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Considering the bilateral deficit, the sum of forces produced by each limb in a unilateral condition is generally greater than that produced by them in a bilateral condition. Therefore, it can be speculated that performing unilateral strength exercises may allow greater training workloads and subsequently greater neuromuscular adaptations when compared to bilateral training. Hence, the purpose of this study was to compare neuromuscular adaptations to unilateral vs. bilateral training in the knee extensor muscles. Forty-three recreationally active young women were allocated to a control (CG), unilateral (UG) or bilateral (BG) training group, which performed 2 times strength training sessions a week for 12 weeks. Knee extension one repetition maximum (1RM), maximal isometric strength, muscle electrical activity and muscle thickness were obtained before and after the study period. Muscle strength was measured in unilateral (right + left) and bilateral tests. Both UG and BG increased similarly their unilateral 1RM (33.3±14.3% vs. 24.6±11.9%, respectively) and bilateral 1RM (20.3±6.8% vs. 28.5±12.3%, respectively) and isometric strength (14.7±11.3% vs. 13.1±12.5%, respectively). The UG demonstrated greater unilateral isometric strength increase than the BG (21.4±10.5% vs. 10.3±11.1%, respectively) and only the UG increased muscle electrical activity. Muscle thickness increased similarly for both training groups. Neither group exhibited pre-testing 1RM bilateral deficit values, but at post-testing, UG showed a significant bilateral deficit (-6.5±7.8%) while BG showed a significant bilateral facilitation (5.9±9.0%). Thus, performing unilateral or bilateral exercises was not a decisive factor for improving morphological adaptations and bilateral muscle strength in untrained women. Unilateral training, however, potentiate unilateral specific strength gains.
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Exercise Research Laboratory, Physical Education School, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil;
Center for Sport Performance, Human Performance Laboratory, California State University, Fullerton, California
Botton, CE, Radaelli, R, Wilhelm, EN, Rech, A, Brown, LE, and
Pinto, RS. Neuromuscular adaptations to unilateral vs. bilateral
strength training in women. J Strength Cond Res 30(7):
1924–1932, 2016—Considering the bilateral deficit, the sum
of forces produced by each limb in a unilateral condition is
generally greater than that produced by them in a bilateral con-
dition. Therefore, it can be speculated that performing unilateral
strength exercises may allow greater training workloads and
subsequently greater neuromuscular adaptations when com-
pared with bilateral training. Hence, the purpose of this study
was to compare neuromuscular adaptations with unilateral vs.
bilateral training in the knee extensor muscles. Forty-three rec-
reationally active young women were allocated to a control,
unilateral (UG) or bilateral (BG) training group, which per-
formed 2 times strength training sessions a week for 12 weeks.
Knee extension one repetition maximum (1RM), maximal iso-
metric strength, muscle electrical activity, and muscle thick-
ness were obtained before and after the study period.
Muscle strength was measured in unilateral (right + left) and
bilateral tests. Both UG and BG increased similarly their uni-
lateral 1RM (33.3 614.3% vs. 24.6 611.9%, respectively),
bilateral 1RM (20.3 66.8% vs. 28.5 612.3%, respectively),
and isometric strength (14.7 611.3% vs. 13.1 612.5%,
respectively). The UG demonstrated greater unilateral isomet-
ric strength increase than the BG (21.4 610.5% vs. 10.3 6
11.1%, respectively) and only the UG increased muscle elec-
trical activity. Muscle thickness increased similarly for both
training groups. Neither group exhibited pretesting 1RM bilat-
eral deficit values, but at post-testing, UG showed a significant
bilateral deficit (26.5 67.8%) whereas BG showed a signifi-
cant bilateral facilitation (5.9 69.0%). Thus, performing unilat-
eral or bilateral exercises was not a decisive factor for
improving morphological adaptations and bilateral muscle
strength in untrained women. Unilateral training, however,
potentiate unilateral specific strength gains.
KEY WORDS resistance exercise, muscle thickness, deficit
Strength exercises are often performed in 2 different
fashions, with 1 limb at a time (unilateral) or both
limbs simultaneously (bilateral). Previous studies
have shown that it is possible to produce greater
force in the sum of unilateral compared with bilateral (2,8).
The mechanisms explaining differences between these con-
ditions are not completely understood. However, the most
consistent explanation is that there is a neural limitation
during bilateral exercise, blunting maximal force produc-
tion (16,23). This phenomenon is known as the bilateral
deficit and is well documented by cross-sectional studies
in different muscle groups (21), populations, (14) and test
conditions (2).
Because of the bilateral deficit, it is possible to use greater
loads when exercise is performed unilaterally, which may be
a strategy to optimize strength gains. However, a limited
number of studies have compared the chronic neuromuscu-
lar adaptations of unilateral and bilateral strength training
(5,11,21,22). Some previous studies (5,11) have demon-
strated that despite either unilateral or bilateral training,
there are strength gains in the specific trained condition,
and an increase in the untrained condition. In contrast,
Taniguchi (21) showed that strength gains occurred only
after bilateral training.
A cross-sectional study reported that subjects who trained
at least 1 year unilaterally demonstrated bilateral deficit on
the knee extensor muscles compared with subjects bilaterally
trained (8). However, longitudinal studies (12–26 weeks)
with untrained people have found that unilateral training
had a slight nonsignificant increase in the bilateral deficit,
possibly due to a similar percentage change in the bilateral
and unilateral strength (5,21). On the other hand, bilateral
training resulted in significant decrease of bilateral deficit
(5,11,21) as a consequence of a greater magnitude of increase
in bilateral compared with unilateral strength.
Address correspondence to Cı
´ntia Ehlers Botton, cintiabotton@yahoo.
Journal of Strength and Conditioning Research
Ó2015 National Strength and Conditioning Association
Journal of Strength and Conditioning Research
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The divergent results among few studies found in the
literature may be explained by different populations (males,
females, or mixed groups), period of training (6–26 weeks),
and type of resistance machine used during training (isoiner-
tial or isokinetic). For example, Ha
¨kkinen et al. (5) investi-
gated the effect of 12 weeks of isoinertial knee extension
training on middle-aged and older men and women, while
Janzen et al. (11) performed 26 weeks of knee extension
training in postmenopausal women. Differently of the afore-
mentioned studies (5,11), Taniguchi (21) performed 6 weeks
of isokinetic knee extension training in young men and
women. In addition, Kuruganti et al. (13) investigated the
effect of isokinetic bilateral training on the bilateral deficit,
but unilateral training was not studied. Moreover, previous
studies (21,22) have focused primarily on strength measure-
ment while investigating differences between training con-
ditions. Thus, there is a paucity of research regarding
unilateral vs. bilateral training differences related to morpho-
logical and neural adaptations.
Because unilateral training enables one to exercise with
greater load per trained limb, it may be speculated that
unilateral strength training would elicit greater skeletal muscle
adaptations compared with bilateral exercises. Therefore, the
purpose of this study was to investigate neuromuscular
adaptations to unilateral vs. bilateral training, and their
influence on the bilateral deficit in young women, because
the few studies in this area were performed with middle-aged
and elderly subjects and nonhomogeneous gender.
Experimental Approach to the Problem
To compare the effects of unilateral and bilateral training,
subjects were required to visit the laboratory on 3 separate
days before study (pre) and twice after 12 weeks (post) with 4
days of interval between visits. On the first visit, muscle
thickness measurements were taken and subjects were famil-
iarized with the dynamic and isometric strength tests. On the
second day, anthropometric data were obtained and subjects
performed a maximal isometric strength test with simultaneous
collection of the electromyographic (EMG) signal. The
Thereafter, subjects were randomized on a control group or
training group, which exercised 2 times per week for 12 weeks.
Post-testing took place 3 to 5 days after the last training session
and was identical to pretesting. Intraclass correlation coeffi-
cients were calculated with data collected on day one and 2 for
the isometric test; and day one and 3 for dynamic test.
Forty-three young women (18–30 years) volunteered for
this study. They were randomly assigned to either unilateral
group (UG) (n= 14: 24.8 61.4 years; 60.8 66.4 kg; 163.0 6
6.5 cm), bilateral group (BG) (n= 15: 24.3 63.7 years; 57.0 6
4.8 kg; 160.2 65.8 cm), or control group (CG) (n= 14: 22.7 6
2.8 years; 58.0 65.7 kg; 163.6 66.2 cm). Sample size was
based on standard deviations and differences between means
from Ha
¨kkinen et al. (5), with an alpha level of 0.05 and
power of 80%, and resulted in a minimum of 12 subjects
per group.
All subjects had not been involved in a systematic strength
training program for at least 3 months before this study, and 6
participants had never practiced strength training before.
Participants were not taking medications other than oral
contraceptives and were instructed to avoid changes in their
diet and recreational physical habits (e.g., sports, jogging, and
walking) throughout the study period. Only 6 women did not
take oral contraceptives (2 for each group). They were
informed of possible risks and discomforts of participation
and all gave their written informed consent before any testing.
This study was conducted according to the Declaration of
Helsinki and all procedures were approved by the Ethics
Committee of the Federal University of Rio Grande do Sul.
