Content uploaded by Sumiaki Maeo
Author content
All content in this area was uploaded by Sumiaki Maeo on Mar 04, 2015
Content may be subject to copyright.
©Journal of Sports Science and Medicine (2013) 12, 467-474
http://www.jssm.org
Received: 04 April 2013 / Accepted: 07 May 2013 / Available (online): 20 June 2013 / Published: 01 September 2013
Trunk Muscle Activities during Abdominal Bracing: Comparison among
Muscles and Exercises
Sumiaki Maeo 1, 2, Takumi Takahashi 1, Yohei Takai 1 and Hiroaki Kanehisa 1
1 National Institute of Fitness and Sports in Kanoya, Kagoshima, Japan
2 Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan
Abstract
Abdominal bracing is often adopted in fitness and sports condi-
tioning programs. However, there is little information on how
muscular activities during the task differ among the muscle
groups located in the trunk and from those during other trunk
exercises. The present study aimed to quantify muscular activity
levels during abdominal bracing with respect to muscle- and
exercise-related differences. Ten healthy young adult men per-
formed five static (abdominal bracing, abdominal hollowing,
prone, side, and supine plank) and five dynamic (V-sits, curl-
ups, sit-ups, and back extensions on the floor and on a bench)
exercises. Surface electromyogram (EMG) activities of the
rectus abdominis (RA), external oblique (EO), internal oblique
(IO), and erector spinae (ES) muscles were recorded in each of
the exercises. The EMG data were normalized to those obtained
during maximal voluntary contraction of each muscle (%
EMGmax). The % EMGmax value during abdominal bracing
was significantly higher in IO (60%) than in the other muscles
(RA: 18%, EO: 27%, ES: 19%). The % EMGmax values for
RA, EO, and ES were significantly lower in the abdominal
bracing than in some of the other exercises such as V-sits and
sit-ups for RA and EO and back extensions for ES muscle.
However, the % EMGmax value for IO during the abdominal
bracing was significantly higher than those in most of the other
exercises including dynamic ones such as curl-ups and sit-ups.
These results suggest that abdominal bracing is one of the most
effective techniques for inducing a higher activation in deep
abdominal muscles, such as IO muscle, even compared to dy-
namic exercises involving trunk flexion/extension movements.
Key words: Static and dynamic exercises, electromyogram,
voluntary co-contraction, muscle- and exercise-related
differences.
Introduction
Trunk stability training for enhanced health, rehabilita-
tion, and athletic performance has received renewed em-
phasis (Behm et al., 2010). In the past, these types of
exercises were performed only by individuals with low
back problems in physical therapy clinics (McGill, 2001).
In recent years, however, fitness professionals have in-
creasingly emphasized trunk stability exercises in sports
conditioning programs because it is considered that
greater trunk stability may benefit sports performance by
providing a foundation for greater force production in the
upper and lower extremities (Willardson, 2007). Trunk
muscles function in transferring torques and angular mo-
mentum during the performance of integrated kinetic
chain activities, such as throwing or kicking (Kibler et al.,
2006; Willardson, 2007). Weakness in the trunk muscula-
ture may interrupt the transfer of torques and angular
momentum, resulting in decreased performance (Behm et
al., 2010). Kibler et al. (2006) summarized trunk stability
in a sporting environment as “the ability to control the
position and motion of the trunk over the pelvis to allow
optimum production, transfer, and control of force and
motion to the terminal segment in integrated athletic
activities”. Thus, specific training practices aimed at tar-
geting the trunk stabilizing muscles are an important
consideration not only for activities of daily living or
rehabilitation of low back pain, but also for athletic per-
formance (Behm et al., 2010).
Monfort-Panego et al. (2009) suggested that ab-
dominal co-contraction (bracing) is one of the most effec-
tive exercise techniques for trunk stabilization training.
In fact, abdominal bracing has been shown to increase the
stiffness of the spine, promoting stability in the vertebral
segments (Vera-Garcia et al., 2006; 2007), and is often
recommended and/or included in rehabilitation and/or
fitness programs (Marshall et al., 2011; Monfort-Panego
et al., 2009). Some studies (Allison et al., 1998; Bressel et
al., 2011; 2012; Vera-Garcia et al., 2010) have measured
the electromyogram (EMG) activities of trunk muscles
during abdominal bracing exercise together with some
other trunk exercises. Bressel et al. (2012), who examined
EMG activities during various trunk exercises (e.g., ab-
dominal hollowing, anteroposterior/mediolateral pelvic
tilts, and swiss ball exercises) performed underwater,
reported that abdominal bracing was one of the most
effective exercises to maximize the global trunk muscle
activities. In addition, Vera-Garcia et al. (2007) compared
the effects of abdominal bracing and abdominal hollow-
ing maneuvers on the control of spine motion and stability
against sudden trunk perturbations in healthy males. They
found that abdominal bracing was more effective than
abdominal hollowing for stabilizing the spine against
posterior and rapid loading.
