Meta-analysis — 2016 — Training frequency · Hypertrophy
Effects of Resistance Training Frequency on Measures of Muscle Hypertrophy: A Systematic Review and Meta-Analysis
What did the researchers investigate?
How the number of times a muscle is trained per week affects muscle growth, across ten studies.
What did they find?
Higher frequency was associated with a larger effect on muscle growth than lower frequency. In studies of 1-3 days per week on a volume-equated basis, twice a week produced better growth than once a week. Whether three times beats twice could not be determined.
What does this mean for training?
Splitting a muscle's weekly sets over two sessions is a reasonable default.
How does FitX AI use this evidence?
FitX AI trains each muscle twice a week by default.
Where FitX AI's own choices go beyond this paper
Once or twice a week. Twice a week is a default that spreads the sets, not a requirement.
Limitations
Only ten studies, too few to analyse total session frequency separately. A larger 2019 analysis by the same group found that frequency mattered little once weekly sets were matched.