How does muscle growth actually progress over time?

Our new systematic review and meta-analysis, posted as a preprint (DOI:10.51224/SportRxiv.910), pooled 3,237 observations from 480 studies to model the trajectory of resistance training-induced muscle growth.

As expected, muscle growth follows a curvilinear trajectory.

Gains occur relatively rapidly during the early stages of training and then progressively slow as training continues. At 10 weeks, the model estimated an average increase in muscle size of approximately 7%. This increased to ~7.5% at 12 weeks, ~8.9% at 20 weeks, ~10.5% at 36 weeks, and ~12.6% at 78 weeks.

In other words, hypertrophy displays diminishing returns—but diminishing returns do not mean no returns. Gains continue to accumulate; they simply become progressively smaller over time.

Importantly, there was substantial variability around these averages. At 10 weeks, for example, the 95% prediction interval ranged from approximately −7% to +22%, highlighting just how much hypertrophic responses can differ across studies and individuals. Moreover, most of the included studies were relatively short in duration, limiting our ability to draw conclusions about the rate of hypertrophy over longer training periods.

Perhaps more importantly, research studies are generally designed to determine group-level effects rather than to optimize muscle development for each individual. Thus, these findings provide a useful framework for understanding the general trajectory of hypertrophy over time, but should not be interpreted as defining the limits of what a person can achieve with a customized, well-designed training program.

Take-home: Muscle growth tends to occur most rapidly during the early stages of resistance training, with the rate of gain progressively slowing as training exposure accumulates. However, diminishing returns do not mean an end to progress, and early rates of growth should not be extrapolated linearly over the long term.

Shout out to Brandon Roberts for spearheading the project 💪🏽