RPE, RIR, and muscle failure: how do you manage effort in strength training?

What is muscle failure?

You reach momentary muscular failure when, despite maximal effort, you can no longer complete another repetition with the required range of motion and technique, as in a curl when you try to lift the dumbbell but cannot finish the movement correctly.

The burning sensation or the urge to put the weight down can occur while several more reps are still possible, so stopping a set that has become very uncomfortable does not necessarily mean you have reached failure in strength training.

The term technical failure is also used when continuing would require a clear breakdown in form: during a curl, you may still be able to move the dumbbell by swinging your back forcefully, but no longer under the conditions chosen for that exercise.

To track your workouts, define what you count as a clean rep and keep that standard from one set to the next, because an extra rep achieved by substantially shortening the movement can give a false impression of progress.

RIR in strength training: understanding reps in reserve

RIR comes from the English term reps in reserve and refers to repetitions in reserve, meaning the reps you estimate you could still perform before failure.

If your program calls for 2 RIR and, after ten reps, you think you could still complete two more without changing your technique, you stop the set even though you have not exhausted everything you could do.

This number remains an estimate: you assess what you could have done without systematically checking it by continuing to failure.

RPE in strength training: how does the scale work?

RPE means rating of perceived exertion, or an assessment of perceived effort; in the version used here for strength training, the difficulty of the set is rated based on how many reps you have left.

A prescription of ten reps at RPE 8 therefore calls for a weight with which you can perform those ten reps while keeping about two reps in reserve. The number 8 means neither 80% of your maximum weight nor a rating based solely on the burning sensation you feel.

This correspondence applies to the RIR-based RPE scale, as other exertion scales exist in sports. The farther you are from failure, the harder it becomes to distinguish exactly how many reps are still possible: use these ratings as reference points without assigning them a level of precision they do not have.

Intensity, load, and effort: what is the difference?

In the strength training literature, intensity often refers to the relative load, expressed as a percentage of 1RM, the maximum weight you can lift once. In gyms, an “intense set” also describes a very demanding effort, even with a light weight if you continue long enough to approach failure.

To know what you actually did, record the weight, reps, and your reserve: none of these elements alone describes the full difficulty of the set.

Do you need to train to muscle failure to build muscle?

You can build muscle without reaching complete failure on every set. Proximity to failure still matters for hypertrophy, meaning an increase in muscle size: stopping when two more reps are possible does not represent the same effort as stopping when you could still do ten more.

The meta-analysis by Robinson and colleagues, published in 2024, found a trend toward greater muscle growth when sets ended closer to failure. Because the researchers estimated RIR from the study protocols, this analysis cannot establish a precise ideal distance from failure or conclude that 0 RIR is always better than 1 or 2 RIR.

Keeping a small reserve may be enough

In a study by Refalo and colleagues published in 2024, trained lifters achieved similar quadriceps growth after eight weeks of leg presses and leg extensions, a machine-based knee extension exercise, either training to failure or keeping an estimated reserve of two reps on the leg press and one on the leg extension. However, sets taken to failure caused more fatigue during the effort, showing the potential value of a small reserve on these exercises.

In a study by Hermann and colleagues published in 2025, participants performed just one set per exercise per workout, either to failure or at 2 RIR; differences in muscle growth were generally modest, although several measurements tended to favor failure. This result applies to a program with a low number of sets and does not, on its own, demonstrate that any potential advantage of failure depends on the amount of work performed.

To build muscle, a range such as 1 to 3 RIR can serve as a practical starting point for some of your sets, to be adjusted based on the exercise and your progress rather than applied as a universal rule proven for every muscle or every lifter.

What about gaining strength?

Strength also depends on your ability to master a movement with a heavy load, making practice and rep quality important. The American College of Sports Medicine (ACSM) review published in 2026 specifically highlights the value of heavy loads for improving maximal strength, without finding a consistent advantage to continuing to failure.

In Robinson’s analysis, strength gains were fairly similar across a wide range of RIR, unlike the trend observed for muscle growth; if you want to improve your bench press, keeping reps in reserve on your heavy sets can therefore help you repeat the movement correctly and better manage the rest of the workout.

