Accuracy in predicting repetitions in reserve during resistance training: Differences Across load intensities, distance from muscular failure, sexes, and exercises

Abstract

Resistance training adaptations depend not only on external load but also on the accurate regulation of effort, particularly the ability to estimate proximity to muscular concentric failure. The Repetitions in Reserve (RIR) scale has emerged as a practical tool to quantify relative intensity, but evidence suggests that several factors may influence the ability for individuals to accurately report RIR. This study investigates the influence of load intensity, distance from muscular concentric failure, sex, and exercise type on the accuracy of predicting RIR during resistance training. Thirty-four healthy young adults aged 21.76 ± 2.35 years old with at least 6 months of resistance training experience participated in the study. Participants performed exercises at 50% and 75% of their one-repetition maximum (1RM), reporting perceived RIR at 3RIR and 1RIR. Results indicated higher accuracy in RIR reporting at 1RIR compared to 3RIR (all p ≤ 0.001, except for the lying leg curl, p = 0.097) and at 75% of 1RM compared to 50% (all p < 0.001). Sex did not impact RIR accuracy except for the cable triceps pushdown (3RIR at 50% of 1RM), and minor differences were observed between exercises in which more accuracy was observed during the lying leg curl. The findings highlight the importance of educating individuals on the intensity of effort and relative intensity ratio (RIR) for effective training intensity regulation. Practitioners should consider these factors, particularly load intensity and distance from muscular concentric failure when prescribing resistance training programs to optimize training outcomes and support the achievement of fitness and performance goals.