Comparing how much volume, intensity, and frequency matter
Effect size is a statistic that expresses how large a training effect is in standardized terms, letting researchers compare the influence of different variables across studies. For muscle growth, the body of evidence points to training volume, broadly the number of hard working sets per muscle over a week, as a major driver, with a generally dose-responsive relationship up to a point before added volume yields diminishing returns.
Intensity, in the sense of load relative to maximum, appears to allow growth across a fairly wide range as long as sets are taken close enough to failure, which is part of why moderate and heavy loads can both build muscle. Frequency seems to matter mostly as a way to distribute volume rather than as a strong independent driver.
Reading effect sizes with appropriate caution
Effect sizes vary between studies because of differences in participants, measurement, and how variables were defined, so the rank order is a general trend rather than an exact recipe. Volume tends to lead for hypertrophy, while heavier loading carries more weight specifically for maximal strength.
This is general educational information, not coaching or medical advice. Individual responses differ, and program design is best tailored with a qualified professional.