You Probably Have More Reps Left Than You Think: Why RIR Estimates Are Off by 3-4

Yes — most lifters, and beginners especially, are bad at estimating reps in reserve, and the error runs in one specific direction: you almost always have more reps left than you think. When you call a set "2 RIR," the research says you may genuinely have four, five, even six clean reps still in the tank. The mistake isn't random noise that cancels out. It's a systematic undershoot, and it's quietly capping the results of millions of hard-looking sets.

Picture the lifter who finishes a set of leg extensions, drops the load with a grimace, and says "that was everything." Three minutes later, fresh again, he could have done five more. I've watched that happen more times than I can count. The set looked maximal. It wasn't. Let me show you exactly how big the gap is, why your own nervous system lies to you about it, and how an objective measurement quietly fixes the problem.

Are beginners bad at estimating reps in reserve?

Yes, and worse than experienced lifters by a wide margin — but the headline finding is that everyone underpredicts, beginners just do it most. The single cleanest dataset on this is Steele and colleagues (2017), who had 141 participants predict the number of reps they could complete to momentary failure, then made them actually grind to failure to see who was right.

The result was lopsided and consistent. The least experienced group underpredicted their true capacity by roughly four to five repetitions across exercises. The most experienced group, with years under the bar, was off by about one to two reps. Note the direction: under-prediction. They could all do more than they guessed. And even the experienced lifters weren't sharp — the standard error of measurement across the whole sample ran between about 2.6 and 3.4 reps depending on the exercise, meaning inaccuracy of a couple of reps is baked in no matter how long you've trained.

So the "off by 3-4" in the title isn't hyperbole. It's roughly the beginner error in this study, and it's a chronic stop-too-early bias, not an even spread of mistakes.

Think 2 RIR, actually 4-6: how big is the gap really?

The gap is large enough to change what your set is actually doing. Stack the two best datasets and the picture is unambiguous. A trained lifter who stops at self-perceived failure — what feels like 0 RIR — still has reps left: Armes and colleagues (2020) found trained participants stopped about 2.0 reps short of true momentary failure on knee extensions even when they believed they had reached their limit. Now layer Steele's beginner error on top. A novice who feels like they're at "2 RIR" is reading a sensation that's already a couple of reps optimistic, then adding a 4-5 rep prediction error on top.

That bottom row matters most. Estimates get worse the farther you are from failure. Your sense of "reps left" is decent in the last rep or two and turns to fog above three reps out — which is exactly the deep-reserve zone where light, high-rep "pump" sets live. The number you trust the least is the one you lean on the most.

Why does effort feel maxed before it actually is?

Because your brain rates the cost of the current rep, not the count of reps remaining — and those two things come apart under fatigue. Perceived effort climbs steeply in the back half of a set: the burn, the breath, the slowing bar, a training partner watching. All of that floods the "I'm done" signal long before the muscle's force-producing machinery actually quits.

This is the core mix-up that wrecks most RIR discussions. Effort perception and reps-remaining prediction are two different measurements, and they have opposite biases. Beginners tend to overrate effort — a hard-feeling set reads as RPE 9 or 10 — which means they underrate proximity to failure and stop with reps to spare. Zourdos and colleagues (2016) saw exactly this: at near-maximal loads, novices and experienced lifters scored their effort differently for the same true distance from failure, with novices showing far more scatter in their reads. The set felt maximal. The physiology disagreed.

There's a useful corollary here. Remmert, Laurson and Zourdos (2023) found that on single-joint machine work, training experience and sex didn't significantly change RIR accuracy — what mattered was proximity. Predictions sharpened the closer people got to failure and in later, more fatigued sets. So the fix isn't just "lift for more years." It's getting genuinely close to failure often enough to recalibrate what the edge feels like. If you stop reading what muscle failure actually feels like as "this is uncomfortable" and start reading it as "the bar physically stopped," your estimates tighten fast.

What does chronically sandbagging your sets cost you?

It costs you stimulus — the exact thing the set was supposed to buy. Muscle growth is dose-dependent on proximity to failure: the last few reps before failure, where motor-unit recruitment is highest and bar speed is lowest, carry disproportionate hypertrophic signal. If your "2 RIR" is really 5 RIR, you're routinely leaving the most productive reps of every set on the table.

