the number of predictors that could be included in the
statistical model. Thus, interactions between set volume and
factors such as training experience could not be explored, as
had been done in a previous meta-analysis on strength (23).
Also, the majority of studies in this analysis compared 1 set
with 3 sets per exercise; only 2 studies in this analysis
incorporated $4 sets per exercise. This limits the statistical
power to compare 3 sets with greater set volumes, as the SE
for the 4–6 set category was large. Given that the ES for 4–6
sets (0.44) is considered a moderate effect, whereas the ES for
2–3 sets (0.34) is considered a small effect according to
Cohen’s classiﬁcations (9), more research involving $4 sets is
needed to clarify whether this is a chance difference or a true
difference. Another limitation is that meta-regression, like
epidemiological research, can only support observational
associations and cannot demonstrate causation (42). A ﬁnal
limitation is the availability of data (42). Some studies, despite
meeting the design criteria (comparison of single vs. multiple
sets while keeping other variables constant), were excluded
because hypertrophy was not measured. Because an analysis
can only be undertaken for trials where all information is
available, bias can be introduced in the results (42). However,
most of the excluded studies reported greater strength gains
in the multiple-set groups. Given the relationship between
strength and muscle size, the consistency of the mean
difference during the sensitivity analysis, the fact that the
study-level ES favored the multiple-set group in all 8 studies,
and the lack of evidence of publication bias, it is unlikely that
the addition of more studies would alter the results, other
than improving statistical power.
Multiple sets per exercise were associated with signiﬁcantly
greater changes in muscle size than a single set per exercise
during a resistance exercise program. Speciﬁcally, hyper-
trophy-related ESs were 40% greater with multiple sets
compared with single sets. This was true regardless of subject
training status or training program duration. There was
a trend for an increasing hypertrophic response to an
increasing number of sets. Thus, individuals interested in
achieving maximal hypertrophy should do a minimum of
2–3 sets per exercise. It is possible that 4–6 sets could give
an even greater response, but the small number of studies
incorporating volumes of $4 sets limits the statistical power
and the ability to form any deﬁnitive conclusions. If time is
a limiting factor, then single sets can produce hypertrophy,
but improvements may not be optimal. More research is
necessary to compare the effects of 2–3 sets per exercise to
$4 sets. Future research should also focus on the effects of
resistance training volume on protein synthesis and other
cellular and molecular changes that may impact hypertrophy.
Finally, resistance training studies comparing hypertrophic
responses between treatments should include sufﬁcient
numbers of subjects to obtain adequate statistical power to
detect differences; studies should also report power analyses.
The author thanks Dr. Dan Wagman for his help in
obtaining some articles. There were no ﬁnancial or personal
conﬂicts of interest and no external funding for this study.
The results of this study do not constitute endorsement by
the National Strength and Conditioning Association.
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