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This study assessed variability in muscle size and strength changes in a large cohort of men and women after a unilateral resistance training program in the elbow flexors. A secondary purpose was to assess sex differences in size and strength changes after training. Five hundred eighty-five subjects (342 women, 243 men) were tested at one of eight study centers. Isometric (MVC) and dynamic strength (one-repetition maximum (1RM)) of the elbow flexor muscles of each arm and magnetic resonance imaging (MRI) of the biceps brachii (to determine cross-sectional area (CSA)) were assessed before and after 12 wk of progressive dynamic resistance training of the nondominant arm. Size changes ranged from -2 to +59% (-0.4 to +13.6 cm), 1RM strength gains ranged from 0 to +250% (0 to +10.2 kg), and MVC changes ranged from -32 to +149% (-15.9 to +52.6 kg). Coefficients of variation were 0.48 and 0.51 for changes in CSA (P = 0.44), 1.07 and 0.89 for changes in MVC (P < 0.01), and 0.55 and 0.59 for changes in CSA (P < 0.01) in men and women, respectively. Men experienced 2.5% greater gains for CSA (P < 0.01) compared with women. Despite greater absolute gains in men, relative increases in strength measures were greater in women versus men (P < 0.05). Men and women exhibit wide ranges of response to resistance training, with some subjects showing little to no gain, and others showing profound changes, increasing size by over 10 cm and doubling their strength. Men had only a slight advantage in relative size gains compared with women, whereas women outpaced men considerably in relative gains in strength.
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Variability in Muscle Size and Strength Gain
after Unilateral Resistance Training
MONICA J. HUBAL
1
, HEATHER GORDISH-DRESSMAN
2
, PAUL D. THOMPSON
3
, THOMAS B. PRICE
1,3,4
,
ERIC P. HOFFMAN
2
, THEODORE J. ANGELOPOULOS
5
, PAUL M. GORDON
6
, NIALL M. MOYNA
7
,
LINDA S. PESCATELLO
8
, PAUL S. VISICH
9
, ROBERT F. ZOELLER
10
, RICHARD L. SEIP
3
, and
PRISCILLA M. CLARKSON
1
1
Department of Exercise Science, Totman Building, University of Massachusetts, Amherst, MA;
2
Research Center for
Genetic Medicine, Children’s National Medical Center, Washington DC;
3
Division of Cardiology, Henry Low Heart
Center, Hartford Hospital, Hartford, CT;
4
Department of Diagnostic Radiology, Yale University School of Medicine, New
Haven, CT;
5
Child, Family and Community Sciences, University of Central Florida, Orlando, FL;
6
Division of Exercise
Physiology, School of Medicine, West Virginia University, Morgantown, WV;
7
Department of Sport Science and Health,
Dublin City University, Dublin, IRELAND;
8
School of Allied Health, University of Connecticut, Storrs, CT;
9
Human
Performance Laboratory, Central Michigan University, Mount Pleasant, MI; and
10
Department of Exercise Science and
Health Promotion, Florida Atlantic University, Davie, FL
ABSTRACT
HUBAL, M. J., H. GORDISH-DRESSMAN, P. D. THOMPSON, T. B. PRICE, E. P. HOFFMAN, T. J. ANGELOPOULOS, P. M.
GORDON, N. M. MOYNA, L. S. PESCATELLO, P. S. VISICH, R. F. ZOELLER, R. L. SEIP, and P. M. CLARKSON. Variability
in Muscle Size and Strength Gain after Unilateral Resistance Training. Med. Sci. Sports Exerc., Vol. 37, No. 6, pp. 964 –972, 2005.
Purpose: This study assessed variability in muscle size and strength changes in a large cohort of men and women after a unilateral
resistance training program in the elbow flexors. A secondary purpose was to assess sex differences in size and strength changes after
training. Methods: Five hundred eighty-five subjects (342 women, 243 men) were tested at one of eight study centers. Isometric (MVC)
and dynamic strength (one-repetition maximum (1RM)) of the elbow flexor muscles of each arm and magnetic resonance imaging
(MRI) of the biceps brachii (to determine cross-sectional area (CSA)) were assessed before and after 12 wk of progressive dynamic
resistance training of the nondominant arm. Results: Size changes ranged from 2to59% (0.4 to 13.6 cm
2
), 1RM strength gains
ranged from 0 to 250% (0 to 10.2 kg), and MVC changes ranged from 32 to 149% (15.9 to 52.6 kg). Coefficients of
variation were 0.48 and 0.51 for changes in CSA (P0.44), 1.07 and 0.89 for changes in MVC (P0.01), and 0.55 and 0.59 for
changes in CSA (P0.01) in men and women, respectively. Men experienced 2.5% greater gains for CSA (P0.01) compared with
women. Despite greater absolute gains in men, relative increases in strength measures were greater in women versus men (P0.05).
Conclusion: Men and women exhibit wide ranges of response to resistance training, with some subjects showing little to no gain, and
others showing profound changes, increasing size by over 10 cm
2
and doubling their strength. Men had only a slight advantage in
relative size gains compared with women, whereas women outpaced men considerably in relative gains in strength. Key Words:
HYPERTROPHY, GENDER DIFFERENCES, VARIATION, 1RM, MRI
Numerous studies have documented that progressive
resistance training causes gains in both strength and
skeletal muscle size (for recent review see (17)). It
has been commonly observed that some people who take up
resistance training experience vastly different gains in
strength and size than others. This was noted in 1954, when
Sheldon et al. (28) observed that individuals with different
physiques had different abilities to gain muscle mass in
response to training. However, to date, no study has been
undertaken with a large enough sample size of subjects to
fully quantify the range of human responses to a given
strength training program. This information is needed to
help define which factors significantly influence a muscle’s
response to resistance exercise, including genetic underpin-
nings of muscle growth capabilities.
Factors known to affect strength gain and hypertrophy
include gender, age, physical activity level, previous train-
ing status, and endocrine status (for reviews see (12,27)).
Gender has a large effect on skeletal muscle morphology
and function (6,27). Men have greater muscle size and
strength than women, due to greater body size and higher
levels of anabolic hormones. However, it is unknown
whether men and women exhibit different levels of vari-
ability in size and strength responses after a resistance
training program. The only data available are coefficients of
variations (CV) of baseline and posttraining measures, as
calculated from published means and standard deviations,
and these have been equivocal as to whether men or women
Address for correspondence: Priscilla M. Clarkson, Department of Exercise
Science, 110 Totman Building, University of Massachusetts, Amherst, MA
01003; E-mail: clarkson@excsci.umass.edu.
Submitted for publication October 2004.
Accepted for publication January 2005.
0195-9131/05/3706-0964/0
MEDICINE & SCIENCE IN SPORTS & EXERCISE
®
Copyright © 2005 by the American College of Sports Medicine
DOI: 10.1249.01.mss.0000170469.90461.5f
964
show greater variability in muscle size or muscle strength
(2,15,25,26). Furthermore, data are also equivocal regarding
whether there is an effect of training, gender, or an interac-
tion effect between training and gender. The lack of a
definitive answer concerning potential gender differences in
variability is likely due to relatively small sample sizes used
in previous studies (fewer than 20 men and women per
group). However, because some of these studies indicate the
existence of gender differences, and based on higher ranges
of androgens in men, we hypothesized that men would have
greater variability in both absolute and relative size and
strength gains than women.
Although men gain greater amounts of absolute strength
and muscle mass than women after resistance training, data
concerning relative changes are equivocal. Some previous
studies found gender differences in either strength or size
changes after resistance training (16,19,32), whereas the ma-
jority of recent studies have documented similarities in relative
strength and size changes after training (2,9,10,15). Again, one
factor that may explain these equivocal findings is the small
sample sizes used in previous studies, limiting the statistical
power of these studies to detect significant differences between
men and women. Based on data from studies showing similar
size and strength gains (2,10,11,23,32), we hypothesized that
men and women will display similar relative changes in CSA
and strength gains.
