Reps in Reserve & RPE: How Close to Failure Should You Train?

Few questions shape your results as much as this one: how hard should a set actually be? All the way to muscular failure, where not one more clean rep is possible? Or with a couple of reps in the tank for safety? This is exactly what Reps in Reserve (RIR) and RPE are about. They make the intensity of a set measurable – and therefore controllable. In this article we explain what RIR and RPE mean, what current research says about proximity to failure, and which training apps help you regulate your intensity.

What Reps in Reserve and RPE mean

Reps in Reserve describes how many repetitions you could still perform at the end of a set. If you finish a set feeling that exactly two more clean reps were possible, you trained at 2 RIR. At 0 RIR, you're done – that's true muscular failure.

RPE stands for Rate of Perceived Exertion. In the modern version tailored to resistance training, the RPE scale is tied directly to Reps in Reserve: RPE 10 equals 0 RIR (no rep left), RPE 9 means 1 RIR, RPE 8 means 2 RIR, and RPE 7 means roughly 3 reps remaining. Instead of "as hard as possible," you give your effort a concrete number – one you can compare from set to set and week to week.

What the research says about proximity to failure

Training to muscular failure was long seen as the gold standard. The evidence today is far more nuanced. A large meta-regression by Robinson and colleagues (2024) examined the relationship between proximity to failure, muscle growth, and strength – and clearly separated the two goals.

For muscle growth, a dose-response relationship emerged: the closer sets were taken to failure (that is, the lower the RIR), the larger the gains in muscle size tended to be. If you train for hypertrophy, you benefit from pushing your working sets relatively close to the limit.

For pure maximal strength, however, the effect was negligible. Whether you end a set with several reps in reserve or right at failure barely influenced strength gains – as long as the load is high enough. That creates flexibility: strength athletes can train with a bit more in reserve, reduce fatigue and injury risk, and still get strong. We explore this interplay of stimulus, progression, and load in our article on progressive overload.

Why we often misjudge failure

As useful as RIR is, estimating it is harder than most people think. Studies show that less experienced trainees in particular overestimate how close to failure they are: they believe they're near the limit but actually have several reps left. Accuracy improves with training experience – and the closer you actually get to failure. Lifters who have repeatedly experienced true muscular failure can gauge their remaining reps far more reliably.

In practice, this means: if RIR is new to you, it's worth taking individual sets to genuine failure now and then, so you learn what 0 RIR really feels like. That uncompromising drive to the limit sits at the heart of high-intensity concepts. The Editor's Choice app HIT Trainer, for instance, builds entire sessions around the idea of taking a few sets to maximum effort with controlled rep execution all the way to the limit.

How to use RIR and RPE in your training

A proven framework looks like this: for muscle growth, your main lifts usually sit between 0 and 3 RIR (RPE 7 to 10), with the hardest sets placed toward the end of an exercise or a training block. For pure strength blocks, 1 to 3 RIR is often enough, because here load and technique take priority over grinding out every last rep.

The biggest advantage of RIR and RPE is autoregulation: on a strong day, the same RPE might mean more reps or more weight, and on a tired day correspondingly less. Instead of rigidly working through a fixed number scheme, you adapt the load to your daily form – which protects against overload and keeps quality high. To learn how to combine these stimuli with enough recovery so progress actually shows up, read our article on recovery and deload weeks.

How apps help you with RIR and RPE

The practical value of training apps lies in capturing RIR and RPE and making them visible over time. Logging apps like Strong and Hevy let you note an RPE or RIR value for every set – so you can see whether your intensity holds up over the weeks or whether you're systematically staying too far from failure. AI-driven planners like Fitbod use your effort feedback to adjust the load and volume of your next session. And apps with a clear focus on progressive overload like Push-pull help you dial the load up methodically without losing track. If you prefer guided training, programs like Movyn offer a clear structure that prescribes intensity and volume for you.

Conclusion

RIR and RPE turn the vague "as hard as possible" into a controllable variable. Research suggests going relatively close to failure for muscle growth, while a bit more reserve is perfectly fine for maximal strength. Because we often overestimate our remaining reps early on, it's worth getting acquainted with true failure now and then to train your own judgment. A good app takes the remembering off your hands: it logs your RPE values, shows trends, and makes sure you regulate your intensity deliberately – instead of leaving every set to chance or to how you feel that day.