The findings cited above support the assertion that
abdominal bracing is an effective technique for improving
spine stability. What seems to be lacking, however, is
substantial information on how the activity levels of the
muscle groups located in the trunk differ during abdomi-
nal bracing and other trunk exercises such as prone plank,
curl-ups, or back extensions. As cited above, EMG activi-
ties during abdominal bracing have been already reported
for some of the trunk muscles, such as the rectus ab-
dominis, external oblique, internal oblique, transversus
abdominis, and erector spinae muscles (Allison et al.,
Research article
Electromyographic activity during abdominal bracing
468
1998; Bressel et al., 2011; Urquhart et al., 2005; Vera-
Garcia et al., 2010). However, muscle-related differences
in the activation level during abdominal bracing have not
been thoroughly discussed. For example, some studies
reported muscle-related differences in EMG activities
during abdominal bracing (Allison et al., 1998; Urquhart
et al., 2005). In the prior studies, however, the EMG ac-
tivities were not normalized to the maximum value
(Allison et al., 1998), or the task was performed with mild
effort (Urquhart et al., 2005). Vera-Garcia et al. (2010)
and Bressel et al. (2011) expressed each of the EMG
activities of the trunk muscles during abdominal bracing
as the value relative to that during the maximal voluntary
contraction (MVC) task for the corresponding muscle.
However, they focused on the difference in the activation
level of each muscle between the abdominal bracing and
other MVC tasks (Vera-Garcia et al., 2010), or between
terrestrial and underwater conditions (Bressel et al.,
2011). Thus, muscle-related differences in muscular ac-
tivities during abdominal bracing are not well established.
Furthermore, the exercises measured with and compared
to abdominal bracing in the previous study (Bressel et al.,
2012) were therapeutic aquatic exercises designed for
patients with lower back pain. Trunk exercises, which are
conducted in not only rehabilitative but also athletic situa-
tions, usually include much more dynamic exercises, such
as V-sits and curl-ups. To clarify the efficacy of abdomi-
nal bracing as a training modality for improving the func-
tion of trunk muscles, the magnitude of muscular activi-
ties during abdominal bracing should be examined
through comparison with those during other trunk exer-
cises including dynamic tasks.
In this study, we aimed to clarify the characteristics
of trunk muscle activities during abdominal bracing with
regard to muscle- and exercise-related differences. For
comparison of exercises, 5 static exercises, which are
often prescribed in rehabilitation programs, and 5 dy-
namic exercises, which are usually conducted for
strength-training purposes, were chosen. The results of
this study may be useful information for clinicians and
trainers who prescribe trunk exercises including abdomi-
nal bracing.
Methods
Subjects
This study was approved by the Ethics Committee of the
National Institute of Fitness and Sports in Kanoya and
was consistent with institutional ethical requirements for
human experimentation in accordance with the Declara-
tion of Helsinki. Prior to the measurement session, candi-
dates who volunteered to participate in this study visited
the laboratory and were fully informed about the proce-
dures and possible risks involved as well as the purpose of
the study. After their written informed consent was ob-
tained, they performed all types of task involved in the
study to ensure that they had no difficulties or discomfort
in any procedures, as well as to familiarize themselves
with the procedures. The subjects who could not perform
any of the tasks properly were excluded from the study.
Ten healthy young adult men participated in this study.
The means and standard deviations (SDs) of their age,
body height, and body mass were 21.2 ± 1.5 yr, 1.70 ±
0.05 m, and 65.6 ± 4.8 kg, respectively. All subjects were
college students majoring in physical education and were
habitually active, but none had been currently involved in
any type of regular exercise program (≥ 30 min·day-1, ≥ 2
days·week-1). In addition, none had experienced muscu-
loskeletal injury or pain in the previous 12 months.
Within 72 h of the familiarization session mentioned
above, the subjects attended the measurement session.
Procedure
In the measurement session, isometric MVCs for each
muscle were performed for the purpose of normalization.
