Reps in reserve (RIR): how close to failure you should train

There are two kinds of lifters: the ones who end every set grinding, purple-faced, convinced that anything short of failure is a waste, and the ones who stop when it "starts to feel like work". Both are leaving progress on the table. Reps in reserve is the fix.

What is reps in reserve? It's the number of extra reps you could have done at the end of a set, with good form, before hitting failure. Stop with two left and that's 2 RIR. It's the simplest way to describe how hard a set was, and how close to failure you should train depends on your goal more than your ego. This post covers what RIR means, how it lines up with RPE, what the research says for muscle size and strength, and how accurate you're likely to be. If you'd rather not do the math every set, that's what an app that does the programming for you is for.

What is reps in reserve?

Reps in reserve (RIR) is a way to rate a set by what's left, not by what you did. Ten reps with 3 RIR means you could have done 13. Ten reps with 0 RIR means the tenth was the last one possible.

It's a strength-training cousin of RPE-based effort, and it's what lets a program prescribe "3 × 8 at 2 RIR" instead of an exact weight. The load adjusts to the day, the target doesn't. That matters most in a mixed week, where yesterday's run changes how heavy today's squats feel, which is exactly why a run + lift training plan needs a flexible way to set intensity.

Reps in reserve and RPE

The two scales are tied together. Zourdos and colleagues (2016) built a lifting-specific RPE scale on RIR, with RPE 10 = 0 RIR, RPE 9 = 1 RIR, and so on.

So "what are reps in reserve" and "what does RPE 8 mean" are the same question asked two ways. For more on the RPE side, including what 7, 8 and 9 feel like under the bar, see what does RPE mean in lifting.

RIR only makes sense for lifting. Runs don't have reps you can count down to failure, so running uses general effort instead; our guide to RPE in running covers that scale, and training by heart rate covers the zone side. The research world also uses an older 6–20 scale for effort, but the short version of our guide to the Borg 6–20 scale vs the 1–10 RPE scale is that the gym runs on 1–10.

How close to failure should you train?

Short answer: closer than "comfortable", not necessarily all the way. The details depend on what you're after.

Reps in reserve for hypertrophy training

For muscle size, going closer to failure seems to help, up to a point.

• ›A series of meta-regressions that estimated RIR across studies found muscle growth improved as sets were taken closer to failure (Robinson et al., 2024). The authors flag that RIR had to be estimated from study descriptions, so the exact shape of the curve is uncertain.
• ›A systematic review of 15 studies found only a trivial hypertrophy advantage for set failure over non-failure, no advantage for momentary failure specifically, and evidence of a non-linear relationship between proximity to failure and growth (Refalo et al., 2023).
• ›Another meta-analysis found training to failure isn't required for strength or size gains, with a small hypertrophy effect of failure training in resistance-trained people (Grgic et al., 2022).

Put together: sets need to be genuinely hard to drive growth, but the last rep or two before failure adds little and costs a lot of fatigue. That's why the common reps in reserve 1–3 hypertrophy recommendation is a sensible coaching default. It keeps sets close enough to count without turning every session into a grind. Taking the last set of a safe exercise (machines, cables, isolation work) to 0–1 RIR now and then is a reasonable way to push.

Reps in reserve for strength

For strength, the picture is different. The same meta-regressions found strength gains were similar across a wide range of RIR (Robinson et al., 2024). And in the Grgic meta-analysis, when total volume wasn't matched between groups, non-failure training actually came out ahead for strength (Grgic et al., 2022).

Strength is a skill as much as a capacity. Clean, fast, repeatable reps at 1–3 RIR let you practice the lift heavy without the fatigue of grinders. For heavy power work, Helms and colleagues suggest stopping about 2–3 reps short of failure (Helms et al., 2016).

What about training to failure?

It has a place, mostly on safer exercises and the last set of a movement. Regular failure on heavy squats and deadlifts is a different matter: more fatigue, more risk of form breaking down, and, per the research above, not much extra reward. The full trade-off of training to failure is about when it helps and when it just costs you.

