Science
Rate of Perceived Exertion (RPE)
RPE is a way to express the reps you left in reserve at the end of a set. An RPE 9 means one more rep was possible; an RPE 7 means three more were possible.
What the evidence says
Mike Tuchscherer adapted RPE from the Borg scale for barbell training in Reactive Training Systems. The practical value is autoregulation: two lifters at the same 1RM can have very different days, and RPE lets programming bend to the day instead of forcing the day to bend to the programming.
Studies reviewing RPE-based vs percentage-based training report comparable hypertrophy and strength outcomes when volume is equated, with RPE offering better session-to-session flexibility. RPE is not an objective physiologic measurement — it is a self-report — and reliability depends on how honest and calibrated the lifter is.
In LiftProof, RPE logging is optional per set. Programs like GZCLP and 5/3/1 Beyond can be run on percentages alone; adding RPE augments the training-max adjustment signal.
Evidence base
Sources
Source 01
Helms et al. 2016 — RPE and RIR for resistance training(opens in a new tab)Review of RPE/RIR reliability for auto-regulated resistance training.
Source 02
Greg Nuckols — RPE: What is it and how to use it(opens in a new tab)
LiftProof defaults draw from the published strength literature.