The Resistance Training Dose-response: effEcts Of Weekly Frequency On Muscle Hypertrophy And Strength Gain

PURPOSE: This meta-analysis explored the nature of the continuous dose-response relationships between weekly resistance training (RT) frequency and muscle hypertrophy and strength gain using various quantification methods. METHODS: Each RT intervention included healthy participants <70 years old, utilized a dynamic RT intervention ≥4 weeks differing in set volume and/or frequency while controlling for other RT variables, and measured hypertrophy using a direct, site-specific measurement or maximal strength using a dynamic (up to a 10RM), isometric, or isokinetic assessment. All contributing RT sets were classified as direct or indirect, depending on their specificity to the hypertrophy/strength measurement. Then, weekly frequency for indirect sets was quantified as 1 for ‘total,’ 0.5 for ‘fractional,’ and 0 for ‘direct.’ A series of multi-level meta-regressions were performed for hypertrophy and strength, with all models adjusted for volume, intervention duration, and training status. RESULTS: The relative evidence was strongest for the ‘fractional’ quantification method for both muscle hypertrophy (2 x Log(BF) = 9.96 to 10.82) and strength gain (2 x Log(BF) = 31.27 to 54.84). Model comparisons revealed the reciprocal model was the best fit for both muscle hypertrophy and strength gain, with a marginal slope of 0.32% [95% CrI: -0.14%, 0.82%] and 3.27% [95% CrI: 2.74%, 3.84%], respectively. CONCLUSIONS: The dose-response relationships for the independent effects of frequency exhibit diminishing returns, especially for muscle hypertrophy. Further, the effect for muscle hypertrophy is small and compatible with negligible effects. Although best fit models have been identified, the dose-response relationships remain compatible with multiple functional forms, especially upon the addition of new data at frequency levels with limited data.