ArticlePDF AvailableLiterature Review

Sex Differences in Resistance Training: A Systematic Review and Meta-Analysis

Authors:

Abstract and Figures

Roberts, BM, Nuckols, G, and Krieger, JW. Sex differences in resistance training: A systematic review and meta-analysis. J Strength Cond Res XX(X): 000-000, 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] = 0.07 ± 0.06; P = 0.31; I = 0). The analysis of upper-body strength comprised 19 outcomes from 17 studies with a significant effect favoring females (ES = -0.60 ± 0.16; P = 0.002; I = 72.1). The analysis of lower-body strength comprised 23 outcomes from 23 studies with no significant difference between sexes (ES = -0.21 ± 0.16; P = 0.20; I = 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.
Content may be subject to copyright.
Downloaded from https://journals.lww.com/nsca-jscr by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3ZI03TR16A94VHK3/2XIzGdiQb7hchtOdvZAMrsIBjMs= on 03/28/2020
Downloadedfromhttps://journals.lww.com/nsca-jscr by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3ZI03TR16A94VHK3/2XIzGdiQb7hchtOdvZAMrsIBjMs= on 03/28/2020
Brief Review
Sex Differences in Resistance Training: A
Systematic Review and Meta-Analysis
Brandon M. Roberts,
1
Greg Nuckols,
2
and James W. Krieger
3
1
University of Alabama at Birmingham, Birmingham, Alabama;
2
Stronger by Science LLC, Raleigh, North Carolina; and
3
Weightology
LLC, Issaquah, Washington
Abstract
Roberts,BM,Nuckols,G,andKrieger,JW.Sexdifferencesinresistance training: A systematic review and meta-analysis. J
Strength Cond Res XX(X): 000–000, 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] 50.07 60.06; P50.31; I
2
50). The analysis of upper-body
strength comprised 19 outcomes from 17 studies with a significant effect favoring females (ES 5-0.60 60.16; P50.002; I
2
5
72.1). The analysis of lower-body strength comprised 23 outcomes from 23 studies with no significant difference between sexes
(ES 520.21 60.16; P50.20; I
2
574.7). 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 hyper-
trophy and strength adaptations. There also may be some
differences in types of occupation that could cause basal strength
differences. However, there is currently no review bringing to-
gether 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 un-
derstand sex differences in response to RT if they exist. Therefore,
the purpose of this study is to determine whether there are dif-
ferent 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.
Address correspondence to Dr. Brandon M. Roberts, robertsb21@gmail.com.
Journal of Strength and Conditioning Research 00(00)/1–13
ª2020 National Strength and Conditioning Association
1
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Table 1
Overview of studies meeting inclusion criteria.*
Hypertrophy and strength adaptations to resistance training in males and females
Study nSession per week Training status Study duration (wks) Strength measurement Within-sex ES for strength Measurement Within-sex ES for hypertrophy
Abe et al. (1) Male: 17
Female: 15
3 Untrained .12 mo 12 Chest press
Knee extension
Male: 1.33
Female: 0.96
Ultrasound Male: 1.31
Female: 1.03
Ahtiainen et al. (2) Male: 61
Female: 27
2 Untrained 24 Leg press Male: 1.06
Female: 0.96
MRI
DXA
Ultrasound
NR
Alway et al. (4) Male: 5
Female 5
2 Trained body builders 24 NR NR Computed tomography,
fiber cross-sectional area
CT
Male: 0.42
Female: 0.25
fCSA
Male: 0.08
Female: 0.41
Carlsson et al. (7) Male: 7
Female: 7
2NR
Athletes
6 Bar-dips, chin-ups Male: 0.20
Female: 0.64
NR NR
Colliander et al. (8) Male: 11
Female: 11
3 Untrained
Physically active
12 Leg extension Male: 2.3
Female: 1.61
NR NR
Cureton et al. (9) Male: 8
Female: 7
3 Untrained .6 mo 16 Elbow flexion
Leg extension
Male: 0.43
Female: 1.14
Computed tomography Arm
Male: 1.2
Female: 1.03
Thigh
Male: 0.43
Female: 0.25
Daniels et al. (10) Male: 11
Female: 7
5NR
Physically active
104 Pull-down
Leg extension
Upper body
Male: 1.41
Female: 1
Lower body
Male: 1.3
Female: 1.54
NR NR
Dias et al. (12) Male: 23
Female: 15
3 Untrained .6mo
Physically active
12 Bench press
Squat
Upper body
Male: 0.52
Female: 0.98
Lower body
Male: 0.36
Female: 0.75
NR NR
Donges et al. (13) Male: 16
Female: 19
3 Untrained .12 mo
Sedentary
10 Chest press
Leg press
NR NR NR
Dorgo et al. (14) Male: 14
Female: 14
2 Untrained
Physically active
12 Leg extension Male: 1.28
Female: 2.45
NR NR
Fernandez-Gonzalo et al. (15) Male: 16
Female: 16
2–3 Untrained .6mo
Physically active
6 Leg press Male: 1.92
Female: 0.88
NR NR
Garthe et al. (17) Male: 11
Female: 13
4NR
Athletes
12 Squat NR NR NR
Gentil et al. (18) Male: 44
Female: 47
2 No systematic RT .3 mo 10 Elbow flexion Male: 0.56
Female: 0.6
NR NR
Guadalupe-Grau et al. (19) Male: 24
Female: 23
2NR
Physically active
9 Leg press Male: 1.15
Female: 5.63
NR NR
Sex Differences in Training (2020) 00:00
2
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Table 1
Overview of studies meeting inclusion criteria.* (Continued)
Hypertrophy and strength adaptations to resistance training in males and females
Study nSession per week Training status Study duration (wks) Strength measurement Within-sex ES for strength Measurement Within-sex ES for hypertrophy
akkinen et al. (24) Male: 9
Female: 9
2–3 Untrained
Physically active
12 Leg extension Male: 2.45
Female: 0.62
NR NR
akkinen et al. (22) Male: 12
Female: 12
2 Untrained
Physically active
12 Leg extension Male: 0.98
Female: 1.2
NR NR
Hakkinen et al. (21)
Hakkinen et al. (23)
Hakkinen et al. (25)
Male: 42
Female: 39
2 Untrained
Physically active
24 Leg extension Male: 0.31
Female: 0.38
Muscle fiber size Male: 0.66
Female: 0.59
Hostler et al. (28) Male: 5
Female: 5
3 Untrained .6 mo 16 Bench press Male: 1.18
Female: 3.49
NR NR
Male: 5
Female: 4
2 Male: 1.9
Female: 1.74
Hurlbut et al. (32)
Lemmer et al. (42)
Lemmer et al. (43)
Roth et al. (67)
Male: 10
Female: 9
3 Untrained .6mo
Sedentary
24 Chest press
Leg press
Upper body
Male: 0.94
Female: 2
Lower body
Male: 1.38
Female: 2.23
MRI Male: 0.43
