Investigating the Impact of Less Than or Greater Than 60 Seconds of Inter-Set Rest on Muscle Hypertrophy and Strength Increases in Males with >1 Year of Resistance Training Experience: Systematic Review with Meta-Analysis

BackgroundInter-set rest intervals (ISR) influence resistance training adaptations. Shorter intervals (<60s) promote metabolic stress, while longer intervals (>60s) are thought to enhance recovery, mechanical tension, and strength. AimThe systematic review and meta-analysis examined the effects of <60s vs. >60s ISR on hypertrophy, strength, and secondary outcomes in resistance-trained males. MethodsSix studies met the inclusion criteria, evaluating muscle hypertrophy, strength, metabolic hormones, power output, and motor unit recruitment. Standardised mean differences (SMDs) with 95% confidence intervals (CIs) were calculated, and forest plots were generated to visualise pooled effects. ResultsStrength was modestly improved with longer ISRs (SMD = -0.74) but only trivial differences in hypertrophy (SMD = 0.08). Metabolic hormone responses showed negligible variation between conditions (SMD = 0.11). Secondary outcomes were mixed, with motor unit recruitment slightly favouring shorter ISRs (SMD = -0.66), while power output tended to favour longer ISRs (SMD = -0.64). Forest plots illustrated the heterogeneity of effects across studies. ConclusionShorter ISRs appear to slightly reduce strength and power outcomes, while longer ISRs offer minimal benefit for hypertrophy. These findings suggest that longer ISRs may not confer superior benefits for muscle growth, as previously assumed in the literature (e.g., Schoenfeld, 2016). The variability across outcomes underscores the need for further research to refine ISR recommendations, particularly in trained individuals. What is already known on this topicO_LIInter-set rest intervals (ISR) influence hypertrophy and strength outcomes in resistance training. C_LIO_LIShort rest (<60 s) increases metabolic stress but may impair recovery and force output. C_LIO_LILonger rest (>60 s) consistently supports strength gains, but evidence for hypertrophy advantages remains inconclusive. C_LI What this study addsO_LISynthesises evidence specifically in resistance-trained males ([&ge;]1 year RT experience). C_LIO_LIShows hypertrophy outcomes are trivial and do not favour longer ISRs over shorter ISRs. C_LIO_LIConfirms longer ISRs modestly improve strength and power, while hormonal and motor unit responses remain inconsistent. C_LIO_LIUnderscores the absence of robust evidence supporting longer ISRs as a superior hypertrophy strategy in trained populations. C_LI