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Muscle activity of the core during bilateral, unilateral, seated and standing resistance exercise

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Little is known about the effect of performing common resistance exercises standing compared to seated and unilaterally compared to bilaterally on muscle activation of the core. Thus, the purpose of this study was to compare the electromyographic activity (EMG) of the superficial core muscles (i.e. rectus abdominis, external oblique and erector spinae) between seated, standing, bilateral and unilateral dumbbell shoulder presses. 15 healthy males performed five repetitions at 80% of one-repetition maximum of the exercises in randomized order. Results were analyzed with a two-way analysis of variance and a Bonferroni post hoc test. The position × exercise interaction was significantly different for rectus abdominis (P = 0.016), but not for external oblique (P = 0.100) and erector spinae (P = 0.151). The following EMG results were observed: For rectus abdominis: ~49% lower in seated bilateral versus unilateral (P < 0.001), similar in standing bilateral versus unilateral (P = 0.408), ~81% lower in bilateral seated versus standing (P < 0.001), ~59% lower in unilateral seated versus standing (P < 0.001); For external oblique: ~81% lower in seated bilateral versus unilateral (P < 0.001), ~68% lower in standing bilateral than unilateral (P < 0.001), ~58% lower in bilateral seated versus standing (P < 0.001), ~28% lower in unilateral seated versus standing (P = 0.002); For erector spinae: similar in seated bilateral versus unilateral (P = 0.737), ~18% lower in standing bilateral versus unilateral (P = 0.001), similar in seated versus standing bilateral (P = 0.480) and unilateral (P = 0.690). In conclusion, to enhance neuromuscular activation of the superficial core muscles, standing exercises should be used instead of seated exercises, and unilateral exercises should be used instead of bilateral exercises.
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ORIGINAL ARTICLE
Muscle activity of the core during bilateral, unilateral, seated
and standing resistance exercise
Atle Hole Saeterbakken Marius Steiro Fimland
Received: 12 June 2011 / Accepted: 18 August 2011
ÓSpringer-Verlag 2011
Abstract Little is known about the effect of performing
common resistance exercises standing compared to seated
and unilaterally compared to bilaterally on muscle activa-
tion of the core. Thus, the purpose of this study was to
compare the electromyographic activity (EMG) of the
superficial core muscles (i.e. rectus abdominis, external
oblique and erector spinae) between seated, standing,
bilateral and unilateral dumbbell shoulder presses. 15
healthy males performed five repetitions at 80% of one-
repetition maximum of the exercises in randomized order.
Results were analyzed with a two-way analysis of variance
and a Bonferroni post hoc test. The position 9exercise
interaction was significantly different for rectus abdominis
(P=0.016), but not for external oblique (P=0.100) and
erector spinae (P=0.151). The following EMG results
were observed: For rectus abdominis: *49% lower in
seated bilateral versus unilateral (P\0.001), similar in
standing bilateral versus unilateral (P=0.408), *81%
lower in bilateral seated versus standing (P\0.001),
*59% lower in unilateral seated versus standing
(P\0.001); For external oblique: *81% lower in seated
bilateral versus unilateral (P\0.001), *68% lower in
standing bilateral than unilateral (P\0.001), *58% lower
in bilateral seated versus standing (P\0.001), *28%
lower in unilateral seated versus standing (P=0.002); For
erector spinae: similar in seated bilateral versus unilateral
(P=0.737), *18% lower in standing bilateral versus
unilateral (P=0.001), similar in seated versus standing
bilateral (P=0.480) and unilateral (P=0.690). In con-
clusion, to enhance neuromuscular activation of the super-
ficial core muscles, standing exercises should be used
instead of seated exercises, and unilateral exercises should
be used instead of bilateral exercises.
Keywords EMG Resistance exercise Unilateral
Bilateral Shoulder press Instability
Introduction
The term core has been used to describe the lumbopelvic-
hip complex and the musculature that surrounds it (Berg-
mark 1989). Core muscles are classified into global or local
muscle subsystems, based on their primary role in stabi-
lizing (local) or generating force (global) in the core.
