You walk into the gym, your log says "4 × 5" and you don't know what weight to use. Go too heavy and you fail. Go too light and you waste the day. That's exactly what RIR and RPE are for.
What RIR is
RIR stands for reps in reserve: how many more reps you could have done with good technique before failing.
- You finish the set and had two reps left: RIR 2.
- You finish and couldn't do a single more: RIR 0.
What RPE is
RPE stands for rate of perceived exertion and goes from 1 to 10. In strength training, a scale tied to RIR is used:
- @10: you had no reps left (RIR 0).
- @9: you had one left (RIR 1).
- @8: you had two left (RIR 2).
- @7: you had three left (RIR 3).
- @6: you had four or more left.
Half points are used too. An @8.5 means you definitely had one rep left and maybe two.
This way of measuring effort became very popular in powerlifting, and in 2016 a group of researchers (Zourdos and colleagues) published an RPE scale based on reps in reserve for strength training.
Why it works
Because not every day is a good day. If you slept badly or you're coming off a tough week, the same weight will feel harder. With fixed percentages, you overshoot that day. With RPE, you adjust the weight to how you feel today and put in the effort that was planned.
That's called autoregulation: the plan sets the effort and you choose the weight that matches it.
How to use it in your training
If your plan says 3 × 5 @8:
- Warm up gradually.
- Pick a weight you think you could do for 7 reps.
- Do your first set of 5. If you had 2 left, perfect. If you had 4 left, go up. If you had none left, go down.
And always log it: weight, reps and the @. Over time you'll see the same weight feel like a lower RPE. That's progress too.
Common mistakes when starting out
- Stopping short. At first almost everyone thinks they're at @9 when they're at @7. That's normal: learning to read effort takes weeks.
- Using RPE on very long sets. With more than 10 reps it's very hard to be accurate. It works best between 1 and 8.
- Forgetting about technique. An ugly rep doesn't count as "in reserve".
A trick: film yourself. If the last rep was much slower than the first, you were probably closer to failure than you thought.
RPE and your 1RM
If you know the weight, reps and @ of your best set, you can estimate your 1RM without maxing out. Try it with the calculator: with the @ the estimate is far more accurate than with a formula alone.
Save this for your next leg day. And if you want a plan with the @ dialed in for you, start here.