Define the repetition first
If one person counts repetitions with a full intended range and another counts partial movements after technique changes, their estimates may refer to different tasks. “Two more” needs an answer to “two more of what?”
An invented example makes the issue clearer. After eight repetitions, someone believes they could do two more controlled repetitions. If they could also do five shorter, assisted movements, those do not necessarily contradict the estimate. The stopping rule differs.
Why the estimate can move
Familiarity with the exercise, the load, fatigue, and experience judging effort can affect confidence in an RIR estimate. It can be recorded as approximate: “probably two or three left” may be more honest than a precise-looking number.
ACSM's current resistance-training guidance includes effort as a relevant training variable. A randomized trial by Izquierdo and colleagues also compared training to failure and nonfailure under a specific protocol. Such studies concern defined programs and populations; they do not establish one ideal RIR for every person or exercise.
Three terms that can get mixed together
- Effort: how close the set feels to its defined limit.
- Load: the resistance being moved.
- Discomfort: a sensation that may or may not reflect useful muscular effort.
A light load can eventually require high effort. Pain is not a required confirmation that the estimate is correct.
What the number is good for
RIR can add context to a training log. Eight repetitions with many left and eight with almost none left describe different experiences. The estimate can help compare sessions without requiring a maximal attempt every time. It remains a tool for describing training, not a score someone needs to maximize or minimize.