We had the unique opportunity to study a cohort of 585
subjects participating in an investigation of genetic varia-
tions and their associations with strength and size changes
after unilateral resistance training in the elbow flexors. Here
we document the range of responses of men and women to
12 wk of progressive resistance training of the nondominant
elbow flexors, and compare between genders for differences
in relative size and strength gains.
METHODS
Study Overview
This study was part of the FAMuSS, or Functional Poly-
morphisms Associated with Human Muscle Size and
Strength study, a large multiinstitutional cooperative effort
designed to identify synonymous single nucleotide poly-
morphisms (SNP) in selected muscle proteins contributing
to baseline elbow flexor muscle size and strength and their
response to 12 wk of resistance exercise training (29).
Briefly, after obtaining written informed consent (approved
through each participating institution’s institutional review
board) from all individuals, isometric and dynamic strength
of the forearm flexors and cross-sectional diameter of the
upper-arm musculature was measured before and after 12 wk
of elbow flexor and extensor resistance training in 585 subjects
aged 18 40 yr. Subjects over 40 yr old were excluded to avoid
studying men who have potentially experienced the marked
decrease in testosterone levels that occur in older age groups
(18). Pretraining isometric strength measurements were per-
formed over three testing days. Posttraining strength measure-
ments were performed on two testing days. Cross-sectional
area of the upper-arm musculature was measured using mag-
netic resonance imaging (MRI).
Subjects
Men and women were excluded if they used medications
known to affect skeletal muscle such as corticosteroids; had
any restriction of activity; had chronic medical conditions
such as diabetes; had metal implants in arms, eyes, head,
brain, neck, or heart that would prohibit MRI testing; had
performed strength training or employment requiring repet-
itive use of the arms within the prior 12 months; consumed
on average more than two alcoholic drinks daily; or had
used dietary supplements reported to build muscle size/
strength or cause weight gain such as protein supplements,
creatine, or androgenic precursors.
A total of 585 subjects (243 M, 342 W) completed the
study at the time of manuscript revision and were used for
data analyses. Demographics are included in Table 1. On
average, men were approximately 1 yr older than the women
at the onset of the study (24.8 vs 23.9 yr, respectively; P
0.05). At baseline, men were taller and heavier than the
women, with a slightly higher body mass index than women
(24.7 vs 23.7, respectively; P0.05).
Dietary Control Procedures
Subjects were instructed to maintain their habitual dietary
intake and physical activity levels (with the exception of the
addition of the unilateral arm training) over the course of the
study so that significant weight loss or gain was avoided.
Individuals who had supplemented their diet with additional
protein or taken any dietary supplement reported to build
muscle or to cause weight gain (dietary supplements containing
protein, creatine, or androgenic precursors) were not included.
Data for subjects who lost a significant amount of body weight
were excluded from analysis. As slight weight gain would be
expected with the addition of muscle volume, those that in-
creased body weight were included in the analysis.
Muscle Testing
Isometric biceps strength testing. Isometric strength
(MVC) of the elbow flexor muscles of each arm was deter-
mined before and after 12 wk of strength training using a
specially constructed, modified preacher bench and strain
gauge (model 32628CTL, Lafayette Instrument Company,
TABLE 1. Pre- and posttraining subject characteristics of entire cohort and grouped
by gender; data represent means SEM.
Group Age (yr) Height (cm) Weight (kg) BMI
All (N585)
Pretraining 24.3 0.2 169.8 0.5 70.3 0.7 24.1 0.2
Posttraining 170.0 0.5 70.6 0.6 24.3 0.2
Men (N243)
Pretraining 24.8 0.4* 176.3 0.9* 77.8 1.0* 24.7 0.3*
Posttraining 176.8 0.5* 78.0 1.0* 24.9 0.3*
Women (N342)
Pretraining 23.9 0.3 165.2 0.4 65.0 0.7 23.7 0.2
Posttraining 165.2 0.4 65.4 0.7 23.9 0.2
* Denotes a significantly greater mean in men vs women (P0.05). No significant
interactions were detected between gender and time.
VARIATION IN RESPONSE TO RESISTANCE TRAINING Medicine & Science in Sports & Exercise
965
Lafayette, IN). Baseline measures of isometric strength were
assessed on three separate days spaced 24 48 h apart in the
week before the onset of training (29). The first of these
sessions was used for familiarization of the subjects to the
MVC testing protocol, and the pretraining MVC was calcu-
lated as the average of the second and third pretraining testing
sessions. Only two posttraining sessions were used, as subjects
had already been familiarized with the protocol. The first
posttraining MVC test occurred immediately before the final
training session. The second posttraining MVC test occurred
48 –72 h after the final training session.
Intraclass reliability coefficient (r) values for elbow
flexor isometric strength at 90° elbow flexion range from
0.95 to 0.99 (7,8). The average of the results obtained on the
second and third testing days was used as the baseline
criterion measurement. Details of the testing procedure have
been published previously (29).
One-repetition maximum biceps strength test-
ing. The dynamic strength of the elbow flexor muscles of
each arm was assessed by determining the one-repetition
maximum (1RM) on the standard preacher curl exercise.
The 1RM testing was performed before and after 12 wk of
strength training. Unlike the isometric strength testing, base-
line 1RM testing was completed in one day, during the third
and second strength testing visits at baseline and at the end
of the study, respectively. Posttraining 1RM was measured
48 –72 h after the final training session (either after the final
MRI scan or 48 h before the final MRI scan).
The 1RM test protocol modified from Baechle et al. (4)
was used and investigators were carefully trained to carry
out the test. To ensure that the investigators were trained, all
investigators received on-site training at least once per year,
and an instructional video was made for all sites to follow
describing the procedure in detail. At each site, one expe-
rienced investigator typically supervised all 1RM tests both
before and after training. Details on subject position were
recorded at baseline to assure proper position during post-
training testing. Each subject performed two warm-up sets
with increasing weight, with 3 min of rest between sets.
During the test, subjects were instructed to go through a full
range of motion starting from 180º to full flexion. Care was
taken to assure that the subject completed the full range of
motion. After warm-up, weights were increased, and each
subject attempted to perform one full contraction. If the
subject successfully completed one contraction without as-
sistance, weights were raised slightly (0.563–1.125 kg), and
the subject again attempted to complete one repetition. One
minute of rest was given between attempts. The need for
assistance on an attempt or failure to extend the arm fully
during the contraction was not considered to be successful
attempt. Weights were chosen so that the 1RM could be
determined in three to five attempts, though more attempts
were completed when necessary. The test was terminated
when the subject completed a contraction with a given
weight and failed at the next weight increment. Further
details can be found in Thompson et al. (29).
Muscle size: cross-sectional area testing. MRI
was performed before and after exercise training to assess
changes in the biceps brachii cross-sectional area (CSA) as
previously described (13,24). Pretraining MRI was per-
formed either before or after strength testing, and at least
48 h before or after 1RM testing to ensure temporary effects
of the 1RM protocol were avoided. Posttraining MRI was
performed 48 –96 h after the final training session, ensuring
that temporary exercise effects such as water shifts were
again avoided, while also avoiding any reduction of muscle
size from detraining. Posttraining CSA data were compared
with pretraining values to determine training-induced
changes. Pre- and posttraining MR images were obtained
separately from both the dominant (untrained) and non-
dominant (trained) arms, thereby allowing the dominant arm
to act as a control.
Because MR images were collected on two separate oc-
casions, it was important that each subject’s positioning
within the MR magnet be reliably reproduced in order to
avoid coregistration errors. To accomplish this, MRI of each
arm was performed at the site corresponding to the maxi-
mum circumference of the upper arm (i.e., in the belly of the
muscle). The maximum circumference was identified with
the arm abducted 90º at the shoulder, flexed 90º at the
elbow, and the biceps maximally contracted. This location,
or the point of measure (POM) was marked on the subject’s
skin using a radiographic bead (Beekley Spots, Beekley
Corp., Bristol, CT) and the circumference of the arm mea-
sured with a vinyl, nonstretchable tape measure. At each
imaging site, the on-site investigator located and marked the
POM before each MRI measurement.