Force during isometric MVC was measured using a cus-
tom-made force-measurement device with ten-
sion/compression load cells (LUR-A-SA1; Kyowa, Ja-
pan). The force signals obtained via a 16-bit A/D con-
verter (Power Lab 16s; ADInstruments, Australia) were
recorded on a personal computer at a sampling frequency
of 2,000 Hz. In the MVC tasks, as well as subsequent
trunk exercise tasks, the surface EMG activities of the
trunk muscles were recorded. The repeatability of force
measurements during MVC tests was assessed on 2 sepa-
rate days in a pilot study with 5 young adult men. There
was no significant difference between the MVC force
values of the two measurements in each task. The intra-
class correlation coefficients (ICC) and coefficient of
variations (CV) for MVC force were 0.896 and 8.1% for
trunk flexion, 0.841 and 11.2% for trunk lateral flexion,
and 0.912 and 7.6% for trunk extension. Prior to maximal
test, the subjects were asked to exert submaximal force
isometrically at each of the test positions to familiarize
themselves with the test procedure. After warming-up and
a rest period of 3 min, the subjects were encouraged to
exert maximal force (progressively increasing the force
taking about 5 s) two times with at least 3 min between
trials to exclude the influence of fatigue. Subsequent trials
were performed if the difference in the peak forces of the
two MVCs was greater than 5%. The trial with the highest
peak force was selected for analysis. The positions and
tasks for MVC were adopted on the basis of the result of
Vera-Garcia et al. (2010), and each of the MVC tasks was
performed as follows (Figure 1).
Trunk flexion: The subjects lay supine on a stable
bench seat with knees flexed, and feet flat on the seat and
fixed with a strap. By the use of a custom-made belt
linked with a chain, which covered the upper torso and
was securely connected to the load cells, the subjects were
held tightly in position. The subjects then performed
maximal isometric trunk flexion in the sagittal plane.
Trunk lateral flexion: The subjects lay on their left
side on the seat with the legs extended, the hips and feet
fixed on the seat with a strap, and the upper torso con-
nected to the load cells using the belt. The subjects then
performed maximal isometric lateral flexion (bending
right) in the frontal plane.
Trunk extension: The subjects lay prone on the
bench with the legs extended, the hips and feet fixed on
the seat with a strap, and the upper trunk connected to the
load cells using the belt. The subjects then performed
Maeo et al.
469
Figure 1. Pictures of MVC tasks; (a) trunk flexion, (b) trunk lateral flexion, and (c) trunk extension.
maximal isometric trunk extension in the sagittal plane.
After the completion of MVC tasks, the subjects
performed 5 static (abdominal bracing, abdominal hol-
lowing, prone, lateral, and supine plank) and 5 dynamic
(V-sits, curl-ups, sit-ups, and back extensions on the floor
and on a bench) exercises. During the exercise tasks, the
hip joint angles were measured using an electrogoniome-
ter (SG110; Biometrics, UK) and recorded together with
the EMG activities and stored on a personal computer.
After the subjects were instructed and familiarized with
the tasks, a measurement trial for each task was per-
formed with at least 2-min rest interval between each trial.
Subsequent trials in each task were performed until both
the subject and the researcher considered that the task
performed was successful. Static exercises were main-
tained for 10 s and dynamic exercises were repeated 10
times (1 s for each of raising and lowering phases), and
each exercise was performed as follows.
Abdominal bracing: In a standing neutral-spine po-
sition with the feet shoulder-width apart, participants were
instructed to activate the abdominals maximally without
hollowing the lower abdomen.
Abdominal hollowing: In the same position as for
the abdominal bracing task, participants were instructed to
draw the navel maximally in toward the spine.
Prone plank: In a prone position on the floor with
the elbow angle at 90 deg (180 = full extension) and the
forearms placed underneath the chest, pelvis raised off the
floor and their body weight distributed on the forearms
and toes, the subjects were instructed to maintain a flat
position.
Lateral plank: While lying on the right side on the
floor with the right elbow bent at 90 deg and positioned
directly under the shoulder, pelvis raised off the floor and
their body weight distributed on the forearms and the
right side of the foot, the subjects were instructed to main-
tain the position.
Supine plank: In a supine position on the floor with
the elbow angle at 90 deg and the forearms placed under-
neath the back, pelvis rose off the floor and their body
weight distributed on the forearms and heels, participants
were instructed to maintain the position.
V-sits: In a supine position on the floor with the
arms extended over the head and the legs extended, sub-
jects were instructed to lift the legs up to a 45 deg angle
and extend the arms up toward the ankle.
Curl-ups: In a supine position on the floor with the
hands behind the head, the knees flexed at 90 deg, and the
feet flat on the floor, the subjects were instructed to curl
the upper torso up to a 45 deg angle toward the knees.
Sit-ups: In the same position as for the curl-up task,
the subjects were instructed to raise the upper torso up to
a 45 deg without the curling-up movement.
