Influence of Varying Proximity-to-Failure on Muscular Adaptations and Repetitions-in-Reserve Estimation Accuracy in Resistance-Trained Individuals

Abstract

Purpose

The effects of varying proximity-to-failure during a resistance training (RT) program remain undetermined. Hence, we explored the influence of varying proximity-to-failure on muscular adaptations.

Methods

Young, resistance-trained individuals were randomized to repetitions-in-reserve (RIR)1-4 (n = 16 finished) or RIR1 (n = 15) groups for 10 weeks. Across two 5-week training blocks, RIR1-4 gradually decreased the weekly RIR target from 4 to 1 while RIR1 maintained a constant RIR of 1. Back squat and bench press 1 repetition maximum (1RM), muscle cross-sectional area (CSA) of the vastus lateralis (VL) and muscle thickness of triceps brachii were measured, and session ratings of perceived exertion (RPE) were assessed. RIR1 and RIR3 accuracy was tested in 80% 1RM repetition tests in squat and bench press.

Results

No statistical differences were observed between groups in changes in muscle strength or size. Both groups increased 1RM in bench press (RIR1-4: 7.0% ± 6.0%; RIR1: 9.6% ± 7.3%) and squat (RIR1-4: 9.8% ± 3.9%; RIR1: 9.2% ± 7.7%), and VL CSA (RIR1-4: 6.5% ± 4.2%; RIR1: 5.5% ± 3.6%). Triceps brachii thickness statistically increased only in RIR1-4 (RIR1-4: 5.8% ± 5.9%; RIR1: 2.2% ± 4.9%). Total volume-loads did not statistically differ between the groups, but session RPEs were lower in RIR1-4 than in RIR1. Although RIR accuracy was satisfactory at baseline, it further improved in RIR1-4.

Conclusion

Varying proximity-to-failure may not enhance short-term RT adaptations, but it allows RT with lower RPE. We also showed that RIR accuracy is already acceptable at baseline in resistance-trained individuals and that it may be further improved by RT, supporting its use to guide training practices.

Keywords

RIR / Muscle hypertrophy / Muscle strength / Resistance training / Squat / Bench press

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Funding

University of Jyväskylä (JYU)

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