Do that across a whole training block and the math gets ugly. A lifter running, say, 16 working sets a week who's secretly three reps shy of their target on most of them is training closer to a maintenance dose than a growth dose — without ever feeling like they're slacking, because the sets feel hard. This is one of the quietest reasons people stall out. It often looks like a programming problem when it's really a proximity problem, and it's a prime suspect any time you find yourself not building muscle despite training hard. The flip side is real too: chasing failure on everything to "be safe" buries you in fatigue you don't need. The goal isn't max effort everywhere — it's knowing your true distance from failure so you can actually hit your target.

What objective cues do coaches use to check proximity to failure?

The main one is bar speed — how much a rep slows down across a set — because, unlike feel, it doesn't inflate. As a muscle fatigues, the bar physically decelerates, and that slowdown tracks proximity to failure in a way your perception doesn't. This is the entire premise of velocity-based training, and good coaches have used it for years as a sanity check on a lifter's self-reported RIR.

The numbers are clean and verified. Refalo and colleagues (2023) took 24 trained lifters through bench press and measured how much velocity dropped at different stopping points. The acute velocity loss they measured climbed with proximity to failure: roughly −25% after sets taken to true failure, about −13% after stopping at 1 RIR, and about −8% at 3 RIR. Across the whole session, velocity loss from the first set to the last was −22% to failure versus −9% at 1-RIR and −6% at 3-RIR. In other words, the magnitude of the slowdown is a quantitative fingerprint of how close you pushed — one that doesn't care how the set felt. Zourdos and colleagues found the same logic at the rep level: bar velocity correlated strongly with reported effort, with the relationship tighter in experienced lifters (r ≈ −0.88) than novices (r ≈ −0.77).

This is why velocity is the coach's lie detector. If a lifter says "2 RIR" but the bar already crawled to a near-stop, the velocity says they were at failure. If they say "0 RIR" and the bar is still flying, they stopped early. The bar slowing down is the thing your RIR is trying to perceive — measured directly instead of guessed.

Can velocity loss give you an unbiased RIR check?

It can give you an unbiased second opinion — which is exactly what a systematically biased guess needs. Velocity loss is the rare failure cue you can actually measure, and because a sensor has no ego, no burn, and no training partner to impress, it doesn't inflate effort the way your nervous system does. When your felt RIR and your rep-speed curve disagree, the velocity curve is usually the one telling the truth.

Here's where Riven fits. Riven uses the Apple Watch you already own — its 100 Hz motion sensors plus heart rate, no camera, no barbell clip, no extra hardware — to measure how much your reps slow down across a set, then converts that velocity decay into a 0-100 failure-proximity score in real time, per muscle group. It turns the cues you half-know — the grind, the shake, the "that felt hard" — into an objective on-wrist number, so you can see when you called "2 left" but moved like you hit failure, or stopped at "failure" with obvious speed to spare. If you want the deeper mechanics, I broke down why your reps slow down at the end of a set separately.

Now the honest caveats, because they're the whole point of trusting a number. The wrist signal is a proxy, not lab-grade — it reads roughly half the velocity-loss magnitude of a barbell linear position transducer at the same true fatigue, so you calibrate to your own readings, not to a textbook cutoff. And velocity is complementary to feel, not a universal replacement: across nearly 3,000 measurements, Paulsen and colleagues (2025) found bar velocity explained only about 30% of the variance in perceived RIR, with the relationship shifting by exercise, load, and set number. Heart rate, in Riven's model, is supporting context only — never a standalone failure signal. None of that makes velocity useless. It makes it an objective second opinion that beats guessing — and guessing, with a documented 3-4 rep bias, is what almost everyone is doing.