Back extensions on the floor: In a prone position on
the floor with the hands behind the head and the legs
extended and supported by a researcher, subjects were
instructed to raise the upper torso up to a 30 deg angle.
Back extensions on a bench: In a prone position on
a bench, with the upper torso placed over the end of the
bench and bent down vertically to the floor, hands behind
the head, and the legs extended and supported by a re-
searcher, the subjects were instructed to raise the torso
straight up to a 180 deg angle (parallel to the floor).
EMG measurements and analysis
In the isometric MVC and trunk exercise tasks, the sur-
face EMG activities of rectus abdominis (RA), external
oblique (EO), internal oblique (IO), and erector spinae
(ES) muscles of the right side were measured by a bipolar
configuration using a portable EMG recording apparatus
(ME6000T16; MEGA Electronics, Finland). The elec-
trode locations described by Vera-Garcia et al. (2007)
were followed and a B-mode ultrasound apparatus (Pro-
sound 2; Aloka, Japan) was used for positioning the elec-
trodes over muscles. Ag-AgCl electrodes of 15 mm di-
ameter (N-00-S Blue sensor; Ambu, Denmark) were at-
tached over the bellies of the muscles with an interelec-
trode distance of 20 mm after the skin surface was
shaved, rubbed with sandpaper, and cleaned with alcohol.
Another electrode for each muscle was attached and func-
tioned as a ground electrode as well as a preamplifier. The
EMG signals were 412-fold-amplified through the pream-
plifier, A/D-converted through a band-pass-filter (8-500
Hz/3 dB) at a sampling frequency of 2,000 Hz, and stored
on a personal computer together with the hip joint angle
data for later analysis. From EMG data, the root-mean-
square (RMS) amplitude of EMG for each muscle was
calculated using data analysis software (Chart version 7;
ADInstruments, Australia). In the MVC task, the peak
amplitude of EMG (EMGmax) in each muscle was de-
termined over a 500-ms window centered with the time at
which peak torque was attained. For each of the RA, EO,
and IO muscles, higher EMG amplitude obtained during
either trunk flexion or trunk lateral flexion was adopted as
EMGmax, and trunk extension was used for ES muscle.
The EMGs of each muscle during trunk exercise
Electromyographic activity during abdominal bracing
470
Erector spinae
Internal oblique
External oblique
Rectus abdominis
0 20406080100
% EMGmax
*
*
*
Figure 2. The % EMGmax values in each muscle during abdominal bracing.
Values are means ± SDs. * More activity than other muscles (p < 0.05).
tasks are expressed as the value relative to its maximum
(% EMGmax). EMGs during static exercises were ana-
lyzed in an 8-s window following the first 1 s after steady
contractions were achieved. EMGs during dynamic exer-
cises were analyzed for those during the 3rd – 7
th repeti-
tions based on the hip joint angle data and averaged over
the 5 repetitions. The repeatability of % EMGmax meas-
urements during the prescribed tasks was assessed on 2
separate days in a pilot study with 5 young adult men. In
each of the prescribed tasks, there was no significant
difference between the % EMGmax values of the two
measurements for each muscle tested. The mean values of
ICCs and CVs for % EMGmax values during the trunk
exercises were 0.821 and 10.1%, respectively, for RA,
0.861 and 9.2%, respectively, for EO, 0.792 and 14.7%,
respectively, for IO, and 0.833 and 9.7%, respectively, for
ES.
Statistical analysis
Descriptive data are shown as means ± SDs. A one-way
ANOVA and Bonferroni post hoc test was used to test the
differences in the % EMGmax values among the muscles
during abdominal bracing task. A two-way ANOVA
(muscle × exercise) was used to test the effects of muscle
and exercise and their interaction on % EMGmax value.
When a significant interaction was found, a one-way
ANOVA and Dunnett’s post hoc test was used to test
differences in the % EMGmax values during exercises
compared with abdominal bracing for each of the mus-
cles. In addition, effect size (Cohen’s d) was calculated to
express the magnitude of the difference between the two
means of % EMGmax. The threshold level values were <
0.20 (trivial), 0.20 – 0.49 (small), 0.50 – 0.79 (medium),
and ≥ 0.80 (large) (Faul et al., 2007). Statistical signifi-
cance was set at p < 0.05. All data were analyzed using
SPSS software (SPSS statistics 20; IBM, Japan).
Results
The % EMGmax values in each muscle during the ab-
dominal bracing were 18% in RA, 27% in EO, 60% in IO,
and 19% in ES, with a significantly higher value in IO
than in the other muscles (p < 0.05, Cohen’s d = 1.10 –
1.50) (Figure 2).
