RIR in strength training: how close to failure should you go?

What exactly does RIR mean?

RIR describes how hard a set was. You aren't rating how heavy the weight feels. Instead, you estimate how many more reps you could have done with clean technique. An example: you do 8 squats and notice that the 9th and 10th would still have been clean, but the 11th wouldn't. That was a set at RIR 2.

The key word is “clean”. A rep you can only finish with momentum, a half range of motion or by shifting your body out of position doesn't count as reserve. RIR 0 therefore means that no further rep with clean technique would have been possible.

RIR or RPE: what's the difference?

Both scales mean the same thing, they just count from different directions. RPE stands for “rating of perceived exertion”, an effort scale up to 10. The version commonly used in strength training links it directly to RIR: RPE 10 equals RIR 0, RPE 9 equals RIR 1, and so on. The authors of the study that introduced this scale describe it as a practical way to adjust training load from day to day (Zourdos et al., 2016).

I prefer working with RIR, because the question “How many more could I have done?” is easier to grasp than a number on an effort scale. If your plan says RPE 8, that's the same as RIR 2.

Do you have to train to muscle failure?

No. To build muscle, you need to get close to failure, but not all the way there on every set. A meta-analysis of 15 studies found no advantage for training to true muscle failure compared with sets that stop just short of it (Refalo et al., 2023). At the same time, a later analysis across many studies shows that the closer sets ended to failure, the greater the muscle growth was on average. Strength, on the other hand, increased similarly across a wide range of RIR (Robinson et al., 2024). The authors themselves point out that the RIR values in that analysis were only estimated after the fact.

Both analyses point to the same practical rule. A set that stops far short of your limit leaves stimulus on the table. There is no evidence, however, that taking a set to absolute failure adds anything decisive compared with RIR 1 or 2. In my view, that is why it isn't worth doing on every set, because technique often suffers at the end. In my workbooks, RIR 0 to 2 is the target range for most sets, and you use muscle failure deliberately, not everywhere.

Which RIR is right for you?

That depends less on the exercise than on how solid your technique is and how risky a failed rep would be.

Then there is how you feel on the day. After your first working set, compare the actual RIR with the planned one. If your usual weight feels noticeably heavier, reduce the weight or the number of sets for the rest of the session instead of pushing through regardless. If it feels lighter, add a little. If, on the other hand, you rate almost every session as “better go lighter today”, that usually isn't about the day any more. It is a sign that your plan is asking too much. If fatigue builds up over several weeks, a planned deload week is the better answer.

How to learn to estimate RIR honestly

Most people are off at the start, and usually in one direction: they stop too early. An analysis of 12 studies with 414 participants shows that people underestimate their remaining reps by just under one on average, with large differences between studies. Training experience made hardly any difference. Estimates were more accurate close to failure and in sets of 12 reps or fewer (Halperin et al., 2022). In the Basics workbook, I write that there are often two to three reps left behind the feeling of “maximum”. The studies confirm the direction, but on average the error is smaller.

Whether you tend to stop too early or too late, you can find out with a simple test. Do it on a machine or with dumbbells, where a failed rep is harmless:

• Pick a weight you can do about 10 reps with.
• Note the moment you believe you have two reps left, for example after the 8th.
• Keep going until no clean rep is possible. If you manage 12 in total, your supposed RIR 2 was actually RIR 4.
• Repeat the test every few weeks with a different exercise. That way you see in black and white how far feeling and reality are apart for you.

It also helps to read muscle burn correctly. A burning, pulling sensation in the working muscle that gets stronger towards the end of the set is exactly what a set close to your limit is meant to produce. It is no reason to stop.

Writing RIR into your training plan

For RIR to be more than a feeling, it belongs in your log. For each set, note weight times reps and the estimated reserve after it. An example for squats with a target of 3 × 8 to 10 reps at RIR 1 to 2:

All three sets were in the target range, but not all of them reached 10 reps yet. So the weight stays the same next week. Only once you hit the top end in all sets, in two sessions in a row, does more weight go on. How that works in detail is explained in the article When should you increase the weight? Progression made simple. For logging, the free training plan template is all you need: weight times reps in the table, and the RIR simply after it or in the notes.

When to get it checked by a doctor

Training close to your limit doesn't mean ignoring pain. A sudden, sharp or one-sided pain, often in a joint rather than the muscle, is a reason to stop the set immediately. If that pain comes back or lasts for days, have it checked by a doctor or physiotherapist. If you have a cardiovascular condition, are pregnant or are returning after an injury, talk to your doctor beforehand about how close to your limit you should go. This article does not replace medical advice.