Female: 0.09
Hubal et al. (29)
Liu et al. (45)
Peterson et al. (56)
Male: 43
Female: 40
2 Untrained .12 mo 12 Bicep flexion Male: 0.04
Female: 0.06
MRI Male: 0.67
Female: 0.65
Hunter (30) Male: 11
Female: 10
3 NR 7 Bench press Male: 0.08
Female: 0.06
NR NR
Male: 14
Female: 11
4 Male: 0.04
Female: 0.15
Ivey et al. (33)
Ivey et al.(34)
Male: 11
Female: 11
3 Untrained .6mo
Sedentary
9 Leg extension Male: 1.27
Female: 1.88
MRI Male: 0.49
Female: 0.31
Jozsi et al. (36) Male: 6
Female: 9
2 Untrained .12 mo 12 Chest press
Leg press
Upper body
Male: 0.61
Female: 0.62
Lower body
Male: 2.25
Female: 2.41
NR NR
Kell et al. (38) Male: 20
Female: 20
3 Trained
Physically active
12 Bench press
Back squat
Upper body
Male: 1.31
Female: 2.37
Lower body
Male: 1.48
Female: 2.22
NR NR
Kosek et al. (40) Male: 13
Female: 11
3 Untrained .12 mo 16 Leg press Male: 1.8
Female: 2.78
Muscle fiber size Male: 1.84
Female: 1.23
Martin-Ginis et al. (48) Male: 25
Female: 15
5 Untrained .6mo
Sedentary
12 Chest press
Leg press
Upper body
Male: 1.33
Female: 3.31
Lower body
Male: 2.56
Female: 2.62
NR NR
Sex Differences in Training (2020) 00:00 |www.nsca.com
3
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Table 1
Overview of studies meeting inclusion criteria.* (Continued)
Hypertrophy and strength adaptations to resistance training in males and females
Study nSession per week Training status Study duration (wks) Strength measurement Within-sex ES for strength Measurement Within-sex ES for hypertrophy
O’Hagan et al. (55) Male: 6
Female 6
3 NR 20 Elbow flexion Male: 2
Female: 4.18
CT Male: 0.09
Female: 0.43
Reichman et al. (64) Male: 62
Female: 58
3 Trained ,3 h per week 10 wk Chest press
Leg press
NR NR NR
Ribiero et al. (63)
Ribiero et al. (62)
Ribiero et al. (60)
Female: 31
Male: 28
3 Untrained .6 mo 16 wk Bench press Male: 0.69
Female: 1.22
NR NR
Rutherford et al. (68) Male: 11
Female: 9
3 Untrained 12 wk Leg extension Male: 0.81
Female: 0.22
NR NR
Spurway et al. (77) Male: 10
Female: 10
3 Untrained
Physically active
6 wk Leg extension NR NR NR
Salvador et al. (71) Male: 33
Female: 23
3 Untrained .6 mo 8 wk Bench press
Back squat
Upper body
Male: 0.41
Female: 0.81
Lower body
Male: 0.55
Female: 0.67
NR NR
Schmidt et al. (72) Male: 43
Female: 53
3 Untrained
Physically active
8 wk Push-ups NR NR NR
Staron et al. (79) Male: 13
Female: 8
2 Untrained
Physically active
9 wk NR NR Muscle fiber size NR
Stock et al. (80) Male: 17
Female: 17
2 Untrained .6 mo 10 wk Leg extension Male: 0.44
Female: 0.63
NR NR
Washburn et al. (85) Male: 17
Female: 13
3 NR 24 wk Chest press
Leg press
NR NR NR
Weiss et al. (86) Male: 12
Female: 14
3 Untrained .3 mo 8 wk Plantar flexion Male: 0.91
Female: 0.52
Ultrasound Male: 0.24
Female: 0.17
Williamson et al. (90)
Raue et al. (58)
Male: 6
Female: 6
3 Untrained .12 mo 12 wk Leg extension Male: 7.91
Female: 11.8
NR NR
Wilmore et al. (91) Male: 26
Female: 46
2 NR 10 wk Bench press
Leg press
Male: 2.21
Female: 3.5
NR NR
*ES 5effect size; MRI 5magnetic resonance imaging; NR 5Not recorded; DXA 5dual-energy X-ray absorptiometry; CT 5computed tomography; RT 5resistance training; fCSA 5fiber cross-sectional area.
Sex Differences in Training (2020) 00:00
4
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Search Strategy. Our protocol was pre-registered with PROS-
PERO (CRD42018094276). The systematic review was per-
formed in accordance with the guidelines provided by the
Preferred Reporting Items for Systematic Reviews and Meta-
Analyses (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 addi-
tional 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 measure-
ment (magnetic resonance imaging, fiber cross sectional area
[fCSA], ultrasound, and computed tomography). Results were
cross-checked between coders, and any discrepancies were re-
solved 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 pvalue of 0.05 or greater using the Rosenthal
approach.
Figure 1. PRISMA diagram.
Sex Differences in Training (2020) 00:00 |www.nsca.com
5
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
All analyses were performed in R version 3.5 (The R Foun-
dation 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.
Methodological Quality
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
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
Hypertrophy
The analysis of hypertrophy comprised 12 outcomes from 10
studies. There was no significant difference between males and
females (ES 50.07 60.06; 95% CI: 20.09 to 0.23; P50.31;
Figure 2). Heterogeneity was low (I
2
50) (Figure 3).
Figure 2. Forest plot of studies comparing changes in hypertrophy in males and females. The data
shown are mean 695% CI; the size of the plotted squares reflects the statistical weight of each study.
CI 5confidence interval.
Sex Differences in Training (2020) 00:00
6
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Upper-Body Strength
The analysis of upper-body strength comprised 19 outcomes from
17 studies. There was a significant effect favoring females (ES 5
20.60 60.16; 95% CI: 20.93 to 20.26; P50.002; Figure 4).
Heterogeneity was high (I
2
572.1). 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 het-
erogeneity (I
2
569.7) (Figure 5).
Lower-Body Strength
The analysis of lower-body strength comprised 23 outcomes from
23 studies. There was no significant difference between sexes (ES
520.21 60.16; 95% CI: 20.54 to 0.12; P50.20; Figure 6).
Heterogeneity was high (I
2
574.7). 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 het-
erogeneity (I
2
577.4) (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 in-
fluential 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 (P50.41). We also used
a fail-safe N to calculate the number of null studies needed to
achieve a pvalue of 0.05 or greater using the Rosenthal approach.
The fail-safe N was 294. Thus, there was no evidence of publi-
cation bias for the upper-body strength outcomes.
Discussion
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 520.60; 95% CI: 20.93 to 20.26;
P50.002).