How accurate are you at judging RIR?

Not perfectly, and in a predictable direction.

• ›Most people underestimate what's left. A meta-analysis of 12 studies found lifters underpredicted their reps to failure by about one rep on average, with wide variation. Predictions were slightly better closer to failure and on sets of 12 reps or fewer (Halperin et al., 2022).
• ›Experience helps. In the Zourdos study, experienced squatters rated their true max close to RPE 10, while novices rated it closer to 9, suggesting novices think they have more left at their limit than they do (Helms et al., 2016).
• ›High-rep sets are hardest to judge. That's why "2 RIR" on a set of 20 is more of a guess than "2 RIR" on a set of 5.

How to get better:

1. ›Log RIR on every working set for a few weeks.
2. ›Occasionally take the last set of a safe exercise to failure and compare with your estimate.
3. ›Use bar speed as a check: in the Zourdos study, slower reps went with higher RPE (Zourdos et al., 2016).

How to use reps in reserve in a workout

Say the plan reads 3 × 8 at 2 RIR.

1. ›Warm up, rating each set.
2. ›Pick a load you think leaves 2 in the tank after 8. If you're unsure, start lighter; the method for how to choose the right weight for your sets is mostly a few honest test sets.
3. ›After set one, adjust: 4 RIR means add weight; 0 RIR means take some off.
4. ›Expect RIR to drop across sets at the same weight as fatigue builds. If the plan says 2 RIR on all three sets, you may need to reduce the load slightly by set three.

RIR also changes how you count volume. A set at 5 RIR and a set at 1 RIR are not the same workout, which is why a guide to how many sets per workout only makes sense when the sets are reasonably hard.

Reps in reserve for people who also run

If you run, RIR is your best friend in the gym.

• ›In a running-focused block, keep lower-body lifting at 2–4 RIR. You maintain strength without wrecking your legs for intervals.
• ›In a strength-focused block, push to 1–2 RIR on key lifts and keep running mostly easy.
• ›Around hard runs, expect RIR to drop at the same weight. That's fatigue showing up honestly. Lower the load rather than forcing the number.

Common reps in reserve mistakes

• ›Calling every set "2 RIR". If the last rep crawled, it was 0 or 1.
• ›Never checking calibration. Without the occasional test, your 2 RIR quietly becomes 4.
• ›Going to failure on everything. More fatigue, little extra growth, worse sessions later in the week.
• ›Stopping at the first discomfort. Hard sets feel hard. That's the point.

How exrsz uses reps in reserve

exrsz builds a periodized plan from your goal, schedule, level and equipment, and every lift comes with an effort target on the same 1–10 scale as your runs. It balances hard lifting and hard running in one plan, adapts each week to how you actually trained, and reshuffles missed sessions so your heavy sets don't end up the day after intervals.

FAQ

What is reps in reserve?

Reps in reserve (RIR) is the number of extra reps you could have done at the end of a set before reaching failure with good form. 2 RIR means you stopped with two left.

How does RIR relate to RPE?

On the lifting RPE scale, RPE 10 equals 0 RIR, RPE 9 equals 1 RIR, and RPE 8 equals 2 RIR (Zourdos et al., 2016). They describe the same thing from two directions.

How many reps in reserve for hypertrophy?

Most programs use 1–3 RIR. Muscle growth tends to improve as sets get closer to failure (Robinson et al., 2024), but training all the way to failure gives at most a small extra benefit (Refalo et al., 2023).

Do you need to train to failure to build muscle?

No. A meta-analysis found training to failure isn't required for gains in strength or muscle size, though it isn't harmful either (Grgic et al., 2022).

Are people accurate at estimating reps in reserve?

Roughly. On average, lifters underpredict their reps to failure by about one rep, and accuracy improves closer to failure and on lower-rep sets (Halperin et al., 2022).