In the comparison among the exercises, there was a
significant interaction between muscle and exercise for %
EMGmax values. The % EMGmax values for RA, EO,
and ES were significantly lower in the abdominal bracing
than in some of the other exercises such as V-sits and sit-
ups for RA and EO and back extensions for ES muscle (p
< 0.05, Cohen’s d = 0.80 – 3.80) (Figures 3, 4, 6).
However, the % EMGmax value for IO during the
abdominal bracing was significantly higher than those in
most of the other exercises including dynamic ones such
Back extensions on a bench
Back extensions on the floor
Sit-ups
Curl-ups
V-sits
Supine plank
Side plank
Prone plank
Abdominal hollowing
Abdominal bracing
0 20406080100
% EMGmax
Rectus abdominis
#
#
#
#
$
$
$
Figure 3. The % EMGmax values for rectus abdominis (RA) muscle during exercises.
Values are means ± SDs. # More and $ less activity than abdominal bracing (p < 0.05).
Maeo et al.
471
External oblique
Back extensions on a bench
Back extensions on the floo
r
Sit-ups
Curl-ups
V-sits
Supine plank
Side plank
Prone plank
Abdominal hollowing
Abdominal bracing
0 20406080100
% EMGmax
#
#
$
$
$
Figure 4. The % EMGmax values for external oblique (EO) muscle during exercises.
Values are means ± SDs. # More and $ less activity than abdominal bracing (p < 0.05).
as curl-ups and sit-ups (p < 0.05, Cohen’s d = 0.79 – 1.69)
(Figure 5).
Discussion
The main findings of the study were that 1) the %
EMGmax value during abdominal bracing was signifi-
cantly higher in IO than in the other muscles, and 2) while
the % EMGmax values for RA, EO, and ES were signifi-
cantly lower in the abdominal bracing than in some of the
other exercises, the % EMGmax value for IO during the
abdominal bracing was significantly higher than those in
most of the other exercises including the dynamic ones.
These results indicate that abdominal bracing is one of the
most effective techniques for inducing a higher activation
in IO muscle, even compared to dynamic exercises in-
volving trunk flexion/extension movements.
It has been suggested that IO muscle plays a large
role in creating abdominal bracing maneuvers (Vera-
Garcia et al., 2006; 2007). In fact, Vera-Garcia et al.
(2010) observed a higher activation of IO muscle during
abdominal bracing. The current result agrees with this and
indicates that the activation level during abdominal brac-
ing distinctly differs between IO muscle and the other
three muscles. The internal oblique muscles, together with
the transversus abdominis muscles, are considered to be
key deep abdominal muscles that contribute to the stabil-
ity of the spine during physical movements in both ath-
letic and daily events (Rasouli et al., 2011; Teyhen et al.,
2008). However, it is also suggested that all trunk muscles
play an important role in achieving spinal stability and
must work harmoniously to reach this goal (Grenier and
McGill, 2007; McGill et al., 2003). Taking these aspects
into account together with the current results, it can be
considered that abdominal bracing is a modality which
induces selectively higher activity in the deep abdominal
muscles of the trunk musculature which harmoniously
work to stabilize the spine.
The % EMGmax values in each muscle during ab-
dominal bracing were 18% in RA, 27% in EO, 60% in IO,
and 19% in ES muscles. These values are similar to those
(RA: 20 – 25%, EO: 30 – 60%, IO: 50 – 80%, ES: 10 –
40%) reported in previous studies (Bressel et al., 2011;
Vera-Garcia et al., 2010). However, as shown in the cur-
rent and previous studies (Bressel et al., 2011; Vera-
Garcia et al., 2010), it should be noted that all of the trunk
muscles cannot be fully activated under abdominal brac-
ing with maximal effort. The reason for this phenomenon
Internal oblique
Back extensions on a bench
Back extensions on the floo
r
Sit-ups
Curl-ups
V-sits
Supine plank
Side plank
Prone plank
Abdominal hollowing
Abdominal bracing
0 20406080100
% EMGmax
$
$
$
$
$
$
$
Figure 5. The % EMGmax values for internal oblique (IO) muscle during exercises.
Values are means ± SDs. $ Less activity than abdominal bracing (p < 0.05).
Electromyographic activity during abdominal bracing
472
Erector spinae
Back extensions on a bench
Back extensions on the floo
r
Sit-ups
Curl-ups
V-sits
Supine plank
Side plank
Prone plank
Abdominal hollowing
Abdominal bracing
0 20406080100
% EMGmax
$
$
$
$
#
#
#
$
Figure 6. The % EMGmax values for erector spinae (ES) muscle during exercises.
