Brief Review
Sex Differences in Resistance Training: A
Systematic Review and Meta-Analysis
Brandon M. Roberts,1 Greg Nuckols,2 and James W. Krieger3
1
University of Alabama at Birmingham, Birmingham, Alabama; 2Stronger by Science LLC, Raleigh, North Carolina; and 3Weightology
LLC, Issaquah, Washington
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Abstract
Roberts, BM, Nuckols, G, and Krieger, JW. Sex differences in resistance training: A systematic review and meta-analysis. J
Strength Cond Res 34(5): 1448–1460, 2020—The purpose of this study was to determine whether there are different responses
to resistance training for strength or hypertrophy in young to middle-aged males and females using the same resistance training
protocol. The protocol was pre-registered with PROSPERO (CRD42018094276). Meta-analyses were performed using robust
variance random effects modeling for multilevel data structures, with adjustments for small samples using package robumeta in
R. Statistical significance was set at P , 0.05. The analysis of hypertrophy comprised 12 outcomes from 10 studies with no
significant difference between males and females (effect size [ES] 5 0.07 6 0.06; P 5 0.31; I2 5 0). The analysis of upper-body
strength comprised 19 outcomes from 17 studies with a significant effect favoring females (ES 5 -0.60 6 0.16; P 5 0.002; I2 5
72.1). The analysis of lower-body strength comprised 23 outcomes from 23 studies with no significant difference between sexes
(ES 5 20.21 6 0.16; P 5 0.20; I2 5 74.7). We found that males and females adapted to resistance training with similar effect
sizes for hypertrophy and lower-body strength, but females had a larger effect for relative upper-body strength. Given the
moderate effect size favoring females in the upper-body strength analysis, it is possible that untrained females display a higher
capacity to increase upper-body strength than males. Further research is required to clarify why this difference occurs only in the
upper body and whether the differences are due to neural, muscular, motor learning, or are an artifact of the short duration of
studies included.
Key Words: resistance exercise, gender differences, strength, hypertrophy
Introduction
It is well-established that both males and females can increase
muscle size and strength in response to resistance training (RT)
(29). Furthermore, several studies have shown RT has multiple
benefits for overall health (39,41,58). Although there have not
been any studies that use dose-response models to determine
whether males and females respond differently to chronic RT,
several studies have compared the adaptations of males and
females using the same training protocol. However, whether
there are sex-specific adaptations to the same training is still
unclear.
In most studies, males increase absolute strength more than
females (10,12,68). Yet, some find that the relative increase in
muscle strength and hypertrophy are similar between sexes
(1,21,28,30,32,36,40,67,70,78,85). However others find
females have a greater relative strength increase
(7,9,29,34,36,38,48,55,56,63,79). In one of the largest
studies to date, Hubal et al. (29) found females have higher
relative strength increases than males.
A key consideration in comparing the responses in males and
females is that pre-training levels of muscle size and strength are
generally greater in males, independent of training status
(3,35,67). Another well-known set of differences between males
and females are hormonal, which may influence muscle hypertrophy and strength adaptations. There also may be some
Address correspondence to Dr. Brandon M. Roberts, robertsb21@gmail.com.
Journal of Strength and Conditioning Research 34(5)/1448–1460
ª 2020 National Strength and Conditioning Association
differences in types of occupation that could cause basal strength
differences. However, there is currently no review bringing together the major differences between sexes at the neuromuscular,
muscular, and hormonal level in the context of RT.
Considering the importance of muscle strength and size to
overall health and exercise performance, it is important to understand sex differences in response to RT if they exist. Therefore,
the purpose of this study is to determine whether there are different responses to RT for strength or hypertrophy in young to
middle-aged males and females.
Methods
Experimental Approach to the Problem
Inclusion Criteria. Research publications were considered eligible
for this systematic review if they (a) were experimental in design,
(b) were published in a peer-reviewed, English-language journal,
(c) were conducted in human populations, (d) included at least 1
method of estimating changes in muscle mass and/or dynamic,
isometric, or isokinetic strength, and (e) had subjects who were
between 18 and 50 years old (Table 1).
Exclusion Criteria. Studies were considered ineligible for this
review if (a) the training protocol lasted for ,5 weeks, (b) the
study involved subjects with medical conditions, pregnancy, or
injuries impairing training capacity, (c) subjects were taking
supplements or hormone replacement therapy. Case studies were
not included. Studies that were not written in English, conference
abstracts, thesis, or posters were also excluded from this review.