Maximal Dynamic Strength. Knee extension 1 repetition
maximum (1RM) tests for bilateral and unilateral (right and
left) conditions were assessed on the same test day on the
same isoinertial knee extension machine used for training
(Taurus, Porto Alegre, RS, Brazil). The same researchers, with
identical equipment and subject positioning, conducted all
pre- and post-testing. Subjects were carefully familiarized with
the testing procedures and performed a warm-up of 10
repetitions of bilateral knee extensions with a light resistance.
The bilateral extension was always tested first, followed by the
unilateral extension test for the right and left leg in random
order. Ten minutes of interval was given between the bilateral
and unilateral tests. The cadence was fixed at 2 seconds for
the concentric phase and 2 seconds for the eccentric phase
with the aid of an analog metronome (Quartz, Los Angeles,
CA, USA). Subjects started the test at 908of knee flexion (08=
knee fully extended) and moved to full extension which was
individualized for each subject and controlled by a delimiter
device. The maximal load was found within 3 attempts for
each testing condition, with 5-minute interval between trials.
Intraclass correlation coefficients for bilateral and unilateral
right and left were 0.96, 0.95, and 0.93, respectively.
Maximal Isometric Strength. Isometric knee extension test for
bilateral and unilateral (right and left) conditions were
performed on an isokinetic dynamometer (Cybex Norm,
Ronkonkoma, NY, USA), calibrated according to the
manufacturer’s instructions. The unilateral tests were per-
formed with the standard lever arm supplied by the manu-
facturer, whereas a custom made lever arm was used for
bilateral testing (Figure 1). Subjects were seated with their
hips flexed at 858(08= hip fully extended). For both tests, the
dynamometer’s axis of rotation was aligned with the lateral
femoral condyle of the tested limb, while straps secured the
torso and pelvis. Subjects performed 10 repetitions of con-
centric knee extension at 1208per second as a warm-up.
Thereafter, they completed two 5-second knee extension
Journal of Strength and Conditioning Research
VOLUME 30 | NUMBER 7 | JULY 2016 | 1925
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maximal isometric actions at a 608angle (08= knee fully
extended), with 3 minutes rest between attempts. All iso-
metric tests on bilateral and unilateral (right and left) con-
ditions were performed on the same day in randomized
order with 30 minutes rest between bilateral and unilateral
tests. Subjects were instructed and verbally encouraged to
produce maximal torque throughout each trial. Peak torque
values were determined by the dynamometer software
(Humac norm 2009, Version 9.6.2). The greatest isometric
peak torque value for each condition was used for further
analyses. Intraclass correlation coefficients for bilateral and
unilateral right and left were 0.78, 0.86, and 0.76, respectively.
Muscle Electrical Activity. Electromyographic (EMG) activity
was recorded from the vastus lateralis (VL) and rectus femoris
(RF) muscles of the right and left limbs during maximal
isometric strength testing. Before electrode placement, skin
preparation was performed, including shaving excess hair and
cleaning the skin with isopropyl alcohol (to reduce impedance
below 2,000 kV). Bipolar configuration electrodes (20-mm
interelectrode distance) were positioned along the estimated
direction of the muscle fibers on the muscle belly according to
SENIAM ( Electrode position was carefully
mapped using a transparent sheet to ensure replication posi-
tioning at post-testing.
Electromyographic signals were recorded using an electro-
myographic system (Miotool, Miotec-Equipamentos Biome
dicos), amplified by a factor of 100 and digitized at a sampling
frequency of 2,000 Hz. The EMG signal was Butterworth
filtered using cut-off frequencies of 20 Hz and 500 Hz for
lower and upper band-pass respectively. After filtering, the
EMG signal from the highest isometric torque (Nm) attempt
was selected across a one-second torque–time curve plateau,
and the root mean square (RMS) value for each muscle was
calculated. For total muscle electrical activation (EMG
), the
RMS values of each muscle of each limb were summed.
Muscle Thickness. Quadriceps femoris muscle thickness was
obtained using a B-Mode ultrasonographic apparatus (Nemio
XG, Toshiba, Japan), with a 7.5 MHz linear array probe (38-
mm length). Before muscle thickness evaluation, each subject
rested for 15 minutes in a supine position with their legs
extended and relaxed to allow fluid shifts to occur (1). The
probe was coated with a water-soluble transmission gel to
provide acoustic contact without depressing the dermal sur-
face. Great care was taken to apply minimal pressure during
scanning to avoid compression of the muscles. Muscle thick-
ness of the RF, VL, vastus medialis (VM), and vastus interme-
dius (VI) were measured at the same sites described in
previous studies (4,12,15,19). All images were digitized and
later analyzed in Image-J software (National Institutes of
Health, version 1.37; USA). Subcutaneous adipose tissue-
muscle interface and the muscle-bone interface were identified
in each image, and the distance between them was accepted as
muscle thickness. Overall quadriceps femoris muscle thickness
) was calculated from the sum of the four
muscles ( RF + VL + VM + V I) (3,17,19) for each limb followed
by the sum of the right and left. Post-testing measures were
performed 3–5 days after the last training session to avoid any
potential exercise-induced swelling. The same researcher per-
formed all measurements before and after training. These
measurements have demonstrated high reproducibility in our
laboratory and in previous studies (17,19).
Bilateral Index. Bilateral index (BI) was calculated using an
equation proposed previously (8), with peak torque values
), 1RM values (BI
) and RMS values (BI
obtained in the bilateral and unilateral (right and left) con-
ditions. The equation is:
BI ð%Þ¼100xBilateral
Unilateral Right þUnilateral Left2100
Positive values indicate that bilateral condition was greater
than the sum of the unilateral conditions (bilateral
Figure 1. Modified lever arm to perform bilateral testing on the
Unilateral vs. Bilateral Training
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facilitation), and negative values indicate that bilateral
condition was less than the sum of the unilateral conditions
(bilateral deficit).
Strength Training Program
Training occurred across 12 weeks, consisting of 2 sessions
per week on nonconsecutive days (total of 24 training
sessions). Rest between sessions normally ranged from 48
to 72 hours within a week. The UG performed the knee
extension exercise with 1 leg at a time whereas BG
performed with 2 legs simultaneously. All training sessions
were monitored and supervised by at least 1 experienced
investigator. Apart from the knee extension, subjects per-
formed the following exercises: bilateral knee flexion, bench
press, lateral pull-down, hip abduction, hip adduction,
crunch, biceps flexion, and triceps extension. These exercises
were performed in the same way by both groups and were
included to keep participants interested and motivated.
Participants started all training sessions by the knee exten-
sion exercise.
Training intensity was controlled using the repetition
maximum (RM) method as in previous studies (6,18,19),
thus the heaviest possible weight was used for the designated
number of repetitions for each condition. The intensity was
the same for both training groups. Training for weeks 1–3
was 2 sets of 12–15RM; weeks 4–6 was 3 sets of 9–12RM;
weeks 7–9 was 3 sets of 7–10RM; and weeks 10–12 was 4
sets of 5–8RM. Interset rest interval was 1 minute for weeks
1–3, 2 minutes for weeks 4–9 and 3 minutes for weeks 10–12.
When subjects were able to perform more than the desired
number of repetitions, the load was increased for the next
session in increments from 1.0 to 5.0 kg. All subjects at-
tended more than 80% of the training sessions.
Training Loads. To compare differences in knee extension
training loads between groups, the load used during the last
training session of each mesocycle was considered for
analysis. Loads were expressed as an absolute value (kg).
Loads of each limb for UG were summed for comparison.
Statistical Analyses
All data are presented as means 6SD. Normality, homoge-
neity, and sphericity for outcome measures were tested using
the Shapiro–Wilk, Levene, and Mauchly tests, respectively.
TABLE 1. Maximum dynamic and isometric strength values pre- and post-training, in unilateral and bilateral tests
between groups (means 6SD).*
Pre Post Pre Post Pre Post
1RM BIL (kg) 39.0 67.3 46.6 67.2z35.7 67.6 45.5 68.0z36.7 68.1 37.0 69.6
1RM UNI (kg) 38.0 67.8 50.2 68.3z34.9 66.8 43.1 67.339.1 610.0 39.2 610.2
PT BIL (Nm) 286.6 648.3 327.6 657.3z274.2 659.1 307.7 658.0278.5 657.3 265.7 650.7
PT UNI (Nm) 323.7 660.8 390.0 665.8z311.0 662.4 342.5 672.3324.0 655.0 323.9 656.9
*UG = unilateral group; BG = bilateral group; CG = control group; 1RM = one repetition maximum; BIL = bilateral test condition;
UNI = unilateral test condition (right + left); PT = peak torque.
Significantly greater than pre values (p#0.05).
zSignificantly greater than CG at post (p#0.05).
TABLE 2. Total electromyographic activation values, pre- and post-training, in unilateral and bilateral test condition
(means 6SD).*
Pre Post Pre Post Pre Post
BIL (mV)
476.0 6110.5 591.4 6136.4 565.8 6264.8 610.9 6208.6 576.7 6380.6 596.69 6357.3
UNI (mV)
523.9 699.0 731.2 6152.7680.9 6265.2 748.0 6288.0 715.8 6401.7 693.9 6256.5
*UG = unilateral group; BG = bilateral group; CG = control group; EMG
= total electromyographic activation, sum of vastus
lateralis and rectus femoris muscles of the right and left limbs; BIL = bilateral test condition; UNI = unilateral test condition (right + left).