Values are means ± SDs. # More and $ less activity than abdominal bracing (p < 0.05).
is unknown. Pashler (1994) indicated that when two tasks
are performed simultaneously, the performance of each is
often impaired. This phenomenon is referred to as dual-
task interference (Pashler, 1994), and it often occurs even
when performing relatively simple tasks, especially when
the task is unfamiliar. Considering this, it seems that the
task requiring simultaneous contractions of multiple mus-
cles induces a similar phenomenon to the dual-task inter-
ference, and it might have resulted in the lower %
EMGmax values during the bracing task. Furthermore, as
described earlier, abdominal bracing can be considered a
mode of antagonist co-contraction (Cholewicki et al.,
1999; Gardner-Morse and Stokes, 2001). Some studies
reported that an influence of reciprocal inhibition might
be assumed to be involved as a factor limiting the maxi-
mal activation of antagonistic muscles (Serrau et al.,
2011; Tyler and Hutton, 1986). If this finding can be
applied to abdominal bracing, it seems that the antagonis-
tic pairs located in the trunk might never reach their
maximum level of muscle activation due to neural inhibi-
tion during voluntary co-contraction.
Another interesting finding obtained here was that
while % EMGmax values for RA, EO, and ES were sig-
nificantly lower in the abdominal bracing than in some of
the other exercises such as V-sits and sit-ups for RA and
EO and back extensions for ES muscle, the % EMGmax
value for IO during the abdominal bracing was signifi-
cantly higher than those in most of the other exercises
such as sit-ups and curl-ups. This implies that abdominal
bracing is one of the most effective techniques for induc-
ing a higher activation in deep abdominal muscles, such
as IO muscle, even compared to dynamic exercises in-
volving trunk flexion/extension movements. From an
athletic perspective, dynamic exercises involving spine
flexion and extension are usually preferred for strengthen-
ing the trunk muscles (Hibbs et al., 2008). In addition, a
recent review article (Martuscello et al., 2013) suggested
that multi-joint free weight exercises, rather than trunk-
specific exercises, should be implemented in training
programs in order to adequately strengthen the trunk
muscles. These types of exercise, however, are recom-
mended for advanced trained individuals because the
lumbar spine is subjected to high loads, which are not
advisable for inexperienced individuals or patients with
spine instability, spine lesion, or lower back pain
(Monfort-Panego et al., 2009). Therefore, from a clinical
point of view, static exercises are usually recommended
for rehabilitation and/or fitness programs at the expense
of muscular activity. In IO muscle, nevertheless, abdomi-
nal bracing showed greater activity than most of the other
exercises including dynamic ones. This suggests that IO
muscle is not highly activated by most exercises con-
ducted in many athletic and rehabilitative programs, but is
selectively recruited by such specific exercise as abdomi-
nal bracing.
It is recommended that in the initial stage of spine-
strengthening programs, participants should be instructed
to become aware of motor patterns and to recruit muscles
in isolation (Hibbs et al., 2008). These programs can then
progress to functional positions and dynamic activities
(Akuthota and Nadler, 2004). It is also suggested that
trunk stability training should range from isolated activa-
tion of the deep abdominal muscles, such as internal
oblique or transversus abdominis, to lifting weights on
uneven surfaces (Hibbs et al., 2008). This is due to the
different functional roles of the muscles during specific
exercise tasks. Therefore, it is advised that exercises
should be performed to activate the trunk musculature in
all three planes and full ranges of motion for developing
total spine stability (Bergmark, 1989). In addition, trunk
stabilization and trunk-strengthening programs that target
the deep abdominal muscles have been designed to im-
prove motor control and strength of the trunk region
(Teyhen et al., 2008). Considering these, abdominal brac-
ing should be included in both rehabilitation and athletic
training programs when the goal is to improve spine sta-
bility. However, as demonstrated by the present study, it
should be noted that abdominal bracing is not the best
exercise for maximizing the activities of all the trunk
muscles.
In view of establishing the efficacy of a training
modality for improving muscle function, it must be con-
sidered whether the muscle activation during the exercise
is sufficient in terms of training intensity. A recent study
(MacKenzie et al., 2010) reported that a resistance train-
ing program, in which subjects performed voluntary co-
Maeo et al.