Subjects were scanned in the supine position with the arm
of interest at their side and their palms up, taped in place on
the scanner bed surface. The POM was centered to the
alignment light of the MRI. A sagittal scout image (six to
nine slices) was obtained to locate the long axis of the
humerus. Fifteen serial fast spoiled gradient images of each
arm were obtained (TE 1.9 s, TR 200 ms, flow artifact
suppression, 30° flip angle) using the POM as the center
most point. These axial/oblique image slices (i.e., perpen-
dicular to the humerus) began at the top of the arm and
proceeded toward the elbow such that the belly of the
muscle occurred at slices 8 and 9. The slices were 16 mm
thick witha0mminterslice gap, 256 192 matrix reso-
lution, 22 22 cm field of view, number of acquisitions
(NEX) 6. Subjects were repositioned for each arm so that
the arm was centered in the magnet. This method imaged a
24-cm length of each arm.
MR images from each investigational site were trans-
ferred to the central MR imaging facility at Yale University
via either magneto optical disk (MOD) or CD-ROM. Images
were analyzed using a custom-designed interactive process-
ing and visualization program that operates in Matlab (The
Math Works, Inc., Natick, MA). This software enabled the
user to assign regions of interest (ROI) in an image set by
tracing region borders with a mouse. Muscle is easily iden-
tifiable on MR images and its CSA was measured using this
computerized planimetry technique. Intraobserver reliability
for ROI assignment, tested by repeated measures, was less
than 1%. When interobserver reliability was tested between
966
Official Journal of the American College of Sports Medicine http://www.acsm-msse.org
two different observers over 74 different subjects the mean
difference was 1.1% and the two series’ were significantly
correlated (r
2
0.9636). Once the ROI was defined, the
program reported the number of pixels contained in the
selected ROI. Based upon the MR acquisition data (i.e., field
of view and matrix resolution), the CSA (cm
2
) of the defined
ROI was then calculated. When the pretraining CSA (cm
2
)
was subtracted from the posttraining CSA (cm
2
), the train-
ing effect (cm
2
) could be compared between subjects.
Exercise training. Subjects underwent gradually pro-
gressive, supervised strength training of their nondominant
arm in one of the eight collaborating exercise sites. The
1RM measured during pretraining testing was used to esti-
mate the weights that could be lifted for 12, 8, and 6
repetitions using standard formulas (30). Training typically
began 1–7 d after the completion of pretraining strength and
size measurements, and no longer than 14 d after pretraining
assessments.
Exercises were performed with the nondominant arm only.
The exercises consisted of the biceps preacher curl, biceps
concentration curl, standing biceps curl, overhead triceps ex-
tension, and triceps kickback. All training sessions were su-
pervised and lasted approximately 45– 60 min each. Two
warm-up sets were used before the first biceps and first triceps
exercise. Subjects rested for 3 min after each warm-up set and
for 2 min after each testing set, and investigators used timers
throughout the session to monitor the length of rest periods.
Subjects were not allowed to perform any metabolically
demanding activities during each rest period. The exercise
progression used the following weekly training protocol:
weeks 1– 4: 3 sets with 12 repetitions of the 12RM weight;
weeks 5–9: 3 sets with 8 repetitions of the 8RM weight;
weeks 10 –12: 3 sets with 6 repetitions of the 6RM weight.
The primary interest was to train the elbow flexors, but we
also trained the elbow extensors to balance muscle strength
across the joint.
Standardization between sites. Adaptations to re-
sistance training are highly specific to the training protocol.
To control for differences among training sites, each site
used an identical training protocol and identical exercise
equipment purchased from the same manufacturers. The
techniques for MRI, strength and anthropometrical measure-
ments, and exercise training were videotaped, and research
personnel from each study site reviewed the videotape be-
fore the start of each training group. In addition, meetings
were held several times per year among group members to
maximize compliance to the standard protocol, including
hands-on training sessions.
Statistical analysis. Reliability of the baseline iso-
metric test was assessed by intraclass correlation coefficient
for the entire cohort and individually by site. Differences
between men and women at baseline were tested by inde-
pendent t-tests for each variable in question within each arm
for the entire cohort.
Variability within the entire cohort and within each gen-
der was calculated for each of the independent variables.
Variability was calculated as the coefficient of variation and
each resultant distribution is graphed as a histogram and de-
scribed using skewness and kurtosis. Additionally, Levene’s
test was used to test for equality of variances between genders.
All analyses were assessed independently for each arm.
The effect of exercise on muscle size and strength (MVC
and 1RM) was assessed using repeated measures ANCOVA
(gender as grouping factor, baseline values as the covariate,
and repeated measures over time) within the nondominant
arm. Analyses were repeated on the nontrained arm.
RESULTS
Subject Characteristics
Pre- and posttraining subject characteristics are provided
in Table 1. Slight weight and BMI gains across the training
period in both genders were not significantly different (P
0.44). These weight gains averaged less than 0.5 kg
and could have been influenced by increased muscle mass in
the arm.
Baseline Measures
The intraclass correlation coefficient between the second
and third isometric strength baseline days was R 0.986 for
the nondominant arm and R 0.985 for the dominant arm,
respectively, and t-tests showed no overall difference be-
tween days for all sites (P0.15). Thus the reliability of
this measure was good. Therefore, all values for MVC
reported here are the average of the mean strength from day
2 and the mean strength from day 3. The 1RM test and the
muscle cross-sectional area were performed only once at
baseline. At baseline, men had greater values for all strength
and size variables (P0.01) for CSA, MVC, and 1RM for
each arm; Tables 2 and 3.
Training Effect
Muscle size. Baseline and posttraining biceps cross-
sectional area measures for the trained arm are presented in
Table 2, as well as calculated differences in the means and
percent changes from baseline to posttraining. Coefficients
of variation within each gender are also reported in Table 2,
and a histogram of changes in CSA within each gender is
depicted in Figure 1. Men demonstrated a skewness of 0.35
and a kurtosis of 0.44, whereas women demonstrated a
skewness of 0.39 and a kurtosis of 0.62. Levene’s test found
a significant difference between men and women for abso-
lute CSA change (P0.00), but no differences for variance
were found for relative CSA change (P0.44). Further-
more, the number of subjects found to be outliers (2SD
from the mean) were similar between genders. We found
that 0.08% of both men (N2) and women (N3) were
low responders, whereas 3% of men (N7) and 2% of
women (N7) were high responders.
An ANCOVA of cross-sectional area in the trained arm
detected significant effects of gender and time (P0.001).
Additionally, men gained significantly more absolute and
relative biceps CSA in the trained arm than women after 12
VARIATION IN RESPONSE TO RESISTANCE TRAINING Medicine & Science in Sports & Exercise
967
wk of training (relative gains of 20.4 vs 17.9% for men vs
women, respectively, P0.001).
Muscle strength. Baseline and posttraining 1RM
strength measures for the trained arm are presented in Table
2, as well as calculated differences in the means and percent
changes from baseline to posttraining. Coefficients of vari-
ation within each gender are also reported in Table 2, and a
histogram of changes in 1RM within each gender is depicted
in Figure 2. Men demonstrated a skewness of 1.14 and a
kurtosis of 2.84, whereas women demonstrated a skewness
of 1.08 and a kurtosis of 2.67. Levene’s test found no
differences between men and women for variance in abso-
lute 1RM change (P0.48), but a significant difference in
relative 1RM change (P0.01). The percentage of subjects
found to be outliers (2 SD from the mean) was slightly
higher in men versus women. No subject lost dynamic
strength so that there were no low responders, whereas 3.4%
of men (N8) and 2.6% of women (N9) were high
responders.
An ANCOVA of 1RM detected significant effects of
gender and time for both absolute and relative 1RM change
(P0.001) in the trained arm. Additionally, the interaction
term (gender time) determined a significantly greater
relative gain in 1RM for women versus men after 12 wk of
training (64.1 vs 39.8% for women vs men, respectively;
P0.001), despite greater absolute gains in the men.
