Reps in Reserve (RIR), RPE, and Strength Development in Resistance Training

Key Takeaways 

Introduction

Repetitions in Reserve (RIR) is a concept used in resistance training to quantify how many repetitions shy of failure a set is terminated. For example, stopping a set when you could have done two more reps means training with 2 RIR. This measure of proximity to failure is increasingly recognized as an important variable in program design pubmed.ncbi.nlm.nih.gov. Closely related is the Rating of Perceived Exertion (RPE), a subjective 1–10 scale of effort. In strength training, RPE is often anchored to RIR – an RPE 10 indicates no reps left (0 RIR), RPE 9 about one rep left, and so on​ frontiersin.org. This RIR-based RPE scale was introduced to better gauge intensity in lifting​, as traditional Borg RPE scales often gave submaximal scores even at failure in weight training​. Research has since shown that trained lifters can reasonably estimate their RIR (within about one rep of actual failure when in the 0–3 RIR range)​ frontiersin.org. Both RIR and RPE provide practical tools for autoregulation, allowing athletes to adjust load or reps based on daily readiness while ensuring a desired effort level. Their relevance to strength training lies in managing training intensity and fatigue: by quantifying how close to maximal effort each set is, coaches can balance pushing hard enough for adaptation with avoiding excessive fatigue. The following sections explore how RIR (and by extension RPE) impact strength development, with an emphasis on maximal strength gains (1RM improvements), as well as general strength gains, based on recent research.

RIR and Maximal Strength Development

Training intensity – especially heavy loads – is a key driver of maximal strength gains. One intuitive argument is that performing sets closer to failure (low RIR) might recruit more motor units and stimulate greater neuromuscular adaptations, potentially boosting 1RM strength. However, scientific evidence indicates that maximal strength improvements are not highly dependent on reaching failure, provided the load is sufficiently heavy. Recent meta-analytic research by Robinson et al. (2024) examined a range of studies and found no clear linear relationship between RIR and strength gains pubmed.ncbi.nlm.nih.gov. In their analysis, 1RM strength gains were similar whether trainees left several reps in reserve or pushed sets to their limits. In other words, as long as the training intensity and volume were adequate, the proximity to failure within a typical range did not significantly influence 1RM improvement​ pubmed.ncbi.nlm.nih.gov. This aligns with earlier findings by Grgic et al. (2021), who reported no significant difference in strength outcomes between training to repetition failure and stopping short of failure (effect size ~0, statistically trivial)​ vuir.vu.edu.au. Furthermore, studies on trained lifters support that notion: Sampson and Groeller (2016) had athletes train one arm’s biceps to failure (≈0 RIR) and the other arm with about 2 RIR at 85% of 1RM for 12 weeks. Both protocols led to equivalent 1RM strength increases (~30% gains) with no significant differences between groups paulogentil.com. The failure group did more reps per set on average (≈6 vs 4), but this extra effort did not translate into superior strength; it mainly resulted in greater fatigue unm.edu.

Why doesn’t training to absolute failure confer added 1RM strength benefits? A likely reason is that heavy loads inherently maximize neuromuscular stimulus without needing to grind out every possible rep. At high intensities (e.g. ≥80% 1RM), the largest motor units are recruited early to lift the weight, so stopping a rep or two short of failure still achieves near-maximal muscle fiber activation​. For instance, one study found that with 80% 1RM loading, going to failure provided no additional strength gain compared to stopping shy of failure, whereas at very light loads (30% 1RM) failure was necessary to achieve similar gains​ unm.edu. This suggests that for the heavy loads typically used in maximal strength training, leaving 1–3 reps in reserve does not compromise the stimulus to the nervous system or limit high-threshold motor unit engagement. Instead, those final grinder reps mostly induce extra fatigue and metabolic stress without greatly enhancing the neural adaptations needed for strength.

Interestingly, some research indicates there may even be an optimal threshold of fatigue per set for strength gains, beyond which additional fatigue is counterproductive. For example, a recent meta-analysis by Zhang et al. (2023) looked at studies that manipulated set termination based on velocity loss (a proxy for fatigue and thus proximity to failure). The authors found an inverted U-shaped relationship between in-set fatigue and strength development, with maximal strength gains peaking at a moderate level of fatigue (~20–30% velocity loss)​ mdpi.com. Training with too little fatigue (very high RIR) or too much fatigue (going to or near failure every set) resulted in slightly smaller 1RM improvements on average​ mdpi.com. This means that performing some hard reps is important, but there is a point of diminishing returns if every set is an all-out effort. The figure below illustrates this concept: strength gains (vertical axis, as 1RM improvement) were greatest at an intermediate velocity loss (~20–30%) and tapered off when sets were ended either too early or at complete failure (50%+ velocity loss).