Significantly greater than pre values (p#0.05).
Journal of Strength and Conditioning Research
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Two-way analysis of variance (ANOVA) with repeated
measures was used to examine interactions between time x
group for 1RM, isometric peak torque, EMG
, and MT
values. Whenever a significant interaction was
observed, a paired t-test was used to determine within-
group differences, and a one-way ANOVA to determine
between-group differences for unilateral and bilateral condi-
tions. Analysis of variance also examined interactions
between group 3condition for percent change values for
1RM, isometric peak torque, and EMG
measures. When-
ever a significant interaction was observed, a paired t-test
was used to determine within-group differences, and
a one-way ANOVA to determine between-group differences.
A one-sample t-test was used to determine if bilateral index
was significantly different from zero at baseline and post-
testing for BI
and BI
. A 2-way (time 3group)
ANOVA with repeated measures was used to determine
differences in the time course of workloads. Tukey post
hoc tests were used when necessary, to verify differences
between groups. Test-retest reliability of force measurements
(dynamic and isometric) were calculated at baseline for typ-
ical error = standard-deviation of the difference between day
1 and day 2 measurements/O2; and coefficient of variation
(%) = (typical error of the difference between day 1 and day
2/means of day 1 and day 2) * 100 (7). Significance level was
set a priori at p#0.05. All statistical procedures were
performed using the Statistical Package for the Social Scien-
ces (SPSS) version 18.0 software (IBM SPSS, Inc., Chicago,
There were no significant (p$0.05) differences between
groups at baseline for 1 RM, isometric peak torque, EMG
Maximum Strength (Dynamic and Isometric)
There were significant (p#0.05) time 3group interactions
for 1RM and isometric peak torque where UG and BG sig-
nificantly increased after training but CG showed no change.
Both UG and BG showed greater bilateral 1RM values than
CG at post. However, only UG showed greater values than
CG in the unilateral 1RM test at post. For isometric peak
torque only UG showed greater values than CG for both test
conditions at post (Table 1).
The typical error for 1RM measures was 1.44 kg (3.92%),
1.03 kg (5.70%), and 0.90 kg (5.16%) for bilateral, unilateral
right and left tests, respectively. Typical error for peak torque
measures was 38.50 Nm (10.03%), 15.15 Nm (7.12%), and
20.49 Nm (9.48%) for bilateral, unilateral right and left tests,
For 1RM percentage changes, there was a significant (p#
0.05) interaction for group 3condition. The UG and BG
TABLE 3. Sum of muscle thickness values of quadriceps muscles, pre- and post-training (means 6SD).*
Pre Post Pre Post Pre Post
(mm) 141.0 621.9 152.8 619.7138.7 613.7 151.0 614.5151.5 618.3 149.2 618.2
*UG = unilateral group; BG = bilateral group; CG = control group; MT QUA
= sum of the quadriceps muscles thickness of the
right and left limbs.
Significantly different of the pre values (p#0.05).
TABLE 4. Percentage values of bilateral index at pre- and post-training (means 6SD).*
Pre Post Pre Post Pre Post
(%) 3.7 614.4 26.5 67.82.6 69.2 5.9 6925.4 613.7 24.7 613.3
(%) 210.5 610.7215.7 67.7211.5 69.929.3 611.3213.8 6210.7217.8 66.7
(%) 29.5 67.9218.8 69.2217.4 614.6215.3 623.4221.7 611.624.8 622.5
*UG = unilateral group; BG = bilateral group; CG = control group; BI
= bilateral index with 1 repetition maximum values; BI
bilateral index with peak torque values; BI
= bilateral index with maximal electromyographic activation values.
Significantly different from zero (p#0.05).
Unilateral vs. Bilateral Training
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increased unilateral 1RM (33.3 614.3% vs. 24.6 611.9%,
respectively) and bilateral 1RM (20.3 66.8% vs. 28.5 6
12.3%, respectively) similarly and both groups showed signifi-
cantly (p#0.05) greater values than the CG in unilateral (0.1 6
5.5%) and bilateral (0.8 65.0%). Moreover, UG showed
a greater (p#0.05) increase in unilateral than in bilateral
whereas the BG was not different. In contrast, for peak torque
percentage values, there was only a significant (p#0.05) main
effect for group. For the unilateral test, UG increased peak
torque values 21.4 610.5% which was significantly greater
(p#0.05) than the BG (14.7 611.3%). In the bilateral test,
groups increased similarly (p$0.05) (UG 14.7 611.3% vs. BG
13.1 612.5%). Both BG and UG showed significantly (p#
0.05) greater values than the CG in both tests.
Muscle Electrical Activity
There was a significant (p#0.05) group 3time interaction
for muscle electrical activity in unilateral only. The UG
showed a significant (p#0.05) increase in maximal EMG
activity values at post training in unilateral (Table 2), show-
ing greater (p#0.05) percentage change (39.9 618.3%) in
comparison to the BG (12.0 621.7%) and CG (5.1 6
21.4%). For bilateral, there was no significant (p$0.05)
difference between UG (25.4 618.0%), BG (15.7 6
31.8%), and CG (6.9 620.7%). The BG and CG showed
no significant increase (p$0.05) on muscle electrical activity
at post training for unilateral and bilateral conditions.
Muscle Thickness
A significant (p#0.05) group 3time interaction was
observed for muscle thickness. The training groups signifi-
cantly (p#0.05) increased MT QUA
at post, while the
CG significantly (p#0.05) decreased it (Table 3). There was
no difference on muscle thickness between training groups
(p$0.05) at post training.
Bilateral Index
At baseline, there were no significant (p$0.05) BI
for any group. At post training BI
values of the training
groups were significantly different from zero (p#0.05),
indicating bilateral deficit and bilateral facilitation for UG
and BG, respectively (Table 4). For BI
all groups showed
values significantly lower than zero (p#0.05), and post
training values did not show any significant changes. For
values, there was a significant difference from zero
(p#0.05) at baseline and post training for both training
groups (Table 4). There was large variability of BI
between subjects within the same group (Figure 2).
Training Loads
A significant time 3group interaction (p#0.05) for training
load was observed. Both training groups significantly
increased (p#0.05) at every mesocycle, but the UG trained
with a significantly greater (p#0.05) loads in the last mes-
ocyle (Figure 3).
The aim of this study was to compare the effects that
unilateral and bilateral strength training have on muscle
strength, neural, and morphological adaptations of the knee
extensors in young women after 12 weeks of training. This
Figure 2. Individual percentage bilateral index with 1 repetition maximum values (BI
) before and after training. UG = unilateral group; BG = bilateral group;
CG = control group.
Figure 3. Absolute loads used during the training period (mean 6SD).
UG: unilateral group; BG: bilateral group; *Significantly greater than the
previous mesocycle (p#0.05); dSignificantly greater than BG workload
Journal of Strength and Conditioning Research
VOLUME 30 | NUMBER 7 | JULY 2016 | 1929
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study investigated the responses in a homogenous popula-
tion, and is the first to consider only young women for
training. In general, we found that the 2 forms of training
resulted in increases in quadriceps muscle strength and
thickness after training. Strength increases were not
restricted to the specific training condition, but interestingly
and for the first time, the lateral specificity was shown only
for UG in both strength and muscle activation changes. The
training loads were similar between groups for almost all
training periods, but in the last mesocycle, the UG trained
with greater workload than the BG. Moreover, training
specificity seems to influence the bilateral index differently
when considering isometric or dynamic strength. The BI
seems to be reduced by bilateral training and raised by uni-
lateral training, whereas BI
values were not altered as
a function of the intervention.
The outcomes of this study relative to maximum strength
gains showed that both UG and BG demonstrated signifi-
cant increases in trained and untrained conditions. In
relation to dynamic strength, our results are in agreement
with others (5,11,13) that have found increases in both bilat-
eral and unilateral strength, after knee extension training
performed bilaterally or unilaterally. Even when only bilat-
eral isokinetic training was performed, Kuruganti et al. (13)
found knee extension strength increases in both conditions
for men and women. However, our results do not support
some previous findings (21), that demonstrated increases in
isokinetic knee extensor strength in men and women only
for BG in the specific trained condition. These authors con-
clude that one of the reasons for this may be the lower initial
physical activity level of subjects included in the BG, thus
demonstrating greater potential for adaptation. Participants
in both training groups of this study had not being involved
with strength training for a similar time (10.2 66 months for
UG and 13 611.6 months for BG) between training groups
and 2 participants in each group had never undertook
strength training routines.
Although the 2 groups increased strength in both test
conditions, Ha
¨kkinen et al. (5) and Janzen et al. (11) showed
a greater percentage change for each group in their specific
trained condition. Our results partially corroborate with
these findings, since only UG showed greater 1RM gains
in the specific trained condition. The BG strength changes
were similar between bilateral and unilateral tests, suggesting
no lateral specificity. It is possible that differences in study
populations, level of physical activity of the subjects, selec-
tion criteria and randomization of the sample may have
influenced these study differences (5,11). To our knowledge
this study is the first that studied only young women.
