Reps in reserve (RIR)

Reps in reserve (RIR) is the number of reps a client could still complete before muscular failure at the end of a set.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.} To prescribe it, give a target rep range and have the client stop a specified number of reps short of failure.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.} RIR reflects how the client is performing that day, allowing load adjustments between sets that a fixed percentage of one rep max can’t provide.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.}

RIR corresponds to the 1 to 10 rating of perceived exertion (RPE) scale: RPE 10 means maximal effort with no reps left, while RPE 8 or 9 indicates 1 or 2 reps left.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.}

In practice

Stopping short of failure tends to reduce fatigue and soreness, which can help clients stick with training.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.} RIR estimates are most accurate close to failure and unreliable far from fatigue; novices also judge them less accurately.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.}

The NSCA describes a calibration exercise: stop a set 3 reps short of failure, rest 1 to 2 minutes, then repeat with the same load to failure and compare.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 421.} Experienced lifters estimate RIR well, while filming sets or occasionally training to failure with a spotter can help others learn.^{2Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 65.}