RIR and RPE
RIR is often paired with a 1–10 rating of perceived exertion (RPE). On the resistance-training RPE scale, each point below 10 is one more rep in reserve [Zourdos 2016]:
| RPE | Reps in reserve | What it feels like |
|---|---|---|
| 10 | 0 | No more good reps possible |
| 9 | 1 | One more rep, maybe |
| 8 | 2 | Two more reps |
| 7 | 3 | Three more reps |
| 6 or less | 4 or more | Comfortable; far from failure |
How accurate is it?
It is an estimate. Across 12 studies, people underpredicted how many reps they had left by about one rep on average, with wide differences between people and exercises. Estimates were better close to failure and in lower-rep sets [Halperin 2022]. So a “2 reps left” target is a range in practice, not an exact number, and it gets easier to judge with practice.
TrainHere treats reserve the same way: when it compares sets over time, it counts at most 4 reps in reserve, because estimates further from failure are less reliable.
Do you need to train to failure?
For most people, no. A meta-analysis of 15 studies found no evidence that training to momentary failure builds more muscle than stopping short of it [Refalo 2023], and the 2026 ACSM position stand reports that training to failure did not consistently change outcomes for healthy adults [ACSM 2026]. Sets that end with a few reps in reserve can still be effective when they are genuinely challenging. Pain or a clear breakdown in technique ends a set, whatever the target.
How TrainHere uses RIR
- Every working set has a target, such as “Aim for 3 reps left”. Beginner plans aim for about 3; plans for experienced lifters aim for about 2, or 1 on some muscle-building work.
- You log the reps you did and how many you had left.
- Load goes up only when every set reaches the top of its rep range at the target reserve. If the reps came at a harder effort than planned, the app keeps the load and lets you build reps first.