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Abe et al. (1)
Ahtiainen et al. (2)
n
Session per week
Male: 17
Female: 15
Male: 61
Female: 27
3
Untrained .12 mo
12
2
Untrained
Training status
Study duration (wks) Strength measurement Within-sex ES for strength
24
Chest press
Knee extension
Leg press
Male: 1.33
Female: 0.96
Male: 1.06
Female: 0.96
Alway et al. (4)
Male: 5
Female 5
2
Trained body builders
24
NR
NR
Carlsson et al. (7)
Male: 7
Female: 7
Male: 11
Female: 11
Male: 8
Female: 7
2
NR
Athletes
Untrained
Physically active
Untrained .6 mo
6
Bar-dips, chin-ups
12
Leg extension
16
Elbow flexion
Leg extension
Male: 0.20
Female: 0.64
Male: 2.3
Female: 1.61
Male: 0.43
Female: 1.14
Colliander et al. (8)
Cureton et al. (9)
3
3
Measurement
Ultrasound
MRI
DXA
Ultrasound
Computed tomography, CT
fiber cross-sectional area
Male: 0.42
Female: 0.25
fCSA
Male: 0.08
Female: 0.41
NR
NR
NR
NR
Computed tomography
Upper body
Male: 1.41
Female: 1
Lower body
Male: 1.3
Female: 1.54
Upper body
Male: 0.52
Female: 0.98
Lower body
Male: 0.36
Female: 0.75
NR
NR
Arm
Male: 1.2
Female: 1.03
Thigh
Male: 0.43
Female: 0.25
NR
Male: 11
Female: 7
5
NR
Physically active
104
Pull-down
Leg extension
Dias et al. (12)
Male: 23
Female: 15
3
Untrained .6 mo
Physically active
12
Bench press
Squat
NR
NR
Male: 16
Female: 19
Dorgo et al. (14)
Male: 14
Female: 14
Fernandez-Gonzalo et al. (15) Male: 16
Female: 16
Garthe et al. (17)
Male: 11
Female: 13
Gentil et al. (18)
Male: 44
Female: 47
Guadalupe-Grau et al. (19)
Male: 24
Female: 23
3
Untrained .12 mo
Sedentary
Untrained
Physically active
Untrained .6 mo
Physically active
NR
Athletes
No systematic RT .3 mo
10
12
Chest press
Leg press
Leg extension
6
Leg press
12
Squat
10
Elbow flexion
NR
Physically active
9
Leg press
Donges et al. (13)
NR
NR
2
Male: 1.28
Female: 2.45
Male: 1.92
Female: 0.88
NR
NR
NR
2–3
NR
NR
4
NR
NR
2
NR
NR
2
NR
NR
Male: 0.56
Female: 0.6
Male: 1.15
Female: 5.63
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Daniels et al. (10)
Within-sex ES for hypertrophy
Male: 1.31
Female: 1.03
NR
Sex Differences in Training (2020) 34:5
Hypertrophy and strength adaptations to resistance training in males and females
Study
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Table 1
Overview of studies meeting inclusion criteria.*
Häkkinen et al. (24)
Häkkinen et al. (22)
Hakkinen et al. (21)
Hakkinen et al. (23)
Hakkinen et al. (25)
Hostler et al. (28)
Hurlbut et al. (32)
Lemmer et al. (42)
Lemmer et al. (43)
Roth et al. (67)
Hubal et al. (29)
Liu et al. (45)
Peterson et al. (56)
Hunter (30)
Ivey et al. (33)
Ivey et al.(34)
Jozsi et al. (36)
n
Session per week
Male: 9
Female: 9
Male: 12
Female: 12
Male: 42
Female: 39
2–3
Male: 5
Female: 5
Male: 5
Female: 4
Male: 10
Female: 9
3
Training status
Study duration (wks) Strength measurement Within-sex ES for strength
Untrained
Physically active
Untrained
Physically active
Untrained
Physically active
12
Leg extension
12
Leg extension
24
Leg extension
Untrained .6 mo
16
Bench press
3
Untrained .6 mo
Sedentary
24
Chest press
Leg press
Male: 43
Female: 40
2
Untrained .12 mo
12
Bicep flexion
Male: 11
Female: 10
Male: 14
Female: 11
Male: 11
Female: 11
Male: 6
Female: 9
3
NR
7
Bench press
Untrained .6 mo
Sedentary
Untrained .12 mo
9
Leg extension
12
Chest press
Leg press
2
2
2
4
3
2
Kell et al. (38)
Male: 20
Female: 20
3
Trained
Physically active
12
Bench press
Back squat
Kosek et al. (40)
Male: 13
Female: 11
Male: 25
Female: 15
3
Untrained .12 mo
16
Leg press
5
Untrained .6 mo
Sedentary
12
Chest press
Leg press
Martin-Ginis et al. (48)
Measurement
Within-sex ES for hypertrophy
Male: 2.45
Female: 0.62
Male: 0.98
Female: 1.2
Male: 0.31
Female: 0.38
NR
NR
NR
NR
Muscle fiber size
Male: 0.66
Female: 0.59
Male: 1.18
Female: 3.49
Male: 1.9
Female: 1.74
Upper body
Male: 0.94
Female: 2
Lower body
Male: 1.38
Female: 2.23
Male: 0.04
Female: 0.06
NR
NR
MRI
Male: 0.43
Female: 0.09
MRI
Male: 0.67
Female: 0.65
NR
NR
MRI
NR
Male: 0.49
Female: 0.31
NR
NR
NR
Muscle fiber size
Male: 1.84
Female: 1.23
NR
Male: 0.08
Female: 0.06
Male: 0.04
Female: 0.15
Male: 1.27
Female: 1.88
Upper body
Male: 0.61
Female: 0.62
Lower body
Male: 2.25
Female: 2.41
Upper body
Male: 1.31
Female: 2.37
Lower body
Male: 1.48
Female: 2.22
Male: 1.8
Female: 2.78
Upper body
Male: 1.33
Female: 3.31
Lower body
Male: 2.56
Female: 2.62
NR
Sex Differences in Training (2020) 34:5
Hypertrophy and strength adaptations to resistance training in males and females
Study
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Table 1
Overview of studies meeting inclusion criteria.* (Continued)
O’Hagan et al. (55)
Reichman et al. (64)
Ribiero et al. (63)
Ribiero et al. (62)
Ribiero et al. (60)
Rutherford et al. (68)
Spurway et al. (77)
Salvador et al. (71)
Schmidt et al. (72)
Staron et al. (79)
Stock et al. (80)
Washburn et al. (85)
Weiss et al. (86)
Williamson et al. (90)
Raue et al. (58)
Wilmore et al. (91)
n
Session per week
Male: 6
Female 6
Male: 62
Female: 58
Female: 31
Male: 28
3
NR
3
Male: 11
Female: 9
Male: 10
Female: 10
Male: 33
Female: 23
Male: 43
Female: 53
Male: 13
Female: 8
Male: 17
Female: 17
Male: 17
Female: 13
Male: 12
Female: 14
Male: 6
Female: 6
Male: 26
Female: 46
Training status
Study duration (wks) Strength measurement Within-sex ES for strength
20
Elbow flexion
Trained ,3 h per week
10 wk
3
Untrained .6 mo
16 wk
Chest press
Leg press
Bench press
3
Untrained
12 wk
Leg extension
3
Untrained
Physically active
Untrained .6 mo
6 wk
Leg extension
8 wk
Bench press
