“Train hard.” Great advice – and completely useless as an instruction. Hard compared to what? Hard enough to grow, or hard enough to bury yourself for three days? Every lifter has felt that fog: you finish a set with no idea whether you left gains on the table or blew past the point of diminishing returns.
That’s the problem RIR and RPE solve. They take the vague feeling of “close to failure” and turn it into a number you can aim at, hit, and repeat. This isn’t the old question of whether you should train to failure at all – that’s its own debate. This is about the dial in between, and how to read it.
RIR and RPE, in Plain English
RIR stands for Reps In Reserve – how many more clean reps you could have done before hitting technical failure. Finish a set thinking “I had maybe two more in me”? That’s 2 RIR.
RPE stands for Rate of Perceived Exertion. On the lifting-specific version of the scale, a 10 means all-out, nothing left. A 9 means one rep in reserve, an 8 means two or three, and so on down.
They’re two sides of the same coin. RIR counts up from failure; RPE counts toward it. RPE 8 and 2 RIR describe the exact same set. Pick whichever language clicks in your head – most lifters find RIR more intuitive because you’re literally counting reps, not rating a feeling.
Why Not Just Go to Failure Every Set?
Because failure is expensive. Grinding every set to a dead stop hammers your recovery, spikes fatigue, and wrecks your performance on the sets and sessions that follow – and a lot of that extra work is what coaches call junk fatigue. It’s cost without much extra benefit.
The research on this is refreshingly clear: sets taken close to failure – but not all the way – drive nearly the same muscle growth as sets to failure, while leaving you fresh enough to hit your volume with real quality. Stopping a rep or two short lets you do more good sets, more often. That’s the whole game.
Leaving 1-3 reps in the tank on most of your work is the sweet spot. Close enough that the muscle gets the message. Far enough that you can back it up tomorrow.
How to Actually Gauge Your Reps in Reserve
Here’s the honest part: everyone is bad at this at first, and most people undershoot. Ask a new lifter to stop at 2 RIR and they’ll often stop at 5. The number you feel and the number that’s real are usually miles apart until you calibrate.
Use these tells to read the set:
- Bar speed. As long as the weight is moving fast and smooth, you’ve got reps left. When speed drops noticeably on a rep despite full effort, you’re within about 2-3 of failure.
- The grind. The first rep that gets genuinely slow and grindy is usually your last clean rep or two. That grind is roughly RPE 8-9.
- Form breakdown. When your technique starts to shift – hips shooting up, elbows flaring, a hitch appearing – that’s technical failure knocking. Reserve is gone.
Want to calibrate fast? A few times a month, take an isolation exercise genuinely to failure and count how many reps you get past the point you would have stopped. If you called 2 RIR and then squeezed out five, your gauge is way off – and now you know which way to correct.
RIR for Strength vs. Hypertrophy
The right amount to leave in the tank depends on what you’re chasing.
For hypertrophy (building size), most of your sets should live around 1-3 RIR. That’s close enough to recruit the big motor units and hard-to-reach fibers, while letting you rack up the total volume that actually drives growth. Save the true 0-RIR grinders for the last set of an exercise, if at all.
For strength, especially heavy compound work, you generally want more in reserve on your working sets – think 2-4 RIR. Heavy singles, doubles, and triples are about moving big weight with clean, repeatable technique, not about crawling to failure. Missing a heavy rep costs far more than it teaches. Here, RPE keeps your top sets honest: a planned top single at RPE 8 means heavy but controlled, with a rep still in the bank.
Programming With Effort Numbers
Once you can read RIR, you can build with it. This is autoregulation – letting the day’s readiness set the load instead of forcing a number that ignores how you feel.
Say the plan calls for 4 sets of 6 at RPE 8 (2 RIR). On a strong day, that might be 225. On a bad-sleep, high-stress day, that same effort might land at 205 – and that’s the point. You chase the effort, and the right weight reveals itself. You keep progressing on the good days and stop yourself from digging a hole on the rough ones.
You can also ramp intensity across a training block: start a mesocycle around 3-4 RIR when volume is high and fresh, then let effort creep toward 1-2 RIR as the weeks build, before you back off and deload. Same exercises, rising effort, managed fatigue.
Keep Your Effort Honest Set to Set
Here’s where it quietly falls apart for most people: an effort scale only works if the conditions are consistent – and the biggest variable is rest. Cut your rest short and every set feels like RPE 9 because you’re still gassed from the last one. Let rest balloon to four minutes of scrolling and suddenly your “2 RIR” is really 5. Either way, your numbers lie.
So make rest deliberate. Give your heavy compounds a real 2-3 minutes and your accessories 60-90 seconds, and keep it consistent set to set. A rest timer – on your watch or in an app like Kalaku – keeps that window exact instead of drifting with your attention span.
The other half is memory. You cannot autoregulate against a number you didn’t write down. Log the weight, the reps, and the RIR you actually hit – “185 x 8 @ 2 RIR” – and next session you’re not guessing, you’re building on evidence. That running log is what turns a random hard workout into progress you can see. Plate math and a clean set log in one place means less thumbing through notes and more time under the bar.
RIR and RPE won’t do the work for you. But they’ll tell you, set by set, whether the work you’re doing is enough – or too much. Leave a rep or two in the tank on most sets, calibrate your gauge every few weeks, and let the honest number guide the load. Dial the effort, log the set, and train without the scroll.
Sources & further reading:
- Zourdos et al. – Novel Resistance Training-Specific RPE Scale Measuring Repetitions in Reserve
- Stronger by Science – How to Use RPE in Your Training