Baseline and posttraining isometric strength measures
(MVC) for the trained arm are presented in Table 2, as well
as calculated differences in the means and percent changes
from baseline to posttraining. Coefficients of variation
within each gender are also reported in Table 2 and a
histogram of changes in MVC within each gender is de-
picted in Figure 3. Men demonstrated a skewness of 2.39
and a kurtosis of 16.66, whereas women demonstrated a
skewness of 0.74 and a kurtosis of 1.16. This suggests a
strong tendency for men toward the mean while women
display more of a normal-type distribution. Levene’s test
found differences between men and women for variance in
both absolute and relative MVC (P0.01). With regards to
outliers, we found that 0.9% of men (N2) and 0.6% of
women (N2) were low responders, whereas 3.6% of men
(N8) and 3.8% of women (N12) were high responders.
An ANCOVA of MVC detected significant effects of
gender and time (P0.001) in the trained arm for both
absolute and relative MVC change. Additionally, the inter-
action term (gender time) determined a significantly
greater gain in MVC for women versus men after 12 wk of
training (22.0 vs 15.8% for women vs men, respectively;
P0.001), despite greater absolute gains in the men.
TABLE 3. Size and strength changes in the untrained arm.
Variable Pretrain Posttrain Differences % Change
Muscle size
All 17.4 0.3 17.6 0.3 0.2 0.0 1.4 0.3
Men 22.2 0.4 22.4 0.3 0.2 0.1 1.1 0.4
Women 14.0 0.2 14.2 0.2 0.2 0.0 1.6 0.3
Iso strength
All 46.6 1.0 48.0 1.0 1.7 0.3 5.3 0.7
Men 67.4 1.4 68.6 1.4 1.8 0.5 3.6 1.0
Women 31.8 0.5 33.9 0.6 1.7 0.3 6.4 0.9
1RM strength
All 9.1 0.2 9.9 0.2 0.8 0.1 10.6 0.8
Men 12.6 0.2 13.2 0.2 0.7 0.1 6.2 0.9
Women 6.7 0.1 7.6 0.1 0.9 0.1 13.6 1.1
Units for muscle size are centimeters squared and for MVC and 1RM are kilograms.
Data represent means SEM. Significant gender and time main effects were found for
all variables within the untrained arm (P0.05).
FIGURE 1—Biceps cross-sectional area. Histogram of biceps cross-
sectional area changes (relative to baseline) within each gender for the
trained arm. Black bars denote responses of men while white bars
denote responses of women.
TABLE 2. Size and strength changes in the trained arm.
Absolute Value Relative to Baseline
Variable Pretrain Posttrain Difference Min Max Change (%) Min Max CV
Muscle size
All 16.8 0.2 20.0 0.3 3.2 0.1 18.9 0.4
Men 21.3 0.4 25.5 0.4 4.2 0.1 0.4 13.6 20.4 0.6* 2.5 55.5 0.48
Women 13.6 0.2 16.0 0.2 2.4 0.1 0.5 7.2 17.9 0.5 2.3 59.3 0.51
Iso strength
All 44.6 1.0 52.2 1.1 7.5 0.3 19.5 0.8
Men 64.3 1.4 73.6 1.6 9.5 0.6 13.4 52.6 15.8 1.1 24.3 148.5 1.07
Women 30.8 0.6 37.2 0.7 6.1 0.3 15.9 26.1 22.0 1.1* 31.5 93.4 0.89
1RM strength
All 8.5 0.2 12.4 0.2 3.9 0.1 54.1 1.4
Men 11.7 0.2 15.9 0.2 4.3 0.1 0.0 10.2 39.8 1.4 0.0 150.0 0.55
Women 6.2 0.1 9.9 0.1 3.6 0.1 0.0 9.1 64.1 2.0* 0.0 250.0 0.59
Units for muscle size are centimeters squared and for MVC and 1RM are kilograms. Data represent means SEM. Significant gender and time main effects were found for all variables
within the trained arm (P0.05).
* Denotes significant gender time interaction (P0.001).
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Official Journal of the American College of Sports Medicine http://www.acsm-msse.org
Changes in Size and Strength in the Untrained
Arm
Muscle size. Baseline and posttraining biceps cross-
sectional area measures for the untrained arm are presented
in Table 3, as well as calculated differences in the means and
percent changes from baseline to posttraining. In the un-
trained arm, an ANCOVA of cross-sectional area detected
significant effects of gender and time (P0.001), with very
slight gains in CSA over time (1.5%). No significant inter-
action was detected between genders after 12 wk, indicating
similar small gains in CSA in men and women (P0.97).
Muscle strength. Baseline and posttraining 1RM
strength measures for the untrained arm are presented in Table
3, as well as calculated differences in the means and percent
changes from baseline to posttraining. In the untrained arm, an
ANCOVA of 1RM detected significant effects of gender and
time (P0.001). No significant interaction was detected
between genders after 12 wk, indicating similar gains in 1RM
in men and women (P0.10).
Baseline and posttraining isometric strength measures
(MVC) for the untrained arm are presented in Table 3, as
well as calculated differences in the means and percent
changes from baseline to posttraining. In the untrained arm,
an ANCOVA of MVC detected significant effects of gender
and time (P0.001). No significant interaction was de-
tected between genders after 12 wk, indicating similar gains
in 1RM in men and women (P0.92).
DISCUSSION
Although it is well documented that both men and women
can gain muscle size and strength in response to resistance
training, anecdotal evidence suggests that some people ex-
perience more dramatic size and strength gains than others.
No study to date has attempted to quantify the amount of
variation in size and strength gains in a large cohort of men
and women after a controlled progressive resistance training
program, especially using sensitive techniques such as MRI
to assess muscle size. Additionally, there is some conflict
concerning the existence of sex differences in the response
to resistance training. In this study, we had the opportunity
to document variability in training-induced changes in a
single muscle group in 585 men and women, as well as to
provide a definitive answer as to the existence of sex dif-
ferences in size and strength gains after resistance training.
Variability
Variability in muscle size. Of the 585 subjects, 232
subjects showed an increase in CSA of between 15 and
25%. However, 10 subjects gained over 40%, and 36 sub-
jects gained less than 5%. We hypothesized that men would
demonstrate greater variability for absolute gains in muscle
mass, because they have a much greater range of normal
circulating levels of androgens than women (34). Androgens
(especially testosterone) have been shown to drive muscle
hypertrophy in a dose-dependent manner (5). Additionally,
coefficients of variation calculated from published mean
and standard deviation data from previous studies indicated
that variability in muscle size at baseline (15,26) and after
training (15) was greater in men versus women. In our
study, we found significant differences in variability for
absolute values pre- and posttraining. However, the vari-
ability in the relative change from pre- to posttraining was
not significantly different between men and women. These
data suggest that variation in the relative response of muscle
to hypertrophic stimuli is not sex-dependent in healthy
young adults.
Additionally, the lack of correlation in our study between
age and changes in muscle size provides additional evidence
that testosterone levels do not play a significant role in the
variability of muscle size increases. Despite the large age
range used in this study (18 40 yr of age), the correlation
between age and muscle size was very weak (r ⫽⫺0.09).
We ascribe this to the upper age cutoff of 40 yr, as any
significant decreases in testosterone levels do not occur until
age 60 or older in most individuals (18).
FIGURE 2—One-repetition maximum strength test. Histogram of
1RM changes (relative to baseline) within each gender for the trained
arm, showing similar variability between men and women for muscle
mass gains. Black bars denote responses of men while white bars denote
responses of women.
FIGURE 3—Isometric strength test. Histogram of isometric strength
changes (relative to baseline) within each gender for the trained arm.
Black bars denote responses of men whereas white bars denote re-
sponses of women.