Back squat
8 wk
3
3
Male: 2
Female: 4.18
NR
Measurement
CT
Within-sex ES for hypertrophy
NR
Male: 0.09
Female: 0.43
NR
Male: 0.69
Female: 1.22
NR
NR
Male: 0.81
Female: 0.22
NR
NR
NR
NR
NR
NR
NR
Push-ups
Upper body
Male: 0.41
Female: 0.81
Lower body
Male: 0.55
Female: 0.67
NR
NR
NR
9 wk
NR
NR
Muscle fiber size
NR
2
Untrained
Physically active
Untrained
Physically active
Untrained .6 mo
10 wk
Leg extension
NR
NR
3
NR
24 wk
NR
NR
3
Untrained .3 mo
8 wk
Chest press
Leg press
Plantar flexion
Male: 0.44
Female: 0.63
NR
Ultrasound
3
Untrained .12 mo
12 wk
Leg extension
NR
Male: 0.24
Female: 0.17
NR
2
NR
10 wk
Bench press
Leg press
Male: 0.91
Female: 0.52
Male: 7.91
Female: 11.8
Male: 2.21
Female: 3.5
NR
NR
2
Sex Differences in Training (2020) 34:5
Hypertrophy and strength adaptations to resistance training in males and females
Study
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*ES 5 effect size; MRI 5 magnetic resonance imaging; NR 5 Not recorded; DXA 5 dual-energy X-ray absorptiometry; CT 5 computed tomography; RT 5 resistance training; fCSA 5 fiber cross-sectional area.
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Table 1
Overview of studies meeting inclusion criteria.* (Continued)
Sex Differences in Training (2020) 34:5
Search Strategy. Our protocol was pre-registered with PROSPERO (CRD42018094276). The systematic review was performed in accordance with the guidelines provided by the
Preferred Reporting Items for Systematic Reviews and MetaAnalyses (PRISMA). A literature review was conducted up until
April 2018 using Medline and SportDiscus. Combinations of the
following terms were used to produce search results: gender or sex
AND strength training or RT or powerlifting AND strength or
hypertrophy or 1 repetition maximum. Search terms were added
using the NOT term to reduce the number of irrelevant studies
according to exclusion criteria (concurrent, children, disease,
supplement). Citations from studies were also scanned for additional studies (Figure 1).
Subjects
A total of 1,162 studies were identified using the aforementioned
search terms, and 24 were additionally identified through other
sources. Eighty studies were identified as being eligible for the
review. After full-text review, 30 were removed for not meeting
the inclusion criteria. Ultimately, 50 studies were deemed to have
satisfied the inclusion criteria. Of those studies, 10 were analyzed
for hypertrophy measures, 17 for upper-body strength, and 23 for
lower-body strength.
Procedures
Coding of Studies. Studies were independently searched and
coded by 2 of the authors (G.N. and B.M.R.) for the following
variables: descriptive information (age, sex, training status), the
number of subjects per group, training mode, duration of study,
training frequency, repetition range, mode of muscle measurement (magnetic resonance imaging, fiber cross sectional area
[fCSA], ultrasound, and computed tomography). Results were
cross-checked between coders, and any discrepancies were resolved by mutual consensus.
Calculation of Effect Size. For each hypertrophy and strength
outcome, a within-group effect size (ES) for each male and female
group was calculated as the pretest-posttest change, divided by
the pretest standard deviation (SD) (54). A study level ES was then
calculated as the difference between the male group ES and female
group ES. A small sample bias adjustment was applied to each ES
(54). The sampling variance around each ES was calculated using
the sample size in each study (6).
Statistical Analyses
Meta-analyses were performed using robust variance random
effects modeling for multilevel data structures, with adjustments
for small samples using package robumeta in R (27,82). The study
was used as the clustering variable to account for correlated group
effects within studies. Observations were weighted by the inverse
of the sampling variance. Separate analyses were conducted for
hypertrophy, upper-body strength, and lower-body strength. A
fail-safe N was performed to calculate the number of null studies
needed to achieve a p value of 0.05 or greater using the Rosenthal
approach.
Figure 1. PRISMA diagram.
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Sex Differences in Training (2020) 34:5
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Figure 2. Forest plot of studies comparing changes in hypertrophy in males and females. The data
shown are mean 6 95% CI; the size of the plotted squares reflects the statistical weight of each study.
CI 5 confidence interval.
All analyses were performed in R version 3.5 (The R Foundation for Statistical Computing, Vienna, Austria). Effects were
considered significant at P # 0.05. Data are reported as means 6
SEM and 95% confidence intervals (CIs) unless otherwise
specified.
allocate, which are integral parts of quality assessment.
Because this eliminates half of the questions in most scales, we
felt it was unworthy to perform these types of quality
assessments.
Results
Methodological Quality
Hypertrophy
The quality of studies is important for analysis of systematic
reviews and meta-analysis. However, due to the nature of
studies on sex differences, it is difficult to blind subjects,
therapists, assessors, conceal allocation, or randomly
The analysis of hypertrophy comprised 12 outcomes from 10
studies. There was no significant difference between males and
females (ES 5 0.07 6 0.06; 95% CI: 20.09 to 0.23; P 5 0.31;
Figure 2). Heterogeneity was low (I2 5 0) (Figure 3).