However, several studies have reported that both of these
muscle subsystems stabilize the core (Arokoski et al. 2001;
Cholewicki and Van Vliet 2002; Cresswell and Thor-
stensson 1994). Instability of the core may be associated
with weak core muscles (Souza et al. 2001). Thus,
improving the strength and stability of the core muscles is a
key component in clinical rehabilitation (Struge et al.
2004), training for competitive athletes (Saeterbakken et al.
2011) and for individuals wanting to improve their general
and musculoskeletal health (Liemohn and Pariser 2002).
Communicated by Toshio Moritani.
A. H. Saeterbakken (&)
Faculty of Teacher Education and Sport, Sogn og Fjordane
University College, PB 133, 6851 Sogndal, Norway
e-mail: atle.saeterbakken@hisf.no
M. S. Fimland
Department of Public Health and General Practice, Faculty of
Medicine, Norwegian University of Science and Technology,
Trondheim, Norway
M. S. Fimland
Hysnes Rehabilitation Center, St. Olavs University Hospital,
Trondheim, Norway
123
Eur J Appl Physiol
DOI 10.1007/s00421-011-2141-7
Several studies have attempted to identify exercises that
effectively activate core stabilizers (Arokoski et al. 2001;
Souza et al. 2001; Vera-Garcia et al. 2000). Unstable sur-
faces (e.g. BOSU- or Swiss balls) have been proposed to
increase the neuromuscular activation in core muscles
compared to stable surfaces, but conflicting results have
been reported (Anderson and Behm 2004; Goodman et al.
2008; Kohler et al. 2010; Lehman et al. 2006; Marshall and
Murphy 2006; Norwood et al. 2007). However, most daily
living- and sport activities are performed on stable surfaces.
According to the training principle of specificity (Sale
1988), it may therefore be more relevant to introduce the
instability component by other means than changing the
surface to increase stress of the core muscles. Thus, it is
surprising that, compared to the substantial body of litera-
ture investigating unstable surfaces, so few studies have
attempted to identify strength training approaches that
increase the stability requirement of the core without
altering the surface (Hamlyn et al. 2007; Nuzzo et al. 2008).
Free weight exercises increases the stabilization
requirements of the joint compared to stable machine
exercises (Garhammer 1981; Koyama et al. 2010; McCaw
and Friday 1994). However, not all free weight exercises
are the same. For example, free weight resistance exercises
performed standing should, in theory, increase the stabi-
lizing requirements of the core muscles compared to a
seated position (Baechle and Earle 2000; Garhammer
1981). However, experimental verification of such theo-
retical assumptions is limited. Santana et al. (2007) dem-
onstrated increased neuromuscular activation of the core
muscles during standing cable press compared to supine
bench press. However, the standing cable press was per-
formed unilaterally and may have caused a disruptive
moment arm which stimulated the core stabilizing muscles
to a greater extent than the bilateral supine bench press.
While strength and power adaptations of the prime movers
of unilateral and bilateral resistance exercises are well
documented (Adamson et al. 2008; Goto et al. 2004; Holm
et al. 2008; Munn et al. 2005), few studies have investi-
gated core muscle activation in bilateral and unilateral
resistance exercises. Behm et al. (2005) reported greater
EMG activity in back stabilizers in unilateral shoulder
press and higher activation in all core stabilizers in uni-
lateral chest presses, compared to otherwise identical
bilateral shoulder- and chest presses.
Little is known about the effect of performing common
resistance exercises standing compared to seated and uni-
laterally compared to bilaterally on muscle activation of
the core. The importance of core stability during daily
living activities highlights the need for additional research.
We are not aware of any studies that included these two
instability inducing components (unilateral ?standing) in
the same investigation of core muscle activation.
Therefore, the aim of the study was to examine the elec-
tromyography (EMG) activity of the superficial core
muscles during seated, standing, bilateral and unilateral
dumbbell shoulder presses. It was hypothesized that
standing and unilateral dumbbell presses would result in
greater neuromuscular activation of the core, compared to
seated and bilateral dumbbell presses, respectively, and
that combining these two instability components would
result in the highest muscle activation.