VARIATION IN RESPONSE TO RESISTANCE TRAINING Medicine & Science in Sports & Exercise
969
Variability in muscle strength. Of the 585 subjects,
232 subjects showed an increase in 1RM of between 40 and
60%. However, 36 subjects gained over 100%, and 12
subjects gained less than 5%. For MVC, 119 subjects
showed an increase in strength of between 15 and 25%,
whereas 60 subjects gained over 40%, and 102 subjects
gained less than 5%. As with muscle size gains, we expected
broader androgen ranges in the men to confer higher vari-
ability for strength gains in men. For absolute gains, we
found higher variability in men for MVC gain (but not 1RM
gain). For relative change variability, we observed differ-
ences in variability between men and women regarding both
isometric and dynamic strength gains. However, the pattern
was mode-dependent, in that men had greater variability in
isometric strength gains while women had greater variabil-
ity in dynamic strength gains.
Although men in our study were more variable than women
in the amount of relative change in the isometric strength
measure after training, examination of the histogram (Fig. 3)
shows that the preponderance of responses from men gravitate
toward the mean (as evidenced by the kurtosis score of 16.7).
This could be explained in part by the presence of one very
high responder who displayed a gain of 150% in MVC. With-
out this one individual, the CV for the men drops from 1.07 to
0.94, closer to the 0.89 value demonstrated by the women (but
still significantly different).
Women demonstrated greater variability in dynamic rel-
ative strength gains after training. The greater variability
found in women could be the result of several factors. One
of these could be a greater flexibility level in women at the
elbow (3), making a full-extension maximal effort difficult
and blunting strength gains. Another could be potential
differences in skill acquisition during training, in that
women were, on average, less skilled at the preacher curl
before training than men, leading to higher relative gains
that were not necessarily related to inherent strength gains in
the muscle. This latter idea is in accordance with the theory
put forth by Wilmore in 1979 that lower strength levels in
untrained women is due to social and cultural restrictions
rather than dramatic physiological differences between the
sexes (33).
One factor that could have affected variability in both
muscle size and strength changes differently in men and
women would be the volume of training. In our study, each
subject lifted progressively greater weights across the 12 wk
within general intensity guidelines (i.e., goal in weeks 1– 4
at 3 sets of 12 repetitions at 65–75% 1RM; goal in weeks
5–9 at 3 sets of 8 repetitions at 75– 82% 1RM; goal in weeks
10 –12 at 3 sets of 6 repetitions at 83–90% 1RM). Within
these guidelines, some subjects obviously encountered
greater training volumes (total amount of weight lifted) than
others. One could hypothesize that men would have a
greater range of starting weights and would therefore have
a more variable gains. However, we saw no relationship
between training volume and size gain (r 0.05 for men
and 0.09 for women). MVC change was also poorly
correlated (r ⫽⫺0.06 for men and 0.16 for women),
whereas the 1RM was negatively correlated with training
volume (r ⫽⫺0.29 for men and 0.35 for women), indi-
cating a bias towards higher relative gains in those with the
smallest starting weights.
Training Effect
Training effect on muscle size. Advances in tech-
nology have allowed researchers to use increasingly sensi-
tive measures of muscle size, including CT or MRI (21).
However, because of the cost associated with these tech-
niques, these studies have been limited in sample size pro-
hibiting definitive conclusions concerning sex differences in
size gains. Although some studies found that increases in
CSA were similar in men and women (10,23), Ivey et al.
(15) found greater increases in men versus women for
quadriceps volume increase after training. Each of these
studies used fewer than 15 subjects per group, meaning that
those studies that did not find a significant difference were
simply underpowered.
In our study, we used highly accurate MRI measurements
in a large cohort (N585) of males and females and
demonstrated small, but significant, changes in muscle size
for men and women after resistance training (20% in men
and 18% in women). These increases are similar to those
found by Cureton et al. (10) but greater than those found in
the study by O’Hagen et al. (23), potentially because
O’Hagen et al. used weight training machines rather than
free weights. Although these studies reported that the dif-
ferences were not statistically significant, the 2% difference
in our study was highly significant (P0.001). One could
likely assume that a sample size greater than 500 would
have sufficiently powered the previous studies so that the
6 –7% differences seen by Cureton et al. (10) and O’Hagen
et al. (23) would have been statistically significant. These
results provide conclusive evidence that intense resistance
training produces a small but significantly greater relative
increases in muscle size in the upper arm in men versus
women.
Training effect on muscle strength. Untrained
women are estimated to have approximately half of the
upper-, and approximately two thirds of the lower-body
strength of men (20). It is clear that men have the capability
to increase absolute strength to a greater extent than women,
on average. However, it is not clear whether relative gains
in strength (percentage increases from baseline) are differ-
ent in men and women. Several studies have indicated no
difference in relative strength gains in the lower body
(9,16,31) between men and women, whereas results for
upper-body training have been equivocal (10,11,16,23).
These studies’ small sample sizes prohibit firm conclusions,
because studies that do not find differences between men
and women may simply not be sufficiently powered, and the
chance of selecting a nonnormal distribution of subjects is
increased with smaller sample sizes.
Our results show definitively that women gain significantly
more relative isometric (MVC) strength and dynamic (1RM)
strength with resistance training than men (22 vs 16%, P
0.01; 64 vs 40%, respectively). These increases for dynamic
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Official Journal of the American College of Sports Medicine http://www.acsm-msse.org
strength are similar to those found by Cureton et al. (10)
(36.2% for men and 59.2% for women) for the same muscle
group. This is likely because women have lower initial strength
values. In fact, the correlation between initial 1RM and 1RM
percent gains was 0.55, whereas the correlation between
initial MVC and MVC percent gains was 0.27.
Training model considerations. The effects of re-
sistance training on muscle size and strength are dependent
upon many factors, including the muscle group chosen for
training. Therefore, it is currently unknown whether the
gender differences demonstrated in this study would be seen
given a different training program (i.e., whole-body training
or lower-body training). Our exercise training program led
to an average of 18.9% gain in biceps CSA, which is similar
to that found by Cureton et al. (10), and greater than or
similar to the relative changes found after MRI analysis of
muscle after total-body or lower-body programs (1,14). We
also saw an average 19.5% gain in MVC, which is similar
to gains seen after unilateral training in the leg (14,22),
although direct comparison across studies for both size and
strength gains are limited by differences in training mode or
length. These data suggest that the choice of the unilateral
arm model did not compromise relative size and strength
gains. Although absolute gains would likely be larger with
activation of a larger muscle mass (i.e., use of whole-body
or use of bilateral training), we believe that we provided a
sufficient training stimulus to evoke a significant training
response.
CONCLUSION
Analysis of muscle size and strength changes after 12 wk
of progressive resistance training in the elbow flexors/ex-
tensors in 585 men and women demonstrated the following:
1) a large range of strength and size responses to training,
with the frequency of high responders greater than that of
low responders; 2) similar variability in men and women for
relative size gains and mode-dependent gender differences
for relative strength gains; 3) a slight advantage for men
versus women in relative size gain after training; and 4)
moderate to large advantages for women versus men in
strength gain after exercise.
The Functional Polymorphisms Associated with Muscle Size and
Strength (FAMuSS) Study is funded by the National Institutes of
Health Grant no. 5R01NS040606-03.
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... For muscle strength the dose-response relationship has a proposed trivial favour for moderate to high (≥10) compared to lower (≤5) weekly sets, and marginal between low to moderate (5-9) and low (≤5) weekly sets, for both multi-joint and isolation exercises, with an effect size (ES) difference of 0.19 and 0.15, respectively (Ralston et al., 2017), supported by Marshall et al., (2011). The aforementioned studies all display considerable limitations through either questionable inference, limited measurements or trivial results, and most display a wide inter-individual heterogeneity in their data (Benito et al., 2020;Krieger, 2010;Schoenfeld et al., 2016Schoenfeld et al., & 2018Radaelli et al., 2014;Ralston et al., 2017), a recurring feature throughout exercise science and primarily a result of phenotype variations in the population (Ahtiainen et al., 2016;Carpinelli, 2017;Benito et al., 2020;Hubal et al., 2005;Timmons, 2010). Inter-individual heterogeneity accompanied by other methodological limitations (e.g. ...
