Reps in Reserve: How Close to Failure Should You Train

When a set turns genuinely hard, the last few repetitions feel decisive, as though everything before them was rehearsal for the moment the bar slows. For decades, lifters treated training to failure as the toll you paid for growth, the proof that a set had been worth doing. The evidence now tells a more measured story, and it changes how the final reps of every set should be judged.

Proximity to failure, usually expressed as repetitions in reserve (RIR), describes how many more reps you could have completed before form broke down. It is one of the few variables you influence on every single set, yet it is also one of the easiest to misjudge. Push too far from failure and the stimulus may be diluted. Sit too close, set after set, and fatigue accumulates without a matching return. Understanding where the useful window sits, and how reliably anyone can locate it, is the difference between effort that counts and effort that simply costs.

What proximity to failure actually means

Momentary muscular failure is the point at which a repetition cannot be completed through a full range of motion despite maximal effort. Everything short of that is defined by how many reps remain: two reps in reserve, one rep in reserve, and so on. The resistance-training-specific RPE scale formalised this relationship, anchoring perceived exertion directly to the number of reps a lifter believes they have left.⁸ A set taken to a 9 on that scale corresponds to roughly one rep in reserve, a 10 to genuine failure.

A useful synthesis of the field framed proximity to failure as a continuum rather than a switch, one that simultaneously shapes hypertrophy, neuromuscular fatigue, muscle damage, and perceived discomfort.⁵ That framing matters, because the same proximity that may add a little stimulus also adds disproportionate fatigue. The question is never simply whether harder is better, but how much closer is worth the cost.

Failure is not the gateway to growth

The clearest message from recent meta-analysis is that training to momentary failure is not required for muscle growth. A systematic review with meta-analysis of fifteen studies found no evidence that resistance training performed to failure produces superior hypertrophy compared with stopping short, with only trivial differences between conditions.¹ A separate meta-analysis comparing failure with non-failure training reached the same conclusion across both strength and hypertrophy outcomes.³

Controlled trials in trained lifters reinforce the point. Eight weeks of resistance training taken either to momentary failure or stopped with reps in reserve produced similar muscle growth in resistance-trained individuals.⁶ A single-set protocol comparing failure against a reps-in-reserve approach likewise found comparable adaptations, suggesting that the act of reaching failure itself is not the trigger.⁷ The relationship between proximity to failure and hypertrophy appears non-linear: getting reasonably close captures most of the benefit, and the final grinding reps add far less than their difficulty implies.

Strength answers to load and intent, not to grinding

For maximal strength, the case for stopping short is arguably stronger still. An earlier meta-analysis on training to repetition failure found that non-failure training produced marginally greater strength gains, differences small enough to be practically meaningless but clearly not in favour of failure.⁴ A large series of meta-regressions modelling the dose-response relationship found that strength gains were largely unaffected by how close training came to failure, while hypertrophy showed only a modest positive association with increasing proximity.²

Velocity-based work points the same direction. A randomised trial comparing a 20 percent velocity-loss threshold against a 40 percent threshold found similar squat strength gains despite the lower-loss group performing roughly 40 percent fewer repetitions, alongside better jump performance.¹¹ In other words, leaving reps in reserve preserved the quality of each rep and the freshness of the nervous system, and strength did not suffer for it.

Why the last reps feel different

If failure adds so little, why does it feel so significant? Part of the answer lies in motor unit recruitment. As a set fatigues, the nervous system progressively recruits higher-threshold motor units to sustain force, which is why the closing reps feel maximal even when the load is moderate. Yet recruitment is not unique to grinding sets: research comparing contractions found that neural drive was greater for a single high-intensity contraction than for moderate-intensity contractions taken to fatigue, with larger motor units engaged at high intensity regardless of exhaustion.¹³ High-threshold recruitment, the mechanism most associated with growth, can be reached through heavy load or through accumulated fatigue, and it does not demand that every set end in failure to occur.

The other half of the answer is cost. The same scoping review that mapped the benefits of proximity to failure also mapped its penalties: greater neuromuscular fatigue, more muscle damage, and higher perceived discomfort as sets approach the limit.⁵ Those costs are real and they compound across a session and a week, which is why repeatedly chasing the last rep can quietly erode total quality work.

Can you trust your own reps in reserve?

All of this assumes a lifter can actually tell how close to failure they are, and here the evidence is humbling. Accuracy of reps-in-reserve estimation improves markedly the closer a set gets to failure, and degrades when many repetitions are performed or when the lifter is still several reps away from the limit.⁹ A study of intraset predictions during the bench press found that lifters became more accurate as they neared failure but tended to underestimate how many reps they truly had in hand earlier in the set.¹⁰ Self-reported RIR is a skill, not a given, and it is least reliable exactly where most lifters spend their working sets.

This is why an objective proxy is valuable. Movement velocity tracks effort closely: the RIR-based RPE scale itself was validated against a strong inverse relationship between average concentric velocity and perceived exertion,⁸ and that velocity-to-effort relationship has since been confirmed across the front squat and trap-bar deadlift in trained men and women.¹² As a set fatigues, rep speed falls in a measurable way, and that decline is a more honest readout of proximity to failure than a number recalled after the set is over.

What this means in practice

The practical brief is straightforward. For most working sets, training to roughly one to three reps in reserve captures the growth stimulus without the recovery debt of repeated failure. Reserve true failure for the occasional set where it is informative, late in a session or on a final set, rather than treating it as the default. Strength work in particular rewards leaving a little in the tank, because the quality of each rep and the readiness of the nervous system matter more than the heroics of the last one.