¨kkinen et al. (5) investigated adults and older, men and
women, while Janzen et al. (11) studied post-menopausal
women. From the results found in our work, we could sug-
gest that there is no restriction in strength gains only in the
trained condition, but that positive lateral specificity seems
to occur with unilateral training. Unlike the results found for
1RM, maximum isometric strength gains in the unilateral
test condition were greater for UG than BG. All groups
began training with greater peak torque values in unilateral
than bilateral, different than 1RM pre values. Therefore, UG
training maximized unilateral strength gains without ham-
pering bilateral adaptations.
The specificity of isometric strength gains for UG can be
explained by an increase in quadriceps muscle activation.
The percentage of increase was greater for UG in the
unilateral test than the BG, which was similar to that
observed in strength changes. Only UG showed significant
increases in muscle activation in their specific training
condition. Muscle activation was not measured during
maximum dynamic tests which was the specific training
condition. Therefore, we cannot rule out neural mechanisms
involved with maximal isoinertial strength, although it can
be speculated that a transfer of strength and muscular
activation gains may have occurred in the nonspecific test
(isometric) condition.
Regarding morphological responses, few studies have
compared the effects of unilateral and bilateral training on
skeletal muscle adaptations (5,11,13). Some previous inves-
tigations have hypothesized that unilateral training might
allow the use of heavier loads, resulting in greater gains than
bilateral training (11). In our current study, both BG and UG
significantly increased muscle thickness similarly which cor-
roborates previous studies (5,11) examining knee extensor
muscles. Furthermore, the absolute training loads were
greater in UG than BG only in the last mesocycle; so it is
possible to suggest that for longer periods of training, the
difference between loads will be more apparent and could
optimize gains from unilateral training. In a 26-week study
by Janzen et al. (11), UG trained with heavier loads than BG
at 3 time points (pre, mid, and post-training). However, the
authors performed their analysis with percent loads relative
to baseline 1RM values. Moreover, the UG began training
with greater loads.
The bilateral index in the present study was measured for
both 1RM and isometric peak torque. For BI
, both training
groups presented a bilateral deficit at baseline, however nei-
ther group showed bilateral deficit or facilitation before
training in BI
. According to Jakobi e Chilibeck (10), iso-
metric muscle actions can best represent the bilateral deficit,
because they are more stable than dynamic actions. In addi-
tion, it is possible that during the isoinertial 1RM test, the
difference between loads for unilateral and bilateral is not
pronounced. Accordingly, Janzen et al. (11) and Ha
et al. (5) did not find significant knee extension 1RM bilateral
deficit at pretraining using a isoinertial equipment. These
results highlight the importance of considering the specific
test designed to measure bilateral deficit. Hence, it seems
that bilateral deficit occurs in maximal isometric and isoki-
netic tests (2), but may be limited when derived from
isoinertial resistance equipment (5,11), suggesting an
action-specific behavior.
Unilateral vs. Bilateral Training
Journal of Strength and Conditioning Research
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Performing bilateral strength exercises has been suggested
to reduce the BI (5,11,21,22) because of the greater magni-
tude of increase in bilateral strength, whereas unilateral
training may increase the bilateral deficit according to
a cross-sectional study (8). Our findings regarding BI
are in accordance with this specificity concept, because the
BG showed bilateral facilitation, whereas bilateral deficit was
evident after training in UG. However, there were no
changes in the bilateral deficit with isometric peak torque
values. Since BI
was large for all groups at pre, it is possible
that the 12 weeks of training was not enough to generate
measurable BI
changes. In addition, the isometric test dif-
fers from specific training condition.
¨kkinen et al. (5) reported that bilateral training signifi-
cantly increased the ratio of bilateral and unilateral force by
7% after 12 weeks of strength training in the knee extensors
of adults and elderly men and women, while unilateral train-
ing showed a not significant 2% change in 1RM. In the
present study, the percent change of the UG was approxi-
mately 10%, whereas BG showed an increase of approxi-
mately 3%. These divergent results between studies could
be related to variability in the BI values among individuals
of the same group, which can be observed in Figure 2. More-
over in a previous study by Hakkinen et al. (5), there is no
information about individual behavior of the subjects. It is
possible that none of the subjects had a bilateral deficit
before training, unlike our investigation where some subjects
showed a bilateral deficit or bilateral facilitation at baseline.
Considering individual variability in the BI, UG had
uniform changes in the BI
after training, showing
a reduction in variability, unlike the heterogeneous response
observed in BG. It is possible that less between-subjects var-
iability in unilateral adaptations might have resulted in the
lateral specificity found after unilateral training. Moreover,
¨kkinen et al. (5) and Janzen et al. (11) did not show any
effect of unilateral training on BI, probably because the per-
centage of change of unilateral and bilateral strength were
similar for UG but not BG, while in present study the BG
had percentage values more similar between conditions that
resulted in only 3% of change in the BI.
The bilateral deficit is probably a result of neural
limitations (16), so it would be expected that lower torque
values in bilateral tests were accompanied by lower levels of
activation. The bilateral index with muscle activation values
was performed only on data obtained during the maximal
isometric test. At pre, all groups showed bilateral deficit for
muscle activation in accordance with the results found in
. At post, both training groups still demonstrated a bilat-
eral deficit, while the CG demonstrated none. Other cross-
sectional studies have not find proportional lower values
between torque and muscle activation (8,9,20).
It should be noted as potential limitation of this study that
it is not possible to extrapolate our results to other muscle
groups and different exercises because only the knee
extension movement was investigated. Furthermore, the
current study was conducted on young women, but no
control for the menstrual cycle variations was done. Thus,
the generalization of the current findings should be done
with caution to other populations and other strength
The use of unilateral or bilateral exercises does not seem to
be decisive in improving neuromuscular adaptations to
strength training in untrained young women. However, if
the training aim is to optimize the increase in force produced
for each lower limb separately, the unilateral training may be
recommended. The increase of BD post unilateral training
means that force in each limb was maximized and more
force is produced for each one separately than simulta-
neously. This may imply in improved performance in daily
activities and in athletic performance during unilateral
movements, such as kicking and running. Although unilat-
eral training enabled the use of heavier training loads, there
were no greater superior gains in muscle mass compared
with bilateral training for 12 weeks. It is worth noting,
however, that longer training periods may have resulted in
greater neuromuscular adaptations in the UG, since differ-
ences in training loads were only evident in the last weeks of
The authors acknowledge the subjects who volunteered for
this study. The authors also to acknowledge CNPq and
CAPES for their funding support for this study. There are no
conflicts of interest among authors or external funding
sources to disclose. The results of this study do not
constitute endorsement by the authors or the National
Strength and Conditioning Association.
1. Berg, HE, Tedner, B, and Tesch, PA. Changes in lower limb muscle
cross-sectional area and tissue fluid volume after transition from
standing to supine. Acta Physiol Scand 148: 379–385, 1993.
2. Botton, CE, Radaelli, R, Wilhelm, EN, Silva, BGC, Brown, LE, and
Pinto, RS. Bilateral deficit between concentric and isometric muscle
actions. Isokinet Exerc Sci 21: 161–165, 2013.
3. Cadore, EL, Izquierdo, M, Alberton, CL, Pinto, RS, Conceicao, M,
Cunha, G, Radaelli, R, Bottaro, M, Trindade, GT, and Kruel, LF.
Strength prior to endurance intra-session exercise sequence
optimizes neuromuscular and cardiovascular gains in elderly men.
Exp Gerontol 47: 164–169, 2012.
4. Chilibeck, PD, Stride, D, Farthing, JP, and Burke, DG. Effect of
creatine ingestion after exercise on muscle thickness in males and
females. Med Sci Sports Exerc 36: 1781–1788, 2004.
5. Ha
¨kkinen, K, Kallinen, M, Linnamo, V, Pastinen, UM, Newton, RU,
and Kraemer, WJ. Neuromuscular adaptations during bilateral
versus unilateral strength training in middle-aged and elderly men
and women. Acta Physiol Scand 158: 77–88, 1996.
6. Hanssen, KE, Kvamme, NH, Nilsen, TS, Ronnestad, B,
Ambjornsen, IK, Norheim, F, Kadi, F, Hallen, J, Drevon, CA, and
Raastad, T. The effect of strength training volume on satellite cells,
myogenic regulatory factors, and growth factors. Scand J Med Sci
Sports 23: 728–739, 2013.
Journal of Strength and Conditioning Research
VOLUME 30 | NUMBER 7 | JULY 2016 | 1931
Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
7. Hopkins, WG. Measures of reliability in sports medicine and
science. Sports Med 30: 1–15, 2000.
8. Howard, JD and Enoka, RM. Maximum bilateral contractions are
modified by neurally mediated interlimb effects. J Appl Physiol 70:
306–316, 1991.
9. Jakobi, JM and Cafarelli, E. Neuromuscular drive and force
production are not altered during bilateral contractions. J Appl
Physiol 84: 200–206, 1998.