473
contractions of antagonistic pairs (elbow flexors and ex-
tensors), produced significant increases in the strength
capability of both muscle pairs without the use of an ex-
ternal load as resistance. Although the intensity level
during maximal voluntary co-contraction exercise was not
discussed in their study, other studies showed that muscu-
lar activity levels of elbow flexors and extensors during
the task were about 40 – 70% of those during MVC
(Serrau et al., 2011; Tyler and Hutton, 1986). Hence, the
60% EMGmax value in IO muscle as shown in the current
study can be considered sufficient to be a training stimu-
lus for improving the function of the deep abdominal
muscles. Hides et al. (2012) applied a training modality
with isometric voluntary contractions of abdominal mus-
cles plus abdominal drawing in upright and forward lean
positions to Australian Football League players with or
without lower back pain. As a result, they observed that
the training modality had more positive effect on multifi-
dus CSA than a Pilates program with abdominal drawing
in horizontal positions. This finding supports the assump-
tion mentioned above and, at the same time, indicates that
abdominal bracing can be a training modality for
strengthening the muscle groups which function to stabi-
lize spine even for athletes. In any case, no study has tried
to examine how a training modality with abdominal brac-
ing influences neuromuscular function which may con-
tribute to spinal stability. Further study is needed to clar-
ify this.
Conclusion
In summary, abdominal bracing was shown to be one of
the most effective exercise techniques for IO muscle even
compared to dynamic exercises involving trunk flex-
ion/extension movements. Thus, abdominal bracing
should be included in exercise programs when the goal is
to improve trunk stability, although further investigation
focusing on its actual effects on spinal stability in reha-
bilitation and/or athletic event is needed.
Acknowledgements
This research was supported by the Sasakawa Scientific Research Grant
from The Japan Science Society (24-620).
References
Akuthota, V. and Nadler, S.F. (2004) Core strengthening. Archives of
Physical Medicine and Rehabilitation 85, S86-92.
Allison, G.T., Godfrey, P. and Robinson, G. (1998) EMG signal
amplitude assessment during abdominal bracing and hollowing.
Journal of Electromyography and Kinesiology 8, 51-57.
Behm, D.G., Drinkwater, E.J., Willardson, J.M. and Cowley, P.M.
(2010) The use of instability to train the core musculature.
Applied Physiology, Nutrition, and Metabolism 35, 91-108.
Bergmark, A. (1989) Stability of the lumbar spine. A study in
mechanical engineering. Acta Orthopaedica Scandinavica
Supplementum 230, 1-54.
Bressel, E., Dolny, D.G. and Gibbons, M. (2011) Trunk muscle activity
during exercises performed on land and in water. Medicine and
Science in Sports and Exercise 43, 1927-1932.
Bressel, E., Dolny, D.G., Vandenberg, C. and Cronin, J.B. (2012) Trunk
muscle activity during spine stabilization exercises performed
in a pool. Physical Therapy in Sport 13, 67-72.
Cholewicki, J., Juluru, K. and McGill, S.M. (1999) Intra-abdominal
pressure mechanism for stabilizing the lumbar spine. Journal of
Biomechanics 32, 13-17.
Faul, F., Erdfelder, E., Lang, A.G. and Buchner, A. (2007) G*Power 3: a
flexible statistical power analysis program for the social,
behavioral, and biomedical sciences. Behavior Research
Methods 39, 175-191.
Gardner-Morse, M.G. and Stokes, I.A. (2001) Trunk stiffness increases
with steady-state effort. Journal of Biomechanics 34, 457-463.
Grenier, S.G. and McGill, S.M. (2007) Quantification of lumbar stability
by using 2 different abdominal activation strategies. Archives of
Physical Medicine and Rehabilitation 88, 54-62.
Hibbs, A.E., Thompson, K.G., French, D., Wrigley, A. and Spears, I.
(2008) Optimizing performance by improving core stability and
core strength. Sports Medicine 38, 995-1008.
Hides, J.A., Stanton, W.R., Mendis, M.D., Gildea, J. and Sexton, M.J.
(2012) Effect of motor control training on muscle size and
football games missed from injury. Medicine and Science in
Sports and Exercise 44, 1141-1149.
Kibler, W.B., Press, J. and Sciascia, A. (2006) The role of core stability
in athletic function. Sports Medicine 36, 189-198.
MacKenzie, S.J., Rannelli, L.A. and Yurchevich, J.J. (2010)
Neuromuscular adaptations following antagonist resisted
training. Journal of Strength and Conditioning Research 24,
156-164.
Marshall, P.W., Desai, I. and Robbins, D.W. (2011) Core stability
exercises in individuals with and without chronic nonspecific
low back pain. Journal of Strength and Conditioning Research
25, 3404-3411.
Martuscello, J.M., Nuzzo, J.L., Ashley, C.D., Campbell, B.I., Orriola,
J.J. and Mayer, J.M. (2013) Systematic review of core muscle
activity during physical fitness exercises. Journal of Strength
and Conditioning Research. (In press).
