Rating how many reps we think we have left in the tank relies on perception of effort. This article discusses factors that directly influence perception of effort and what this means for training.

Key Points:

1. Factors such as music, presence of spotters, and mental fatigue can influence repetition performance despite no apparent influence on muscle physiology. These factors likely influence performance due to their effects on perception of effort.

2. This change in perception of effort likely influences RIR rating accuracy as well, especially for higher repetition sets. This concept can be described by the Psychobiological Model of performance.

3. Awareness of the influence of perception of effort can inform training execution and help contextualize performance. It is also recommended to standardize the training environment and bias lower rep ranges to maximize RIR accuracy.

Introduction

Some degree of autoregulation is built into most modern strength and/or hypertrophy training programs. This allows the session-to-session training stress to be adjusted by the lifter based on their readiness and performance. Likely the most common tool for autoregulating training loads and/or repetitions per set is the Rating of Perceived Exertion (RPE) scale based on Repetitions in Reserve (RIR). (For clarity, I will only use the term Repetitions in Reserve (RIR) for the rest of this article - an RPE 9/10 is 1 RIR, an RPE 8/10 is 2 RIR, etc.)

RIR ratings are self-reported estimates of how close you are to failure and thus rely on perception of effort. In other words, RIR ratings rely on the conscious sensation of how strenuous a repetition was, which informs how many more you think you have in the tank. While we are proponents of autoregulation via RIR, relying on perception of effort has its downsides. For instance, the accuracy of RIR ratings can be influenced by factors such as how close you are to failure, the number of reps in the set, exercise selection, and how many sets you’ve previously done in the session. These factors often have straightforward explanations - for example, repetition speed decreases at a faster rate as you approach failure, which can provide the lifter more accurate feedback for their RIR ratings.

The goal of this article is to take the RIR accuracy discussion one step further by pointing out influential factors with less straightforward explanations. We’ll start by pointing out three factors that influence performance, discuss why perception of effort likely plays a role in these factors modulating performance, and finish by discussing the practical application of these concepts as they relate to using and conceptualizing RIR.

Overlooked Factors Influencing Performance

1) Music

Ballman and colleagues have a series of studies indicating that listening to music you enjoy before (one, two) or during a set enhances the number of reps performed to failure. For example, the authors reported 15.4% (+2.2 reps) more bench press reps to failure with 75% of 1RM when listening to music prior to the set compared to no music.

2) Presence of Spotters

Sheridan and colleagues examined the influence of whether or not you think someone is spotting you on performance. Each subject performed three sets to failure with 60% of 1RM on two separate lab visits in random order. In one visit, subjects could see that there was one spotter on each side of the bench press between sets. In the other visit, the spotters were there during the sets, but subjects did not know due to opaque material around the equipment. Across the 3 sets, subjects performed an average of 11.2% more reps when they were aware of the presence of the spotters. The subjects reported higher self-efficacy before sets two and three when they thought the spotters were present, which points to the role of the social environment on repetition performance.

3) Mental Fatigue

Mental fatigue can be defined as “a psychobiological state characterized by a sensation of tiredness and lack of energy that an individual might experience after a prolonged high-demanding mental or cognitive task.” This definition comes from Gantois and colleagues, who investigated the influence of mental fatigue on repetition performance. Zac reviewed this study here, but briefly, subjects performed two squat training sessions in random order, one with a control task (documentary viewing) and one with a mentally fatiguing task (social media use) for thirty minutes halfway through the session. In the second half of each session, subjects performed three sets to failure with 80% of their 15RM on the squat (I estimate this to be ~50% of 1RM). Based on a visual analog scale for subject-reported mental fatigue, the 30 minutes of social media use successfully induced mental fatigue, and this condition led to 20% (~9-10 reps) less reps across the three sets.