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Sex Differences in Training (2020) 34:5
Figure 3. Percent change in muscle hypertrophy in males and females.
Upper-Body Strength
Discussion
The analysis of upper-body strength comprised 19 outcomes from
17 studies. There was a significant effect favoring females (ES 5
20.60 6 0.16; 95% CI: 20.93 to 20.26; P 5 0.002; Figure 4).
Heterogeneity was high (I2 5 72.1). Adding training status
(trained or untrained), single or multijoint strength measurements
(e.g., leg extension or leg press), training duration (weeks), or
sessions per week as covariates did not substantially reduce heterogeneity (I2 5 69.7) (Figure 5).
This review meta-analyzed studies that compared strength or
direct measures of hypertrophy in males and females who used the
same RT program. A majority of the studies were completed in
untrained individuals. The main finding was that effect sizes in
hypertrophy and lower-body strength were similar between
sexes. However, there was a significant effect in favor of females
for upper-body strength (ES 5 20.60; 95% CI: 20.93 to 20.26;
P 5 0.002).
Muscular strength increases in response to RT are a combination of neurological and muscular adaptations. Initial,
rapid improvements in strength seem to result primarily from
neurological adaptation, whereas subsequent gains are primarily the result of muscular adaptations (53). In one of the
first studies comparing untrained males and females, Wilmore
et al., found that strength was similar when normalized to
body weight after 10 weeks of intensive RT (90). Interestingly,
relative upper-body strength increased 29% in females compared with 17% in males, whereas relative increases in lowerbody strength were similar (90). These data were the first data
to indicate there may be differences in strength changes between sexes. However, a limitation was that both groups experienced considerable decreases in body fat percentage over
the course of the study, indicating they were likely not in an
optimal nutritional environment for gaining or maintaining
muscle mass or strength (90). More recent data have indicated
that both sexes respond to upper-body strength in a similar
manner (18). Yet, in the largest study to date with ;342
females and ;243 males, there was a significant difference in
relative upper strength changes in favor of females (29).
Herein, we cover a number of potential variables that could
help explain the differences in strength we and others have
found.
Neuromuscular adaptations are one factor that could explain
the larger increase for females in upper-body strength. However,
one study compared the number of motor units in the biceps
brachii and vastus medialis but found no differences between
sexes (50). The same research group also found no difference in
Lower-Body Strength
The analysis of lower-body strength comprised 23 outcomes from
23 studies. There was no significant difference between sexes (ES
5 20.21 6 0.16; 95% CI: 20.54 to 0.12; P 5 0.20; Figure 6).
Heterogeneity was high (I2 5 74.7). Adding training status
(trained or untrained), single or multijoint strength measurements
(e.g., leg extension or leg press), training duration (weeks), or
sessions per week as covariates did not substantially reduce heterogeneity (I2 5 77.4) (Figure 7).
Sensitivity Analysis
Because of the limited sample size, we completed a sensitivity
analysis on all 3 outcomes where 1 study at a time was removed to
determine whether that a particular study had any significant
impact on the outcomes. However, we did not identify any influential studies.
Publication Bias
A rank correlation test for funnel plot asymmetry was performed
for the upper-body strength results because there was a significant
finding (Figure 8). It was not significant (P 5 0.41). We also used
a fail-safe N to calculate the number of null studies needed to
achieve a p value of 0.05 or greater using the Rosenthal approach.
The fail-safe N was 294. Thus, there was no evidence of publication bias for the upper-body strength outcomes.
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Figure 4. Forest plot of studies comparing changes in upper-body strength in males and females. The
data shown are mean 6 95% CI; the size of the plotted squares reflects the statistical weight of each
study. CI 5 confidence interval.
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Sex Differences in Training (2020) 34:5
Figure 5. Percent change in muscle upper-body strength in males and females.
motor unit activation for elbow flexion or knee extension (50).
Others have found that males are no better able to activate motor
units than females (5,91). Yet, neuromuscular fatigue from RT is
generally greater in males than females, and acute recovery may
be slower in males (20). Because the included studies are short in
nature, this could have an effect on strength adaptations if subjects are not fully recovered during testing. The average untrained
female may also have a lower initial level of fitness compared with
a male (74). This could cause a ceiling effect for motor skills that
may explain differences in upper-body strength because the
studies were conducted in mostly untrained subjects. Ultimately,
there are very few known differences at the neuromuscular level
between sexes that could explain our findings, but more research
is warranted.
It is well established that sex differences exist in skeletal muscle
mass and distribution (35). Females often have less total and lean
body mass, a higher body fat percentage, and a smaller muscle
fiber cross-sectional area (65,78). One explanation of why differences could occur in strength or hypertrophy is muscle phenotype. Females have a greater proportion of type I fibers (65,75)
in the vastus lateralis and the biceps brachii (3,50,69). There are
currently no studies that compare the number of muscle fibers
between sexes, but a classic study has shown the muscle fiber
number decreases with age in males, although our data did not
include those over 50 (44). Furthermore, there seem to be similar
responses in muscle protein synthesis between sexes (47,76,86),
and muscle damage due to RT is also similar between, yet the
inflammatory response may be attenuated in females compared
with males (80). However, there are some data to indicate that
although there are similar indirect markers of muscle damage
after RT, males could have longer-lasting muscle soreness than
females (11). On a single fiber level, force per CSA and contractile
velocity of type I and type II fibers are similar when comparing
sexes (83). Taken together, there are relatively few differences in
skeletal muscle between sexes, which helps explain our finding
that hypertrophy is similar.
