Effect Of Proximity To Failure During Resistance Training On Pectoralis Major Muscle Thickness

Abstract

PURPOSE: To compare changes in pectoralis major muscle thickness (chest MT) between training programs with different proximities to failure using the repetitions in reserve (RIR)-based rating of perceived exertion (RPE) scale. METHODS: Fourteen males (height: 175.77 ± 5.72 cm, body mass: 80.15 ± 13.12 kg, bench press one-repetition maximum-1RM relative to body mass: 1.27 ± 0.12) with ≥2 yrs of bench press experience were assigned to one of two groups: 1) 4-6 RPE, n = 7 (4-6 RIR) or 2) 7-9 RPE, n = 7 (1-3 RIR) for 8wks. Pre and post chest MT via ultrasound was performed 48 hours before the first training session and 48 hours after the last training session, respectively. Both groups performed the bench press 3x/wk on non-consecutive days (e.g., Mon., Wed., Fri.) using the same number of sets and repetitions on an undulating resistance training program, which linearly decreased repetitions throughout. Weeks 1-3 consisted of 10, 8, and 6 repetitions on sessions 1, 2, and 3, respectively; weeks 4-5 consisted of 9, 7, and 5 repetitions; and weeks 6-7 consisted of 8, 6, and 4 repetitions. Week 1 served as an introductory week in which fewer sets were performed at a lower RPE. Week 8 served as a taper with 4 and 2 repetition days on session 1 and session 2, respectively, followed by post-testing in session 3. In weeks 2-7 (i.e., main training period), 10 weekly sets were performed. Subjects were instructed to select a load in which the set ended with 4-6 RPE or 7-9 RPE. Equivalence testing and 90% confidence intervals were used to compare changes in chest MT. Independent t-tests were used to compare relative intensity (% of 1RM) and relative volume (% of 1RM × reps). RESULTS: Equivalence testing confidence intervals crossed both g = 0.0 and g = ±0.20 thresholds; suggesting changes in chest MT did not statistically differ between 4-6 RPE and 7-9 RPE groups but were also inconclusive (24.21 ± 5.75 to 25.00 ± 5.51 mm; +7.89% vs. 22.50 ± 6.46 to 22.73 ± 4.30 mm; +4.05%). No significant differences were observed between the 4-6 RPE and 7-9 RPE groups for relative intensity (80.1 ± 4.23 vs. 83.9 ± 3.15% of 1RM; p = 0.083) or relative volume (377.0 ± 18.24 vs. 393.5 ± 15.34 kg; p = 0.093). CONCLUSIONS: Our findings do not conclusively indicate whether chest MT changes were statistically similar or statistically different between resistance training with 4-6 RPE and 7-9 RPE.