How accurate is RIR? Research suggests: not very, even for experienced lifters. Across multiple studies, trained lifters consistently underestimate how many reps they actually have left, sometimes by two, three, or more reps, especially the further they are from true failure. Discomfort, it turns out, is a pretty unreliable gauge of your real capacity.
In this episode of Not Another Mindset Show, I’m breaking down what exercise science actually says about how accurate our RIR (reps in reserve) and RPE (rate of perceived exertion) estimates really are, and the mind-body connection I couldn’t stop seeing once I read the research. This isn’t a topic I usually cover on this show (it’s exercise science, not psychology), but I couldn’t resist pulling the thread into what I actually teach inside The Health Mindset Coaching Certification: how we chronically underestimate our own capacity, in the gym and everywhere else.
If you strength train, coach strength training, or program RIR-based workouts for clients, this one’s for you.
What You’ll Learn in This Episode
- How accurate is RIR really, according to the research (the short answer is: not very)
- Why the gap between your perceived limit and your actual limit gets bigger the further you are from failure
- What “anchoring” is, and why the number you predict can become the number you stop at
- Why discomfort is a misleading signal for where your true failure point is
- The mindset and self-efficacy connection I couldn’t stop making (and why that connection is mine, not the exercise scientists’)
- A responsible take on what to actually do with this information
How Accurate Is RIR? What the Research Found
Every time you train, you’re making a judgment call. Rate of perceived exertion. Reps in reserve. How much do I actually have left in the tank? Progressive overload depends on that number being at least roughly accurate. So I went looking: can people actually predict their own failure point?
A 2022 meta-analysis in Sports Medicine (Halperin et al., pulling together 12 studies and over 400 people) found that, on average, people under-predict. They think they’re out of reps when they’ve usually still got about one more, sometimes more, and training status didn’t reliably change that. Experienced lifters weren’t meaningfully better at it than newer ones.
Here’s the pattern that got me interested, though: accuracy gets worse the further you are from true failure. One study (Zourdos et al., 2019) had lifters predict their RIR at different points in a set. When lifters thought they had five reps left, they were often off by close to five reps. At three RIR, off by nearly four. Even at one RIR, close to the end of the set, people were still off by about two reps on average. The earlier you have to guess, the bigger the gap between what you think you can do and what you can actually do.
How Accurate Is RIR When You Factor In Anchoring?
One of the trickier problems in this research is something scientists call anchoring. Once you tell yourself “I’ve got two left,” you tend to stop at two, not because that’s your actual limit, but because that’s the number you committed to, out loud or in your head.
So a group of researchers (Armes et al., 2020, in Frontiers in Psychology) ran a study designed to strip that anchoring effect out. They told participants it was a reliability study, a cover story so people wouldn’t try to game their own predictions. Even with the anchoring removed, trained lifters still underestimated their reps in reserve by around two reps.
That tells you there are two layers happening here. First, the number you predict tends to become your ceiling, simply because you said it. Second, even once you take that effect away, there’s still more capacity sitting there than you think. Your actual limit and your perceived limit just aren’t the same thing.
How Accurate Is RIR When Discomfort Kicks In?
So why does this happen? The researchers’ explanation is the part that stuck with me. As a set goes on, it gets harder. Less comfortable. And we interpret that rising discomfort as a signal: okay, I’m almost done, I’m nearly there.
But discomfort showing up isn’t the same thing as hitting your actual limit. It’s just discomfort. If even experienced lifters are reading “this feels hard” as “I’m at my ceiling,” it’s worth asking how much stock we should put in a client’s RPE or RIR self-report at face value.
To be clear about what belongs to the research and what’s mine: the exercise scientists behind these studies aren’t making any claims about mindset or psychology. They’re not thinking about belief or self-efficacy at all, that’s not their field. What I’m about to connect this to is my own interpretation, layered on top of their findings, not something these papers themselves argue.
How Accurate Is RIR as a Mindset Signal?
Here’s the tie-in I couldn’t not make. I have published research on self-efficacy (your belief in your ability to keep going even in the face of obstacles), and self-efficacy is one of the strongest known predictors of whether someone sticks with a hard thing. It shapes how much effort you put in and how long you persist once things get uncomfortable.
What this research shows, in a physical and measurable way, is that the limit you set for yourself often becomes the limit you actually reach, whether that’s true or not. Miscount the weight on the bar and accidentally hit a PR you “shouldn’t” have been able to get? That’s not a fluke. That’s belief doing exactly what belief does.
