Estimating RIR on the Bench Press
Turns out sex and exercise equipment make a huge difference in accuracy.
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Are you unknowingly leaving reps in the tank or pushing too close to failure when training with lighter loads? A new study published in Sports Health reveals that the popular “Repetitions in Reserve” (RIR) method, widely used by lifters to gauge effort and program training volume, has a few blind spots. Researchers discovered that both equipment choice and biological sex dramatically affect accuracy when estimating proximity to failure during bench press exercises at 65% of one-rep max. Women and anyone using free weights at this intensity consistently underestimate how many reps they have left, potentially sabotaging their training outcomes by either overtraining or undertraining.
PMID: 39382146
Key Points
This investigation examined whether sex differences and exercise equipment (free-weight barbell versus Smith machine) influence the accuracy of RIR estimation during bench press exercises at varying intensities. Twenty-six recreationally trained participants (12 women and 14 men) completed sets to failure at 65%, 75%, and 85% of their one-rep max across four sessions.
Aim
The study aimed to determine whether sex (female versus male) and equipment type (free-weight versus Smith machine) impact the validity of RIR estimation at different relative loads during bench press training.
Methods
Participants
Women (n=12): Average age 26.7 years, free-weight bench press 1RM of 48.8 kg (0.81× body mass), Smith machine 1RM of 50.6 kg (0.84× body mass).
Men (n=14): Average age 24.1 years, free-weight bench press 1RM of 91.3 kg (1.18× body mass), Smith machine 1RM of 94.1 kg (1.22× body mass).
Protocol
Participants completed four sessions over two weeks, with at least 72 hours of rest between sessions. In counterbalanced order, they performed two sessions with free-weight bench press and two with Smith machine bench press. The first session served as familiarisation; the second provided validity data. During each session, participants performed single sets to momentary muscular failure at three loads: 65%, 75%, and 85% of 1RM. Throughout each set, participants verbally reported when they believed they had two repetitions in reserve (RIR-2), which researchers compared against actual repetitions completed.
Results
At 65% 1RM (Light Load)
Significant problems emerged at this intensity. Women underestimated RIR by an average of -1.2 repetitions (meaning they thought they had 2 reps left when they actually had 3.2 reps remaining), while men were nearly accurate at -0.1 repetitions. Equipment also mattered: free-weight bench press produced underestimations of -1.1 repetitions compared to -0.2 repetitions on the Smith machine.
Accuracy rates at 65% 1RM varied considerably:
Free-weight bench press: Women achieved valid estimates only 50% of the time; men 80% of the time.
Smith machine: Women improved to 83.3% accuracy; men to 86.6%
At 75% 1RM (Moderate Load)
Performance improved substantially, with only a minor average underestimation of -0.5 repetitions across all participants. No significant differences emerged between sexes or equipment types. Accuracy ranged from 66.6% to 80% across conditions.
At 85% 1RM (Heavy Load)
RIR estimation proved highly accurate, with no significant errors detected. Men achieved 93.3% to 100% accuracy depending on equipment, while women reached 75% accuracy in both conditions.
Practical Takeaways
Expect underestimation at lighter loads: When bench pressing at 65% 1RM, you’re likely stopping further from failure than you think—especially if you’re female or using a barbell instead of a Smith machine.
Women need greater awareness at lower intensities: Female lifters should be particularly mindful that their perceived effort at 65% 1RM may not reflect reality, potentially leaving significant gains on the table.
Free weights demand greater attention: The stabilisation required during the free-weight bench press can create additional discomfort that can be mistaken for proximity to failure, especially at lighter loads.
Higher intensities are reliable: RIR estimation becomes increasingly accurate as you approach 75-85% 1RM, making it a trustworthy method for moderate to heavy training.
Focus on repetitions, not discomfort: The researchers emphasise distinguishing between muscular fatigue (actual proximity to failure) and general discomfort (which doesn’t necessarily indicate you’re close to failure).
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Key Takeaways
The RIR method remains a valid and practical tool for monitoring training intensity during bench press exercises, requiring no equipment and easily implemented with multiple athletes simultaneously. However, the method’s accuracy is context-dependent. At 65% 1RM, both biological and mechanical factors conspire to reduce estimation accuracy—women experience greater underestimation than men, and free-weight exercises produce larger errors than machine-based variants. These discrepancies likely stem from differences in muscle fiber composition, metabolic responses, and the increased stabilisation demands of free weights, which create discomfort that gets erroneously interpreted as proximity to failure. As training intensity increases to 75-85% 1RM, these differences disappear and RIR estimation becomes highly reliable regardless of sex or equipment. Coaches and lifters should provide additional education and practice with RIR estimation, specifically at lighter loads, emphasising the distinction between discomfort and genuine muscular failure.
Reference
Ruiz-Alias SA, Baena-Raya A, Hernández-Martínez A, Díez-Fernández DM, Rodríguez-Pérez MA, Pérez-Castilla A. Estimating Repetitions in Reserve During the Bench Press Exercise: Should We Consider Sex and the Exercise Equipment? Sports Health. 2025 Sep-Oct;17(5):1007-1012. doi: 10.1177/19417381241285891. Epub 2024 Oct 9. PMID: 39382146; PMCID: PMC11556642.
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