Muscular strength increases in response to RT are a com-
bination of neurological and muscular adaptations. Initial,
rapid improvements in strength seem to result primarily from
neurological adaptation, whereas subsequent gains are pri-
marilytheresultofmuscularadaptations (53). In one of the
first studies comparing untrained males and females, Wilmore
etal.,foundthatstrengthwassimilarwhennormalizedto
body weight after 10 weeks of intensive RT (90). Interestingly,
relative upper-body strength increased 29% in females com-
pared with 17% in males, whereas relative increases in lower-
body strength were similar (90). These data were the first data
to indicate there may be differences in strength changes be-
tween sexes. However, a limitation was that both groups ex-
perienced 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
Figure 3. Percent change in muscle hypertrophy in males and females.
Sex Differences in Training (2020) 00:00 |www.nsca.com
7
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Figure 4. Forest plot of studies comparing changes in upper-body strength in males and females. The
data shown are mean 695% CI; the size of the plotted squares reflects the statistical weight of each
study. CI 5confidence interval.
Sex Differences in Training (2020) 00:00
8
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
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 sub-
jects 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 dif-
ferences could occur in strength or hypertrophy is muscle phe-
notype. 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 pul-
satility in females (66). Males exhibit lower serum cortisol due to
chronic RT, whereas females do not (78). Females do not expe-
rience 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 differ-
ences 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 contri-
bution 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.
Figure 5. Percent change in muscle upper-body strength in males and females.
Sex Differences in Training (2020) 00:00 |www.nsca.com
9
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Figure 6. Forest plot of studies comparing changes in lower-body strength in males and females.
The data shown are mean 695% CI; the size of the plotted squares reflects the statistical weight
of each study. CI 5confidence interval; the size of the plotted squares reflects the statistical
weight of each study.
Sex Differences in Training (2020) 00:00
10
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Although a strength of this study is that it is the first meta-
analysis completed on sex differences, there are several limi-
tations. 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 sub-
jects 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 upper-
body 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 sta-
tistical 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 lower-
body 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 upper-
body 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 un-
derstanding of sex differences in the physiology of RT is in-
complete, which makes studies on sex-differences warranted.
Figure 7. Percent change in lower-body strength in males and females.
Figure 8. Funnel plot, using data from studies with upper-body strength outcomes.
Sex Differences in Training (2020) 00:00 |www.nsca.com
11
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
Practical Applications
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 differ-
ence 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: 174180, 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: 2431, 1989.
4. Alway SE, Grumbt WH, Stray-Gundersen J, Gonyea WJ. Effects of re-
sistance training on elbow flexors of highly competitive bodybuilders. J
Appl Physiol (1985) 72: 15121521, 1992.
5. Belanger AY, McComas AJ. Extent of motor unit activation during effort.
J Appl Physiol Respir Environ Exerc Physiol 51: 11311135, 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: 15231532, 2017.
8. Colliander EB, Tesch PA. Responses to eccentric and concentric resistance
training in females and males. Acta Physiol Scand 141: 149156, 1991.
9. Cureton KJ, Collins MA, Hill DW, McElhannon FM Jr. Muscle hyper-
trophy in men and women. Med Sci Sports Exerc 20: 338344, 1988.
10. Daniels WL, Wright JE, Sharp DS, et al. The effect of two yearstraining
on aerobic power and muscle strength in male and female cadets. Aviat
Space Environ Med 53: 117121, 1982.
11. Dannecker EA, Liu Y, Rector RS, et al. Sex differences in exercise-induced
muscle pain and muscle damage. J Pain 13: 12421249, 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: 213218, 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: 499509, 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: 143151, 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. EurJApplPhysiol114: 10751084, 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: 16151622, 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: 97104, 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: 11001111, 2009.
20. Hakkinen K. Neuromuscular fatigue and recovery in male and female
athletes during heavy resistance exercise. Int J Sports Med 14: 5359,
1993.
21. Hakkinen K, Kallinen M, Izquierdo M, et al. Changes in agonist-antag-
onist EMG, muscle CSA, and force during strength training in middle-
aged and older people. J Appl Physiol (1985) 84: 13411349, 1998.
22. Hakkinen 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: 7788, 1996.
23. Hakkinen K, Newton RU, Gordon SE, et al. Changes in muscle mor-
phology, electromyographic activity, and force production characteristics
during progressive strength training in young and older men. J Gerontol A
Biol Sci Med Sci 53: B415B423, 1998.
24. Hakkinen K, Pakarinen A. Serum hormones and strength development
during strength training in middle-aged and elderly males and females.
Acta Physiol Scand 150: 211219, 1994.
25. Hakkinen K, Pakarinen A, Kraemer WJ, et al. Selective muscle hyper-
trophy, changes in EMG and force, and serum hormones during strength
training in older women. J Appl Physiol (1985) 91: 569580, 2001.
26. Hansen M, Couppe C, Hansen CS, et al. Impact of oral contraceptive use
and menstrual phases on patellar tendon morphology, biochemical com-
position, and biomechanical properties in female athletes. J Appl Physiol
(1985) 114: 9981008, 2013.
27. Hedges LV, Tipton E, Johnson MC. Robust variance estimation in meta-
regression with dependent effect size estimates. Res Synth Methods 1:
3965, 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:
8691, 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: 964972, 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: 2628, 1985.
31. Hunter SK. The relevance of sex differences in performance fatigability.
Med Sci Sports Exerc 48: 22472256, 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: 643650, 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: M641M648, 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: B152B157, 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: 8188, 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: M591M596, 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 self-
administration of androgenic-anabolic steroids. Histochem Cell Biol 113:
2529, 2000.
38. Kell RT. The influence of periodized resistance training on strength
changes in men and women. J Strength Cond Res 25: 735744, 2011.
39. Kelley GA, Kelley KS. Impact of progressive resistance training on lipids
and lipoproteins in adults: A meta-analysis of randomized controlled tri-
als. Prev Med 48: 919, 2009.
40. KosekDJ, 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. JApplPhysiol(1985)101: 531544, 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: 5268, 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: 532541, 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: 731737, 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: 588595, 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.
Sex Differences in Training (2020) 00:00
12
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
46. Markofski MM, Braun WA. Influence of menstrual cycle on indices of
contraction-induced muscle damage. J Strength Cond Res 28: 26492656,
2014.
47. Markofski MM, Volpi E. Protein metabolism in women and men: Simi-
larities and disparities. Curr Opin Clin Nutr Metab Care 14: 9397, 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: 363372, 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 differ-
ences in strength and muscle fiber characteristics. Eur J Appl Physiol
Occup Physiol 66: 254262, 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: E163E168, 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: 541546, 2007.
53. Moritani T, deVries HA. Neural factors versus hypertrophy in the time
course of muscle strength gain. Am J Phys Med 58: 115130, 1979.
54. Morris B. Estimating effect sizes from pretest-posttest-control group
designs. Organ Res Methods 11: 364386, 2008.
55. OHagan FT, Sale DG, MacDougall JD, Garner SH. Response to re-
sistance training in young women and men. Int J Sports Med 16: 314321,
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: 10631071, 2011.