Methods
Participants
Fifteen healthy males (22 ±2 years, mass: 79 ±14 kg,
height: 1.79 ±0.06 m) volunteered for the study. Exclu-
sion criteria were musculoskeletal pain and unfamiliarity
with shoulder press exercises using free weights. All par-
ticipants were informed of testing procedures and possible
risks involved and provided written consent to participate.
Ethical approval was obtained from the regional research
ethics committee.
None of the participants was competitive power lifters,
but had 5.0 (±2.6) years of previous resistance-training
experience. All participants were familiar with the shoulder
press exercise and performed the exercise as part of their
regular training program. The participants were instructed
to refrain from any additional resistance exercise in the
72 h before testing.
Assessment
A single-group, repeated-measures study design was used to
examine neuromuscular activity of superficial core muscles
during seated, standing, bilateral and unilateral dumbbell
presses (preferred arm). The participants attended four
sessions, each separated by 3–5 days. Prior to every session,
the participants performed a standardized warm-up protocol
on a cycle ergometer (10-min, 75–125 W) followed by 6–8
warm-up sets (3–4 sets seated, 3–4 sets standing, 60–85% of
1RM, 6–12 repetitions). A 3 min rest period was given
between each warm-up set (Goodman et al. 2008). The two
first sessions identified one repetition maximum (1RM) for
each of the four shoulder press exercises. The first session
tested 1RM of the seated bilateral and seated unilateral
dumbbell presses. The second session tested 1RM of the
standing bilateral and unilateral dumbbell presses. A 4-min
rest period was given between each 1RM attempt (Good-
man et al. 2008; Schwanbeck et al. 2009).
The third session was identical to the experimental (4th)
session. The participants performed five repetitions on each
of the four shoulder press exercises in randomized order.
Eur J Appl Physiol
123
Loads corresponding to 80% of 1RM were used. The five
repetitions performed in each exercise were fewer than the
participants could perform with this load (i.e. not per-
formed until volitional failure). This number was chosen to
avoid confounding effects of fatigue on the neuromuscular
activation of the subsequent exercise. Prior to a new
exercise, the participants performed five repetitions at 60%
of 1RM to adjust to the exercise. A 3-min rest period was
given between each set and exercise. The participants were
instructed to use a moderate lifting tempo that they felt
comfortable with, approximately 2 s in the eccentric phase
and 2 s in the concentric phase. However, most participants
preferred a faster lifting time, particularly in the eccentric
phase. This was allowed as long as the lifting time, for the
same person, was similar for all exercises. A digital watch
provided visual feedback to the participants during the
lifting phases.
Testing procedures
Two investigators acted as spotters and controlled the lifting
speed, body position and the horizontal position of dumb-
bells in the descending and ascending lifting phases. The
dumbbells had to be lifted to identical horizontal positions.
The investigators assisted the participants in the preload
phase by lifting the dumbbell(s). On audio command, the
participants lowered the center of the dumbbell(s) to outside
of the shoulder(s) before lifting the weight(s) to fully
extended arm(s) (Graham 2008). The dumbbell(s) were
held with the thumb-side towards the ear(s) at all times and
pressed straight upwards. Further details of the exercise
technique are described by Graham (2008).
A standard bench set at 75°upward angle (verti-
cal =90°) was used to stabilize the body in the seated
testing conditions. We chose to support the back in order to
increase the ecological validity of the results, as this in our
experience is the most common way of performing seated
shoulder presses. The gluteus and the upper torso were in
contact with the bench and the legs were placed shoulder
wide with a 90°angle at the knees (Graham 2008).
Excessive postural sway was not allowed in the seated
or standing positions. To prevent postural sway during
standing dumbbell presses, a string was placed in a square
about 1 cm from the skin and 3 cm above the iliac crest.