Should every set have the same RIR?https://www.bodytrainingguide.com/articles/bench-press-technique-muscles-proper-form

You can plan a first set at 3 RIR, a second at 2 RIR, and a final set at 1 RIR, or keep the same target across all sets, in which case fatigue may lead you to perform fewer reps or slightly reduce the weight to maintain the required reserve.

Record the reserve you were aiming for and the reserve you think you actually kept so you can compare your sets.

Training to failure on a curl is not the same as on a squat

On a curl or cable triceps extension, it is generally fairly simple to put the weight down when you cannot continue. A free-weight squat or heavy bench press requires more planning, since you need to be able to stop a difficult rep without getting stuck under the bar.

The fatigue produced also depends on the exercise and load: in a study published in 2026 comparing the squat and chest-supported row, fatigue increased closer to failure, but its magnitude varied with the movement and weight used, and the heaviest sets were not consistently the most fatiguing.

How easily you can stop the set and how much fatigue it produces are two different questions: a machine can allow a very demanding effort even if you can put the weight down easily.

Heavy or light sets: should you be equally close to failure?

With a light load, approaching failure can require substantial effort because, as the fibers already active become fatigued, the nervous system can recruit more fibers to keep moving the weight.

A study by Lasevicius and colleagues published in 2022 on the leg extension found greater muscle growth with a light load taken to failure than with the same load stopped much earlier, whereas this difference did not appear with the heavy load. However, the light-load group that did not train to failure remained far from its limit, so this does not establish that you must reach 0 RIR rather than keep one or two reps in reserve.

If you use high-rep sets to build muscle, focus on distinguishing the burning sensation from your actual ability to continue. A light load does not require systematically training to failure, but a few uncomfortable reps are not always enough to indicate that you are close to it.

Should you train to failure on every set?

Generally, this is not necessary, as the meta-analysis by Vieira and colleagues found greater fatigue immediately after training to failure, while a bench press study observed a more pronounced drop in performance across sets than when one or three reps remained in reserve.

Before aiming for muscle failure on every set, look at how it affects the sets that follow: gaining a rep early on may come with a sharp drop in the number of reps you can perform afterward. You also need to consider technique and your recovery before the next workout, without assuming that more fatigue means better results.

Failure can still have an occasional place, for example on the last set of an isolation exercise that is easy to stop or to check your RIR estimate, while recognizing that placing it at the end of an exercise does not eliminate fatigue for the rest of the workout.

Muscle fatigue, neuromuscular fatigue, and “nervous system failure”

The expression “nervous system fatigue in strength training” is often used to describe feeling drained or struggling to reproduce your strength after demanding sets, although these sensations alone cannot determine whether the drop in performance comes mainly from the muscles or the nervous system.

Neuromuscular fatigue is a decrease in the ability to produce force, which can result from muscle function, the nervous system’s ability to activate the muscles, or both. These are referred to as peripheral and central components, respectively, and their contributions vary with the effort, without a failed rep allowing you to distinguish between them.

“Nervous system failure” is therefore not a precise threshold you can identify simply because the bar no longer moves up. To organize your workouts, it is more useful to track your reps at comparable loads and the consistency of your technique; if your performance declines persistently, review the amount of demanding work, rest periods, and your overall recovery.

How can you tell how many RIR you actually have left?

Estimating can be learned, but it remains imperfect, even among trained lifters. A review with meta-analysis indicates that estimates tend to be more accurate close to failure and on shorter sets, without finding better accuracy clearly linked to experience level alone.

To get a better sense of where you are, you can occasionally check your estimate on an exercise you have mastered that is sufficiently safe and easy to stop:

1. Start your set while maintaining a defined range of motion and technique.
2. When you think you are at 2 RIR, remember your rep count.
3. Continue without an extended pause to see how many clean reps are actually still possible.
4. Compare the result with your estimate and use this reference point in future workouts.

If you thought you were at 2 RIR and complete six more reps, your reserve was simply greater than expected. This test helps you better recognize effort on that exercise; it does not need to be repeated every workout or performed on a movement where a failed rep would be difficult to manage.

In Hermann’s study published in 2025, estimation accuracy improved over the weeks, particularly on the bench press, which encourages comparing estimates with actual situations without assuming that years of training guarantee an exact measurement.