57. Raue U, Trappe TA, Estrem ST, et al. Transcriptome signature of re-
sistance exercise adaptations: Mixed muscle and fiber type specific profiles
in young and old adults. J Appl Physiol (1985) 112: 16251636, 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: 545550, 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: 3540, 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: 256264, 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:
578585, 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:
165174, 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: 300306, 2004.
65. Roberts BM, Lavin KM, Many GM, et al. Human neuromuscular aging:
Sex differences revealed at the myocellular level. Exp Gerontol 106:
116124, 2018.
66. Rogol AD. Growth and growth hormone secretion at puberty: The role of
gonadal steroid hormones. Acta Paediatr Suppl 383: 1520; 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:
14281433, 2001.
68. Rutherford OM, Jones DA. The role of learning and coordination in
strength training. Eur J Appl Physiol Occup Physiol 55: 100105, 1986.
69. Sale DG, MacDougall JD, Alway SE, Sutton JR. Voluntary strength and
muscle characteristics in untrained men and women and male body-
builders. J Appl Physiol (1985) 62: 17861793, 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. Iso-
kinetics Exerc Sci 17: 101106, 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: 534540,
2016.
72. Schoenfeld BJ. The mechanisms of muscle hypertrophy and their appli-
cation to resistance training. J Strength Cond Res 24: 28572872, 2010.
73. Sheel AW. Sex differences in the physiology of exercise: An integrative
perspective. Exp Physiol 101: 211212, 2016.
74. Shephard RJ. Exercise and training in women. Part I: Influence of
gender on exercise and training responses. Can J Appl Physiol 25:
1934, 2000.
75. Simoneau JA, Bouchard C. Human variation in skeletal muscle fiber-
type proportion and enzyme activities. Am J Physiol 257: E567E572,
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 hyper-
insulinemia-hyperaminoacidemia in middle-aged adults. J Appl Physiol
(1985) 107: 13081315, 2009.
77. Spurway NC, Watson H, McMillan K, Connolly G. The effect of strength
training on the apparent inhibition of eccentric force production in vol-
untarily activated human quadriceps. Eur J Appl Physiol 82: 374380,
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: 12471255, 1994.
79. Stock MS, Thompson BJ. Sex comparisons of strength and coactivation
following ten weeks of deadlift training. J Musculoskelet Neuronal In-
teract 14: 387397, 2014.
80. Stupka N, Lowther S, Chorneyko K, et al. Gender differences in muscle
inflammation after eccentric exercise. J Appl Physiol (1985) 89:
23252332, 2000.
81. Sung E, Han A, Hinrichs T, et al. Effects of follicular versus luteal phase-
based 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: 375393, 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: 4758, 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: 273279, 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: 208213, 1988.
86. West DW, Burd NA, Churchward-Venne TA, et al. Sex-based compar-
isons of myofibrillar protein synthesis after resistance exercise in the fed
state. J Appl Physiol (1985) 112: 18051813, 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: 2330, 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: 4352, 2017.
89. Williamson DL, Gallagher PM, Carroll CC, Raue U, Trappe SW. Re-
duction in hybrid single muscle fiber proportions with resistance training
in humans. J Appl Physiol (1985) 91: 19551961, 2001.
90. Wilmore JH. Alterations in strength, body composition and anthropo-
metric measurements consequent to a 10-week weight training program.
Med Sci Sports 6: 133138, 1974.
91. Young A. The relative isometric strength of type I and type II muscle fibres
in the human quadriceps. Clin Physiol 4: 2332, 1984.
Sex Differences in Training (2020) 00:00 |www.nsca.com
13
Copyright © 2020 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.
... A limitation of the aforementioned studies is the lack of calculation of sex differences between groups (Lacio et al., 2021). Even if scientific research showing similar responses in hypertrophy and MSt increases between male and female participants (Roberts et al., 2020) it is a popularly held belief that females show lower adaptations to RT stimuli than males (Lewis et al., 1986). In terms of flexibility, there might be evidence for significantly better baseline ROM values in females compared to males (Cipriani et al., 2012;Yu et al., 2022). ...
... While it is still assumed that male participants show higher absolute MSt and greater muscle crosssectional area (Nonaka et al., 2006;Nagai et al., 2020), which is often attributed to the difference between sexes in testosterone (Handelsman et al., 2018), the differences in strength capacity seem to disappear when normalized for fat-free body mass (Freilich et al., 1995;Nonaka et al., 2006;Sandbakk et al., 2018). Moreover, a metaanalysis performed by Roberts et al. (Roberts et al., 2020) showed no significant differences in hypertrophic response to RT in the lower extremity between sexes, but even higher effects in female participants in the upper body, which was attributed to lower pre-test training status of the female participants. Accordingly, Bishop et al. (Bishop et al., 1989) stated that there was no difference between trained male and female swimmers regarding their fat-free cross-sectional area, using fat free mass as a covariate. ...
Article
Full-text available
Introduction: If the aim is to increase maximal strength (MSt) and muscle mass, resistance training (RT) is primarily used to achieve these outcomes. However, research indicates that long-duration stretching sessions of up to 2 h per day can also provide sufficient stimuli to induce muscle growth. In RT literature, sex-related differences in adaptations are widely discussed, however, there is a lack of evidence addressing the sex-related effects on MSt and muscle thickness (MTh) of longer duration stretch training. Therefore, this study aimed to investigate the effects of 6 weeks of daily (1 h) unilateral static stretch training of the plantar flexors using a calf-muscle stretching device. Methods: Fifty-five healthy (m = 28, f = 27), active participants joined the study. MSt and range of motion (ROM) were measured with extended and flexed knee joint, and MTh was investigated in the medial and lateral heads of the gastrocnemius. Results: Statistically significant increases in MSt of 6%–15% ( p < .001–.049, d = 0.45–1.09), ROM of 6%–21% ( p < .001–.037, d = 0.47–1.38) and MTh of 4%–14% ( p < .001–.005, d = 0.46–0.72) from pre-to post-test were observed, considering both sexes and both legs. Furthermore, there was a significant higher increase in MSt, MTh and ROM in male participants. In both groups, participants showed more pronounced adaptations in MSt and ROM with an extended knee joint as well as MTh in the medial head of the gastrocnemius ( p < .001–.047). Results for relative MSt increases showed a similar result ( p < .001–.036, d = 0.48–1.03). Discussion: Results are in accordance with previous studies pointing out significant increases of MSt, MTh and ROM due to long duration static stretch training. Both sexes showed significant increases in listed parameters however, male participants showed superior increases.
... Results identified that the large threshold was lower for recreationally trained individuals, and greater for female-only groups. These potential differences align with findings from previous research showing greater relative improvements in outcomes such as strength for untrained participants and females (34,35). It has been hypothesised that such differences may be due to greater capacity to improve based on a general lower starting point (35). ...