10. Jakobi, JM and Chilibeck, PD. Bilateral and unilateral contractions:
Possible differences in maximal voluntary force. Can J Appl Physiol
26: 12–33, 2001.
11. Janzen, CL, Chilibeck, PD, and Davison, KS. The effect of unilateral
and bilateral strength training on the bilateral deficit and lean tissue
mass in post-menopausal women. Eur J Appl Physiol 97: 253–260,
12. Korhonen, MT, Mero, AA, Alen, M, Sipila, S, Hakkinen, K,
Liikavainio, T, Viitasalo, JT, Haverinen, MT, and Suominen, H.
Biomechanical and skeletal muscle determinants of maximum
running speed with aging. Med Sci Sports Exerc 41: 844–856, 2009.
13. Kuruganti, U, Parker, P, Rickards, J, Tingley, M, and Sexsmith, J.
Bilateral isokinetic training reduces the bilateral leg strength deficit
for both old and young adults. Eur J Appl Physiol 94: 175–179,
14. Kuruganti, U and Seaman, K. The bilateral leg strength deficit is
present in old, young and adolescent females during isokinetic knee
extension and flexion. Eur J Appl Physiol 97: 322–326, 2006.
15. Miyatani, M, Kanehisa, H, and Fukunaga, T. Validity of
bioelectrical impedance and ultrasonographic methods for
estimating the muscle volume of the upper arm. Eur J Appl Physiol
82: 391–396, 2000.
16. Ohtsuki, T. Decrease in human voluntary isometric arm strength
induced by simultaneous bilateral exertion. Behav Brain Res 7:
165–178, 1983.
17. Pinto, RS, Correa, CS, Radaelli, R, Cadore, EL, Brown, LE, and
Bottaro, M. Short-term strength training improves muscle quality
and functional capacity of elderly women. Age 36: 365–372, 2014.
18. Pinto, RS, Gomes, N, Radaelli, R, Botton, CE, Brown, LE, and
Bottaro, M. Effect of range of motion on muscle strength and
thickness. J Strength Cond Res 26: 2140–2145, 2012.
19. Radaelli, R, Botton, CE, Wilhelm, EN, Bottaro, M, Lacerda, F,
Gaya, A, Moraes, K, Peruzzolo, A, Brown, LE, and Pinto, RS. Low-
and high-volume strength training induces similar neuromuscular
improvements in muscle quality in elderly women. Exp Gerontol 48:
710–716, 2013.
20. Schantz, PG, Moritani, T, Karlson, E, Johansson, E, and Lundh, A.
Maximal voluntary force of bilateral and unilateral leg extension.
Acta Physiol Scand 136: 185–192, 1989.
21. Taniguchi, Y. Lateral specificity in resistance training: The effect of
bilateral and unilateral training. Eur J Appl Physiol Occup Physiol 75:
144–150, 1997.
22. Taniguchi, Y. Relationship between the modifications of bilateral
deficit in upper and lower limbs by resistance training in humans.
Eur J Appl Physiol Occup Physiol 78: 226–230, 1998.
23. Vandervoort, AA, Sale, DG, and Moroz, J. Comparison of motor
unit activation during unilateral and bilateral leg extension. J Appl
Physiol Respir Environ Exerc Physiol 56: 46–51, 1984.
Unilateral vs. Bilateral Training
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... and the reason they were excluded. Three new papers met the inclusion criteria [34][35][36]. Table 1 provides information on the studies that met our inclusion criteria. Five studies [17,[33][34][35][36] reported a change in non-specific strength relative to a control, while five studies [7,9,15,30,32] did not observe a change in non-specific strength. ...
... Table 1 provides information on the studies that met our inclusion criteria. Five studies [17,[33][34][35][36] reported a change in non-specific strength relative to a control, while five studies [7,9,15,30,32] did not observe a change in non-specific strength. Two studies did not report whether non-specific strength changed differently between the intervention and control groups [16,31]. ...
... Two studies did not report whether non-specific strength changed differently between the intervention and control groups [16,31]. Eleven studies reported a change in specific strength relative to control in at least one training group [7,9,15,17,[30][31][32][33][34][35][36]. One study did not report if the change in specific strength was different between exercise and control conditions for specific strength [16]. ...
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Background Isotonic exercise is the most common mode of strength training. Isotonic strength is often measured in the movement that was exercised, but isometric and isokinetic movements are also commonly used to quantify changes in muscular strength. Previous research suggests that increasing strength in one movement may not lead to an increase in strength in a different movement. Quantifying the increase in strength in a movement not trained may be important for understanding strength training adaptations and making recommendations for resistance exercise and rehabilitation programs.Objective To quantify changes in non-specific strength relative to a control.DesignA systematic review and random effects meta-analysis was conducted investigating the effects of isotonic strength training on isotonic and isokinetic/isometric strength.Search and InclusionThis systematic review was conducted in Google scholar, PubMed, Academic Search Premier, and MENDELEY. To be included in this review paper the article needed to meet the following criteria: (1) report sufficient data for our variables of interest (i.e., changes in isotonic strength and changes in isokinetic or isometric strength); (2) include a time-matched non-exercise control; (3) be written in English; (4) include healthy human participants over the age of 18 years; (5) the participants had to train and test isotonically; (6) the participants had to be tested isokinetically or isometrically on a device different from that they trained on; (7) the non-specific strength task had to test a muscle involved in the training (i.e., could not have trained chest press and test handgrip strength); and (8) the control group and the experimental group had to perform the same number of strength tests.ResultsWe completed two separate searches. In the original search a total of 880 papers were screened and nine papers met the inclusion criteria. In the secondary search a total of 2594 papers were screened and three additional papers were added (total of 12 studies). The overall effect of resistance training on changes in strength within a movement that was not directly trained was 0.8 (Cohen’s d) with a standard error of 0.286. This overall effect was significant (t = 2.821, p = 0.01) and the 95% confidence interval (CI) is 0.22–1.4. The overall effect of resistance training on strength changes within a movement that was directly trained was 1.84 (Cohen’s d) with a standard error of 0.296. This overall effect was significant (t = 6.221, p < 0.001) and the 95% CI is 1.23–2.4.Conclusion The results of our meta-analysis suggest that strength increases in both the specific and non-specific strength tests. However, the smaller effect size associated with non-specific strength suggests that it will be difficult for a single study to meaningfully investigate the transfer of strength training adaptions.
... bilateral 1RM (6.8% vs. 12.3%) as well as isometric strength (11.3% vs. 12.5%). The unilateral group recorded a higher increase in unilateral strength as well as increased muscle activity [9,10]. ...
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Introduction: The aim of the study was to compare the effectiveness of unilateral and bilateral training program on changes in the level of speed and speed-strength abilities. Methods: Experimental group 1 (EG1) consisted of 8 young athletes (age = 12.76±1.55 years) and experimental group 2 (EG2) consisted of 8 athletes (age = 12.51±1.59 years) who regularly participate in the training process at a frequency of three times a week. All of our athletes had more than 4 years experiences with regular athletic training 3 times per week prior to this study. During a period of 8 weeks in the preparatory period, such exercises were applied which were performed unilaterally in EG1 and bilaterally in EG2. To determine the effectiveness of takeoff training on change in the level of speed and speed-strength abilities, the following tests were performed: relative strength index (RSI), squat jump (SJ), countermovement jump (CMJ), standing long jump (SLJ), 20 m run from standing start. Results: We found out that in the posttest, the athletes of both groups achieved an improvement in the explosive strength of the lower extremities as well as in the acceleration speed. A significant improvement (p<0.05) was recorded in EG1 in SLJ and in EG2 in RSI. The effect size coefficients showed a large effect in RSI in EG2 and in SLJ in EG1. Conclusion: The results clearly did not confirm a higher effect of the unilateral program in comparison with the bilateral program, but indicated a higher efficiency, especially in the takeoff explosiveness of athletes with a unilateral training program.
... The term bilateral deficit (BLD) refers to the greater expression of force or power obtained when the right and left limb unilateral performances are added together, compared with the force or power measured during the bilateral performance [3,4]. BLD has been reported in different motor tasks, such as isokinetic [5], isometric [6], and dynamic contraction types [7], and in specific sport-related motor tasks; in particular, vertical jumps have often been considered to evaluate inter-limb asymmetries and BLD in relation to different sports-specific performances [7][8][9][10][11][12]. The mechanisms that have been hypothesized to underlie the BLD include neural mechanisms such as interhemispheric inhibition [4], and mechanics, since during bilateral jumps the muscles shorten at a higher speed, resulting in a lower force output and less joint work per leg [13]. ...
