Reps in reserve, RIR for short, is a question you ask after a set: how many more good reps could I have done? If the answer is two, it was a 2 RIR set. If you could not have done another, it was 0 RIR, which is failure. It is a way to describe effort without needing a percentage of a one-rep max.
The short version
- 0 RIR means nothing left. 1 RIR means one more rep was possible, and so on up.
- The American College of Sports Medicine's 2026 position stand gives about 2 to 3 reps in reserve as one example of sufficient effort.
- People guess about one rep too few left on average, and guess better close to failure.
The scale
RIR is usually paired with a 1-to-10 effort scale, RPE. On the version built by Zourdos and colleagues (2016), RPE 10 is 0 reps left, RPE 9 is 1 left, RPE 8 is 2 left, and so on. In their study of 29 lifters, bar speed fell as RPE rose, in both experienced squatters and novices (correlations of -0.88 and -0.77). That is evidence the ratings track real effort.
| Reps in reserve | RPE | Meaning |
|---|---|---|
| 0 | 10 | No more reps. Failure. |
| 1 | 9 | One more rep was possible. |
| 2 | 8 | Two more reps were possible. |
| 3 | 7 | Three more reps were possible. |
| 4 or more | 6 or lower | Easy. Four or more left. |
How to use it
Choose a target, for example 2 RIR on every set. Pick a weight you think fits, do the set, and stop when you reach roughly that effort. Write down the reps and how many were left. Next session, if the sets felt easier than the target, add weight or a rep. Helms and colleagues (2016) describe the scale as a way to match load to how you feel that day, adjusting set by set.
A worked example
The plan is 3 sets of 8 at about 2 RIR. Set 1: 8 reps, and it felt like 3 were left, so it was 3 RIR and you could have done 11. Set 2: 8 reps, 2 left. Set 3: 8 reps, 1 left. That is a good day: the effort rose as you got tired, as it should. If the first set had been 5 RIR, the weight was too light, and you would add some next set.
How accurate are you?
A 2022 review of 12 studies and 414 people found that lifters under-predicted how many reps they had left by 0.95 reps on average (95% confidence interval 0.17 to 1.73). Accuracy improved when the prediction was made closer to failure, with sets of 12 reps or fewer, and in later sets. Training experience made no clear difference (Halperin and colleagues, 2022). In plain terms: if you think you have three left, you may have a little more, and an estimate of "six left" is mostly a guess.
That is why Vital's effort row stops at "4+". After a set you can tap 0, 1, 2, 3 or 4+ for reps left in the tank, and show them as RIR or RPE. The app counts 4+ as exactly 4, so it never gives you more credit than you reported. Your logged sets, with their effort, feed the next-session suggestion.
What we are less sure about
- Whether going near failure matters. A meta-analysis of 15 studies found no advantage for training to momentary failure over stopping short, for muscle growth (effect size 0.12, confidence interval -0.13 to 0.37). It found a trivial edge for "set failure" in the broader grouping (0.19, interval 0.00 to 0.37) (Refalo and colleagues, 2023).
- A dose-response look. A later meta-regression found strength gains similar across a wide range of reps left, while muscle growth rose as sets ended closer to failure. Its authors call it exploratory and note that the reps left in each study had to be estimated from descriptions (Robinson and colleagues, 2024).
- Exact targets. The ACSM position stand says sets to fatigue do not enhance strength, hypertrophy or power gains, that near-failure effort works, and that there is not enough evidence to set exact RIR or RPE targets. It adds that failure may not suit some groups, such as older adults.
- High-rep sets. Estimates get worse as the number of reps goes past 12, so RIR is most useful for heavier sets.
Sources
- Zourdos MC, Klemp A, Dolan C, et al. Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. J Strength Cond Res 2016;30(1):267-275. doi:10.1519/JSC.0000000000001049
- Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength Cond J 2016;38(4):42-49. doi:10.1519/SSC.0000000000000218
- Halperin I, Malleron T, Har-Nir I, et al. Accuracy in predicting repetitions to task failure in resistance exercise: a scoping review and exploratory meta-analysis. Sports Med 2022;52(2):377-390. doi:10.1007/s40279-021-01559-x
- Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ. Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: a systematic review with meta-analysis. Sports Med 2023;53(3):649-665. doi:10.1007/s40279-022-01784-y
- Robinson ZP, Pelland JC, Remmert JF, et al. Exploring the dose-response relationship between estimated resistance training proximity to failure, strength gain, and muscle hypertrophy: a systematic review and meta-regression. Sports Med 2024;54(9):2209-2231. doi:10.1007/s40279-024-02069-2
- Currier BS, D'Souza AC, Fiatarone Singh MA, et al. American College of Sports Medicine position stand: resistance training prescription for muscle function, hypertrophy, and physical performance in healthy adults: an overview of reviews. Med Sci Sports Exerc 2026;58(4):851-872. doi:10.1249/MSS.0000000000003897
- American College of Sports Medicine. Position stand: progression models in resistance training for healthy adults. Med Sci Sports Exerc 2009;41(3):687-708. doi:10.1249/MSS.0b013e3181915670
Written November 5, 2026. This is general information, not medical advice. Talk to a doctor or dietitian before big changes to how you eat or train, especially with a medical condition or a history of disordered eating.