Another recent study by Fortes and colleagues investigated mental fatigue via phone use on squat and bench press performance, but these subjects didn’t train to failure - they used ~70% of 1RM and stopped sets when barbell velocity decreased by 20%, which is probably well shy of failure with this load. In this case, performance can be measured with mean velocity: if force output was higher in a certain condition, barbell velocity was too. However, there was no difference in this variable with or without mental fatigue. This provides some insight into the mechanism of decreased rep performance in the Gantois study - it might be due to perception of effort as opposed to objective performance capabilities. We’ll revisit this example in the next section.

Potential Explanation: Perception of Effort

We’ve now discussed that environmental factors (e.g., music and the social environment) and mental fatigue can influence performance. (To be clear, this is not an exhaustive list - additional factors such as carbohydrate mouth rinsing may also be relevant.) On the surface, the takeaways may seem simple: listen to your preferred music, try to be in your ideal social environment, and avoid high mental fatigue going into a session. I don’t disagree with these takeaways, but these studies may explain something below the surface related to perception of effort. For insight into perception of effort, we first need to consider how failure is defined.

In the series of studies examining the influence of music on rep performance, failure was typically defined as “when the barbell was moving in the downward direction during the concentric phase or when participants verbally terminated the set.” This definition leaves open the possibility of subjects ending sets when they said they had no more reps in the tank even if they actually did. In the study on the presence of spotters, all that is reported is that the subjects were instructed to “lift to failure.” In the mental fatigue study by Gantios and colleagues, failure was defined as “voluntary exhaustion,” which makes it likely that some subjects did not actually fail reps and instead terminated the set when they thought they had no more reps left.

Given the possibility that some of these subjects didn’t actually fail a rep, it’s difficult to determine whether the decreases in rep performance in these studies are due to actual decreases in performance capabilities or instead an increase in the perception of effort of a given task. In other words, if we knew that subjects actually failed a rep, would we still see decreased rep performance? Given the ambiguity in definitions of failure, we can’t know for sure. However, we can get some insight from the mentioned mental fatigue studies: the Fortes study did not find a difference in mean velocity in non-failure sets whereas the Gantois study found ~20% less reps completed to “failure.” This may point to perception of effort (in this case, when you voluntarily “fail”) being impacted but not an objective measure (force production with a given load). I’m not saying this is bulletproof evidence for perception of effort being the driving factor, but I think it is at least indication pointing in that direction.

Psychobiological Model and Resistance Training

So far, I’ve set up actual performance and perception of effort as separate entities, but this is likely inaccurate. This is where things get complicated - especially for longer duration activities, objective performance capabilities and perception of effort may not be able to be separated. This is the basic thought process behind the psychobiological model of endurance performance. This model suggests that the conscious sensation of the difficulty of the task is what ultimately limits endurance performance. Muscle fatigue, mental fatigue, and environmental factors will feed into perception of effort, and this will ultimately determine how hard you’re willing to work before “failing.”

The psychobiological model has been proposed for endurance performance, but I suspect it applies to longer duration resistance training as well. This is why I like to make the joke that sets above 15 to failure don’t exist - even if you did fail rep 16 and dropped the bar on the pins, what if you had a team of researchers verbally encouraging you? What if you won the lottery if you completed 16 reps? As we go along the spectrum from a 1RM to a marathon, “failure” gets more and more hazy, and the role of perception of effort probably plays a bigger and bigger role.

We can see some indication of perception of effort limiting performance in the mentioned studies by looking at RPE ratings (based on general effort, not RIR). In the study on the presence of spotters, RPE ratings were actually higher when subjects did not think spotters were around. The music studies that measured it as well as the mental fatigue studies reported similar RPE (again, based on general effort) ratings between conditions. So, despite worse performance, it feels as if the effort being put forth is similar or even slightly greater. This points to perception of effort regulating failure as opposed to objective performance capabilities.

In addition to when you decide to fail, the psychobiological model suggests that how hard you’re willing to work will depend on how much longer you think you have left in the bout of exercise.