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Strength and power asymmetries have been observed in different sports, including soccer. Such asymmetries, as well as the bilateral deficit (BLD), can be assessed during different tasks, static or dynamic, and with different methods and devices, in order to detect the possible different aspects, as well as the association with physical performance and injuries. The aim of this study was to investigate the association between muscle asymmetries and BLD during a countermovement jump (CMJ), and tensiomyography (TMG) parameters and asymmetries, in the lower limbs of male soccer players. A total of 23 male soccer players (18 ± 4 years) were recruited. Bilateral and unilateral CMJs were performed, and peak power (W) and height (cm) were obtained. TMG was performed on different muscles of the lower limbs, and lateral and functional symmetries were obtained. Playing position and history of injuries were collected. CMJ inter-limb symmetry was found to significantly correlate with biceps femoris (r = 0.574, p = 0.004) and soleus (r = 0.437, p = 0.037) lateral symmetry. Players in central roles presented significantly worse functional symmetry scores of the knee than defense players (−17.5%, 95% CI −31.2–−3.9; p = 0.10). Participants reporting a history of injury at the ankle were characterized by significantly lower functional symmetry in both the dominant (43%, 39.5–48.0 vs. 74.5%, 46.5–89.3, p = 0.019) and non-dominant (45%, 42.5–46.0 vs. 81.0%, 45.8–90.3, p = 0.024) ankle. Findings from this preliminary study suggest an association between lower-limb muscle asymmetries during a dynamic task, such as jumping, and muscle contractile properties evaluated with TMG; moreover, functional asymmetries may be present after ankle injuries. Future studies in larger samples should evaluate the presence of such asymmetries as predictors or characteristics of different muscular and joint injuries.
... Muitos estudos envolvendo idosos fazem uso do teste de repetição máxima, conhecido como teste de 1 RM, para prescrição da intensidade de treino. 8,9 Trata-se de um método, não invasivo, de avaliação da força muscular executando apenas uma repetição, no qual o indivíduo deverá mobilizar a maior carga suportada sem comprometer a eficiência de movimento. 10 Contudo, embora o teste de 1 RM seja considerado padrão ouro na literatura científica, alguns pesquisadores utilizam os testes de repetições máximas (10 RM) em atletas, 11 jovens 12 e idosos. ...
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Pouco se sabe sobre o número de sessões necessárias para estabilização da carga máxima em 10 repetições em idosos não treinados. Objetivo: Verificar a reprodutibilidade do teste de 10 RM em mulheres com mais de 60 anos que não apresentam experiência prévia com treinamento de força. Método: Vinte e duas idosas (67,73 ± 5,43 anos) participantes somente da ginástica do programa Prev Quedas realizaram as sessões de teste-reteste de 10 RM em quatro exercícios: cadeira extensora, tríceps no pulley, mesa flexora e rosca direta bíceps. O programa Prev Quedas é um programa de extensão que oferece atividades físicas ao público de todas as idades de forma gratuita visando contribuir para prevenção de quedas. Foram utilizados os testes de ANOVA unidirecional com post hoc de Bonferroni, plotagem de Bland-Altman e Coeficiente de Correlação Intraclasse (CCI) com intervalo de confiança de 95%. Resultados: Os níveis de reprodutibilidade foram excelentes em todos os exercícios variando de 0,83 a 0,95 não havendo diferença significativa entre as sessões. A concordância entre as sessões teste-reteste foi classificada como boa para todos os exercícios. A literatura apresenta uma carência com relação à reprodutibilidade dos testes de 10 RM, principalmente para idosos. Porém, os dados de reprodutibilidade do presente estudo concordam com aqueles referentes aos testes de 1 RM aplicados em adultos jovens. Conclusão: Com base nos achados apresentados, parece haver necessidade da realização de 2 sessões de avaliação para estabilização da carga em 10 repetições máximas para idosas não treinadas.
... Regimens utilizing heavier weights and repetition schemes with higher 1RM percentages per set activate large muscle fibers, thus providing enhanced strength and hypertrophy gains [25]. Unilateral and bilateral strength training have demonstrated similar improvements in hypertrophy and muscle activation in untrained women, while unilateral training improved unilateral activation and strength gains that may be more beneficial in the setting of imbalance and avoiding falls [95]. To ensure safety, exercise regimens including compound movements and heavy intense lifts should progress from large to small muscle groups and from compound movement patterns to isolated exercises throughout the workout. ...
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There are many benefits to the addition of exercise to cancer treatment and survivorship, particularly with resistance training regimens that target hypertrophy, bone mineral density, strength, functional mobility, and body composition. These goals are best achieved through a series of individualized high-intensity compound movements that mirror functional mobility patterns and sufficiently stress the musculoskeletal system. As a result of adequate stress, the body will engage compensatory cellular mechanisms that improve the structural integrity of bones and muscles, stimulate metabolism and the immune system, optimize functional performance, and minimize mechanical injury risk. The current evidence suggests that application of the above exercise principles, practiced in a safe environment under expert observation, may offer patients with cancer an effective means of improving overall health and cancer-specific outcomes. The following article poses several important questions certified exercise specialists and physicians should consider when prescribing resistance exercise for patients with cancer.
... The difference between the two conditions defines the bilateral deficit (BLD; Henry & Smith, 1961;Samozino et al., 2014). This phenomenon has been the subject of numerous studies and has been tested under several conditions, i.e., different contraction regimes (isometric, dynamic explosive, isokinetic, isotonic; Botton et al., 2016Botton et al., , 2013Dalton et al., 2010;Howard & Enoka, 1991;Samozino et al., 2014;Vandervoort et al., 1984), different intensities (maximum vs. sub-maximum; Vandervoort et al., 1984), occurrence in upper or lower limbs (Škarabot et al., 2016) and in athletes or sedentary/moderately active people [for a review on this topic see, Škarabot et al. (2016)]. The studies reported a lack of consensus, with several factors affecting the BLD occurrence. ...
Movement velocity has been viewed as one of the bilateral deficit (BLD) determinants. This research tested the velocity effect on BLD during a half-squat exercise. The role of muscle excitation in BLD was also assessed. BLD amplitude was assessed in 12 male soccer players while performing a half-squat exercise with incremental load. During the exercise’s pushing phase, the average force and velocity were measured in bilateral and unilateral conditions to provide the bilateral index (BI) at each interpolated velocity. The vastus lateralis and medialis excitation was assessed during the exercise by calculating the surface electromyography signal root mean square (sEMGRMS). The BI for sEMGRMS (sEMG BI) was calculated. The theoretical maximum force (F0) and velocity (v0) were also determined. F0 was +43 (28)% in bilateral compared with unilateral conditions (p < 0.001), whereas v0 was similar in both conditions (p = 0.386). The BI magnitude rose with the increase in velocity from −34 (7)% at 50%v0 to −70 (17)% at 90%v0 (p 0.03-<0.001), whereas no sEMG BI occurred (p: 0.07-0.991 in both muscles). The study reported velocity-dependent changes in the BLD amplitude, with the largest BLD amplitudes occurring at the highest velocities. This behaviour could provide useful information for setting specific contraction velocities to exploit/limit the BLD amplitude as a possible training stimulus.
... In the evaluation of BLD, differences in performance characteristics between each maximal force measure produces altered outcomes, and therefore the enactment of a single decisive maximal force definition is necessary. The BLD phenomenon is considered the ability to produce the greatest force in unilateral and bilateral contractions, and therefore many studies have observed the phenomenon using absolute peak force (Aune et al., 2013;Behm et al., 2003;Botton et al., 2016;Buckthorpe et al., 2013;Howard & Enoka, 1991;Škarabot, Alfonso, et al., 2016). Characteristically, this measure is easy to interpret, but a single maximal measure may be prone to error from ancillary muscle activity, sudden postural adjustments, or instrument noise. ...
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The underlying mechanism(s) of the Bilateral Deficit (BLD) phenomenon is without consensus. Methodological inconsistencies across prior works may be an important source of equivocal results and interpretations. Based on repeatability problems with the BLD measure and maximal force definition, the presence or absence of the BLD phenomenon is altered, shifting conclusions of its mechanistic cause. Our purpose in this study was to examine methodological inconsistencies in applying the BLD measure to establish optimal methods for evaluating the underlying mechanism. Eleven healthy participants engaged in one familiarity and five test sessions, completing bilateral and unilateral elbow maximal voluntary isometric contractions. We defined maximal force by averaged and absolute peak and plateau values. BLD was evident if the bilateral index (BI), the ratio of the bilateral over summed unilateral forces, was statistically different from zero. We addressed interclass correlations (ICC), Chronbach's α, standard error of the mean, and minimal detectable change between and within sessions for all force measures and BI. We evaluated all combinations of sessions (i.e., 1-2, 3-5, 5-6) and maximal forces to establish the optimal number of sessions to achieve reliability. BLD was present for test sessions, but not for familiarization. All measures of maximal force were highly reliable between and within sessions (ICC(2,1) ≥ .895). BI was only considered significantly reliable in sessions 3-5 (p < .027), defined by absolute and average plateau forces, but reliability was still quantifiably poor (absolute: ICC(2,1) = .392; average: ICC(2,1) = .375). These results demonstrate that high force reliability within and between sessions does not translate to stable and reliable BI, potentially exposing the lack of any defined BLD mechanism.
