Effects of Resistance Training Proximity to Failure on Muscle Strength and Physical Performance in Adults: A Systematic Review and Meta-Analysis

Background: Proximity to failure describes how close a person trains to the point where they can no longer complete another repetition — known as momentary muscular failure. It is typically measured using repetitions in reserve or the rating of perceived exertion scale. Despite growing interest from clinicians and practitioners, the ideal level of proximity to failure for improving muscle strength and physical performance in adults is still not clearly established. Objectives: This rapid systematic review and meta-analysis asked a straightforward question: does training closer to failure lead to better gains in muscle strength and physical performance compared to training with more effort held back? We focused on adults aged 18 and over, using the Population, Intervention, Comparator, and Outcomes framework to structure our analysis. Methods: This review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. We searched PubMed/MEDLINE, Scopus, Web of Science, and CINAHL from their earliest records to September 2026. We included randomised controlled trials and controlled trials that compared high-effort training (≤2 repetitions in reserve or rating of perceived exertion ≥8) against lower-effort training (≥3 repetitions in reserve or rating of perceived exertion ≤7) in healthy or clinical adult populations, measuring maximal muscle strength as the primary outcome. Results: Twenty-two studies involving 817 participants (mean age 27.4 ± 6.8 years) were included. Training at high proximity to failure produced a small-to-moderate benefit for maximal strength (standardised mean difference = 0.38, 95% confidence interval: 0.18–0.58, p < 0.001, I² = 46%). People who were new to resistance training gained more (standardised mean difference = 0.51) than those with prior training experience (standardised mean difference = 0.22). For secondary outcomes, small benefits were seen for muscular endurance (standardised mean difference = 0.29, 95% confidence interval: 0.09–0.49) and functional performance (standardised mean difference = 0.21, 95% confidence interval: 0.04–0.38), whereas power output did not differ significantly (standardised mean difference = 0.14, 95% confidence interval: −0.06 to 0.34). The risk of adverse events was similar between high and low proximity to failure (risk ratio = 1.12, 95% confidence interval: 0.74–1.70). Conclusions: Training closer to failure leads to meaningfully greater strength gains in adults, especially for those who are new to resistance training. The benefit becomes smaller as training experience increases. Practitioners are encouraged to tailor effort levels based on each person's training background, the phase of their programme, and how well they are managing fatigue.