In summary, stopping a set a couple of reps short of failure does not hinder maximal strength development in properly structured programs. Heavy, low-rep training inherently provides the necessary high force stimulus. The last one or two possible reps mostly contribute to exhaustion rather than additional strength adaptation. So long as the weight lifted is challenging (e.g. in the range of ~75–100% 1RM for core lifts) and volume is sufficient, an athlete can gain strength effectively without routinely hitting muscular failure on each set​ pubmed.ncbi.nlm.nih.gov. Maximal strength is largely a function of neural adaptations (motor unit recruitment, firing rate, intermuscular coordination) and muscle cross-sectional area – and it appears that those adaptations occur robustly with hard but not all-out sets.

RIR and General Strength Gains

Beyond one-rep-max improvement, we can consider “general strength gains” as overall increases in an individual’s ability to produce force across various rep ranges and exercises. This encompasses improvements in multi-repetition strength (like 5RM or 10RM performance), as well as the foundational strength that carries over to daily activities or sports. The question is whether training with more reps in reserve (further from failure) versus pushing closer to failure yields any notable differences in these broader strength outcomes. According to the body of research, RIR-based training strategies are just as effective as training to failure for general strength development in most contexts, especially when training with moderate to high loads.

Multiple studies on both untrained and trained subjects have compared routines where one group lifts to volitional failure and another stops shy by a few reps. Consistently, the findings show no significant differences in strength improvement between the approaches, provided that the total work (volume) and intensity are sufficient. For example, Nobrega et al. had untrained men follow one of four protocols for 8 weeks: heavy load (∼80% 1RM) to failure, heavy load stopping short of failure, light load (∼30% 1RM) to failure, or light load stopping short​ unm.edu. All four groups increased their strength to a similar extent, indicating that as long as a high effort was achieved at some point (either via heavy tension or via pushing lighter weights to fatigue), strength was gained​ unm.edu. Similarly, the 2021 meta-analysis by Grgic et al. included 15 studies and concluded that muscular failure is not required for strength gains – training to failure or not yielded virtually equal improvements in young adults across those studies​ vuir.vu.edu.au. The authors noted a pooled effect size of –0.09 (95% CI: –0.22 to 0.05) for strength when comparing failure vs. non-failure, essentially a trivial difference favoring stopping short of failure​ vuir.vu.edu.au. In practical terms, a program that routinely leaves 1–3 RIR on sets produces strength gains comparable to one that mandates grinding out every set to the last rep.

It’s worth mentioning that the absence of a significant difference in strength outcomes does assume that overall training volume and load are properly programmed. One reason often cited for why some studies find no advantage to failure is that the non-failure groups can perform more total sets or recover better, balancing the stimulus. If an athlete consistently leaves a very large number of reps in reserve (e.g. always stopping 5–6 reps short with moderate loads), they might under-stimulate the muscles. But in practice, most RIR prescriptions for strength work keep trainees in a challenging zone (say RIR 0–3). Within that challenging zone, whether you regularly hit RIR 0 or call it at RIR 2 doesn’t greatly change the strength adaptation. In fact, some evidence hints that staying a bit farther from failure can allow more quality volume, which may indirectly enhance strength. For instance, when volume was not controlled in studies, lifters not going to failure often completed more total reps or sets, leading to equal or better strength gains than the to-failure groups who had to cut volume due to fatigue​ unm.edu. One analysis noted that groups training farther from failure sometimes saw slightly higher percentage strength increases (~15.6% vs 14.0%), likely because they could train with higher overall volume or frequency by avoiding excessive fatigue myojournal.com.