It was once postulated that females achieved small increases in
muscle size after RT because of low androgen levels whereby
a lesser amount of work-induced muscle hypertrophy would
prevent them from gaining strength to the same extent as males
(85). Although it is true that absolute hypertrophy and gains in
strength are larger in males after RT, it seems that relative
increases in both muscularity and lower-body strength are similar
between the sexes, and relative gains in upper-body strength may
be larger in females. Indeed, it is well established that females have
lower levels of testosterone, free-testosterone, and insulin-like
growth factor-binding protein 1 compared with males (65).
Heavy training decreases gonadotropin-releasing hormone pulsatility in females (66). Males exhibit lower serum cortisol due to
chronic RT, whereas females do not (78). Females do not experience elevations in postexercise testosterone compared with
males (16,86). This differential change in testosterone has led to
speculation that females may have an attenuated potential for
resistance exercise-induced hypertrophy, which we did not find in
our analysis (72). Another difference is that males have more
upper-body muscle, which has more androgen receptors (37).
Gentil et al. (18) suggest that this could affect strength gains over
time. Another potential confounder is the menstrual cycle. Some
evidence suggests that females who complete training during the
follicular phase can have larger strength gains and more muscle
growth (59, 81, 88) while females may take longer to recover
during the luteal phase (46), and most of the studies included did
not adjust for menstrual cycle. However, other evidence suggests
that the changes in protein kinetics across the menstrual cycle may
not play a large role in muscle accrual (51). Although some studies
suggest that hormonal differences play a role in changes, larger
and well-controlled studies are needed to understand why that
occurs or how it affects strength or hypertrophy adaptations.
In a recent review, Hunter presents evidence that sex differences in muscle fatigue of repeated dynamic contractions are
specific to the task requirements (31). Females may have less
skeletal muscle fatigue compared with males during single-limb
isometric contractions. It has also been suggested that there are
independent responses to fatiguing contractions (31). Likewise,
shortening velocity is a potential factor to tease out the contribution of voluntary activation and contractile mechanisms (73).
There is also evidence that female tendons have a smaller capacity
for adaptation to training (52,87), which may be exacerbated by
oral contraceptive use (26) and could potentially affect strength
adaptations.
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Sex Differences in Training (2020) 34:5
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Figure 6. Forest plot of studies comparing changes in lower-body strength in males and females.
The data shown are mean 6 95% CI; the size of the plotted squares reflects the statistical weight
of each study. CI 5 confidence interval; the size of the plotted squares reflects the statistical
weight of each study.
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Sex Differences in Training (2020) 34:5
Figure 7. Percent change in lower-body strength in males and females.
Although a strength of this study is that it is the first metaanalysis completed on sex differences, there are several limitations. First, most subjects included in the analysis are untrained
individuals. It is possible that a longer training duration or other
factors could change the results. In addition, the untrained subjects could have different levels of basal activity between studies as
it is often not well described in exercise science research. The
studies included also vary with regard to mode, duration, and
intensity of exercise utilized. However, our analysis of upperbody strength found no evidence publication bias and no single
studies of major influence. It has been argued (1) that many of the
earlier studies conducted on sex comparisons for both strength
and muscular hypertrophic changes were hampered by low statistical power resulting from small sample sizes (all #20 subjects).
Another potential limitation is missing studies due to unused
search terms or databases. There is also a possibility that male
subjects could be more familiar with upper-body movements
(e.g., bench press) that could have resulted in females having
greater neuromuscular adaptations. Finally, heterogeneity was
high for the outcomes of studies assessing both upper and lowerbody strength, yet incorporating training status, testing modality,
duration, or sessions did not substantially decrease heterogeneity.
Although there was a mean effect in favor of females for upperbody strength gains and no significant difference between the
sexes for lower-body strength gains, more research is needed to
understand the sources of this heterogeneity.
We found that males and females adapted to RT with similar
effect sizes for hypertrophy and lower-body strength, but females
had a larger effect size for relative upper-body strength. Current
research indicates there are few differences at the skeletal muscle
level between sexes. However, hormonal fluctuations, daily
physical activity, and exercise recovery may play a role in our
findings. In sum, well-designed studies with a primary goal of
comparing male and females are relatively few, and our understanding of sex differences in the physiology of RT is incomplete, which makes studies on sex-differences warranted.
Figure 8. Funnel plot, using data from studies with upper-body strength outcomes.
1458
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Sex Differences in Training (2020) 34:5
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Practical Applications
Given the moderate effect size favoring females in the upperbody strength analysis, it is possible that untrained females
display a higher capacity to increase upper-body strength than
males. Further research is required to clarify why this difference occurs only in the upper body and whether the differences
are due to neural, muscular, or motor learning adaptations. In
practice, it is important to know that both males and females
can considerably increase muscle strength and size with RT.
Because there are is a paucity of studies comparing multiple
RT programs between sexes, it is currently difficult to know if
exercise prescription should be different between sexes.
References
1. Abe T, DeHoyos DV, Pollock ML, Garzarella L. Time course for strength
and muscle thickness changes following upper and lower body resistance
training in men and women. Eur J Appl Physiol 81: 174–180, 2000.
2. Ahtiainen JP, Walker S, Peltonen H, et al. Heterogeneity in resistance
training-induced muscle strength and mass responses in men and women
of different ages. Age (Dordr) 38: 10, 2016.
3. Alway SE, Grumbt WH, Gonyea WJ, Stray-Gundersen J. Contrasts in
muscle and myofibers of elite male and female bodybuilders. J Appl
Physiol (1985) 67: 24–31, 1989.
4. Alway SE, Grumbt WH, Stray-Gundersen J, Gonyea WJ. Effects of resistance training on elbow flexors of highly competitive bodybuilders. J
Appl Physiol (1985) 72: 1512–1521, 1992.
5. Belanger AY, McComas AJ. Extent of motor unit activation during effort.
J Appl Physiol Respir Environ Exerc Physiol 51: 1131–1135, 1981.
