How Many Reps in Reserve Should You Leave for Muscle Growth?

Short answer: somewhere between zero and three, and the honest answer is that evidence-based coaches don't converge on one number — they converge on "closer than you think," then split on exactly how close.

What the evidence says

Reps in reserve (RIR) is the shorthand for how many more reps you could have done before true failure — 0 RIR means the bar didn't move on the next rep no matter how hard you tried; 3 RIR means you left a clearly gettable rep or two on the table. The debate isn't whether effort matters (nobody disputes that); it's whether the last rep or two before true failure adds meaningfully more growth than stopping just short of it — and whether that extra stimulus is worth its recovery cost.

Jeff Nippard's data point comes from necessity rather than theory: working with only 1–2 available sets per exercise, he noticed every single set got pushed to genuine failure — a "focus effect" of having fewer sets to spend. He backs the near-failure case with Robinson et al. (2023), which found proximity to failure, not raw set count, is the bigger hypertrophy driver — an argument for 0 RIR, at least when volume is already low.

Sydney Cummings Houdyshell runs the most literal version of "leave nothing in reserve": pick the heaviest weight you can move with good form and still hit failure by the set's end. Zero RIR, as a standing rule, not a special-occasion technique.

Renaissance Periodization's Dr. Mike Israetel complicates the picture from the other direction. In a session built for CrossFit athlete Mat Fraser, he used myo-rep clusters — 25 total reps broken into mini-sets of 3–5, with only 5–10 seconds of rest between them — specifically so no individual mini-set ever reaches true failure, while the cumulative mechanical tension across the whole cluster stays high. The logic: you capture most of the proximity-to-failure benefit without paying the full systemic-fatigue bill of grinding out a true last rep on every set. That's a meaningfully different number than Houdyshell's — closer to 1–3 RIR per mini-set, repeated often, rather than 0 RIR once.

HASfit's Coach Kozak sits at the moderate end of the whole spread, aimed at a home-training audience: pick a weight where the last two or three reps of a set are genuinely tough, then reassess after the first block. That's a working definition of roughly 2–3 RIR — hard, but with a clear buffer.

Where the coaches disagree

• 0 RIR, as standard practice (Houdyshell; Nippard in his reduced-volume protocol): every available set goes to true failure.
• Near-zero RIR per mini-set, spread across more total reps (Israetel's myo-rep clusters): the same cumulative tension, with less single-set fatigue.
• 2–3 RIR, sustainable by design (Coach Kozak): close to the edge without stepping over it every session.

The common thread: real, near-maximal effort is doing the work in all three approaches. What splits them is how much of the recovery cost of the last rep is worth paying for — which plausibly has a different answer for a competitive lifter with unlimited recovery time than for someone training around a job and two kids.

Run your own experiment

Pick an accessory lift, not your heaviest compound movement:

1. Weeks 1–2 — 0 RIR. Every working set to true failure. Log next-day soreness and whether you recovered in time for the next session on that muscle.
2. Weeks 3–4 — 2–3 RIR. Same lift, same rough volume, stopping every set a couple of reps short.
3. Compare reps and weight trend, not just how sore you felt — soreness is a weak proxy for growth. Which approach did you actually finish both weeks of without skipping a session?

FAQ

Is 0 RIR dangerous? Not inherently, on accessory and machine work with good form — the bigger risk is on heavy compound barbell lifts, where form breakdown under true failure carries real injury risk. Most coaches above reserve true failure for exercises where a missed rep is safe.

Do beginners need to worry about RIR at all? Not much yet — learning to recognize effort and form under fatigue is its own skill, and almost any real effort grows a beginner's muscle. RIR precision matters more once easy progress has already been spent.

Is myo-rep training just a fancy way to avoid failure? Not avoid — spread. The cumulative tension across the cluster can rival a single all-out set, with a smaller single-session fatigue cost.

What's the practical starting point if I don't want to overthink it? Coach Kozak's version — last 2–3 reps of a set feeling genuinely hard — is the most sustainable default for someone training frequently without a coach watching every set.

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Related: why-am-i-not-gaining-muscle · is-soreness-a-sign-of-a-good-workout

Zero RIR or three — the tribe at imbatribe.com is the place to argue about which one you actually stuck with, not just which one sounds more hardcore.