... Inter-individual heterogeneity accompanied by other methodological limitations (e.g. volume stratification, exercise prescriptions, sample sizes, measurements, study prevalence, etc) together accumulates to divergent results and uncertainty, questioning external validity -particularly for higher volumes (Ahtiainen et al., 2016;Benito et al., 2020;Hammarström et al., 2019;Hubal et al., 2005;Krieger, 2010;Marshall et al., 2011;Ostrowski et al., 1997;Radaelli et al., 2014;Carpinelli, 2017;Ralston et al., 2017;Schoenfeld et al., 2014Schoenfeld et al., , 2016Schoenfeld et al., , 2016Schoenfeld et al., & 2018Wernbom & Thomee, 2007). ...
... In line with the present study, Schoenfeld et al. (2018) found no difference between high volume conditions in a comparable intervention length, while Radaelli et al. (2014) found 30 weekly sets to be superior to 18 sets over a 6-month intervention, albeit only in the upper limbs. Among the studies employing contralateral designs (Hammarström et al., 2019;Hubal et al., 2005;Mitchell et al., 2012), only Hammarström et al., (2019) with its moderate-volume condition (18 sets) being identical to the current HV-condition remains comparable, whereby 18 sets are superior to 6 sets. Out of the contemporary volume-oriented studies, substantial methodological differences and wide inter-individual heterogeneities highlight the uncertainty surrounding the external validity of their findings (Ahtiainen et al., 2016;Carpinelli, 2017;Benito et al., 2020;Schoenfeld et al., 2016Schoenfeld et al., & 2018Radaelli et al., 2014;Rønnestad et al., 2007). ...
Thesis
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Seven weeks of high volume and very-high volume resistance training leads to indistinguishable adaptations in m. Vastus Lateralis thickness, strength and total-RNA abundance in untrained young adults-using a multigroup contralateral crossover design. Abstract The manipulation of volume elicits differentiated physiological adaptations in response to resistance training (RT). Early accumulation of total-RNA har been suggested as a mediator of muscle accretion in response to varying RT-volumes. The purpose of this study was to investigate the effects of RT-volumes on muscle thickness, strength and total-RNA abundance. Thirty-nine untrained young adults (25 + 4.1 years, 11 males, 28 Females) performed 0, 3 or 6 sets (Control, high volume (HV) or very-high volume (VHV)) of differentiated unilateral leg press and leg extension, 3 times weekly for 7 weeks at 10 repetition maximum (RM) for each leg, after 3 weeks of habituation where two sets of 10 RM were performed on all limbs except control (0 sets). Muscle thickness, strength and total-RNA was assessed by ultrasound-, isometric maximum voluntary contractions (MVC) and biopsies sampled from m. vastus lateralis at weeks-3, 0, 4 and 7. After 7 weeks of RT both volume conditions led to increases in muscle thickness (HV: ~ 36 % CI: [20, 55], VHV: ~32% CI: [15, 52]) and strength (HV: ~10% CI: [3.5, 17], VHV: ~14% CI: [6.5, 22]), with no difference between HV and VHV. RT led to increased total-RNA concentrations in m. vastus lateralis at week 4 (HV: ~20% CI: [3.5, 38], VHV: ~29% CI: [9.5, 51]), with no difference at week 7. There was no benefit to VHV compared with HV conditions on any measures (muscle thickness HV-VHV: ~3.5 % CI: [-16, 11.5], strength HV-VHV: ~3.5% CI: [-3.5, 11.5] and total-RNA HV-VHV: ~1 % CI: [-12, 16]). RT at HV and VHV seems to elicit nearly identical adaptations in young untrained individuals during a 7-week intervention.
... min −1 . Similarly, there is large variability in muscle size and strength changes in men and women after resistance training [10]. Changes in male (n = 243) and female (n = 342) muscle size and strength in the elbow flexors of the non-dominant arm were determined after 12 weeks of progressive unilateral resistance training. ...
... Moreover, the lack of muscle quality associated with ageing may be an underlying factor in diminishing strength gains [23,31]. In addition, increases in fat-free mass and muscle cross-sectional area are greater in males compared to females [10,23], though changes in relative muscle strength are similar between males and females [10]. ...
... Moreover, the lack of muscle quality associated with ageing may be an underlying factor in diminishing strength gains [23,31]. In addition, increases in fat-free mass and muscle cross-sectional area are greater in males compared to females [10,23], though changes in relative muscle strength are similar between males and females [10]. ...
Article
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There is a wide variance in the magnitude of physiological adaptations after resistance or endurance training. The incidence of “non” or “poor” responders to training has been reported to represent as high as 40% of the project’s sample. However, the incidence of poor responders to training can be ameliorated with manipulation of either the training frequency, intensity, type and duration. Additionally, global non-response to cardio-respiratory fitness training is eliminated when evaluating several health measures beyond just the target variables as at least one or more measure improves. More research is required to determine if altering resistance training variables results in a more favourable response in individuals with an initial poor response to resistance training. Moreover, we recommend abandoning the term “poor” responders, as ultimately the magnitude of change in cardiorespiratory fitness in response to endurance training is similar in “poor” and “high” responders if the training frequency is subsequently increased. Therefore, we propose “stubborn” responders as a more appropriate term. Future research should focus on developing viable physiological and lifestyle screening tests that identify likely stubborn responders to conventional exercise training guidelines before the individual engages with training. Exerkines, DNA damage, metabolomic responses in blood, saliva and breath, gene sequence, gene expression and epigenetics are candidate biomarkers that warrant investigation into their relationship with trainability. Crucially, viable biomarker screening tests should show good construct validity to distinguish between different exercise loads, and possess excellent sensitivity and reliability. Furthermore “red flag” tests of likely poor responders to training should be practical to assess in clinical settings and be affordable and non-invasive. Early identification of stubborn responders would enable optimization of training programs from the onset of training to maintain exercise motivation and optimize the impact on training adaptations and health.
... Although such changes may indeed lead older individuals to a decreased skeletal muscle tissue sensitivity to anabolic stimuli (Yang et al., 2012), it prohibits putting on account of aging the occurrence of inexpressive morphological adaptations in response to training exclusively. Regarding this muscle mass response heterogeneity, while some scholars (Atkinson et al., 2019;Dankel and Loenneke, 2020) recommend cautiousness when claiming its existence, emphasizing that individual differences need to be attested in studies that consider the random error, verified from a matched control group, many others widely recognize it (Hubal et al., 2005;Davidsen et al., 2011;Sparks, 2017;Stec et al., 2017;Camera, 2018;Räntilä et al., 2021). Although more studies need to be conducted to demonstrate the true variability of the response, the body of evidence indicates that such heterogeneity should not be ignored. ...
... Supplementary Table S5 provides more information on the specific classification approaches used in each study. Three studies (Hubal et al., 2005;Peltonen et al., 2018) were not categorized because they did not report enough information on how they classified individual responses. ...
... MCID, minimum clinically important difference; SD IR , the standard deviation of individual responses; SWC, smallest worthwhile change. (B) Only contains 113 of the 116 studies that classified individual responses because three studies did not report how individuals were classified (Hubal et al., 2005;Peltonen et al., 2018). differences in trainability because its 90% CI lay fully above zero (Figure 3). ...
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The second volume of the Research Topic entitled “Precision Physical Activity and Exercise Prescriptions for Disease Prevention: The Effect of Interindividual Variability Under Different Training Approaches” has been successfully completed, as expected. As stated in the preface to the first volume, this Research Topic was initially intended to address a challenge in this field, but this topic is becoming, over time, an important cornerstone for scientists who are exploring the fascinating subject of “Precision Physical Activity and Exercise Prescriptions for Disease Prevention” (Ramírez-Vélez et al., 2017). This Research Topic consists of 10 articles, of which seven contain original data, one is a systematic review with meta-analysis and two are opinion/hypothesis articles.