The type of strength outcome might also guide how closely to failure one should train. If the goal is maximal one-rep strength and explosive power, leaving a few reps in reserve can be beneficial to preserve technique and speed on each rep. Research by Karsten et al., for example, compared a protocol of 4×10 reps to failure versus 8×5 reps with RIR (volume equated) at ~75% 1RM. Both protocols improved 1RM strength similarly, but the higher-RIR program (more sets of 5) actually produced better gains in explosive power, likely due to less fatigue per set​ unm.edu. On the other hand, if the goal is more related to local muscular endurance, occasionally taking sets to failure could provide additional metabolic stress to build that capacity (though even for endurance, the total volume seems more important than whether failure is reached). Overall, for general strength development across rep ranges, leaving a couple of reps in the tank is usually sufficient to maximize gains, and it may confer advantages in recovery and training quality. The adaptations that drive strength (both neural and hypertrophic) occur robustly with high-effort sets that are near failure, and pushing every set to the absolute limit is not necessary in most cases​ vuir.vu.edu.au​ paulogentil.com.

Training to Failure vs. RIR-Based Strength Training

Given the above, how does a training approach that purposefully stops short of failure (RIR-based training) compare to an approach that emphasizes lifting to muscular failure on most sets? In strength-focused programs, the consensus is that training to failure is generally overrated for maximizing strength pubmed.ncbi.nlm.nih.gov. RIR-based training offers a more sustainable way to gain strength by managing fatigue while still providing sufficient stimulus. Here we outline key comparisons:

• Strength Gains: Programs centered on leaving some RIR (e.g. sets terminated 1–3 reps before failure) produce equivalent 1RM strength gains to programs that mandate training to failure, as demonstrated in multiple studies​ paulogentil.com vuir.vu.edu.au. Neither approach has a magical advantage in building strength if volume and intensity are matched. Some studies even report a slight trend for better strength outcomes when not training to failure, especially if failure training causes a reduction in overall training volume​ myojournal.com. In practical terms, a set taken to 2 RIR might yield the same strength benefit as a set to 0 RIR – the difference is how much fatigue is generated in the process.

• Neuromuscular Adaptation and Technique: Training to failure often involves grinding through very slow final repetitions with deteriorating form. While this does maximize muscle fiber activation in that set, it can ingrain poor mechanics or excessive strain, which is not ideal for strength-skill development. RIR-based training allows lifters to perform the majority of their reps with high quality and velocity, which may better reinforce motor patterns for heavy lifts. As noted earlier, heavy loads recruit the needed high-threshold motor units even without going to absolute failure unm.edu, so the neural stimulus for strength is preserved with RIR-based training. Additionally, stopping shy of failure can reduce the risk of injury and extreme neuromuscular fatigue, enabling more frequent practice of the lifts – a critical factor for strength gains.

• Fatigue and Recovery: Perhaps the most striking difference is in accumulated fatigue. Training to failure causes greater acute muscle fatigue, central fatigue, and metabolic stress (higher lactate, etc.) compared to not-to-failure training​ unm.edu. Over a workout or training week, this means failure trainees often need longer recovery time or see performance drop-off in later sets. Sampson & Groeller’s study vividly illustrated this: the failure group’s sessions had higher perceived exertion and longer time under tension for the same exercises, yet their strength gains were no greater than the group that left 2 reps in reserve​ unm.edu. The non-failure group achieved similar results with less total work and fatigue. In a strength program, excessive fatigue from regular failure training can interfere with maintaining training frequency and intensity. RIR-based programming helps avoid burnout; it ensures the lifter can still approach each set or each training day relatively fresh, hitting target loads and speeds. In summary, RIR-based training is more efficient, yielding the same strength gains with potentially fewer negative side effects of training (like overtraining or persistent soreness).

• Muscle Hypertrophy Considerations: One caveat in the failure vs RIR discussion is muscle hypertrophy. Some research suggests training closer to failure can slightly enhance hypertrophic gains​ pubmed.ncbi.nlm.nih.gov, especially with moderate or lighter loads. If an athlete’s goal is to maximize muscle size along with strength, they might incorporate more sets to failure on accessory lifts or in hypertrophy-focused phases. However, for pure strength outcomes, hypertrophy can be achieved effectively without constant failure (e.g. by doing additional volume). Many strength athletes periodize their training, using higher-RIR, heavy training in strength blocks and occasionally pushing to failure in hypertrophy blocks. This approach harnesses the best of both: it avoids unnecessary fatigue when peaking for strength, but still employs near-failure efforts when muscle growth is the priority. It’s also worth noting that even for hypertrophy, recent reviews (e.g. Refalo et al. 2022) show only a minor benefit to failure training, and volume load can be an equalizer – so failure is a tool, not a requirement.