... These potential differences align with findings from previous research showing greater relative improvements in outcomes such as strength for untrained participants and females (34,35). It has been hypothesised that such differences may be due to greater capacity to improve based on a general lower starting point (35). Greater confidence in these findings would have been obtained if ordered effects were observed such that the effect size distribution was narrower for highly trained participants (untrained > recreational > highly), and effects for mixed sex groups were between male-and female-only groups. ...
... Furthermore, research investigating sex-related differences is often performed on untrained or moderately trained individuals [24]. It is therefore of interest to investigate if the association of anthropometric variables for maximal strength, relative strength, and strength endurance varies between males and females in a strength-trained population. ...
Article
Full-text available
Individual differences in the appropriate percentage of 1-RM for a given repetition range could be a result of variation in anthropometrics and/or sex. Strength endurance is the term used to describe the ability to perform a number of repetitions prior to failure (AMRAP) in sub-maximal lifts and is important in determining the appropriate load for the targeted repetition range. Earlier research investigating the association of AMRAP performance and anthropometric variables was often performed in a sample of pooled sexes or one sex only or by utilizing tests with low ecological validity. As such, this randomized cross-over study investigates the association of anthropometrics with different measures of strength (maximal and relative strength and AMRAP) in the squat and bench press for resistance-trained males (n = 19, 24.3 ± 3.5 years, 182 ± 7.3 cm, 87.1 ± 13.3 kg) and females (n = 17, 22.1 ± 3 years, 166.1 ± 3.7 cm, 65.5 ± 5.6 kg) and whether the association differs between the sexes. Participants were tested for 1-RM strength and AMRAP performance, with 60% of 1-RM in the squat and bench press. Correlational analysis revealed that for all participants, lean mass and body height were associated with 1-RM strength in the squat and bench press (0.66, p ≤ 0.01), while body height was inversely associated with AMRAP performance (r ≤ −0.36, p ≤ 0.02). Females had lower maximal and relative strength with a greater AMRAP performance. In the AMRAP squat, thigh length was inversely associated with performance in males, while fat percentage was inversely associated with performance in females. It was concluded that associations between strength performance and anthropometric variables differed for males and females in fat percentage, lean mass, and thigh length.
... It has been suggested that albeit the adaptations to strength training in hypertrophy and lower-body strength were similar between sexes, there was a significant effect in favor of females for upper-body strength. 24 The sample size was justified by a priori power analysis (using G*Power, version 3.1.9.5, University of Dusseldorf) for a repeated measures (within-between interaction) introducing the following parameters: effect size (ES) index (0.40) assuming a large partial eta-squared (.14), α error probability (.05), power (0.90), number of groups (2) and measurements (3), and correlation among repeated measurements (.5) which resulted in a sample size of 16 subjects. Participants had training volume of 20 hours per week comprising 3 hours of technical and tactical tennis practice and 1 hour of physical conditioning per day from Monday to Friday; 87.5% of tennis players were right-handed. ...
Purpose: Evaluate the effects of 6 weeks of specific-joint isometric strength training on serve velocity (SV), serve accuracy (SA), and force-time curve variables. Methods: Sixteen young competition tennis players were divided into an intervention (n = 10) or control group (n = 6). SV, SA, maximal voluntary isometric contraction, peak rate of force development, rate of force development, and impulse (IMP) at different time frames while performing a shoulder internal rotation (SHIR) or flexion were tested at weeks 0, 3, and 6. Results: The intervention group showed significant increases in SV from pretest to posttest (7.0%, effect size [ES] = 0.87) and no variations in SA. Moreover, the intervention group showed significant increases from pretest to posttest in shoulder-flexion rate of force development at 150 (30.4%, ES = 2.44), 200 (36.5%, ES = 1.26), and 250 ms (43.7%, ES = 1.67) and in SHIR IMP at 150 (35.7%, ES = 1.18), 200 (33.4%, ES = 1.19), and 250 ms (35.6%, ES = 1.08). Furthermore, significant increases were found in shoulder-flexion rate of force development from intertest to posttest at 150 ms (24.5%, ES = 1.07) and in SHIR IMP at 150 (13.5%, ES = 0.90), 200 (19.1%, ES = 0.98), and 250 ms (27.2%, ES = 1.16). SHIR IMP changes from pretest to intertest were found at 150 ms (25.6%, ES = 1.04). The control group did not show changes in any of the tested variables. Conclusions: Six weeks of upper-limb specific-joint isometric strength training alongside habitual technical-tactical workouts results in significant increases in SV without SA detriment in young tennis players.
... The present study only included male participants; therefore, the results are presently limited to a male population. Previous studies, however, have shown similar physiological differences between resistance-trained and untrained individuals regardless of sex (57). The additional challenge is employing HDsEMG recordings in a female population which typically results in a substantially smaller yield of discerned MU firings (58), possibly due to sex differences in adipose tissue that acts as a biological low-pass filter (59), though the direct comparison of sexes and factors associated with differences in MU yield remains to be investigated. ...
Article
Purpose Adjustments in motor unit (MU) discharge properties have been shown following short-term resistance training, however MU adaptations in long-term resistance-trained individuals are less clear. Here, we concurrently assessed MU discharge characteristics and MU conduction velocity in long-term resistance-trained (RT) and untrained (UT) men. Methods MU discharge characteristics (discharge rate, recruitment and derecruitment threshold) and MU conduction velocity were assessed after the decomposition of high-density electromyograms recorded from vastus lateralis (VL) and medialis (VM) of RT (>3 years; N = 14) and UT (N = 13) during submaximal and maximal isometric knee extension. Results RT were on average 42% stronger (maximal voluntary force, MVF: 976.7 ± 85.4 vs. 685.5 ± 123.1 N; p < 0.0001), but exhibited similar relative MU recruitment (VL: 21.3 ± 4.3 vs. 21.0 ± 2.3 %MVF; VM: 24.5 ± 4.2 vs. 22.7 ± 5.3 %MVF) and derecruitment thresholds (VL: 20.3 ± 4.3 vs. 19.8 ± 2.9 %MVF; VM: 24.2 ± 4.8 vs. 22.9 ± 3.7 %MVF; p ≥ 0.4543). There were also no differences between groups in MU discharge rate at recruitment and derecruitment, or at the plateau phase of submaximal contractions (VL: 10.6 ± 1.2 vs. 10.3 ± 1.5 pps, VM: 10.7 ± 1.6 vs. 10.8 ± 1.7 pps; p ≥ 0.3028). During maximal contractions of a subsample population (10 RT, 9 UT), MU discharge rate was also similar in RT compared to UT (VL: 21.1 ± 4.1 vs. 14.0 ± 4.5 pps, VM: 19.5 ± 5.0 vs. 17.0 ± 6.3 pps; p = 0.7173). MU conduction velocity was greater in RT compared to UT individuals in both VL (4.9 ± 0.5 vs. 4.5 ± 0.3 m.s-1; p < 0.0013) and VM (4.8 ± 0.5 vs. 4.4 ± 0.3 m.s-1; p < 0.0073). Conclusions RT and UT display similar MU discharge characteristics in the knee extensor muscles during maximal and submaximal contractions. The between-group strength difference is likely explained by superior muscle morphology of RT as suggested by greater MU conduction velocity.
