RIR stands for "Reps in Reserve" and is a method used in weightlifting to quantify the intensity of a strength training exercise by considering how many more repetitions you could perform before technical failure or before missing a lift. Technical failure means that you cannot do another rep without proper form. RIR is used to measure the extra reps that you could perform with proper form. It is best to employ this method after you are comfortable with resistance training and have been familiarized with the scale. RIR can be the most useful in building muscular endurance, muscular development (hypertrophy), strength, or the max strength exercises in the power phase. RIR can be applied to Phases 2-5 of the OPT Model. RIR is also useful when you do not know your 1RM for a given lift. RIR gives you an opportunity to personalize the prescription in each session to meet your demands. Due to differences in preparedness, daily readiness, and neuromuscular efficiency, there can be big differences between athletes on how hard a given %1RM is going to be in a given training session. RIR is an effective tool to measure the intensity of your workout and helps you train smart by allowing you to push yourself but only to the right extent. RIR is beneficial for maximizing muscle growth, helping hit volume targets, accomplishing progressive overload, and sustaining intensity despite imbalances. RIR is similar to the RPE (Rate of Perceived Exertion) scale, which is a technique used to express how hard you feel like you are working during an exercise on a scale of 1-10. The difference is that the lifter reports how they feel (RPE) versus the number of repetitions they could still perform (RIR) .