Repetitions in Reserve

Repetitions in reserve, written RIR, is how many more repetitions you could have completed when you stopped a set. Finishing a set of eight with two still in you is eight at 2 RIR; going to the point where one more was impossible is 0 RIR, or failure.

It is a way of writing a program in terms of effort rather than weight. A session calling for three sets of eight at 2 RIR adjusts itself to how you feel: on a strong day you use more weight to arrive at the same effort, and on a tired day you use less. A session calling for a fixed percentage cannot do that.

It also keeps most training short of failure, which the research increasingly supports. Taking every set to failure adds a great deal of fatigue for very little extra adaptation, and makes the sets that follow worse.

What it is not

It is not an exact measurement, and beginners are consistently bad at it, typically having three or four more repetitions left than they believe. The estimate improves with experience, and it improves fastest if you occasionally take a set to actual failure to recalibrate.

Where you see it in FitnessSyncer

FitnessSyncer does not record a repetitions in reserve figure of its own. You will meet it in a plan written by a coach or an app, beside a set, saying how much to leave in the tank; the set you actually complete arrives here as an activity carrying its weight and repetitions.