Variability in resistance training volume can influence muscle hypertrophy, where individuals non-responsive to one volume may exhibit significant muscle growth when exposed to a different, more appropriate volume, suggesting that individual sensitivity to training volume is a key determinant of hypertrophy outcomes.

When muscles are worked with enough repetitions and sets, mechanical stress triggers a molecular signal that turns on protein building in muscle cells. This signal makes the cells produce more muscle proteins, which adds size to the fibers. Some people need more work to turn on this signal, while others respond to less. Those who don't grow with light training grow when they do more, because their muscle cells only activate protein building when the workload reaches their personal threshold.