What Is ‘Reps in Reserve’ & How Can It Help You Build Muscle?

If you're curious about how to build muscle without completely overdoing it, implementing "reps in reserve" (RIR) into your workouts could be a total game-changer. RIR is a training method that helps you gauge how many more reps you're able to complete before failure. It can help you structure your workouts more effectively while maximizing strength and muscle gains.

We spoke with a certified personal trainer who explains everything you need to know about RIR and how you can incorporate it into your own fitness routine.

What Is Reps in Reserve?

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"Reps in receive refers to when you complete a set but [can still] perform more reps," explains Domenic Angelino, CPT with International Personal Trainer Academy (IPTA).

For instance, if you complete a set of 10 reps but know you could have performed 12 reps if you had continued lifting, your reps in reserve amounts to two reps.

"[The concept of] reps in reserve only applies to reps that you could do with good form through a full range of motion," Angelino points out. "So if you completed a set of 10 reps, and you knew that you could have only performed two extra reps with bad form, then you do not have two reps in reserve. You have zero reps in reserve."

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How To Calculate RIR

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Calculating RIR and adding this method to a workout is something many fitness enthusiasts familiar with weightlifting do naturally.

"If you want to directly calculate reps in reserve, use a [one-rep max] (1RM) chart, and identify the percentage of your 1RM you would need to lift to perform two more reps than your target rep number," Angelino recommends. "So if you [plan] to perform a set of 10 reps, look for the percentage of 1RM associated with 12 reps, which is around 67% or so of your 1RM. Use that weight, but only perform sets of 10 reps."

For reference, your 1RM is the maximum amount of weight you can lift to complete one rep of a particular exercise. "In other words, you can figure out which weight to use by using a weight appropriate for two reps higher than your target rep number when using a 1RM chart," Angelino adds.

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How Can Reps in Reserve Help You Build Muscle?

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You may wonder, "If I'm keeping these reps in 'reserve,' how will that help me build muscle?" The process may seem counterintuitive, but Angelino assures you that holding back the number of reps you complete for the majority of your sets can increase the total number of reps you perform.

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"This is because training at max capacity—going until you can't perform any more reps—is very fatiguing," he explains. "If you get fatigued too quickly, you will do [fewer] reps in your later sets and exercises during that workout. If you experience too much overall fatigue, [it] might even impact how many reps you can perform in your next workout."

According to Angelino, it's usually recommended to choose a weight that allows you to keep a minimum of two reps in reserve for every set. "So, if you [aim] to perform 10 reps, use a weight that you can perform 12 reps with," he says. "But stop the set when you hit your 10-rep target despite still having two reps in reserve."