The participants had to be clear of the string at all times. In
the standing position, the participants stood with their feet
shoulder-wide apart with extended knees.
Measurements
The vertical positions and lifting speed of the weights were
measured by a linear encoder (Ergotest Technology A/S,
Langesund, Norway) attached to the dumbbell of the
dominant hand. The linear encoder had the same sampling
frequency (100 Hz) as the EMG recording and was syn-
chronized with the EMG recordings using a 4020e Mus-
clelab (Ergotest Technology A/S, Langesund, Norway).
Commercial software (Musclelab V8.13, Ergotest Tech-
nology AS, Langesund, Norway) was used to analyze the
EMG, vertical position and time data. We identified the
beginning of the second repetition and the ending of
the fifth repetition, and root-mean-square (RMS) EMG was
calculated as the mean over the last four repetitions and
used in further analyses.
The skin was prepared (shaved, washed with alcohol,
abraded) before placement of gel coated self-adhesive
electrodes (Dri-Stick Silver circular sEMG Electrodes AE-
131, NeuroDyne Medical, USA) during the experimental
session. The electrodes (11 mm contact diameter) were
placed in the presumed direction of the underlying muscle
fibers with a center-to-center distance of 2.0 cm, according
to the recommendations by SENIAM (Hermens et al.
2000). The surface EMG electrodes were positioned at the
rectus abdominis (3 cm lateral to the umbilicus), external
abdominal oblique (approximately 15 cm to the umbilicus)
and erector spinae (at L1 and 3 cm lateral to the spinous
process) at the side contralateral to the preferred lifting arm
(Behm et al. 2005). To minimize noise induced from
external sources, the raw EMG signal was amplified and
filtered using a preamplifier located as near the pickup
point as possible. Signals were low pass filtered with a
maximum cut off frequency of 8 Hz, and high pass filtered
with a minimum cut off frequency of 600 Hz, and then
rectified and integrated. The raw EMG signals were con-
verted to RMS signals using a hardware circuit network
(frequency response 450 kHz, averaging constant 12 ms,
total error ±0.5%). The RMS were sampled at a rate of
100 Hz using a 16 bit A/D converter and with a common
mode rejection rate of 106 dB (Saeterbakken et al. 2011).
The stored data were analyzed using commercial software
(Musclelab V8.13, Ergotest Technology AS, Langesund,
Norway).
Statistical analysis
To assess differences in neuromuscular activity of the core
muscles between seated and standing dumbbell presses
performed bilaterally and unilaterally, we used a two-way
analysis of variance (ANOVA) to compare position (seated
vs. standing) and exercise (bilateral vs. unilateral). The
EMG activity from the three muscles was the dependent
variables. To compare the lifting time of the exercises, we
used a one-way ANOVA. Statistical significance was
accepted at PB0.05. SPSS (version 18.0; Inc., Chicago,
IL, USA) was used to analyze the data. When a significant
interaction was found, paired ttests with a Bonferroni
Eur J Appl Physiol
123
correction were used as a post hoc to locate the differences.
All results are presented as mean ±SD and with Cohen’s d
effect size (ES). ES of 0.2 was considered small, 0.5
medium and 0.8 large.
Results
Representative filtered EMG signals of the exercises are
presented in Fig. 1. For rectus abdominis, the position 9
exercise interaction was significantly different (F=7.53,
P=0.016, Fig. 2). After post hoc analysis, a *49% lower
EMG activity in rectus abdominis in seated bilateral versus
unilateral shoulder presses was observed (0.033 ±0.017
vs. 0.017 ±0.007, P\0.001, ES =0.93). There was a
*8% non-significantly greater EMG activity in standing
bilateral versus unilateral shoulder presses (0.088 ±0.049
vs. 0.080 ±0.038, P=0.408, ES =0.20). Further, there
was a *81% lower EMG activity in rectus abdominis for
bilateral seated versus standing (0.017 ±0.007 vs.
0.088 ±0.049, P\0.001, ES =1.98) shoulder presses.