... Although such changes may indeed lead older individuals to a decreased skeletal muscle tissue sensitivity to anabolic stimuli (Yang et al., 2012), it prohibits putting on account of aging the occurrence of inexpressive morphological adaptations in response to training exclusively. Regarding this muscle mass response heterogeneity, while some scholars (Atkinson et al., 2019;Dankel and Loenneke, 2020) recommend cautiousness when claiming its existence, emphasizing that individual differences need to be attested in studies that consider the random error, verified from a matched control group, many others widely recognize it (Hubal et al., 2005;Davidsen et al., 2011;Sparks, 2017;Stec et al., 2017;Camera, 2018;Räntilä et al., 2021). Although more studies need to be conducted to demonstrate the true variability of the response, the body of evidence indicates that such heterogeneity should not be ignored. ...
... Supplementary Table S5 provides more information on the specific classification approaches used in each study. Three studies (Hubal et al., 2005;Peltonen et al., 2018) were not categorized because they did not report enough information on how they classified individual responses. ...
... MCID, minimum clinically important difference; SD IR , the standard deviation of individual responses; SWC, smallest worthwhile change. (B) Only contains 113 of the 116 studies that classified individual responses because three studies did not report how individuals were classified (Hubal et al., 2005;Peltonen et al., 2018). differences in trainability because its 90% CI lay fully above zero (Figure 3). ...
Article
The novel coronavirus disease (COVID-19) has emerged at the end of 2019 and caused a global pandemic. The disease predominantly affects the respiratory system; however, there is evidence that it is a multisystem disease that also impacts the cardiovascular system. Although the long-term consequences of COVID-19 are not well-known, evidence from similar diseases alerts for the possibility of long-term impaired physical function and reduced quality of life, especially in those requiring critical care. Therefore, rehabilitation strategies are needed to improve outcomes in COVID-19 survivors. Among the possible strategies, resistance training (RT) might be particularly interesting, since it has been shown to increase functional capacity both in acute and chronic respiratory conditions and in cardiac patients. The present article aims to propose evidence-based and practical suggestions for RT prescription for people who have been diagnosed with COVID-19 with a special focus on immune, respiratory, and cardiovascular systems. Based on the current literature, we present RT as a possible safe and feasible activity that can be time-efficient and easy to be implemented in different settings.
... Additionally, resistance training effectively increases muscle strength and size [5], which also reduces the risk of all-cause mortality [6]. This emphasises the importance of undertaking aerobic and resistance training, however not every individual experiences the same magnitude of improvement during exercise interventions [7,8]. ...
... Inter-individual response to an exercise intervention is a major area of interest in the field of exercise physiology. Landmark studies such as the HERITAGE (n = 481) and FAMuSS (n = 585) have highlighted large variability of physiological adaptations following aerobic [7] and resistance exercise training [8]. Subsequent studies that have observed exercise response variability categorise participants depending on the magnitude of change and are classified accordingly as "high responders", "low responders", "non-responders" or "adverse responders" [9,10]. ...
Article
Participation in resistance training improves muscle strength and size, as well as reduced risk of chronic disease and frailty. However, the exercise response to resistance training is highly variable. In part this may be attributed to individual physiological differences. Identification of biomarkers that can distinguish between high and low responders to exercise are therefore of interest. Exhaled volatile organic compounds may provide a non-invasive method of monitoring the physiological response to resistance training. However, the relationship between exhaled organic compounds and the acute response to resistance exercise is not fully understood. Therefore, this research will investigate exhaled volatile organic compounds in acute response to resistance exercise with an aim to discover a common group of compounds that can predict high and low responders to standardised resistance training.
... Meanwhile, the current result does not concur with Kolber and Corrao [14] who reported a nonsignificant difference in this ratio between both female groups. It was found that, following resistance training, the absolute strength gain in males is greater than females [33]. Moreover, the self-selected resistance load of women often does not exceed 60% of onerepetition maximum (1 RM) which is suboptimal for increasing the muscle strength [34]. ...
Article
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Background: Isokinetic strength imbalance is a risk factor for movement dysfunctions and injuries related to shoulder complex. The effects of recreational weightlifting on developing the imbalances between the shoulder muscles are not yet known. Objectives: To investigate the isokinetic concentric shoulder muscle strength values (peak torque normalized to body weight) in recreational weightlifters (RWL) and to compare the shoulder muscles agonist/antagonist ratios with nonweightlifters. Methods: Thirty male RWL with mean age, weight, height, and body mass index (BMI) of 21.56 years, 84.25 kg, 175.34 cm, and 26.51 kg/m2, respectively, matched with nonweightlifters served as a control group. The normalized concentric peak torque values of shoulder flexors, extensors, abductors, adductors, and internal and external rotators were measured at angular velocity 120°/sec by using Biodex isokinetic system. Moreover, the agonist/antagonist strength ratio for all muscle groups were calculated. Results: The normalized peak torques of RWL group were significantly greater than the control group (p < 0.05). The abductor/adductor and external rotator/internal rotator ratios of the RWL were significantly lower than the control group (p = 0.008 and 0.009, respectively). Conversely, there was no significant difference between both groups in relation to the flexor/extensor ratio (p = 0.259). Conclusion: These results suggested that the recreational weightlifting exercises place trainees at risk of muscle imbalances. Therefore, the restoration of a normal concentric abductor/adductor and external rotator/internal rotator strength ratios may decrease the risk of possible shoulder injury.
... Resistance training generally leads to muscle hypertrophy in both males and females (1), although the range of hypertrophic responses shows considerable inter-individual differences (2). ...
Article
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Purpose: Resistance training induces skeletal muscle hypertrophy via the summated effects of post-exercise elevations in myofibrillar protein synthesis (MyoPS) that persist for up to 48 h, although research in females is currently lacking. MyoPS is regulated by mTOR translocation and colocalization; however, the effects of resistance training on these intracellular processes is unknown. We hypothesized that MyoPS would correlate with hypertrophy only after training in both sexes and would be associated with intracellular redistribution of mTOR. Methods: Recreationally active males and females (n = 10 each) underwent 8 weeks of whole-body resistance exercise 3x/week. Fasted muscle biopsies were obtained immediately before (REST) and 24 and 48 h after acute resistance exercise in the untrained (UT) and trained (T) state to determine integrated MyoPS over 48 h (D2O ingestion) and intracellular mTOR colocalization (immunofluorescence microscopy). Results: Training increased (P < 0.01) muscle strength (~20-126%), muscle thickness (MT;~8-11%), and average fibre cross sectional area (fCSA;~15-20%). MyoPS increased above REST in UT (P = 0.032) and T (P < 0.01), but to a greater extent in males (~23%;P = 0.023), and was positively (P < 0.01) associated with MT and fCSA at T only in both males and females. mTOR colocalization with the cell periphery increased (P < 0.01) in T, irrespective of sex or acute exercise. Training increased (P ≤ 0.043) total mTOR, LAMP2 (lysosomal marker), and their colocalization (P < 0.01), although their colocalization was greater in males at 24 and 48 h independent of training status (P < 0.01). Conclusions: MyoPS during prolonged recovery from exercise is greater in males but related to muscle hypertrophy regardless of sex only in the trained state, which may be underpinned by altered mTOR localization.
Article
Objectives: This study aimed to construct a profile of specific fitness indices for male teenage sprinters on the Chinese National Team to provide sprinting fitness assessments for teenage training. Material and Methods: 229 male teenage sprinters at the same level were recruited to participate in this test for the indices. The t- and Kruskal-Wallis tests were conducted for the first selection of fitness indices. In the second selection, principal components analysis was applied to select common factors with greater characteristic values. The fitness indices chosen were height, leg length, measurement B (ankle circumference/heel length×100%) and measurement A (thigh circumference/leg length×100%), hemoglobin, 60m sprint time, 100m sprint time, countermovement jump (CMJ), maximum countermovement jump velocity, CMJ flight time, CMJ maximum force, and CMJ force. Results: Thirteen indices were chosen for the specific fitness of male teenage Chinese male sprinters with 3 general categories and 9 subcategories. The weight of each fitness index was confirmed and used to construct a standard fitness assessment scale. Conclusion: Anthropometric indices indicate the athlete’s innate limits in the structure of the sprinting motion. Physiological indices indicate the athlete’s potential to expend energy and recover in a short time. Motor indices indicate the athlete’s maximum sprinting ability, lower limb reaction strength, power, and maximum strength. Level of evidence II, Diagnostic studies - Investigation of a diagnostic test.
