The Effect of Resistance Training Proximity to Failure on Muscular Adaptations and Longitudinal Fatigue in Trained Men

Purpose: This study examined the effect of proximity to failure on hypertrophy, strength, and fatigue. We hypothesized strength gains would be superior in non-failure groups compared to those that include sets to momentary failure, while hypertrophy would be similar in all groups. Methods: 38 men were randomized into four groups (4–6 repetitions in reserve [RIR] per set, 1–3 RIR per set, 0–3 RIR [last set taken to momentary failure], and 0 RIR per set) and completed an eight-week program. Back squat and bench press strength, muscle thickness, subjective fatigue, muscle soreness, and biomarkers (creatine kinase-CK and lactate dehydrogenase-LDH) were assessed. Results: Bench Press strength gains were comparable between the 4–6 RIR (9.05 kg [95% CI: 6.31, 11.8]) and 1–3 RIR (9.72 kg [95% CI: 7, 12.45]) groups, while outcomes in the 0–3 (5.07 kg [95% CI: 2.2, 7.93]) and 0 RIR (0.71 kg [95% CI: -4.41, 5.62]) groups were slightly inferior. Squat strength gains were comparable between 4–6 RIR (13.79 kg [95% CI: 7.43, 20.28]) and 1–3 RIR (18.05 kg [95% CI: 12.12, 23.88]) groups, but data for 0–3 RIR and 0 RIR are difficult to interpret due to poor feasibility of the protocols. For muscle hypertrophy, our data do not provide strong conclusions as to the effects of proximity to failure due to the large variability observed. The indices of fatigue were largely comparable between groups, without strong evidence of the repeated bout effect. Conclusion: These data suggest strength outcomes are comparable when taking sets to either a self-reported 4–6 RIR or 1–3 RIR, while training that includes sets to momentary failure may result in slightly inferior outcomes (i.e., 0–3 and 0 RIR). However, the influence of proximity to failure on hypertrophy remains unclear and our data did not reveal clear differences between groups in any measure of fatigue.