There was a *59% lower EMG activity for unilateral
seated versus standing (0.033 ±0.017 vs. 0.080 ±0.038,
P\0.001, ES =1.60) shoulder presses.
For external oblique, the position 9exercise interaction
was not significantly different (F=3.11, P=0.100,
Fig. 3). However, significant simple main effects were
observed for position (F=33.179, PB0.001) and exer-
cise (F=66.160, PB0.001), revealing a *81% lower
EMG activity in seated bilateral versus unilateral shoulder
presses (0.057 ±0.034 vs. 0.300 ±0.152, P\0.001,
ES =2.21). Further, there was a *68% lower EMG
activity in standing bilateral versus unilateral shoulder
presses (0.137 ±0.081 vs. 0.419 ±0.199, P\0.001,
ES =1.85). A *58% lower EMG activity in external
oblique in bilateral seated versus standing (0.057 ±0.034
vs. 0.137 ±0.081, P\0.001, ES =1.29) was observed.
There was a *28% lower EMG activity for unilateral
seated versus standing (0.300 ±0.152 vs. 0.419 ±0.199,
P=0.002, ES =0.67).
For erector spinae, the position 9exercise interaction
was not significantly different (F=2.31, P=0.151,
Fig. 4). The main effect of position was not statistically
different, (F=0.117, P=0.737) even if a *45% lower
EMG activity in seated bilateral versus unilateral
(0.056 ±0.038 vs. 0.102 ±0.070, ES =0.65) shoulder
presses was observed. However, there was a main effect for
exercise (F=8.074, P=0.013). The simple main effects
Standing bilateral
0.00
0.05
0.10
0.15
0.20
0.25
Repetition
RMS (mV)
0
20
40
60
80
100
120
140
160
180
200
Vertical movement (cm)
Rectus abdomins
External oblique
Erector spinae
Position
1234
c
Seated bilateral
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Repetition
RMS (mV)
0
20
40
60
80
100
120
140
160
Vertical distance (cm)
Rectus abdominis
External oblique
Erector spinae
Posistion
a
1234
Seated unilateral
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Repetition
RMS (mV)
0
20
40
60
80
100
120
140
160
Vertical movement (cm)
Rectus abdominis
External oblique
Erector spinae
Position
1234
b
d
Standing unilateral
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Repetion
RMS (mV)
0
50
100
150
200
Vertical movement (cm)
Rectus abdominis
External oblique
Erector spinae
Position
12 34
Fig. 1 adTypical examples of the filtered and RMS converted
EMG signals in seated bilateral (Fig. 1a), seated unilateral (Fig. 1b),
standing bilateral (Fig. 1c), standing unilateral (Fig. 1d) and the
temporal changes in the arm up and down movement. Note the
different scaling on the yaxes of the figures
Eur J Appl Physiol
123
observed a *18% lower EMG activity in standing bilateral
versus unilateral (0.078 ±0.112 vs. 0.095 ±0.117, P=
0.001, ES =0.15) shoulder presses were observed.
Further, there was a non-significant *28% lower EMG
activity in erector spinae in bilateral seated versus standing
(0.056 ±0.038 vs. 0.078 ±0.112, P=0.480) shoulder
presses. There was a non-significant *7% greater EMG
activity in unilateral seated versus standing (0.102 ±0.070
vs. 0.095 ±0.117, P=0.690) shoulder presses.
There were no differences in total lifting time of the
shoulder press exercises: seated bilateral 11.8 ±2.5 s, seated
unilateral 11.5 ±2.3 s, standing bilateral 12.3 ±3.5 s,
standing unilateral 10.9 ±2.1 s, (P=0.929–1.000).
Discussion
The main findings of the present study were that unilateral
and standing shoulder presses broadly resulted in greater
neuromuscular activation of the superficial core muscles
than bilateral and seated shoulder presses, respectively.