... The cellular responses to resistance training have been extensively examined in both young and older males (23)(24)(25)(26)(27); however, females (28,29) and middle-aged adults (30,31) are under-studied. Males and females of all ages have similar increases in relative strength and hypertrophy as measured by fiber cross-sectional area (CSA) (32,33). Conversely, the results regarding MuSCs and FAPs are equivocal, although they do seem to respond similarly to resistance training in general (25). ...
Article
Resistance training combined with adequate protein intake supports skeletal muscle strength and hypertrophy. These adaptations are supported by the action of muscle stem cells (MuSCs) which are regulated, in part, by fibro-adipogenic progenitors (FAPs) and circulating factors delivered through capillaries. It is unclear if middle-aged males and females have similar adaptations to resistance training at the cellular level. To address this gap, 27 (13 males, 14 females) middle-aged (40-64 years) adults participated in 10-weeks of whole-body resistance training with dietary counselling. Muscle biopsies were collected from the vastus lateralis pre- and post-training. Type II fibre cross-sectional area increased similarly with training in both sexes (P = 0.014). MuSC content was not altered with training; however, training increased PDGFRα+/CD90+ FAP content (P < 0.0001) and reduced PDGFRα+/CD90- FAP content (P = 0.044), independent of sex. The number of CD31+ capillaries per fibre also increased similarly in both sexes (p<0.05). These results suggest that muscle fibre hypertrophy, stem/progenitor cell, and capillary adaptations are similar between middle-aged males and females in response to whole-body resistance training.
... Evidence has disclosed that there are different responses to resistance training for muscle strength between male and female genders. 42 However, further subgroup analysis for the sex difference on the effectiveness after EBT cannot be performed in this meta-analysis owing to the small number of included studies. Third, the diagnostic criteria for sarcopenia and the protocol of EBT varied among the studies, which may have caused bias in participants' selection and treatment consistency. ...
Article
Full-text available
Although resistance exercise is a well-known and accepted method for treatment of sarcopenia, its effectiveness varies. Through this meta-analysis, we investigated the effectiveness of elastic band resistance exercises in improving the physical performance of individuals with sarcopenia. Well-controlled prospective clinical trials investigating the treatment effect of elastic band training for sarcopenia were found from the PubMed, Embase, Cochrane Library, and Google scholar databases up to July 2021 by using “sarcopenia” and “elastic band” as the search terms. Four studies—three randomized controlled trials and one quasiexperimental study — met our inclusion criteria. A total of 231 older adults with sarcopenia were included. After 12 weeks of training, significant improvements were observed in the timed up and go test result, maximal grip strength, gait speed, and appendicular skeletal muscle index in the elastic band training group compared with the control group (95% CI, –2.93 to –1.41, 1.14 to 5.27, –0.06 to –0.02, and 0.03 to 0.26, respectively). However, no significant differences were observed in performance in the 6-minute-walk test (95% CI, –11.00 to 27.00). Elastic band resistance training may benefit older adults with sarcopenia. Further randomized controlled studies with larger samples and longer follow-up periods are warranted to strengthen the clinical evidence regarding the effectiveness of elastic band training for sarcopenia
... Interestingly, recreationally active men performing a high training volume of the Nordic hamstring exercise did not improve their eccentric strength more than those performing a low training volume (440 vs. 128 total reps over 6 weeks), and the muscular adaptations for both groups occurred early during the intervention [24]. However, the training volumes needed to improve strength can be affected by training status [25], concurrent training [26], and sex [27], so the results from recreationally active men may not be transferable to female football players. erefore, we conducted a training intervention with female football players where the primary aim was to determine if using the evidence-based high-volume programme of the Nordic hamstring exercise was more effective on hamstring strength, jump height, and speed than a lowvolume programme. ...
Article
Full-text available
The evidence-based hamstring strengthening programme for prevention of hamstring injuries is not adopted by football teams because of its high training volume. This study on female football players investigated if high-volume training with the Nordic hamstring exercise is more effective on hamstring strength, jump height, and sprint performance than low-volume training. We also examined the time course of changes in muscle strength during the intervention period. Forty-five female football players were randomised to a high- (21 sessions, 538 total reps) or low-volume group (10 sessions, 144 total reps) and performed an 8-week training intervention with the Nordic hamstring exercise during the preseason. We tested hamstring strength (maximal eccentric force with NordBord and maximal eccentric torque with isokinetic dynamometer), jump height, and 40 m sprint before and after the intervention. The NordBord test was also performed during training weeks 4 and 6. Both groups increased maximal eccentric force (high-volume: 29 N (10%), 95% CI: 19–38 N, p < 0.001 , low-volume: 37 N (13%), 95% CI: 18–55 N, p = 0.001 ), but there were no between-group differences ( p = 0.38 ). Maximal eccentric torque, jump height, and sprint performance did not change. Maximal eccentric force increased from the pretest to week 6 (20 N (7%), 95% CI: 8 to 31 N, p < 0.001 ), but not week 4 (8 N (3%), 95% CI: −2 to 18 N, p = 0.22 ). High training volume with the Nordic hamstrings exercise did not lead to greater adaptations in strength, jump height, or speed than a low-volume programme. Players in both groups had to train for at least 6 weeks to improve maximal eccentric force significantly.
Article
Nuzzo, JL. Narrative review of sex differences in muscle strength, endurance, activation, size, fiber type, and strength training participation rates, preferences, motivations, injuries, and neuromuscular adaptations. J Strength Cond Res 37(2): 494-536, 2023-Biological sex and its relation with exercise participation and sports performance continue to be discussed. Here, the purpose was to inform such discussions by summarizing the literature on sex differences in numerous strength training-related variables and outcomes-muscle strength and endurance, muscle mass and size, muscle fiber type, muscle twitch forces, and voluntary activation; strength training participation rates, motivations, preferences, and practices; and injuries and changes in muscle size and strength with strength training. Male subjects become notably stronger than female subjects around age 15 years. In adults, sex differences in strength are more pronounced in upper-body than lower-body muscles and in concentric than eccentric contractions. Greater male than female strength is not because of higher voluntary activation but to greater muscle mass and type II fiber areas. Men participate in strength training more frequently than women. Men are motivated more by challenge, competition, social recognition, and a desire to increase muscle size and strength. Men also have greater preference for competitive, high-intensity, and upper-body exercise. Women are motivated more by improved attractiveness, muscle "toning," and body mass management. Women have greater preference for supervised and lower-body exercise. Intrasexual competition, mate selection, and the drive for muscularity are likely fundamental causes of exercise behaviors in men and women. Men and women increase muscle size and strength after weeks of strength training, but women experience greater relative strength improvements depending on age and muscle group. Men exhibit higher strength training injury rates. No sex difference exists in strength loss and muscle soreness after muscle-damaging exercise.