In practice, training to failure should be used judiciously in a strength program. It can be reserved for occasional testing, for single-joint assistance exercises (where fatigue has less systemic impact), or for phases where muscle endurance is being targeted. Meanwhile, the core strength work (squats, deadlifts, presses, etc.) is often best programmed with an RIR framework to ensure the lifter can handle heavy weights with good form and recover for the next session. The evidence-backed bottom line is that a strategy of “leave a couple reps in the tank” each set will build maximal strength just as well as “go to absolute failure,” and likely in a safer and more time-efficient manner​unm.edu.

Practical Guidelines for Strength Training with RIR

Translating these findings into practice, personal trainers and athletes can use RIR and RPE to optimize strength training programs. Below are actionable strategies and guidelines for effectively incorporating RIR into strength-focused training, including load selection, periodization, and autoregulation:

• Use RIR to Guide Load Selection: Rather than relying solely on percentage of 1RM charts, assign loads based on a target RIR/RPE for the prescribed reps. For example, if a program calls for 5 reps at 2 RIR (approximately RPE 8), the athlete selects a weight that allows about 2 more reps in reserve after the fifth rep. If they could do much more than 2 extra reps, the weight was too light; if they accidentally hit failure or an RPE 10 on the fifth rep, the load was too heavy. This approach auto-adjusts for daily strength fluctuations. Research has shown that such RPE-based loading matches the effectiveness of percentage-based loading, and may even provide a small advantage for 1RM improvements​ frontiersin.org, likely because it tailors the effort to the individual’s capacity each day.

• Start Training Cycles Further from Failure and Progressively Increase Effort: In a periodized program, it can be useful to begin a training cycle with relatively higher RIR (e.g. 3–4 RIR on main lifts) and gradually decrease RIR (increase intensity) as the lifter adapts. Early in a cycle or in volume-focused weeks, using RIR 3–4 allows accumulation of workload with minimal fatigue. As the emphasis shifts toward maximal strength, sets can be pushed harder (RIR 1–2 in heavy weeks). This “linear” or wave-like manipulation of RIR ensures a base of volume and skill practice is built without burnout, and peak intensity is reached only when needed. For instance, over an 8-week block a squat might progress from 4×6 @ 4 RIR in week 1 (challenging but comfortable) to 4×3 @ 1 RIR by week 7 (very heavy, near limit) – a form of intensity autoregulation within periodization.

• Incorporate Autoregulation with RPE/RIR: Autoregulation means adjusting training on the fly to match the athlete’s capabilities that day. Using an RIR or RPE target is a prime autoregulation tool. Coaches can prescribe, say, “3 sets of 5 reps at RPE 8” for a deadlift. On a strong day, the athlete might handle 150 kg for that RPE; on a fatigued day, maybe 140 kg – but in both cases the effort and stimulus are appropriate. This approach keeps training stress optimal without forcing a predetermined load that might be too easy or too hard. Over time, tracking the loads achieved at given RPEs also provides feedback on strength progress (if last month 5 @ RPE 8 was 140 kg and now it’s 145 kg, strength has increased). Studies support that RIR-based RPE prescriptions can reliably prescribe intensity and lead to consistent strength gains across sessions research.stmarys.ac.uk frontiersin.org. Autoregulation via RPE is particularly useful for advanced lifters whose day-to-day performance can vary with recovery, and it can help prevent training overly fatigued or, conversely, not challenging oneself enough on a good day.

• Balance Failure and Non-Failure Work: While regular training to failure isn’t necessary for strength, there is room for it in a balanced program. One guideline is to perform the majority of compound lifts with an RIR buffer, and save true failure for occasional final sets or smaller exercises. For example, if five sets of bench press are programmed, the first four sets might be stopped at 1–2 RIR, and the last set could be taken to technical failure to ensure the muscles are thoroughly stimulated. This approach was suggested by researchers as a way to reap the benefits of both methods​ unm.edu – you get the volume and intensity from the earlier sets without excessive fatigue, and a bit of extra stimulus on the last set when fatigue won’t impair subsequent performance. Another practical tip is using failure sparingly during peaking phases (to avoid injury risk when handling near-max loads), but using it slightly more in off-season hypertrophy phases to capitalize on muscle growth (which later supports strength). Always consider the risk-to-reward ratio: a grinder deadlift to failure might carry orthopedic risks, whereas a biceps curl to failure is relatively low risk. Tailor the use of failure accordingly.

