Reps in Reserve (RIR) is a method used to estimate how many more repetitions a person could perform before reaching failure during a set of resistance training. It is often used alongside the Rate of Perceived Exertion (RPE) scale to track training effort and intensity. The accuracy of RIR depends largely on the lifter’s experience and familiarity with the scale.
Experienced lifters tend to be quite accurate at estimating their RIR because they have a better sense of how close they are to failure and how their body feels at different effort levels. Research shows that participants, especially those with training experience, can reliably estimate the number of reps they have left in a set, and this accuracy improves with fatigue over multiple sets[2]. This means as a workout progresses, lifters get better at judging their remaining capacity.
However, for novice lifters, RIR can be less reliable because they may not yet understand what true muscular failure feels like or how to gauge their effort precisely. It generally takes about 6 to 12 weeks of consistent training for someone to develop the ability to accurately perceive proximity to failure using RIR[6]. Beginners might underestimate or overestimate their reps left, which can affect training quality.
Studies comparing training to failure versus stopping with some reps in reserve suggest that training with RIR can produce similar strength and hypertrophy gains while reducing fatigue and improving recovery[1][4]. This makes RIR a useful tool for managing training load without the excessive strain that comes from always training to failure.
In summary, RIR is a fairly accurate way to track training effort for those with experience, helping to balance intensity and recovery. Its accuracy improves with practice and fatigue, but beginners may need time to learn how to use it effectively.
Sources
https://rippedbody.com/rpe/
https://www.empower.physio/blog-all/rpe-vs-rir-1
https://pmc.ncbi.nlm.nih.gov/articles/PMC12560393/
https://www.youtube.com/watch?v=QJFEqvzHl10
https://www.minimumviablepump.com/guides/rir