Zusammenfassung Hintergrund Eine generalisierte Hypermobilität liegt vor, wenn die Beweglichkeit in mehreren Gelenken das übliche Maß übersteigt. Bis zu 30 % der Frauen und 10 % der Männer sind davon betroffen. Hypermobilität ist keine Pathologie, wenn sie jedoch mit Schmerzen und weiteren Symptomen einhergeht, kann sie die Gesundheit und Alltagsfunktionen beeinträchtigen. Zur physiotherapeutischen Behandlung gibt es wenige Studien, wobei Krafttraining eine mögliche Intervention sein könnte. Ziel Erfassung der Machbarkeit und des Effekts eines Krafttrainings für Frauen mit generalisierter Hypermobilität. Methode Pre-post-Studie, in der hypermobile Frauen (Beighton-Score > 5) zwischen 20 und 40 Jahren während 12 Wochen ein Krafttraining an Geräten, fokussiert auf Beine und Rücken, absolvierten. Mithilfe eines Protokolls und wöchentlicher Fragebogen wurden das Training und dadurch ausgelöste Beschwerden analysiert. Vor und nach dem Training wurde die Kraft der Knieflexoren und -extensoren sowie der Muskelquerschnitt am Oberschenkel gemessen. Die Analyse erfolgte primär deskriptiv, zusätzlich erfolgte ein Vergleich von 2 Subgruppen mittels Mann-Whitney-U und Chi2-Test. Ergebnisse 46 Teilnehmerinnen (26,3 ± 4,3 Jahre) absolvierten das Training. 6 davon brachen die Studie vorzeitig ab, davon eine wegen Rückenschmerzen aufgrund einer Diskushernie. 72,5 % der verbleibenden 40 Teilnehmerinnen absolvierten 20 oder mehr Trainings. In 34 % der Trainingswochen wurden geringe Beschwerden angegeben, mehrheitlich an Knie und Rücken. Der Einsatz der verwendeten Gewichte war oft tief, so wurde auf der Legpress mit durchschnittlich 44,8 % des Körpergewichts begonnen, nach 12 Wochen lag das Trainingsgewicht im Mittel bei 52,2 kg, was 85,7 % des Körpergewichts entspricht. Bei der Kraft und beim Muskelquerschnitt wurden keine signifikanten Verbesserungen erreicht, wobei bis zu 17 Teilnehmerinnen (42,5 %) eine Verbesserung von mehr als 10 % erreichten. Schlussfolgerung Das Krafttraining war für die meisten Teilnehmerinnen machbar und gut verträglich. Das mehrheitlich selbstgesteuerte Training war zu wenig intensiv, um eindeutige Auswirkungen auf Kraft oder Muskelmasse zu erreichen, obwohl einzelne Teilnehmerinnen durchaus davon profitierten. In weiteren Studien sollten individuellere und enger begleitete Trainingsprogramme untersucht werden.
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Whole-body vibration (WBV) has been used to improve jumping ability, muscle strength, power, and performance in various sports. Bilateral deficit (BLD) is defined as the difference in the magnitude of the maximum force during single or double support. The present study investigated the effect of unilateral and bilateral whole-body vibration (WBV) exercise on jumping ability, asymmetry and BLD on former artistic gymnasts. Twenty-eight former artistic gymnasts volunteered to participate in this study. Participants performed 4 experimental protocols on nonconsecutive days in a random order. Each protocol included a 3-min-warm-up running on the treadmill at 2.22 m.s -1, followed by a 2-min rest. The intervention protocols were: a) WBV with feet [bipedal] (WBVB), b) WBV with single foot [unilateral] (WBVU), c) WBVB with the device turn-off (NWBVB), and d) WBVU with the device turn-off (NWBVU). The dependent variables were the squat jump (SJ) and counter movement jump (CMJ) with both feet (bilateral) and with single leg (unilateral). Results showed a significant interaction effect between the condition and time on SJ on both condition (bilateral and unilateral) and CMJ, whereas significant main effect was found for the condition and for time on SJ. Conclusively, the WBV unilateral condition improves significantly lower limbs symmetry during SJ performance. Further, bilateral WBV (WBV B) was the most effective condition on bilateral and unilateral SJ and CMJ performance.
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Background Lower limb muscle strength symmetry has been suggested as an essential criterion for the safe return to sports after anterior cruciate ligament (ACL) reconstruction. Limited evidence is available regarding the most effective intervention to achieve symmetry after reconstruction with contralateral bone–patellar tendon–bone (BPTB) graft. Purpose To verify whether unilateral isotonic resistance exercise is more effective than bilateral exercise for obtaining postoperative functional and muscular strength symmetry between the donor limb and reconstructed limb for patients who received BPTB graft. Study Design Randomized controlled trial; Level of evidence, 1. Methods A total of 88 patients were randomly divided into a control group (n = 44) and an intervention group (n = 44). All participants performed an 8-week exercise program starting at the beginning of the fourth postoperative month and were evaluated before and after the program. The control group performed bilateral exercises, and the intervention group performed unilateral exercises for the donor limb only (the limb with the greatest disability). The primary outcome was muscle strength (peak torque and hamstrings to quadriceps [H:Q] ratio), and the secondary outcomes were range of motion (ROM; goniometry), KT-1000 arthrometer side-to-side difference in anteroposterior knee laxity, and objective (single-leg hop test) and subjective (Lysholm score) functionality. Results Both groups improved significantly from before to after the exercise program. The improvements were significantly greater in the intervention group regarding peak torque, H:Q ratio, flexion ROM, single-leg hop test, and Lysholm score in the donor limb ( P < .001 for all), and the improvements were significantly greater in the control group regarding peak torque and single-leg hop test in the reconstructed limb ( P < .001 for both). Comparison between the groups showed significantly increased symmetry regarding peak torque, H:Q ratio, and single-leg hop test in the intervention group compared with the control group ( P < .001), with large effect sizes (>0.80) except for the H:Q ratio. Conclusion Although postoperative, bilateral, isotonic resistance exercise provided better strength gains to the reconstructed limb, unilateral exercise was more effective in obtaining functional and muscle strength between-limb symmetry in patients who underwent ACL reconstruction with contralateral BPTB graft. Registration Brazilian Registry of Clinical Trials (number RBR-22rnjh).
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To assess effects of a short-term strength training (ST) program on muscle quality (MQ) and functional capacity, 36 sedentary elderly women (age = 66.0 ± 8 year, height = 159.1 ± 9.2 cm, body mass = 68.3 ± 12.1 kg, body fat = 37.0 ± 4.2 %) were randomly divided into an experimental group (EG; n = 19) or a control group (CG; n = 17). The EG performed two to three sets of 12-15 repeats of leg press, knee extension, and knee flexion exercises, 2 days/week for 6 weeks. Before and after training, lower body one repetition maximum (1RM), functional performance tests, quadriceps femoris muscle thickness (MT), and muscle quality (MQ) (1RM and quadriceps MT quotient) were assessed. After training, only the EG showed significant improvements in 1RM (p < 0.05), 30-s sit-to-stand (p < 0.001), and 8 foot up-and-go (p < 0.001). In addition, only in the EG, significant increases in all quadriceps femoris MT measurements (vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris) (p ≤ 0.05), and MQ (p < 0.001) were demonstrated. No changes were observed in the CG. Furthermore, there were significant associations between individual changes in MQ and corresponding changes in 30-s sit-to-stand (r = 0.62, p < 0.001), and 8 foot up-and-go (r = -0.71, p < 0.001). In conclusion, a ST program of only 6 weeks was sufficient to enhance MQ of the knee extensors in elderly women, which resulted in beneficial changes in functional capacity.
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The aim of this study was to compare the effects of low- and high-volume strength training on strength, muscle activation and muscle thickness (MT) of the lower- and upper-body, and on muscle quality (MQ) of the lower-body in older women. Twenty apparently healthy elderly women were randomly assigned into two groups: low-volume (LV, n=11) and high-volume (HV, n=9). The LV group performed one-set of each exercise, while the HV group performed three-sets of each exercise, twice weekly for 13 weeks. MQ was measured by echo intensity obtained by ultrasonography (MQEI), strength per unit of muscle mass (MQST), and strength per unit of muscle mass adjusted with an allometric scale (MQAS). Following training, there was a significant increase (p≤0.001) in knee extension 1-RM (31.8 ± 20.5% for LV and 38.3 ± 7.3% for HV) and in elbow flexion 1-RM (25.1 ± 9.5% for LV and 26.6 ± 8.9% for HV) and in isometric maximal strength of the lower-body (p≤0.05) and upper-body (p≤0.001), with no difference between groups. The maximal electromyographic activation for both groups increased significantly (p≤0.05) in the vastus medialis and biceps brachii, with no difference between groups. All MT measurements of the lower- and upper-body increased similarly in both groups (p≤0.001). Similar improvements were also observed in MQEI (p≤0.01), MQST, and MQAS (p≤0.001) for both groups. These results demonstrate that low- and high-volume strength training promote similar increases in neuromuscular adaptations of the lower- and upper-body, and in MQ of the lower-body in elderly women.
