Repetitions in Reserve (RIR)

Repetitions in reserve, or RIR, is a resistance-training measure that estimates how many additional repetitions a person believes they could complete before reaching momentary muscular failure. If a set ends at 2 RIR, the lifter estimates that about two more repetitions could have been performed with the required technique. A set at 0 RIR corresponds to perceived failure .¹

RIR is used to describe or prescribe how close a set is taken to failure without requiring every set to reach failure. It can therefore help regulate training effort across different loads, exercises, and day-to-day readiness. RIR is related to rating of perceived exertion systems used in resistance training, but the two are not identical because RIR expresses the estimate directly as remaining repetitions .¹

RIR is a subjective estimate, not a direct physiological measurement. Studies show that its accuracy can vary with load, exercise, training experience, fatigue, and how close the set is to failure. Estimates tend to be more useful when relatively few repetitions remain and when lifters are familiar with the task. The value should therefore be interpreted as a practical self-regulation tool rather than an exact count of an unknowable future performance .^1,2