6. Bornstein M. Introduction to Meta-Analysis. Hoboken, NJ: John Wiley &
Sons, 2009.
7. Carlsson T, Wedholm L, Nilsson J, Carlsson M. The effects of strength
training versus ski-ergometer training on double-poling capacity of elite
junior cross-country skiers. Eur J Appl Physiol 117: 1523–1532, 2017.
8. Colliander EB, Tesch PA. Responses to eccentric and concentric resistance
training in females and males. Acta Physiol Scand 141: 149–156, 1991.
9. Cureton KJ, Collins MA, Hill DW, McElhannon FM Jr. Muscle hypertrophy in men and women. Med Sci Sports Exerc 20: 338–344, 1988.
10. Daniels WL, Wright JE, Sharp DS, et al. The effect of two years’ training
on aerobic power and muscle strength in male and female cadets. Aviat
Space Environ Med 53: 117–121, 1982.
11. Dannecker EA, Liu Y, Rector RS, et al. Sex differences in exercise-induced
muscle pain and muscle damage. J Pain 13: 1242–1249, 2012.
12. Dias RM, Cyrino ES, Salvador ES, et al. Impact of an eight-week weight
training program on the muscular strength of men and women. Revista
Brasileira de Medicina do Esporte 11: 213–218, 2005.
13. Donges CE, Duffield R. Effects of resistance or aerobic exercise training on
total and regional body composition in sedentary overweight middle-aged
adults. Appl Physiol Nutr Metab 37: 499–509, 2012.
14. Dorgo S, Edupuganti P, Smith DR, Ortiz M. Comparison of lower body
specific resistance training on the hamstring to quadriceps strength ratios
in men and women. Res Q Exerc Sport 83: 143–151, 2012.
15. Fernandez-Gonzalo R, Lundberg TR, Alvarez-Alvarez L, de Paz JA. Muscle
damage responses and adaptations to eccentric-overload resistance exercise
in men and women. Eur J Appl Physiol 114: 1075–1084, 2014.
16. Fujita S, Rasmussen BB, Cadenas JG, et al. Aerobic exercise overcomes the
age-related insulin resistance of muscle protein metabolism by improving
endothelial function and Akt/mammalian target of rapamycin signaling.
Diabetes 56: 1615–1622, 2007.
17. Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J. Effect of
two different weight-loss rates on body composition and strength and
power-related performance in elite athletes. Int J Sport Nutr Exerc Metab
21: 97–104, 2011.
18. Gentil P, Steele J, Pereira MC, et al. Comparison of upper body strength
gains between men and women after 10 weeks of resistance training. PeerJ
4: e1627, 2016.
19. Guadalupe-Grau A, Perez-Gomez J, Olmedillas H, et al. Strength training
combined with plyometric jumps in adults: Sex differences in fat-bone axis
adaptations. J Appl Physiol (1985) 106: 1100–1111, 2009.
20. Häkkinen K. Neuromuscular fatigue and recovery in male and female
athletes during heavy resistance exercise. Int J Sports Med 14: 53–59,
1993.
21. Häkkinen K, Kallinen M, Izquierdo M, et al. Changes in agonist-antagonist EMG, muscle CSA, and force during strength training in middleaged and older people. J Appl Physiol (1985) 84: 1341–1349, 1998.
22. Häkkinen K, Kallinen M, Linnamo V, et al. Neuromuscular adaptations
during bilateral versus unilateral strength training in middle-aged and
elderly men and women. Acta Physiol Scand 158: 77–88, 1996.
23. Häkkinen K, Newton RU, Gordon SE, et al. Changes in muscle morphology, electromyographic activity, and force production characteristics
during progressive strength training in young and older men. J Gerontol A
Biol Sci Med Sci 53: B415–B423, 1998.
24. Häkkinen K, Pakarinen A. Serum hormones and strength development
during strength training in middle-aged and elderly males and females.
Acta Physiol Scand 150: 211–219, 1994.
25. Häkkinen K, Pakarinen A, Kraemer WJ, et al. Selective muscle hypertrophy, changes in EMG and force, and serum hormones during strength
training in older women. J Appl Physiol (1985) 91: 569–580, 2001.
26. Hansen M, Couppe C, Hansen CS, et al. Impact of oral contraceptive use
and menstrual phases on patellar tendon morphology, biochemical composition, and biomechanical properties in female athletes. J Appl Physiol
(1985) 114: 998–1008, 2013.
27. Hedges LV, Tipton E, Johnson MC. Robust variance estimation in metaregression with dependent effect size estimates. Res Synth Methods 1:
39–65, 2010.
28. Hostler D, Crill MT, Hagerman FC, Staron RS. The effectiveness of 0.5-lb
increments in progressive resistance exercise. J Strength Cond Res 15:
86–91, 2001.
29. Hubal MJ, Gordish-Dressman H, Thompson PD, et al. Variability in
muscle size and strength gain after unilateral resistance training. Med Sci
Sports Exerc 37: 964–972, 2005.
30. Hunter GR. Research: Changes in body composition, body build and
performance associated with different weight training frequencies in males
and females. Natl Strength Cond J 7: 26–28, 1985.
31. Hunter SK. The relevance of sex differences in performance fatigability.
Med Sci Sports Exerc 48: 2247–2256, 2016.
32. Hurlbut DE, Lott ME, Ryan AS, et al. Does age, sex, or ACE genotype
affect glucose and insulin responses to strength training? J Appl Physiol
(1985) 92: 643–650, 2002.
33. Ivey FM, Roth SM, Ferrell RE, et al. Effects of age, gender, and myostatin
genotype on the hypertrophic response to heavy resistance strength
training. J Gerontol A Biol Sci Med Sci 55: M641–M648, 2000.