How to actually fix your RIR this week

You don't fix a systematic undershoot by trying harder to feel it. You fix it by recalibrating against reality. Here's the protocol I give people:

1. Take 2-3 sets to true failure on a safe machine. Leg extension, chest press, or a Smith-machine movement — somewhere a stuck rep can't hurt you. Go until the bar genuinely stops moving. This resets your reference for what 0 RIR actually feels like, and the "edge" almost always sits further out than you remembered.
2. Re-rate your normal "2 RIR" right after. Now that you've met real failure, do a working set, call your RIR, then keep going to see how many you actually had. Most people discover their old "2" was a 4 or 5.
3. Trust feel most on heavy, low-rep sets. That's where self-estimates are sharpest. On 80%-plus work, your read is fairly reliable — lean on it.
4. Distrust feel most on light, high-rep work. Deep-reserve, 15-plus-rep sets are where the guess collapses. Either push noticeably closer than feels necessary, or use an objective check.
5. Watch your rep speed on the last 2-3 reps. If they're still moving fast, you had more in the tank. A near-stalled rep means you're genuinely close. This is the manual version of what a velocity tool automates.
6. Cross-check the disagreements. When your felt RIR and an objective read part ways, log it. Over a few weeks you'll learn your personal bias — and start correcting for it before the set, not after.

Do this and your "2 RIR" stops being a hopeful guess and starts being a calibrated target. For a fuller walkthrough, I put together a complete guide to measuring your reps in reserve that builds on this.

FAQ

Do beginners underestimate or overestimate their reps in reserve?

Beginners underestimate their capacity — they stop too early. In Steele and colleagues' data, the least experienced lifters underpredicted their reps to failure by about four to five reps, while the most experienced were off by one to two. The error is a consistent undershoot: you almost always have more reps left than you think, and that gap shrinks but never fully closes with experience.

If a set feels like failure, am I at failure?

Usually not. Trained lifters who stop at self-perceived failure still average around two real reps left (Armes et al., 2020), because perceived effort spikes before the muscle's actual force-producing capacity quits. "Felt maximal" and "was maximal" are different events, and the gap is wider for beginners and on high-rep sets.

How much do reps slow down near failure?

A lot, and predictably. In Refalo and colleagues' bench-press data, acute velocity loss was about 25% after sets to true failure, roughly 13% after stopping at 1 RIR, and about 8% at 3 RIR. That measurable slowdown is why bar speed works as an objective proximity-to-failure cue when your feel is unreliable.

Can an Apple Watch actually check my RIR?

Partly, and honestly. Apps like Riven read velocity loss from the watch's motion sensors and convert it into a real-time failure-proximity score, giving you an unbiased second opinion when your felt RIR and your rep speed disagree. The caveats are real: the wrist signal is a proxy that reads about half the magnitude of a barbell transducer, and velocity explains only ~30% of perceived-RIR variance, so it's a complement to feel, not a hard cutoff. But against a guess with a documented 3-4 rep bias, it's a clear upgrade.

Will my RIR accuracy improve if I just train for years?

Somewhat, but not as much as people hope. Experience helped in Steele's data, yet even the most experienced lifters carried a 1-2 rep error and a couple-rep standard error. Other work found training experience didn't significantly change accuracy on isolation machines — what mattered was getting genuinely close to failure to recalibrate. Years help; deliberate calibration helps more.

Sources

• Steele et al. (2017), Ability to predict repetitions to momentary failure is not perfectly accurate, though improves with resistance training experience, PeerJ — https://pmc.ncbi.nlm.nih.gov/articles/PMC5712461/
• Armes et al. (2020), "Just One More Rep!" — Ability to Predict Proximity to Task Failure in Resistance Trained Persons, Frontiers in Psychology — https://pmc.ncbi.nlm.nih.gov/articles/PMC7785525/
• Refalo et al. (2023), Influence of Resistance Training Proximity-to-Failure on Neuromuscular Fatigue in Resistance-Trained Males and Females, Sports Medicine - Open — https://pmc.ncbi.nlm.nih.gov/articles/PMC9908800/
• Zourdos et al. (2016), Novel Resistance Training-Specific RPE Scale Measuring Repetitions in Reserve, Journal of Strength and Conditioning Research — https://pmc.ncbi.nlm.nih.gov/articles/PMC4961270/
• Remmert, Laurson & Zourdos (2023), Accuracy of Predicted Intraset Repetitions in Reserve (RIR) in Single- and Multi-Joint Resistance Exercises Among Trained and Untrained Men and Women, Perceptual and Motor Skills — https://pubmed.ncbi.nlm.nih.gov/37036795/
• Paulsen et al. (2025), Exercise type, training load, velocity loss threshold, and sets affect the relationship between lifting velocity and perceived repetitions in reserve, PeerJ — https://pmc.ncbi.nlm.nih.gov/articles/PMC12360324/