Conclusion: Lower Body. These studies support the
hypothesis that a large percentage of an individu-
al’s muscle growth potential will likely be achieved
within the first 3 months (12 weeks) of training. It
seems unlikely that individuals will increase their
muscle mass by appreciable amounts beyond what
is gained by the time of plateau. However, most of
these studies were performed for durations of 6–12
weeks; a longer study duration would be required
to test this hypothesis. In an older population, it
may take longer for muscle growth to occur and
plateau, although some of this may be related to
this population requiring a greater exercise vol-
ume for a given response within a training ses-
sion.18 For example, a recent article found no age-
related differences in how muscle size changed
across time.37 This lack of age effect is likely due
to the accumulated volume from doing multiple
sets of exercise on multiple different exercises tar-
geting similar muscle groups in the lower body.
Furthermore, in a trained population, similar to
the upper body, muscle growth did not occur.38 In
conclusion, statistically significant increases in ante-
rior upper leg muscle size from baseline are likely
to occur within the first month of training, with a
potential plateau 4–6 weeks after the initial statisti-
cal increase in baseline muscle size. In addition,
the population studied (elderly, trained, etc.) can
result in a prolonged or limited response to resis-
tance training.