Modulation of Effort

A series of studies by Halperin and colleagues (one, two, three) provide some insight into when we may avoid maximal effort during resistance training. I reviewed the first of these studies here, but briefly, they utilized a deception design in which each subject underwent all three conditions in random order differing in what the researchers told them at the visit. However, all three conditions consisted of the same protocol: 12 five second maximal biceps contractions with ten seconds rest between them. The Control condition was told the truth, the Unknown condition was not told how many reps they will perform, and the Deception condition was told they will only perform 6 reps. This design investigates a phenomenon called repetition pacing, which modulates “maximal” force output based on how many reps you think you have left to perform. For instance, in the first of these studies, force production of the 6th rep was 5-7% higher in the Deception condition, presumably because subjects thought this was their last rep. Keep in mind that during all conditions, subjects were verbally encouraged to produce maximal force.

At each lab visit prior to being told one of the above instructions, subjects performed three pre-testing maximal contractions in order to anchor performance for the day. Force output from the first rep of all conditions was typically ~7.5% lower than the maximal force output from earlier in that lab visit. Based on the reporting, there was plenty of rest between these pre-testing contractions and the experimental set. Again, given subjects are instructed to push as hard as they can, it appears they are either subconsciously or consciously not performing to their maximum capabilities.

Interlude: Isn’t RPE supposed to be subjective?

I’m sure at least a few readers will think “Okay, I see what you’re saying about perception of effort, but isn’t the point of RPE to be your perceived exertion?” This is a good point, and I think there are good arguments both ways. On one hand, perception of effort could be inflated due to factors that should also decrease the amount of training stress applied - if your perception of effort is inflated due to poor recovery from life stressors or poor sleep, it may make sense to lean into the reduced stress. However, think through the examples provided above - music, presence of spotters, knowledge of future repetitions - these probably aren’t factors that should influence the amount of training stress applied. My opinion is that while RIR is a subjective rating, we should almost always think of it in terms of trying to quantify an objective variable: how many reps shy of failure you are. If we want to adjust the proximity to failure of a set and thus the stress applied, that can be done via different means.

Practical Application

I see three applications of the concepts discussed. First, these concepts can be incorporated in discussions related to proximity to failure (i.e., RIR) recommendations for strength/hypertrophy. We’ve discussed the potential utility of training with more than 4 RIR, and this is an unconventional take in a lot of circles. However, we like to add the caveat that this assumes accurate RIR ratings and that a lot of higher rep sets in practice that are reported as 1-3 RIR may be more like 4-6 RIR.

Second, awareness of these factors could potentially have a positive effect. With the knowledge that a given load will probably feel easier when you’re blasting your favorite music compared to training with a podcast in the background, you can contextualize your perception of effort accordingly. Also, I think this is a reason to standardize your training the best you can. If there are considerable fluctuations in the accuracy of your RIR’s (some days you are underreporting and some days you are overreporting), this is going to muddy the waters of tracking progress and the utility of your individual training data.

Lastly, when looking to maximize RIR accuracy, lower rep ranges should be biased. As discussed, longer duration bouts are more prone to inaccurate perception of how hard you’re working. Indeed, studies investigating the influence of mental fatigue on power or maximal strength typically find no difference (one, two, three). Although no influence on maximal force output may lead to the assumption that 1RM squat, bench, and deadlift strength wouldn’t be influenced, the strength measures in these studies use unskilled movements. Maximal lifts in the gym require motor skill, and there’s some evidence that mental fatigue can harm motor skill. This study is on table tennis, so I don’t claim this to be evidence for mental fatigue influencing 1RM strength; I don’t think we can make a determination either way at this point.

Final Thoughts

I want to be clear that I do not claim the psychobiological model explains all resistance training performance. Even within the endurance literature, where the psychobiological model is even more relevant, many proposed models likely hold weight.

That said, I think it’s clear that a ton goes into performance. While factors modulating resistance training performance likely fall on the more muscle-centric side, the mentioned research is a proof of concept that resistance training is not immune to psychological influences on performance. Overall, I hope this article provides an additional lens for conceptualizing performance in the gym and RIR accuracy.

Thank you to Zac Robinson and Jake Remmert for their help in editing this piece.