RPE and RIR: Two Systems for Regulating Training Intensity

Most people regulate training intensity by feel. “That felt heavy” or “I could have done more” are common post-set assessments, but they’re too vague to drive systematic progress. Two structured systems exist for turning subjective effort into programmable data: RPE (Rate of Perceived Exertion) and RIR (Reps in Reserve). They measure related but distinct things, and each is better suited to different training contexts.

Understanding when to use which system makes every training decision more precise.

RPE is a scale of perceived effort across any physical task. The original Borg scale (developed in the 1960s for exercise physiology research) ran from 6 to 20, mapping loosely to heart rate. The modified version used in most training contexts today runs from 1 to 10, where 1 is essentially resting and 10 is maximum possible effort.

RPE measures how hard something feels globally. It accounts for cardiovascular stress, muscular fatigue, mental effort, breathing difficulty, and overall systemic load. When you finish a 15-minute conditioning piece and rate it an 8 out of 10, you’re describing your total experience of effort, not a single muscle’s proximity to failure.

This makes RPE ideal for activities where the limiting factor isn’t one muscle group reaching failure but rather the cumulative demand on your entire system: conditioning work, interval training, running, rowing, circuit-style metcons. In these contexts, no single muscle is “failing.” Your heart rate is high, your breathing is labored, your legs are burning, and your grip is challenged all at once. RPE captures that holistic experience in a single number.

RIR measures something much more specific: how many additional reps you could have completed on a given exercise before reaching muscular failure with acceptable technique. It’s a countdown from failure rather than a rating of overall effort.

0 RIR: Failure. You attempted to complete another rep and could not, or your technique broke down to the point where continuing would be unsafe.

1 RIR: One rep left. You’re confident you could complete one more quality rep but not two.