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The aim of this work was to study the effect of training volume on activation of satellite cells. Healthy untrained men were randomly assigned into two groups. The 3L-1UB group (n = 10) performed three-set leg exercises and single-set upper body exercises, and the 1L-3UB group (n = 11) performed single-set leg exercises and three-set upper body exercises. Both groups performed three sessions (80-90 min) per week for 11 weeks. Biopsies were taken from m. vastus lateralis and m. trapezius. The number of satellite cells, satellite cells positive for myogenin and MyoD, and the number of myonuclei were counted. Homogenized muscle was analyzed for myogenin and MyoD, and extracted ribonucleic acid (RNA) was monitored for selected growth factor transcripts. Knee extensor strength increased more in the 3L-1UB group than in the 1L-3UB group (48 ± 4% vs 29 ± 4%), whereas the strength gain in shoulder press was similar in both training groups. The number of satellite cells in m. vastus lateralis increased more in the 3L-1UB group than in the 1L-3UB group. The number of myonuclei increased similarly in both groups. The messenger RNA expression of growth factors peaked after 2 weeks of training. In conclusion, increasing training volume enhanced satellite cell numbers in the leg muscle, but not in the upper body muscle.
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The purpose of this investigation was to compare partial range-of-motion vs. full range-of-motion upper-body resistance training on strength and muscle thickness (MT) in young men. Volunteers were randomly assigned to 3 groups: (a) full range of motion (FULL; n = 15), (b) partial range of motion (PART; n = 15), or (c) control (CON; n = 10). The subjects trained 2 d · wk(-1) for 10 weeks in a periodized program. Primary outcome measures included elbow flexion maximal strength measured by 1 repetition maximum (1RM) and elbow flexors MT measured by ultrasound. The results indicated that elbow flexion 1RM significantly increased (p < 0.05) for the FULL (25.7 ± 9.6%) and PART groups (16.0 ± 6.7%) but not for the CON group (1.7 ± 5.5%). Also, FULL 1RM strength was significantly greater than the PART 1RM after the training period. Average elbow flexor MT significantly increased for both training groups (9.65 ± 4.4% for FULL and 7.83 ± 4.9 for PART). These data suggest that muscle strength and MT can be improved with both FULL and PART resistance training, but FULL may lead to greater strength gains.
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Aging diminishes the ability to run fast, but the specific mechanisms responsible for this deterioration remain largely unknown. In the present study, we investigated the age-related decline in sprint running ability through a cross-sectional examination of biomechanical and skeletal muscle characteristics in 77 competitive male sprinters aged 17-82 yr. Ground reaction force (GRF) and kinematic stride cycle parameters were measured during the maximum-velocity phase using a 9.4-m-long force platform. Knee extensor (KE) and ankle plantar flexor (PF) structural characteristics were investigated using ultrasonography and muscle biopsies (vastus lateralis). Force production characteristics of leg extensor muscles were determined by dynamic and isometric contractions. The main findings were as follows: 1) the progressive age-related decline in maximum running velocity (Vmax) was mainly related to a reduction in stride length (Lstr) and an increase in ground contact time (tc), whereas stride frequency showed a minor decline and swing time remained unaffected; 2) the magnitude of average braking and push-off resultant GRFs declined with age and associated with Lstr, tc, and Vmax; 3) there was an age-related decline in muscle thickness, Type II fiber area and maximal and rapid force-generating capacity of the lower limb muscles; and 4) muscle thickness (KE + PF) was a significant predictor of braking GRF, whereas the countermovement jump height explained most of the variance in push-off GRF in stepwise regression analysis. Age-related slowing of maximum running speed was characterized by a decline in stride length and an increase in contact time along with a lower magnitude of GRFs. The sprint-trained athletes demonstrated an age-related selective muscular atrophy and reduced force capacity that contributed to the deterioration in sprint running ability with age.
The issue of whether there is a difference in the amount of force produced from a simultaneous two-limb maximal contraction compared to the sum of individual one-limb contractions has received considerable debate in the literature. A bilateral deficit (BLD) is when the resultant force from bilateral homonymous limb contractions is less than the summed force of individual limb contractions. Determining whether differences exist between one-and two-limb movements may provide insight into complex neuromuscular control patterns. Many dynamic two-limb studies report a BLD, whereas isometric studies are more numerous and controversial. It is important to categorize the movements studied in order to establish consistency. This paper purports that the BLD is an unstable phenomenon, and its presence should be considered in the context of the movement studied. Most likely, this phenomenon is dependent upon some minor deviation in descending drive between the cortical level and peripheral motor neuron.
The greater torque generation capacity of muscles when contracted alone than in combination with contralateral muscles, characterizes the bilateral limb deficit (BLD) phenomenon. Few studies have explored the BLD in dynamic movements, because isometric actions are considered ideal for evaluating strength. Therefore, the aim of this study was to compare BLD between isometric and concentric actions of the knee extensors. Eleven healthy young men (age = 20.6 ± 1 yrs; weight = 71.4 ± 6.4 kg; height = 174.4 ± 7 cm) volunteered to participate. Initially, subjects visited the laboratory for familiarization with the test protocols. On two subsequent randomized days they performed a test protocol with either a unilateral (right and left limbs) or bilateral condition, with 48 h rest between. The test protocol was composed of five isokinetic concentric actions of the knee extensors at 60 • /s and three isometric actions at a 60 • angle of knee flexion. The greatest peak torque of the two conditions was used for analyses. Both muscle actions demonstrated greater values unilaterally (p < 0.05) than bilaterally and BLD values were not significantly different between them (p > 0.05). Therefore, if muscle torque production is greater unilaterally, athletes and coaches may utilize unilateral exercises to increase training loads.
Maximal voluntary strength of simultaneous bilateral exertion has been shown to be small compared to the sum of the unilateral exertions. Three experiments were conducted to determine the effects of bilateral and unilateral resistance training on this bilateral deficit and to compare these in hands, arms, and legs. In each experiment, the subjects were divided into three groups: unilateral training group, bilateral training group, and control group. The subjects of the training group performed maximal isometric handgrip training in experiment I, and maximal isokinetic arm and leg extension training in experiments II and III. In each experiment, the subjects of the training group continued one of these resistance training exercises three times a week, for 6 weeks. The increase in handgrip strength of the bilateral training group produced in the bilateral condition [5.1 (SEM 2.4)%, after 3 weeks, 6.4 (SEM 2.3) %, after 6 weeks] was significantly greater compared with the control group [-1.1 (SEM 1.0) %, after 3 weeks, -1.5 (SEM 1.1) %, after 6 weeks. The increase in leg extension power of the bilateral training group produced in the bilateral condition [16.1 (SEM 9.6) %, after 3 weeks, 24.1 (SEM 7.4) %, after 6 weeks] was significantly greater compared with the unilateral training group [-5.0 (SEM 3.4) %, after 3 weeks, -3.4 (SEM 4.2) %, after 6 weeks] and the control group [-4.3 (SEM 2.5) %, after 3 weeks, 1.5 (SEM 5.5) %, after 6 weeks]. The increase in handgrip strength of the unilateral training group produced in the unilateral condition [7.3 (SEM 1.7) %, after 3 weeks] was significantly greater compared with the control group [-0.9 (SEM 1.8) %, after 3 weeks]. The increase in arm extension power of the unilateral training group produced in the unilateral condition [7.2 (SEM 1.8) %, after 6 weeks] was significantly greater compared with the bilateral training group [-3.0 (SEM 2.3) %, after 6 weeks] and the control group [-2.1 (SEM 2.6) %, after 6 weeks]. Bilateral indexes (BI) were shifted in a positive direction by bilateral training and tended to shift in a negative direction by unilateral training. With regard to the magnitude of change in BI, there were no significant differences among handgrip, arm extension, and leg extension training. It is suggested that there is lateral specificity in resistance training and that there is no difference among body parts in the modification of bilateral deficit by lateral training.
This study investigated the effects of different intra-session exercise sequences in the cardiovascular and neuromuscular adaptations induced by concurrent training in elderly. Twenty-six healthy elderly men (64.7±4.1years), were randomly placed into two concurrent training groups: strength training prior to (SE, n=13) or after (ES, n=13) endurance training. Subjects trained strength and endurance training 3 times per week performing both exercise types in the same training session. The peak oxygen uptake (VO(2peak)), maximum aerobic workload (W(máx)), absolute (VT(1) and VT(2)) and relative (VT(1)% and VT(2)%) ventilatory thresholds, as well as workloads at VT(1) and VT(2) (W(VT1) and W(VT2)) were evaluated during a maximal incremental test on a cycle ergometer before and after the training. In addition, muscle quality (MQ) was evaluated by the quotient between maximal dynamic strength (one repetition maximum test) of the knee extensors and the quadriceps femoris muscle thickness determined by ultrasonography. There were no modifications after training in the VT(1), VT(2), VT(1)%, and VT(2)%. There was significant increase in the W(VT1) only in SE (P<0.05), as well as significant increase in the W(VT2) in both groups (P<0.001). There was significant increase in the VO(2peak), with both groups showing increases (P<0.001), with no difference between groups; as well significant increase in the W(máx) (P<0.001) with no difference between SE and ES. The force per unit of muscle mass of knee extensors increased in both groups (P<0.001), but the increase was significantly higher in SE than in ES (27.5±12.7 vs. 15.2±10.3%, P<0.02). Hence, the intra-session exercise sequence had no influence in the maximal endurance power adaptations to concurrent training, but had influence in the magnitude of the muscle quality enhancements.