Article
Physique athletes lose substantial weight preparing for competitions, potentially altering systemic metabolism. We investigated sex differences in body composition, resting energy expenditure (REE), and appetite-regulating and thyroid hormone changes during a competition preparation among drug-free physique athletes. The participants were female (10 competing (COMP) and 10 non-dieting controls (CTRL)) and male (13 COMP) and 10 CTRL)) physique athletes. COMP were tested before they started their diet 23 weeks before competing (PRE), during their diet one week before competing (MID), and 23 weeks after competing (POST) whereas CTRL were tested at similar intervals but did not diet. Measurements included body composition by DXA, muscle size, and subcutaneous fat thickness (SFA) by ultrasound, REE by indirect calorimetry, circulating ghrelin, leptin T3, and T4 hormone analysis. Fat mass (FM) and SFA decreased in both sexes (p<0.001), while males (p<0.001) lost more lean mass (LM) than females (p<0.05). Weight loss, decreased energy intake, and increased aerobic exercise (p<0.05) led to decreased LM and FM-adjusted REE (p<0.05), reflecting metabolic adaptation. Absolute leptin levels decreased in both sexes (p<0.001) but more among females (p<0.001) due to higher baseline leptin levels. These changes occurred with similar decreases in T3 (p<0.001) and resting heart rate (p<0.01) in both sexes. CTRL, who were former or upcoming physique athletes, showed no systematic changes in any measured variables. In conclusion, while dieting, female and male physique athletes experience REE and hormonal changes leading to adaptive thermogenesis. However, responses seemed temporary as they returned toward baseline after the recovery phase. ClinicalTrials.gov (NCT04392752).
Article
Full-text available
Resting heart rate (RHR) is positively related with mortality. Regular exercise causes a reduction in RHR. The aim of the systematic review was to assess whether regular exercise or sports have an impact on the RHR in healthy subjects by taking different types of sports into account. A systematic literature research was conducted in six databases for the identification of controlled trials dealing with the effects of exercise or sports on the RHR in healthy subjects was performed. The studies were summarized by meta-analyses. The literature search analyzed 191 studies presenting 215 samples fitting the eligibility criteria. 121 trials examined the effects of endurance training, 43 strength training, 15 combined endurance and strength training, 5 additional school sport programs. 21 yoga, 5 tai chi, 3 qigong, and 2 unspecified types of sports. All types of sports decreased the RHR. However, only endurance training and yoga significantly decreased the RHR in both sexes. The exercise-induced decreases of RHR were positively related with the pre-interventional RHR and negatively with the average age of the participants. From this, we can conclude that exercise—especially endurance training and yoga—decreases RHR. This effect may contribute to a reduction in all-cause mortality due to regular exercise or sports.
Article
Full-text available
Purpose To compare the relative changes in muscle-tendon complex (MTC) properties following high load resistance training (RT) in young males and females, and determine any link with circulating TGFβ-1 and IGF-I levels. Methods Twenty-eight participants were assigned to a training group and subdivided by sex (T males [TM] aged 20±1 year, n = 8, T females [TF] aged 19±3 year, n = 8), whilst age-matched 6 males and 6 females were assigned to control groups (ConM/F). The training groups completed 8 weeks of resistance training (RT). MTC properties (Vastus Lateralis, VL) physiological cross-sectional area (pCSA), quadriceps torque, patella tendon stiffness [K], Young’s modulus, volume, cross-sectional area, and length, circulating levels of TGFβ-1 and IGF-I were assessed at baseline and post RT. Results Post RT, there was a significant increase in the mechanical and morphological properties of the MTC in both training groups, compared to ConM/F (p<0.001). However, there were no significant sex-specific changes in most MTC variables. There were however significant sex differences in changes in K, with females exhibiting greater changes than males at lower MVC (Maximal Voluntary Contraction) force levels (10% p = 0.030 & 20% MVC p = 0.032) and the opposite effect seen at higher force levels (90% p = 0.040 & 100% MVC p = 0.044). There were significant increases (p<0.05) in IGF-I in both TF and TM following training, with no change in TGFβ-1. There were no gender differences (p>0.05) in IGF-I or TGFβ-1. Interestingly, pooled population data showed that TGFβ-1 correlated with K at baseline, with no correlations identified between IGF-I and MTC properties. Conclusions Greater resting TGFβ-1 levels are associated with superior tendon mechanical properties. RT can impact opposite ends of the patella tendon force-elongation relationship in each sex. Thus, different loading patterns may be needed to maximize resistance training adaptations in each sex.
Article
Full-text available
Effects of strength training (ST) for 21 wk were examined in 10 older women (64 ± 3 yr). Electromyogram, maximal isometric force, one-repetition maximum strength, and rate of force development of the leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris (QF) and of vastus lateralis (VL), medialis (VM), intermedius (VI) and rectus femoris (RF) throughout the lengths of 3/12–12/15 (Lf) of the femur, muscle fiber proportion and areas of types I, IIa, and IIb of the VL were evaluated. Serum hormone concentrations of testosterone, growth hormone (GH), cortisol, and IGF-I were analyzed for the resting, preexercise, and postexercise conditions. After the 21-wk ST, maximal force increased by 37% ( P < 0.001) and 1-RM by 29% ( P < 0.001), accompanied by an increase ( P < 0.01) in rate of force development. The integrated electromyograms of the vastus muscles increased ( P < 0.05). The CSA of the total QF increased ( P < 0.05) throughout the length of the femur by 5–9%. The increases were significant ( P< 0.05) at 7/15–12/15 Lf for VL and at 3/15–8/15 Lf for VM, at 5/15–9/15 for VI and at 9/15 ( P < 0.05) for RF. The fiber areas of type I ( P < 0.05), IIa ( P < 0.001), and IIb ( P < 0.001) increased by 22–36%. No changes occurred during ST in serum basal concentrations of the hormones examined, but the level of testosterone correlated with the changes in the CSA of the QF ( r = 0.64, P < 0.05). An acute increase of GH ( P < 0.05), remaining elevated up to 30 min ( P < 0.05) postloading, was observed only at posttraining. Both neural adaptations and the capacity of skeletal muscle to undergo training-induced hypertrophy even in older women explain the strength gains. The increases in the CSA of the QF occurred throughout its length but differed selectively between the individual muscles. The serum concentrations of hormones remained unaltered, but a low level of testosterone may be a limiting factor in training-induced muscle hypertrophy. The magnitude and time duration of the acute GH response may be important physiological indicators of anabolic adaptations during strength training even in older women.