How do you use RPE and RIR in your program?

In a strength training program, combine a number of sets, a rep range, and an effort target, as in the following examples, which illustrate how to use RIR without constituting the same prescription for everyone.

Three sets of 8 to 12 reps at 1 to 3 RIR

Choose a weight that allows you to perform between eight and twelve reps while keeping one to three clean reps in reserve, then stop each set when you reach that effort level. If you reach twelve reps and could still do six more, increase the weight slightly on your next attempt; if the eighth rep is already the last one possible, reduce it to return to the planned reserve.

As fatigue builds, you can perform twelve, ten, and then nine reps while still following the program if each set ends within the prescribed RIR range, without having to force twelve reps on every set at the risk of reaching failure.

Progressing at a comparable effort level

Going from ten to twelve reps with the same weight and about 2 RIR indicates progress, provided you maintain comparable technique, range of motion, and conditions. When your sets reach the top of the range with the planned reserve, you can try a small weight increase and start again with fewer reps.

Adjusting a less successful workout

If your usual weight takes you much closer to failure than planned, reduce it slightly or perform fewer reps to stay within the effort target. Record this adjustment along with your results to distinguish a one-time variation from a decline that repeats over several workouts.

RIR or RPE: which should you use?

RIR may be more intuitive if you prefer to ask yourself how many more reps are possible, while RPE works well when your program already uses that scale. In the version presented here, 2 RIR and RPE 8 describe the same target: choose the reference point you understand best and use it consistently, without requiring yourself to record both.

Common mistakes with failure, RIR, and RPE

• Mistaking discomfort for your limit: believing you are at 1 RIR when five more reps are possible can make you stop too early relative to the planned effort.
• Wanting every set to be maximal: systematically seeking failure because “otherwise the set does not count” can impair the work that follows; conversely, keeping a large reserve on every set can limit the intended effort for hypertrophy.
• Changing technique to maintain a number: substantially reducing the range of motion or using momentum makes reps less comparable, even if your log shows a better result.
• Increasing the weight while forgetting RIR: performing ten heavier reps at 0 RIR after previously doing them at 3 RIR does not, on its own, prove a strength gain, since you have also increased the effort.
• Using a single strategy everywhere: the reserve you choose must account for the movement, its demands, and the ability to stop the set.
• Treating an estimate as an exact measurement: an isolated rating of RPE 8 or 2 RIR is best interpreted alongside results from previous workouts.

Unusual pain is another reason to stop: it does not tell you your RIR and should not be confused with muscle burning or an effort you should push through to finish the set.

Scientific sources

• Helms et al., 2016 — Introduction to the reps-in-reserve-based RPE scale and its use in strength training. View the publication. PMC
• Robinson et al., 2024 — Meta-analysis exploring the relationship between proximity to failure, strength gains, and muscle growth. View the publication. PubMed
• Refalo et al., 2024 — Comparison of training to failure and with one to two reps in reserve for quadriceps growth and fatigue. View the publication. PubMed
• Hermann et al., 2025 — Comparison of failure and two reps in reserve in a program involving a single set per exercise. View the publication. pubmed.ncbi.nlm.nih.gov
• American College of Sports Medicine, 2026 — Review of the evidence and recommendations on resistance training prescription. View the publication. PubMed
• Journal of Sports Sciences, 2026 — Study of the effects of load, exercise, and proximity to failure on fatigue in the squat and chest-supported row. View the publication. pubmed.ncbi.nlm.nih.gov
• Lasevicius et al., 2022 — Comparison of training with light and heavy loads, with or without failure, for strength and hypertrophy. View the publication. PubMed
• Vieira et al., 2022 — Systematic review and meta-analysis of the immediate effects of training to failure on fatigue and recovery markers. View the publication. pubmed.ncbi.nlm.nih.gov
• Refalo et al., 2023 — Comparison of neuromuscular fatigue in the bench press at failure, one rep in reserve, and three reps in reserve. View the publication. PMC
• Halperin et al., 2022 — Review and meta-analysis on the accuracy of estimates of the number of reps remaining before failure. View the publication.