How accurate are repetitions-in-reserve estimates?

Understanding the question

Repetitions in reserve, or RIR, estimates how many more repetitions someone believes they could complete before reaching a defined endpoint. It can help describe set difficulty and adjust training to daily readiness, but it is a subjective estimate rather than a direct count of unused capacity. Accuracy varies with exercise, experience, repetition range and proximity to failure. An estimate of two repetitions remaining is only meaningful if the person also defines acceptable technique and range of motion. Learning to use the scale requires calibration, and a familiar rating should not be presented as proof of a specific amount of hypertrophic stimulus.

What a useful investigation needs to consider

Technical failure, inability to complete another repetition and stopping because of discomfort are different endpoints. Without a shared definition, two people can report the same RIR while doing different things.

Calibration sets taken near an endpoint should be appropriate to the exercise and performed safely. There is no need to make every free-weight compound set a maximal test just to improve a rating.

A subjective rating becomes more useful when combined with load, completed repetitions and technique notes. It should not replace investigation of pain, unusual fatigue or a consistently deteriorating training pattern.

Read the detailed explanation

The companion article explores repetitions in reserve as a measure in more depth, with topic-specific explanations and source material.