34. Ivey FM, Tracy BL, Lemmer JT, et al. Effects of strength training and
detraining on muscle quality: Age and gender comparisons. J Gerontol A
Biol Sci Med Sci 55: B152–B157, 2000. discussion B158-159.
35. Janssen I, Heymsfield SB, Wang ZM, Ross R. Skeletal muscle mass and
distribution in 468 men and women aged 18-88 yr. J Appl Physiol (1985)
89: 81–88, 2000.
36. Jozsi AC, Campbell WW, Joseph L, Davey SL, Evans WJ. Changes in
power with resistance training in older and younger men and women. J
Gerontol A Biol Sci Med Sci 54: M591–M596, 1999.
37. Kadi F, Bonnerud P, Eriksson A, Thornell LE. The expression of androgen
receptors in human neck and limb muscles: Effects of training and selfadministration of androgenic-anabolic steroids. Histochem Cell Biol 113:
25–29, 2000.
38. Kell RT. The influence of periodized resistance training on strength
changes in men and women. J Strength Cond Res 25: 735–744, 2011.
39. Kelley GA, Kelley KS. Impact of progressive resistance training on lipids
and lipoproteins in adults: A meta-analysis of randomized controlled trials. Prev Med 48: 9–19, 2009.
40. Kosek DJ, Kim JS, Petrella JK, Cross JM, Bamman MM. Efficacy of 3 days/
wk resistance training on myofiber hypertrophy and myogenic mechanisms
in young vs. older adults. J Appl Physiol (1985) 101: 531–544, 2006.
41. Kovacevic A, Mavros Y, Heisz JJ, Fiatarone Singh MA. The effect of
resistance exercise on sleep: A systematic review of randomized controlled
trials. Sleep Med Rev 39: 52–68, 2018.
42. Lemmer JT, Ivey FM, Ryan AS, et al. Effect of strength training on resting
metabolic rate and physical activity: Age and gender comparisons. Med
Sci Sports Exerc 33: 532–541, 2001.
43. Lemmer JT, Martel GF, Hurlbut DE, Hurley BF. Age and sex differentially
affect regional changes in one repetition maximum strength. J Strength
Cond Res 21: 731–737, 2007.
44. Lexell J, Henriksson-Larsen K, Winblad B, Sjostrom M. Distribution of
different fiber types in human skeletal muscles: Effects of aging studied in
whole muscle cross sections. Muscle Nerve 6: 588–595, 1983.
45. Liu D, Sartor MA, Nader GA, et al. Skeletal muscle gene expression in
response to resistance exercise: Sex specific regulation. BMC Genomics
11: 659, 2010.
1459
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Sex Differences in Training (2020) 34:5
46. Markofski MM, Braun WA. Influence of menstrual cycle on indices of
contraction-induced muscle damage. J Strength Cond Res 28: 2649–2656,
2014.
47. Markofski MM, Volpi E. Protein metabolism in women and men: Similarities and disparities. Curr Opin Clin Nutr Metab Care 14: 93–97, 2011.
48. Martin Ginis KA, Eng JJ, Arbour KP, Hartman JW, Phillips SM. Mind
over muscle? Sex differences in the relationship between body image
change and subjective and objective physical changes following a 12-week
strength-training program. Body Image 2: 363–372, 2005.
49. McMahon G, Morse CI, Winwood K, Burden A, Onambele GL. Gender
associated muscle-tendon adaptations to resistance training. PLoS One
13: e0197852, 2018.
50. Miller AE, MacDougall JD, Tarnopolsky MA, Sale DG. Gender differences in strength and muscle fiber characteristics. Eur J Appl Physiol
Occup Physiol 66: 254–262, 1993.
51. Miller BF, Hansen M, Olesen JL, et al. No effect of menstrual cycle on
myofibrillar and connective tissue protein synthesis in contracting skeletal
muscle. Am J Physiol Endocrinol Metab 290: E163–E168, 2006.
52. Miller BF, Hansen M, Olesen JL, et al. Tendon collagen synthesis at rest
and after exercise in women. J Appl Physiol (1985) 102: 541–546, 2007.
53. Moritani T, deVries HA. Neural factors versus hypertrophy in the time
course of muscle strength gain. Am J Phys Med 58: 115–130, 1979.
54. Morris B. Estimating effect sizes from pretest-posttest-control group
designs. Organ Res Methods 11: 364–386, 2008.
55. O’Hagan FT, Sale DG, MacDougall JD, Garner SH. Response to resistance training in young women and men. Int J Sports Med 16: 314–321,
1995.
56. Peterson MD, Pistilli E, Haff GG, Hoffman EP, Gordon PM. Progression
of volume load and muscular adaptation during resistance exercise. Eur J
Appl Physiol 111: 1063–1071, 2011.
57. Raue U, Trappe TA, Estrem ST, et al. Transcriptome signature of resistance exercise adaptations: Mixed muscle and fiber type specific profiles
in young and old adults. J Appl Physiol (1985) 112: 1625–1636, 2012.
58. Reimers AK, Knapp G, Reimers CD. Effects of exercise on the resting heart
rate: A systematic review and meta-analysis of interventional studies. J
Clin Med 7: 503, 2018.
59. Reis E, Frick U, Schmidtbleicher D. Frequency variations of strength
training sessions triggered by the phases of the menstrual cycle. Int J Sports
Med 16: 545–550, 1995.
60. Ribeiro AS, Avelar A, Dos Santos L, et al. Hypertrophy-type resistance
training improves phase Angle in young adult men and women. Int J
Sports Med 38: 35–40, 2017.
61. Ribeiro AS, Avelar A, Schoenfeld BJ, et al. Analysis of the training load
during a hypertrophy-type resistance training programme in men and
women. Eur J Sport Sci 15: 256–264, 2015.