McGill, S.M. (2001) Low back stability: from formal description to
issues for performance and rehabilitation. Exercise and Sport
Sciences Reviews 29, 26-31.
McGill, S.M., Grenier, S., Kavcic, N. and Cholewicki, J. (2003)
Coordination of muscle activity to assure stability of the lumbar
spine. Journal of Electromyography and Kinesiology 13, 353-
359.
Monfort-Panego, M., Vera-Garcia, F.J., Sanchez-Zuriaga, D. and Sarti-
Martinez, M.A. (2009) Electromyographic studies in abdominal
exercises: a literature synthesis. Journal of Manipulative and
Physiological Therapeutics 32, 232-244.
Pashler, H. (1994) Dual-task interference in simple tasks: data and
theory. Psychological Bulletin 116, 220-244.
Rasouli, O., Arab, A.M., Amiri, M. and Jaberzadeh, S. (2011)
Ultrasound measurement of deep abdominal muscle activity in
sitting positions with different stability levels in subjects with
and without chronic low back pain. Manual Therapy 16, 388-
393.
Serrau, V., Driss, T., Vandewalle, H., Behm, D.G., Lesne-Chabran, E.
and Le Pellec-Muller, A. (2011) Muscle activation of the elbow
flexor and extensor muscles during self-resistance exercises:
comparison of unilateral maximal co-contraction and bilateral
self-resistance. Journal of Strength and Conditioning Research
26, 2468-2477.
Teyhen, D.S., Rieger, J.L., Westrick, R.B., Miller, A.C., Molloy, J.M.
and Childs, J.D. (2008) Changes in deep abdominal muscle
thickness during common trunk-strengthening exercises using
ultrasound imaging. The Journal of Orthopaedic and Sports
Physical Therapy 38, 596-605.
Tyler, A.E. and Hutton, R.S. (1986) Was Sherrington right about co-
contractions? Brain Research 370, 171-175.
Urquhart, D.M., Hodges, P.W., Allen, T.J., and Story, I.H. (2005)
Abdominal muscle recruitment during a range of voluntary
exercises. Manual Therapy 10, 144-153.
Vera-Garcia, F.J., Brown, S.H., Gray, J.R. and McGill, S.M. (2006)
Effects of different levels of torso coactivation on trunk
muscular and kinematic responses to posteriorly applied sudden
loads. Clinical Biomechanics 21, 443-455.
Vera-Garcia, F.J., Elvira, J.L., Brown, S.H. and McGill, S.M. (2007)
Effects of abdominal stabilization maneuvers on the control of
spine motion and stability against sudden trunk perturbations.
Journal of Electromyography and Kinesiology 17, 556-567.
Vera-Garcia, F.J., Moreside, J.M. and McGill, S.M. (2010) MVC
techniques to normalize trunk muscle EMG in healthy women.
Journal of Electromyography and Kinesiology 20, 10-16.
Electromyographic activity during abdominal bracing
474
Willardson, J.M. (2007) Core stability training: applications to sports
conditioning programs. Journal of Strength and Conditioning
Research 21, 979-985.
Key points
• Trunk muscle activities during abdominal bracing
was examined with regard to muscle- and exercise-
related differences.
• Abdominal bracing preferentially activates internal
oblique muscles even compared to dynamic exer-
cises involving trunk flexion/extension movements.
• Abdominal bracing should be included in exercise
programs when the goal is to improve spine stabil-
ity.
AUTHORS BIOGRAPHY
Sumiaki MAEO
Employment
National Institute of Fitness and Sports in
Kanoya, Research Fellow of Japan Soci-
ety for the Promotion of Science
Degree
MSc
Research interests
Exercise physiology, Neurosciece
E-mail: smaeo1985@gmail.com
Takumi TAKAHASHI
Employment
National Institute of Fitness and Sports in
Kanoya
Degree
BSc
Research interests
Exercise physiology
E-mail: m126007@sky.nifs-k.ac.jp
Yohei TAKAI
Employment
National Institute of Fitness and Sports in
Kanoya
Degree
PhD
Research interests
Exercise physiology, Aging, Growth and
development
E-mail: y-takai@nifs-k.ac.jp
Hiroaki KANEHISA
Employment
National Institute of Fitness and Sports in
Kanoya
Degree
PhD
Research interests
Exercise physiology
E-mail: hkane@nifs-k.ac.jp
Sumiaki Maeo
National Institute of Fitness and Sports in Kanoya, 1 Shiromizu,
Kanoya, Kagoshima 891-2393, Japan