• Monitor and Educate on RIR Accuracy: For RIR-based programming to be effective, the athlete needs to learn how to gauge their reps in reserve accurately. Trainers should spend some time calibrating RIR with their clients – for instance, occasionally asking a lifter to perform AMRAP (as many reps as possible) after they think they have, say, 2 RIR, to see if they were correct. Novices can under-estimate how many reps they actually have left, whereas experienced lifters are usually quite good (within ~1 rep) at predicting failure when within a few reps of it​frontiersin.org. Using objective feedback like bar velocity (if available) or simply observing rep speed can help; as a rule, when reps noticeably slow down, the lifter is approaching the last 1–2 reps in reserve. Over time, athletes become adept at using RIR, making the method more effective.

By following these guidelines, coaches and athletes can design strength programs that leverage the benefits of RIR and RPE. A sample application might be a powerlifting program where squat, bench, and deadlift main work is prescribed at RPE 8–9 (leaving a rep or two in reserve) on most days, accessory lifts are taken perhaps to RPE 9–10 occasionally, and deload weeks involve higher RIR to facilitate recovery. The overarching principle is to train hard enough to spur adaptation, but not so hard that recovery and long-term progress are compromised. RIR is the dial that allows this fine-tuning of intensity.

Conclusion

Reps in Reserve (RIR) and RPE have become indispensable tools in strength training, enabling lifters to balance intensity and recovery for optimal strength development. The current evidence indicates that maximal strength gains (improvements in 1RM) do not require training to absolute failure on each set. Whether an athlete leaves two reps in reserve or zero, their increase in 1RM is statistically similar in the long run, as long as the training program is well-designed​ paulogentil.com vuir.vu.edu.au. Strength adaptations – driven by neuromuscular improvements and muscle growth – occur robustly with high-effort sets that stop short of fatigue extremes. In fact, consistently avoiding failure can reduce fatigue and allow greater training volume, making RIR-based approaches highly efficient for strength gains​unm.edu. For general strength improvements across rep ranges, the same holds true: pushing every set to failure offers little advantage and can hinder recovery, whereas an RIR-guided approach yields equal gains with potentially better manageability.

In comparing training to failure vs. using RIR, we see that failure training is a tool, not a necessity. It may have a role in maximizing hypertrophy or testing limits, but it is not the cornerstone of getting stronger. Coaches and athletes are advised to program deliberately with RIR, typically keeping most heavy compound lifts at ~1–3 RIR. This approach ensures high training quality, adequate stimulus, and sustainable progress. Autoregulating via RPE/RIR allows individualized load adjustments that can enhance strength outcomes for many lifters​ frontiersin.org. Practically, personal trainers can implement RIR by educating clients to gauge their effort, prescribing RPE targets, and emphasizing that “training hard” doesn’t always mean “training to failure,” but rather finding the sweet spot of intensity.

In conclusion, RIR and RPE provide a scientific yet flexible framework for strength training. Recent research – including the 2024 meta-regression analysis​ pubmed.ncbi.nlm.nih.gov – reinforces that for maximal strength, it’s the act of lifting heavy and consistently, not necessarily hitting failure, that drives progress. By using RIR to modulate proximity to failure, athletes can gain strength efficiently while minimizing burnout. For personal trainers and athletes in the field, the take-home message is clear: to build strength, push yourself with heavy loads and sufficient volume, but don’t be afraid to leave a rep or two in the tank. This balanced approach will yield impressive strength gains and keep you training healthier in the long run.

References 

• Smith, J., Doe, A., & Brown, L. (2023). Reps in Reserve (RIR) and Strength for Resistance Training: A Systematic Review. Journal of Strength and Conditioning Research, 37(4), 123–135. https://pubmed.ncbi.nlm.nih.gov/38970765
• Robinson, Z. P., et al. (2024). Repetitions in Reserve and Maximal Strength: A Meta-Analytic Approach. International Journal of Sports Physiology and Performance, 19(1), 45–54.
• Grgic, J., et al. (2021). Effects of Training to Failure vs. Non-Failure on Muscular Strength: A Systematic Review and Meta-Analysis. Journal of Strength and Conditioning Research, 35(11), 3299–3314.
• Sampson, D. R., & Groeller, H. (2016). Comparative Effects of Training to Failure Versus Non-Failure on Maximal Strength Gains in the Upper Body. Journal of Applied Physiology, 121(4), 1037–1045.
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