Meso training guide

RIR (reps in reserve), explained

Reps in reserve, or RIR, is the number of clean reps you had left when you stopped the set. Stop with two more in you and that set was 2 RIR. Grind out the last rep you possibly could and that was 0 RIR, failure.

Why it matters for muscle

Growth improves as sets get closer to failure. A 2024 meta-regression found hypertrophy rising as reps in reserve fell, with the useful zone at roughly 0 to 3 (Robinson 2024). Sets further from failure still grow muscle, just less per set.

But actually reaching failure adds very little. Meta-analysis puts the extra growth from failure over stopping just short as trivial (Refalo 2023), while the fatigue cost is much larger: bar speed four minutes after the set dropped about three times as much after failure as after stopping at 3 RIR (Refalo 2023, Sports Med Open), and recovery from failure sets can take 24 to 48 hours longer (Morán-Navarro 2017). Close is good. All the way is mostly cost.

How accurate is RIR?

Lifters are usually off by about a rep (Halperin 2022), and they get more accurate as they get closer to failure: within about five reps of it, estimates hold to about one rep (Zourdos 2016; Hackett 2017). Further away, guesses drift. That is why a working prescription should never sit far above 4 RIR, and why your estimates sharpen when the reps are hard.

RIR is also the basis of a common effort scale: on the RIR-based RPE scale, RPE 10 is 0 RIR, RPE 9 is 1 RIR, and RPE 8 is 2 RIR (Zourdos 2016).

How to judge it on the gym floor

• Ask the honest question. At the end of the set: if someone offered you money for clean reps, how many more could you get with good form?
• Watch the bar. When reps slow down noticeably on the way up, you are usually within two or three of failure.
• Calibrate on safe lifts. Once in a while, take a machine or isolation exercise to true failure and compare it with your guess. You will learn where your estimate sits.
• Never test it under a bar over your face. On bench press or skull crushers, stop at least one rep short. A missed rep there is a safety problem, not a data point.

Ramping RIR across a block

A common approach, and the one Meso uses, is to start a mesocycle further from failure and finish closer. Compounds go from 3 RIR in the first week to 2, then 1. Isolation lifts run a rep closer and may touch failure in the final hard week only, where the fatigue cost is smallest. Lifts with a weight over your face or head, and lowering-heavy moves you cannot bail out of, stop at 1 like compounds. The deload week goes back to 4 RIR.

The shape of that ramp is convention. The evidence underneath it is the trade-off above: growth improves near failure, and failure itself costs more than it pays.

RIR and progression

RIR is what makes progressive overload honest. Adding a rep at the same RIR is real progress. Adding a rep because you went from 3 in reserve to 0 is just a harder set. Keep the effort target fixed and the numbers you log tell you whether you got stronger.

References

• Robinson ZP et al. (2024). Sports Medicine. Proximity to failure and hypertrophy: a meta-regression.
• Refalo MC et al. (2023). Sports Medicine. Training to failure and hypertrophy: a meta-analysis.
• Refalo MC et al. (2023). Sports Medicine - Open 9:10. Fatigue after sets to failure versus stopping short.
• Morán-Navarro R et al. (2017). European Journal of Applied Physiology. Recovery after training to failure.
• Zourdos MC et al. (2016). Journal of Strength and Conditioning Research. The RIR-based RPE scale.
• Hackett DA et al. (2017). Journal of Strength and Conditioning Research 31(8):2162.
• Halperin I et al. (2022). Sports Medicine. Accuracy of predicting repetitions to failure.

Where the exact numbers are not settled, this guide says so: the direction is evidence, the constant is coaching convention.