Exploring The Dose-response Relationship Between Estimated Resistance Training Proximity To Failure, Strength, And Muscle Hypertrophy

PURPOSE: To meta-analyze the aforementioned areas of relevant research, proximity to failure was quantified as the number of repetitions in reserve (RIR). METHODS: The RIR associated with each effect in the analysis was estimated based on the available descriptions of the training interventions in each study. Data were extracted and a series of exploratory multi-level meta-regressions were performed for outcomes related to both strength and muscle hypertrophy. All models were adjusted for the effects of load, method of volume equating, duration of intervention, and training status. RESULTS: The best fit models for both strength and muscle hypertrophy outcomes demonstrated modest quality of overall fit. In all of the best-fit models for strength, the confidence intervals of the marginal slopes for estimated RIR contained a null point estimate, indicating a negligible relationship with strength gains. However, in all of the best-fit models for muscle hypertrophy, the marginal slopes for estimated RIR were negative and their confidence intervals did not contain a null point estimate, indicating that changes in muscle size increased as sets were terminated closer to failure. CONCLUSIONS: The dose-response relationship between proximity to failure and strength gain appears to differ from the relationship with muscle hypertrophy, with only the latter being meaningfully influenced by RIR. Strength gains were similar across a wide range of RIR, while muscle hypertrophy improves as sets are terminated closer to failure. Considering the RIR estimation procedures used, however, the exact relationship between RIR and muscle hypertrophy and strength remains unclear. Researchers and practitioners should be aware that optimal proximity to failure may differ between strength and muscle hypertrophy outcomes, but caution is warranted when interpreting the present analysis due to its exploratory nature.