Effect Of Proximity To Failure During Resistance Training On Vastus Lateralis Muscle Thickness

Abstract

PURPOSE: To compare changes in muscle thickness at two sites (50% and 70%) of the vastus lateralis (VL50 MT, VL70 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, squat one-repetition maximum-1RM relative to body mass: 1.72 ± 0.25) with ≥2 yrs of back squat experience were assigned to either 4-6 RPE, n = 7 (4-6 RIR) or 7-9 RPE, n = 7 (1-3 RIR) for 8wks. Ultrasonography was performed 48 hours before the first training session and 48 hours after the last session. Both groups performed the back squat 3x/wk on non-consecutive days (e.g., Mon., Wed., Fri.) using an undulating resistance training program, which 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 was an introductory week in which fewer sets were performed at a lower RPE. Week 8 was 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 for both the squat and bench press. 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 VL50 MT and VL70 MT. Independent t-tests compared average intensity (% of 1RM) and total relative volume (% of 1RM × reps) performed. RESULTS: Equivalence testing confidence intervals crossed both g = 0.0 and g = ±0.20 thresholds; suggesting changes in VL50 MT and VL70 MT did not statistically differ between groups but were also inconclusive (VL50: 22.77 ± 4.77 to 21.74 ± 4.17 mm; -3.50% vs. 22.10 ± 4.25 to 20.73 ± 4.49 mm; -6.33%; VL70: 18.47 ± 6.59 to 19.93 ± 7.1 mm; +9.43% vs. 16.91 ± 6.67 to 17.04 ± 5.2 mm; +3.47%). The 7-9 RPE group trained with significantly higher intensity (82.2 ± 5.18 vs. 72.0 ± 4.57% of 1RM, p = 0.002) and performed more relative volume (338.7 ± 21.46 vs. 380.1 ± 25.83 kg, p = 0.007). CONCLUSIONS: Our findings do not conclusively indicate whether vastus lateralis MT changes were statistically similar or statistically different between groups.