Gauging proximity to failure in the bench press: generalized velocity-based vs. %1RM-repetitions-to-failure approaches

Abstract

Background: This study compared the accuracy of three generalized approaches for estimating proximity to failure during the Smith machine bench press: (i) the relationship between relative load (%1RM) and maximum repetitions performed to failure (%1RM-RTF), (ii) the relationship between maximum repetitions to failure and fastest set velocity (RTF-velocity), and (iii) the relationship between repetitions left in reserve (RIR) and lifting velocity (RIR-velocity). Methods: Nineteen physically active men (22.9 ± 2.7 years old) with at least two years of resistance training experience participated. Their 1-repetition maximum (1RM = 86.8 ± 16.7 kg) was determined during the first session. In the second session, participants performed single sets to failure at 60% and 80% 1RM, with proximity to failure (2RIR and 4RIR) estimated using each approach. Results: The RIR-velocity relationship was the only approach that did not significantly deviate from the intended RIR (errors = -0.4 to 0.6 repetitions). In contrast, both the %1RM-RTF and RTF-velocity relationships overestimated the intended RIR at 60%1RM for both 2RIR (2.9 and 5.8 repetitions, respectively) and 4RIR (2.8 and 5.7 repetitions, respectively), while no significant differences were observed at 80%1RM (errors = -0.6 to 0.9 repetitions). The RIR-velocity relationship generally demonstrated the lowest absolute errors compared to the actual RIR (1.3 ± 0.7 repetitions), with greater differences compared to the other two approaches at lighter loads and closer proximities to failure. Conclusions: In the absence of individual relationships, the general RIR-velocity relationship should be used by coaches to control the proximity to failure of their athletes during the bench press exercise.