The harder problem is knowing where you actually are. Stopping a set is a judgement, and that judgement is only as good as the information behind it. This is where a wearable that reads the working muscle in real time changes the conversation. By surfacing how output and rep speed decay across a set, it turns a vague sense of "I think I had two left" into something closer to an observation: why this set was complete, why the next rep would have cost more than it returned, and why the set counted. The interpretation, not the raw signal, is the point. The aim is not a fatigue percentage on a screen, but a clear answer to the only question that matters in the moment, which is whether to stop or continue.

Key takeaways

• Training to momentary failure is not required for hypertrophy; getting reasonably close captures most of the benefit, and the final grinding reps add disproportionately little.¹³⁶⁷

• Maximal strength is largely indifferent to proximity to failure, and may even favour stopping short to preserve rep quality and neural freshness.²⁴¹¹

• High-threshold motor unit recruitment can be achieved through load as well as fatigue, so failure is not the only route to a meaningful stimulus.¹³

• Self-reported reps in reserve is least accurate when you are still several reps from failure, the very zone most working sets occupy.⁹¹⁰

• Movement velocity offers an objective proxy for effort, declining measurably as a set nears its limit.⁸¹²

References

1. Refalo, M. C., Helms, E. R., Trexler, E. T., Hamilton, D. L., & Fyfe, J. J. (2023). Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: A systematic review with meta-analysis. Sports Medicine, 53(3), 649–665.

2. Robinson, Z. P., Pelland, J. C., Remmert, J. F., Refalo, M. C., Jukic, I., Steele, J., & Zourdos, M. C. (2024). Exploring the dose-response relationship between estimated resistance training proximity to failure, strength gain, and muscle hypertrophy: A series of meta-regressions. Sports Medicine, 54(9), 2209–2231.

3. Grgic, J., Schoenfeld, B. J., Orazem, J., & Sabol, F. (2022). Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: A systematic review and meta-analysis. Journal of Sport and Health Science, 11(2), 202–211.

4. Davies, T., Orr, R., Halaki, M., & Hackett, D. (2016). Effect of training leading to repetition failure on muscular strength: A systematic review and meta-analysis. Sports Medicine, 46(4), 487–502.

5. Refalo, M. C., Helms, E. R., Hamilton, D. L., & Fyfe, J. J. (2022). Towards an improved understanding of proximity-to-failure in resistance training and its influence on skeletal muscle hypertrophy, neuromuscular fatigue, muscle damage, and perceived discomfort: A scoping review. Journal of Sports Sciences, 40(12), 1369–1391.

6. Refalo, M. C., Helms, E. R., Robinson, Z. P., Hamilton, D. L., & Fyfe, J. J. (2024). Similar muscle hypertrophy following eight weeks of resistance training to momentary muscular failure or with repetitions-in-reserve in resistance-trained individuals. Journal of Sports Sciences, 42(1), 85–101.

7. Hermann, T., Mohan, A. E., Enes, A., Sapuppo, M., Refalo, M. C., et al. (2025). Without fail: Muscular adaptations in single-set resistance training performed to failure or with repetitions-in-reserve. Medicine & Science in Sports & Exercise, 57(9), 2021–2031.

8. Zourdos, M. C., Klemp, A., Dolan, C., Quiles, J. M., Schau, K. A., Jo, E., Helms, E., Esgro, B., Duncan, S., Garcia Merino, S., & Blanco, R. (2016). Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. Journal of Strength and Conditioning Research, 30(1), 267–275.

9. Zourdos, M. C., Goldsmith, J. A., Helms, E. R., Trepeck, C., Halle, J. L., Mendez, K. M., Cooke, D. M., Haischer, M. H., Sousa, C. A., Klemp, A., & Byrnes, R. K. (2021). Proximity to failure and total repetitions performed in a set influences accuracy of intraset repetitions in reserve-based rating of perceived exertion. Journal of Strength and Conditioning Research, 35(Suppl. 1), S158–S165.

10. Refalo, M. C., Helms, E. R., Hamilton, D. L., & Fyfe, J. J. (2024). Accuracy of intraset repetitions-in-reserve predictions during the bench press exercise. Journal of Strength and Conditioning Research, 38(3), e78–e85.

11. Pareja-Blanco, F., Rodríguez-Rosell, D., Sánchez-Medina, L., Sanchis-Moysi, J., Dorado, C., Mora-Custodio, R., Yáñez-García, J. M., Morales-Alamo, D., Pérez-Suárez, I., Calbet, J. A. L., & González-Badillo, J. J. (2017). Effects of velocity loss during resistance training on athletic performance, strength gains and muscle adaptations. Scandinavian Journal of Medicine & Science in Sports, 27(7), 724–735.

12. Odgers, J. B., Zourdos, M. C., Helms, E. R., Candow, D. G., Dahlstrom, B., Bruno, P., & Sousa, C. A. (2021). Rating of perceived exertion and velocity relationships among trained males and females in the front squat and hexagonal bar deadlift. Journal of Strength and Conditioning Research, 35(Suppl. 1), S6–S13.

13. Miller, J. D., Lippman, J. D., Trevino, M. A., & Herda, T. J. (2020). Neural drive is greater for a high-intensity contraction than for moderate-intensity contractions performed to fatigue. Journal of Strength and Conditioning Research, 34(11), 3013–3021.