RIR and RPE are autoregulation scales that let lifters quantify how close a set was to failure. RIR stands for Reps in Reserve. RPE stands for Rate of Perceived Exertion. They are the practical alternative to rigid percentage-based programs, which assume your 1RM is the same every day. It is not.
The full picture
RPE was adapted from Gunnar Borg's perceived exertion work in cardiovascular research. Powerlifting coach Mike Tuchscherer popularized the resistance-training version in the 2000s. Sports scientist Eric Helms and powerlifter Eric Helms further validated it in the 2010s. Mike Zourdos published the now-standard 1-to-10 RPE chart in 2016, with corresponding RIR values and percent-of-1RM equivalents at each rep count.
The translation between the two scales is direct. RPE 10 is true muscular failure with zero reps left, equal to RIR 0. RPE 9.5 is one more rep maybe. RPE 9 is one rep left, or RIR 1. RPE 8 is two reps left, RIR 2. RPE 7 is three reps left, RIR 3.
Most evidence-based hypertrophy programs prescribe working sets at RPE 7 to 9. Strength work tends to live at RPE 7 to 9 in accessory lifts and RPE 8 to 9.5 in main lifts. True RPE 10 is reserved for testing or occasional drop-the-hammer sets, because failure accumulates fatigue disproportionate to its hypertrophic return.
How it converts to percent of 1RM
From the Zourdos chart, a few anchor points. RPE 10 for 1 rep = 100 percent of 1RM. RPE 10 for 5 reps = roughly 85 percent. RPE 8 for 5 reps = roughly 80 percent. RPE 8 for 8 reps = roughly 72 percent. Each rep below maximum subtracts roughly 2 to 3 percent of 1RM at a given RPE.
Common misconceptions
- RPE is not just "how it felt." It is a specific estimate of reps left in the tank at that bar speed and form. Discomfort, soreness, and breathing rate are confounders, not the signal.
- Heart rate does not predict RPE for lifting. A heavy single can produce a 120 bpm response while a 20-rep squat hits 180.
- You do not need to test 1RM to use RPE. That is the whole point. Pick a target rep range and target RPE, and load the bar until both line up.
Citations
- Zourdos MC et al. (2016). Novel resistance training-specific rating of perceived exertion scale measuring repetitions in reserve. JSCR, 30(1), 267-275.
- Helms ER et al. (2018). Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength Cond J, 38(4), 42-49.
- Borg GA. (1982). Psychophysical bases of perceived exertion. Med Sci Sports Exerc, 14(5), 377-381.