Article
Full-text available
Purpose: To compare the effects of strength training versus ski-ergometer training on double-poling gross efficiency (GE), maximal speed (V max), peak oxygen uptake ([Formula: see text]) for elite male and female junior cross-country skiers. Methods: Thirty-three elite junior cross-country skiers completed a 6-week training-intervention period with two additional 40-min training sessions per week. The participants were matched in pairs and within each pair randomly assigned to either a strength-training group (STR) or a ski-ergometer-training group (ERG). Before and after the intervention, the participants completed three treadmill roller-skiing tests to determine GE, V max, and [Formula: see text]. Mixed between-within subjects analysis of variance (ANOVA) was conducted to evaluate differences between and within groups. Paired samples t tests were used as post hoc tests to investigate within-group differences. Results: Both groups improved their V max and [Formula: see text] expressed absolutely (all P < 0.01). For the gender-specific sub-groups, it was found that the female skiers in both groups improved both V max and [Formula: see text] expressed absolutely (all P < 0.05), whereas the only within-group differences found for the men were improvements of V max in the STR group. No between-group differences were found for any of the investigated variables. Conclusions: Physiological and performance-related variables of importance for skiers were improved for both training regimes. The results demonstrate that the female skiers' physiological adaptations to training, in general, were greater than those of the men. The magnitude of the physiological adaptations was similar for both training regimes.
Article
Full-text available
The purpose of this study was to investigate the effect of hypertrophy-type resistance training (RT) on upper limb fatigue resistance in young adult men and women. Fifty-eight men (22.7±3.7 years, 70.6±9.3 kg, and 176.8±6.4 cm) and 65 women (21.6±3.7 years, 58.8±11.9 kg, and 162.6±6.2 cm) underwent RT for 16 weeks. Training consisted of 10-12 whole body exercises with 3 sets of 8-12 repetitions maximum performed 3 times per week. Before and after the RT intervention participants were submitted to 1RM testing, as well as a fatigue protocol consisting of 4 sets at 80% 1RM on bench press (BP) and arm curl (AC). The sum of the number of repetitions accomplished in the 4 sets in each exercise was used to indicate fatigue resistance. There was a significant (p
Article
Full-text available
We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogeneous sample of 468 men and women. Men had significantly ( P < 0.001) more SM in comparison to women in both absolute terms (33.0 vs. 21.0 kg) and relative to body mass (38.4 vs. 30.6%). The gender differences were greater in the upper (40%) than lower (33%) body ( P < 0.01). We observed a reduction in relative SM mass starting in the third decade; however, a noticeable decrease in absolute SM mass was not observed until the end of the fifth decade. This decrease was primarily attributed to a decrease in lower body SM. Weight and height explained ∼50% of the variance in SM mass in men and women. Although a linear relationship existed between SM and height, the relationship between SM and body weight was curvilinear because the contribution of SM to weight gain decreased with increasing body weight. These findings indicate that men have more SM than women and that these gender differences are greater in the upper body. Independent of gender, aging is associated with a decrease in SM mass that is explained, in large measure, by a decrease in lower body SM occurring after the fifth decade.
Article
Age-related muscle loss (sarcopenia) is a major clinical problem affecting both men and women - accompanied by muscle weakness, dysfunction, disability, and impaired quality of life. Current definitions of sarcopenia do not fully encompass the age-related changes in skeletal muscle. We therefore examined the influence of aging and sex on elements of skeletal muscle health using a thorough histopathological analysis of myocellular aging and assessments of neuromuscular performance. Two-hundred and twenty-one untrained males and females were separated into four age cohorts [mean age 25 y (n = 47), 37 y (n = 79), 61 y (n = 51), and 72 y (n = 44)]. Total (-12%), leg (-17%), and arm (-21%) lean mass were lower in both 61 y and 72 y than in 25 y or 37 y (P < 0.05). Knee extensor strength (-34%) and power (-43%) were lower (P < 0.05) in the older two groups, and explosive sit-to-stand power was lower by 37 y (P < 0.05). At the histological/myocellular level, type IIx atrophy was noted by 37 y and type IIa atrophy by 61 y (P < 0.05). These effects were driven by females, noted by substantial and progressive type IIa and IIx atrophy across age. Aged female muscle displayed greater within-type myofiber size heterogeneity and marked type I myofiber grouping (~5-fold greater) compared to males. These findings suggest the predominant mechanisms leading to whole muscle atrophy differ between aging males and females: myofiber atrophy in females vs. myofiber loss in males. Future studies will be important to better understand the mechanisms underlying sex differences in myocellular aging and optimize exercise prescriptions and adjunctive treatments to mitigate or reverse age-related changes.
Article
Impaired sleep quality and quantity are associated with future morbidity and mortality. Exercise may be an effective non-pharmacological intervention to improve sleep, however, little is known on the effect of resistance exercise. Thus, we performed a systematic review of the literature to determine the acute and chronic effects of resistance exercise on sleep quantity and quality. Thirteen studies were included. Chronic resistance exercise improves all aspects of sleep, with the greatest benefit for sleep quality. These benefits of isolated resistance exercise are attenuated when resistance exercise is combined with aerobic exercise and compared to aerobic exercise alone. However, the acute effects of resistance exercise on sleep remain poorly studied and inconsistent. In addition to the sleep benefits, resistance exercise training improves anxiety and depression. These results suggest that resistance exercise may be an effective intervention to improve sleep quality. Further research is needed to better understand the effects of acute resistance exercise on sleep, the physiological mechanisms underlying changes in sleep, the changes in sleep architecture with chronic resistance exercise, as well its efficacy in clinical cohorts who commonly experience sleep disturbance. Future studies should also examine time-of-day and dose-response effects to determine the optimal exercise prescription for sleep benefits.
Article
Performance fatigability differs between men and women for a range of fatiguing tasks. Women are usually less fatigable than men and this is most widely described for isometric fatiguing contractions, and some dynamic tasks. The sex difference in fatigability is specific to the task demands so that one mechanism is not universal, including any sex differences in skeletal muscle physiology, muscle perfusion and voluntary activation. However, there are substantial knowledge gaps about the task dependency of the sex differences in fatigability, the involved mechanisms and the relevance to clinical populations and with advanced age. The knowledge gaps are in part due to the significant deficits in the number of women included in performance fatigability studies despite a gradual increase in the inclusion of women over the last 20 years. Therefore, this review 1) provides a rationale for the limited knowledge about sex differences in performance fatigability, 2) summarizes the current knowledge on sex differences in fatigability and the potential mechanisms across a range of tasks, 3) highlights emerging areas of opportunity in clinical populations, and 4) suggests strategies to close the knowledge gap and understanding the relevance of sex differences in performance fatigability. The limited understanding about sex differences in fatigability in healthy and clinical population presents as a field ripe with opportunity for high impact studies. Such studies will inform on the limitations of men and women during athletic endeavors, ergonomic tasks and daily activities. Because fatigability is required for effective neuromuscular adaptation, sex difference in fatigability studies will also inform on optimal strategies for training and rehabilitation in both men and women.