Article
Key points: Characterising individual responses to resistance and endurance exercise training can inform optimal strategies for exercise prescription. This study utilised monozygotic and dizygotic twins in a randomised cross-over study to determine individual responsiveness to different modalities of exercise training. The influence of environment versus genetics in cerebrovascular responses to training was determined. It is apparent that individuals respond differently to distinct exercise stimuli and that switching modality may be a beneficial way to obtain positive responses in cerebrovascular function. This study has implications for improving individualised exercise prescription to maintain or improve cerebral structure and function. Abstract: Introduction We studied monozygotic (MZ) and dizygotic (DZ) twin pairs following resistance (RES) and endurance (END) training to assess genetic and environmental contributions to cerebrovascular function. Methods Cerebrovascular function (rest, autoregulation, hypercapnia, exercise) was assessed in 86 healthy same-sex MZ (30 pairs) and DZ (13 pairs) twins, who underwent three-months of END and RES. Carbon dioxide (PET CO2 ), mean arterial pressure (MAP) and middle cerebral artery velocity (MCAv) were measured and MCAv resistance (MCACVRi ) was calculated. Results Resting MCAv reduced by -2.8 cm/s following RES (P = 0.024), with no change following END (-0.3 cm/s, P = 0.758). Change in MCACVRi following RES was +0.11 mmHg/cm/s (P < 0.001), which was significantly greater than END (+0.02 mmHg/cm/s, P = 0.030). MAP also increased following RES (+4 mmHg, P = 0.010), but not END (+1 mmHg, P = 0.518). No changes were apparent in PET CO2 . At rest, positive response rates following RES ranged from 27-71% and 40-64% following END. Intraclass correlations between twins were moderate for most variables at baseline. In response to training, only MZ pairs were significantly correlated for change in MCAv (P = 0.005) and low frequency phase (P = 0.047) following RES. Conclusion This study is the first to compare cerebrovascular function following RES and END in MZ and DZ twins. Most individuals who did not respond to one modality were able to respond by switching modality and baseline heritability estimates were higher than training response. Exercise professionals should therefore consider modality and environmental factors when optimising interventions. Abstract figure legend Schematic summary of the assessment battery of cerebrovascular measures of function and health developed by Ainslie and Green. Transcranial Doppler (TCD) measures are complemented by contemporaneous assessment of whole brain blood flow, derived from simultaneous high-resolution ultrasound via insonation of the internal carotid and vertebral arteries. Results show that group response does not always reflect individual responses, and that switching exercise modality can increase individual responsiveness to exercise training. Low twin correlations in response to exercise training indicate nurture has a larger contribution to training response than nature. This article is protected by copyright. All rights reserved.
Article
The aim of the present review was to focus on normobaric hypoxic resistance training and to discuss to what extent this method can be efficient for athletes to potentiate classical adaptations to resistance training and thereby performance. Search terms related to the topic of the present review such as normobar*, hypox*, resistance exercise, resistance training and performance were inserted in Pubmed and Scopus. In total, 16 articles made the core of this narrative review. Based on the available literature, 2–3 sessions a week performed in hypoxic conditions for 4–6 weeks with a FiO2 of 0.14–0.15 should recommended to athletes looking at potentiating the effects of resistance training. A large range of loads has been found to be efficient at inducing physiological effects in hypoxic vs normoxic conditions, from 20% to 90% of the 1-RM. Ideally, at least the last set should be performed to failure, if not all. Also, inter-set rest periods should be around 30 s for low-load exercise (30%–40% 1-RM), around 60 s for moderate-load exercise (60%–70% 1-RM) and 2 min for high-load exercise (85%–90% 1-RM). While there is no one size fits all and certainly no guarantee of added value over normoxic training, each athlete looking at potentiating the effects of resistance training should try to implement some sessions in hypoxic conditions. Based on the individual response, subtle improvements may be expected on muscle strength and mass, velocity and power, as well as hormonal responses to resistance training.
Article
Photographs representing front, side, and rear views of 1,175 men photographed in identical postures make available a standard file of somatotype variations. Part I, The nature of the somatotype, discusses the need for a biological identification tag, a preliminary exploration, a pilot study, and individual differences within the somatotype. The photographs, with accompanying text and age-height-weight tables, are arranged in Part II, Atlas for somatotyping men, in a manner such that "the seven gradations in the first component (endomorphy) divide the whole series of 88 somatotypes into seven sections within each of which the first component is held at a constant strength." Glossary, tables, and equipment and procedures in somatotyping. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
Objectives: To examine the possible influences of age and gender on muscle volume responses to strength training (ST). Design: Prospective intervention study. Setting: University of Maryland Exercise Science and Wellness Research Laboratories. Participants: Eight young men (age 20-30 years), six young women (age 20-30 years), nine older men (age 65-75 years), and ten older women (age 65-75 years). Intervention: A 6-month whole-body ST program that exercised all major muscle groups of the upper and lower body 3 days/week. Measurements: Thigh and quadriceps muscle volumes and mid-thigh muscle cross-sectional area (CSA) were assessed by magnetic resonance imaging before and after the ST program. Results: Thigh and quadriceps muscle volume increased significantly in all age and gender groups as a result of ST (P < .001), with no significant differences between the groups. Modest correlations were observed between both the change in quadriceps versus the change in total thigh muscle volume (r = 0.65; P < .001) and the change in thigh muscle volume versus the change in mid-thigh CSA (r = 0.76, P < .001). Conclusions: The results indicate that neither age nor gender affects muscle volume response to whole-body ST. Muscle volume, rather than muscle CSA, is recommended for studying muscle mass responses to ST.
Article
Detailed physiological profiles have been established for athletes in various sports for both sexes. This paper synthesizes the results from previous studies in the areas of body composition and phsyique; muscle fiber characteristics; strength; and cardiovascular endurance capacity. Similarities and differences between male and female athletes are discussed. While there are rather substantial physiological differences between the average male and the average female, these differences are reduced considerably when comparisons are made between the highly trained male and female athlete who are competing in the same event or sport. Highly trained male and female athletes are similar in lower body strength, when expressed per unit of body weight; cardiovascular endurance capacity; body composition; and muscle fiber type. What once appeared to be dramatic biological differences in physiological function between the sexes, may, in fact, be more related to cultural and social restrictions placed on the female as she attains puberty, i.e. a sedentary lifestyle.
Article
The purposes of this study were to 1) determine the effect of concentric isokinetic training on strength and cross-sectional area (CSA) of selected extensor and flexor muscles of the forearm and leg, 2) examine the potential for preferential hypertrophy of individual muscles within a muscle group, 3) identify the location (proximal, middle, or distal level) of hypertrophy within an individual muscle, and 4) determine the effect of unilateral concentric isokinetic training on strength and hypertrophy of the contralateral limbs. Thirteen untrained male college students [mean age 25.1 +/- 6.1 (SD) yr] volunteered to perform six sets of 10 repetitions of extension and flexion of the nondominant limbs three times per week for 8 wk, using a Cybex II isokinetic dynamometer. Pretraining and posttraining peak torque and muscle CSA measurements for both the dominant and nondominant limbs were determined utilizing a Cybex II isokinetic dynamometer and magnetic resonance imaging scanner, respectively. The results indicated significant (P less than 0.0008) hypertrophy in all trained muscle groups as well as preferential hypertrophy of individual muscles and at specific levels. None of the muscles of the contralateral limbs increased significantly in CSA. In addition, significant (P less than 0.0008) increases in peak torque occurred for trained forearm extension and flexion as well as trained leg flexion. There were no significant increases in peak torque, however, for trained leg extension or for any movement in the contralateral limbs. These data suggest that concentric isokinetic training results in significant strength and hypertrophic responses in the trained limbs.