Reps in Reserve (RIR) is a way to measure how many more repetitions you could perform at the end of a set before reaching failure. It is often used alongside the Rating of Perceived Exertion (RPE) scale to help lifters gauge effort and manage fatigue. When it comes to isolation exercises, the accuracy of RIR can vary but generally tends to be fairly reliable, especially for experienced trainees.
Isolation exercises, such as bicep curls or leg extensions, typically involve simpler movement patterns and smaller muscle groups compared to compound lifts like squats or deadlifts. Because of this, it is often easier for individuals to estimate how many reps they have left in reserve during isolation work. The controlled nature of these exercises allows for better self-assessment of fatigue and effort, making RIR a useful tool for managing training intensity without always going to failure[1][3].
Research and coaching experience suggest that leaving 1 to 3 reps in reserve during most sets is effective for balancing progress and recovery. For isolation exercises, it is common to take the final set closer to failure, sometimes even to failure, since these movements generally cause less systemic fatigue than compound lifts. This approach helps maximize muscle engagement while reducing the risk of overtraining[1].
However, the accuracy of RIR depends on the lifter’s experience and ability to judge effort. Novices may struggle to estimate reps in reserve accurately, which can lead to either stopping too early or pushing too hard. Over time, as lifters become more familiar with their limits and the sensations of fatigue, their RIR estimates tend to improve[1].
In summary, RIR is a practical and reasonably accurate method for monitoring effort in isolation exercises, especially for those with some training experience. It helps manage fatigue and optimize training without the need to reach failure on every set, which can be beneficial for long-term progress and injury prevention.
Sources
https://rippedbody.com/rpe/
https://pmc.ncbi.nlm.nih.gov/articles/PMC12560331/
https://www.bodyspec.com/blog/post/fitt_principle_a_guide_to_a_smarter_workout_plan
https://betterme.world/articles/building-a-workout-plan/
https://www.cleaneatzkitchen.com/a/blog/gym-talk-a-glossary
