general.
Hopefully this answers your question.
Feel free to veto this post - I know we’ve already flogged this topic. But when I came across this vid from Jeff Nippard, it said a lot to me: https://www.youtube.com/watch?v=deDlhPmT2SY
On a max squat, I look like the example shown at 13:56 - questionable depth, lurchy hips, back hunching or lifting late.
And I’d rather look like the example at 14:20 - chest up, form aligned even though it is max effort.
JN says the first example is just not good, the dude needs to lower his weight. I don’t know your view but in general, JN’s and your comments align: form is going to change as the set progresses, don’t over-think it, just perform to a basic acceptable standard. You went past 10 (Spinal Tap, “ours go up to 11”) if you didn’t even hit your minimum standard.
Correction, the second (better) example starts at 14:40.