62. Ribeiro AS, Avelar A, Schoenfeld BJ, et al. Resistance training promotes
increase in intracellular hydration in men and women. Eur J Sport Sci 14:
578–585, 2014.
63. Ribeiro AS, Avelar A, Schoenfeld BJ, et al. Effect of 16 weeks of resistance
training on fatigue resistance in men and women. J Hum Kinet 42:
165–174, 2014.
64. Riechman SE, Fabian TJ, Kroboth PD, Ferrell RE. Steroid sulfatase gene
variation and DHEA responsiveness to resistance exercise in MERET.
Physiol Genomics 17: 300–306, 2004.
65. Roberts BM, Lavin KM, Many GM, et al. Human neuromuscular aging:
Sex differences revealed at the myocellular level. Exp Gerontol 106:
116–124, 2018.
66. Rogol AD. Growth and growth hormone secretion at puberty: The role of
gonadal steroid hormones. Acta Paediatr Suppl 383: 15–20; discussion
21, 1992.
67. Roth SM, Ivey FM, Martel GF, et al. Muscle size responses to strength
training in young and older men and women. J Am Geriatr Soc 49:
1428–1433, 2001.
68. Rutherford OM, Jones DA. The role of learning and coordination in
strength training. Eur J Appl Physiol Occup Physiol 55: 100–105, 1986.
69. Sale DG, MacDougall JD, Alway SE, Sutton JR. Voluntary strength and
muscle characteristics in untrained men and women and male bodybuilders. J Appl Physiol (1985) 62: 1786–1793, 1987.
70. Salvador EPDR, Gurjao AL, Avelar A, Pinto LG, Cyrino ES. Effect of eight
weeks of strength training on fatigue resistance in men and women. Isokinetics Exerc Sci 17: 101–106, 2009.
71. Schmidt D, Anderson K, Graff M, Strutz V. The effect of high-intensity
circuit training on physical fitness. J Sports Med Phys Fitness 56: 534–540,
2016.
72. Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res 24: 2857–2872, 2010.
73. Sheel AW. Sex differences in the physiology of exercise: An integrative
perspective. Exp Physiol 101: 211–212, 2016.
74. Shephard RJ. Exercise and training in women. Part I: Influence of
gender on exercise and training responses. Can J Appl Physiol 25:
19–34, 2000.
75. Simoneau JA, Bouchard C. Human variation in skeletal muscle fibertype proportion and enzyme activities. Am J Physiol 257: E567–E572,
1989.
76. Smith GI, Atherton P, Reeds DN, et al. No major sex differences in muscle
protein synthesis rates in the postabsorptive state and during hyperinsulinemia-hyperaminoacidemia in middle-aged adults. J Appl Physiol
(1985) 107: 1308–1315, 2009.
77. Spurway NC, Watson H, McMillan K, Connolly G. The effect of strength
training on the apparent inhibition of eccentric force production in voluntarily activated human quadriceps. Eur J Appl Physiol 82: 374–380,
2000.
78. Staron RS, Karapondo DL, Kraemer WJ, et al. Skeletal muscle adaptations
during early phase of heavy-resistance training in men and women. J Appl
Physiol (1985) 76: 1247–1255, 1994.
79. Stock MS, Thompson BJ. Sex comparisons of strength and coactivation
following ten weeks of deadlift training. J Musculoskelet Neuronal Interact 14: 387–397, 2014.
80. Stupka N, Lowther S, Chorneyko K, et al. Gender differences in muscle
inflammation after eccentric exercise. J Appl Physiol (1985) 89:
2325–2332, 2000.
81. Sung E, Han A, Hinrichs T, et al. Effects of follicular versus luteal phasebased strength training in young women. Springerplus 3: 668, 2014.
82. Tipton E. Small sample adjustments for robust variance estimation with
meta-regression. Psychol Methods 20: 375–393, 2015.
83. Trappe S, Gallagher P, Harber M, et al. Single muscle fibre contractile
properties in young and old men and women. J Physiol 552: 47–58, 2003.
84. Washburn RA, Kirk EP, Smith BK, et al. One set resistance training: Effect
on body composition in overweight young adults. J Sports Med Phys
Fitness 52: 273–279, 2012.
85. Weiss LW, Clark FC, Howard DG. Effects of heavy-resistance triceps
surae muscle training on strength and muscularity of men and women.
Phys Ther 68: 208–213, 1988.
86. West DW, Burd NA, Churchward-Venne TA, et al. Sex-based comparisons of myofibrillar protein synthesis after resistance exercise in the fed
state. J Appl Physiol (1985) 112: 1805–1813, 2012.
87. Westh E, Kongsgaard M, Bojsen-Moller J, et al. Effect of habitual exercise
on the structural and mechanical properties of human tendon, in vivo, in
men and women. Scand J Med Sci Sports 18: 23–30, 2008.
88. Wikstrom-Frisen L, Boraxbekk CJ, Henriksson-Larsen K. Effects on
power, strength and lean body mass of menstrual/oral contraceptive cycle
based resistance training. J Sports Med Phys Fitness 57: 43–52, 2017.
89. Williamson DL, Gallagher PM, Carroll CC, Raue U, Trappe SW. Reduction in hybrid single muscle fiber proportions with resistance training
in humans. J Appl Physiol (1985) 91: 1955–1961, 2001.
90. Wilmore JH. Alterations in strength, body composition and anthropometric measurements consequent to a 10-week weight training program.
Med Sci Sports 6: 133–138, 1974.
91. Young A. The relative isometric strength of type I and type II muscle fibres
in the human quadriceps. Clin Physiol 4: 23–32, 1984.
1460
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.