This is where it connects to one pillar of the coaching framework I teach inside HMCC: optimization. You don’t get your best results just by focusing on what’s broken and needs fixing. A lot of it comes from recognizing and building on capacity you already have, capacity you’re probably underestimating. If reps in reserve are unrecognized physical capacity, the same pattern shows up anywhere someone tells themselves “I can’t handle much more of this” before they’ve actually tested that ceiling.
How Accurate Is RIR in Practice?
I can already hear the pushback: “So you’re saying I should grind every set to failure?” No. Please don’t. That’s not what the research says either. There’s good evidence (Refalo et al., 2024, in the Journal of Sports Sciences) that stopping a rep or two before true failure builds just as much muscle as training all the way to failure.
So this isn’t permission to ignore safety or blow past a real limit to prove a point. It’s simply a reminder that your actual capacity tank is probably deeper than you think it is, in the gym and in whatever else feels hard right now. And as a coach, that’s worth remembering the next time a client’s RPE numbers don’t quite line up with what you’re seeing.
Key Takeaways
- How accurate is RIR? Not very, even among experienced lifters, according to a 2022 meta-analysis of 12 studies.
- Accuracy gets worse the further you are from true failure. Predictions at 5 RIR were off by nearly five reps in one study.
- Anchoring plays a role: the number you say becomes the number you stop at, even when a study design removes that bias.
- Discomfort is a misleading signal. Feeling like you’re at your limit isn’t the same as being at your limit.
- Stopping 1-2 reps short of failure still builds muscle, so this isn’t an argument for grinding every set.
- The mindset and self-efficacy connection is my own interpretation of this research, not a claim the exercise scientists themselves make.
Frequently Asked Questions About How Accurate RIR Really Is
How accurate is RIR (reps in reserve)?
Not very accurate, even for experienced lifters. A 2022 meta-analysis in Sports Medicine (Halperin et al.) found that people, on average, underpredict their reps in reserve, often by about one rep, and sometimes more. Training experience didn’t reliably improve accuracy. Other studies found the gap widens further from failure, with lifters off by two to five reps depending on how early in the set they’re asked to estimate.
What is RIR in strength training?
RIR stands for reps in reserve, an estimate of how many more reps you believe you could perform before reaching muscular failure. It’s closely related to RPE (rate of perceived exertion) and is commonly used to guide training intensity and progressive overload. Both rely on a lifter’s ability to accurately judge their own remaining capacity, which research suggests is harder to do than most people assume.
How accurate is RIR for experienced lifters specifically?
Part of it is anchoring: once a lifter tells themselves a number, that number tends to become where they stop. Part of it is that rising discomfort during a set gets misread as a sign of hitting a true limit, when discomfort and actual failure aren’t the same thing. Research designed to remove anchoring bias still found trained lifters underestimating their remaining reps by around two.
Does training to failure build more muscle than stopping a few reps short?
Not necessarily. Research (Refalo et al., 2024, in the Journal of Sports Sciences) found that stopping one to two reps before true failure produced similar muscle growth compared to training all the way to failure. This research isn’t an argument for always leaving reps in the tank, but it does mean lifters don’t need to grind every set to failure to make progress.
What is anchoring bias in RPE or RIR tracking?
Anchoring bias is the tendency for the number a lifter predicts to become the number they actually stop at, simply because they said it (out loud or in their head), rather than because it reflects their true physical limit. Studies designed to remove this effect through a cover story still found underestimation, suggesting anchoring is only part of the accuracy problem.
How does RIR accuracy connect to mindset and self-efficacy?
This connection is not something exercise scientists themselves claim; it’s my own interpretation as a mindset researcher. Self-efficacy (belief in your ability to keep going through discomfort) shapes effort and persistence. If lifters chronically underestimate physical capacity they haven’t actually tested, it mirrors a broader pattern where people limit themselves based on perceived difficulty rather than actual capability.
How accurate is RIR when it’s a client self-report, not your own?
Client-reported RPE and RIR are still useful tools, but this research is a good reminder to treat them as estimates, not exact measurements, especially early in a set. Since even experienced lifters misjudge their own limits, coaches may want to periodically test true capacity in controlled, safe conditions rather than assuming self-reported numbers always reflect what a client can actually do.
Links & Resources
[NEW FREE GUIDE]: Best Questions for More Clients and More Sales Conversions
Strengths-Based Coaching: Why Fix-It Mode Backfires With Clients | EP 107
Stress and Self-Control: Why Stressed Clients Can’t Follow Through | EP 104
Health Mindset Coaching Certification
Follow Dr. Kasey Jo on Instagram: @drkaseyjo
AUTHOR BIO
Dr. Kasey Jo Orvidas, PhD is a published mindset and health behavior change researcher with over a decade of health and fitness coaching experience. She is the founder of the mindset and behavior change coaching program: The Health Mindset Coaching Certification.