We hypothesized that performing dumbbell shoulder
presses (1) standing instead of seated, (2) unilateral instead
of bilateral and (3) a combination of 1 and 2 would increase
the EMG activity in rectus abdominis (Baechle and Earle
2000; Santana et al. 2007; Garhammer 1981). In line with
this, there was greater EMG activity in rectus abdominis for
the standing exercises (bilaterally and unilaterally) versus
the seated counterparts, greater EMG activity for seated
unilateral versus bilateral presses, but in contrast not for
standing unilateral versus bilateral shoulder presses. The
interaction in position 9exercise was therefore caused by
change in position from seated to standing. The similar
EMG activation in standing shoulder presses (bilateral vs.
unilateral) could reflect the increased stability requirement
by performing an exercise standing instead of seated and the
role of rectus abdominis (Santana et al. 2007). That is, the
rectus abdominis was already activated in a co-contraction
with erector spinae to avoid flexion or extension in the trunk
(Arokoski et al. 2001), and perhaps the stability requirement
was augmented to such an extent that further instability
(unilateral) did not increase the muscle activation addi-
tionally. Still, the destabilizing torque on the core, intro-
duced by standing instead of seated execution, did increase
the EMG activity in rectus abdominis. However, this was
expected considering the small base of support during
standing shoulder presses compared to the solid base of
support during seated execution. In this study, seated
presses meant that the legs were placed shoulder wide with
a90°angle of the knees and in combination with the back
rest, a solid base of support was created against movement
in the sagittal plane. In turn, this would cause less instability
to avoid postural sway compared to a standing position, but
increased muscle activity to maintain the position during
unilateral shoulder press (Behm et al. 2005). In support of
this notion, during the seated testing, unilateral presses
resulted in a twofold rectus abdominis activation compared
EMG activity in Rectus Abdominis
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
Seated Standing
RMS (mV)
Bilaterally
Unilaterally
#
**
**
Fig. 2 The mean and SD of the electromyographic (EMG) activity in
rectus abdominis in combinations of seated, standing, bilateral and
unilateral shoulder presses. #The position 9exercise interaction was
significantly different on a 0.05 level. **Significant difference in
EMG activity compared to all other exercises on a 0.05 level
EMG activity in External Oblique
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Seated Standing
RMS (mV)
Bilaterally
Unilaterally
**
*
**
Fig. 3 The mean and SD of the electromyographic (EMG) activity in
external oblique in combinations of seated, standing, bilateral and
unilateral shoulder presses. Significant difference in EMG activity
between exercises on a 0.05 level. **Significantly different from all
other exercises on a 0.05 level
EMG activity in Erector Spinae
0.00
0.05
0.10
0.15
0.20
0.25
Seated Standing
RMS (mV)
Bilaterally
Unilaterally
*
Fig. 4 The mean and SD of the electromyographic (EMG) activity in
erector spinae in combinations of seated, standing, bilateral and
unilateral shoulder presses. *Significant difference in EMG activity
between exercises on a 0.05 level
Eur J Appl Physiol
123
to bilateral presses. These results demonstrate that the
destabilizing torque introduced by unilateral versus bilateral
execution augments rectus abdominis activation in the
seated, but not the standing position.
As hypothesized, the EMG activity of the external
oblique was greater during unilateral exercises compared to
the bilateral exercises both seated and standing (Fig. 2).
The function of the external oblique is to rotate, but also
stabilize the trunk to avoid lateral-flexion (Arokoski et al.
2001). In bilateral exercises, the mass of the contralateral
dumbbell provides a counterbalance and thereby diminish
the destabilizing torque of the movement. When shoulder
presses are performed unilaterally (and without holding a
dumbbell in the opposite arm as a counterweight), the
contralateral external oblique has to stabilize the core to
avoid postural sway. These results are in line with Behm
et al. (2005) and Santana et al. (2007).
The destabilizing torque induced by performing shoul-
der presses seated unilaterally, increased the EMG activity
to a greater extent compared to standing bilateral execu-
tion, but to a lesser extent than standing unilateral execu-
tion. Unsurprisingly, the most stable exercise (seated
bilaterally) had lower EMG activity than the other exer-
cises. To enhance EMG activity in external oblique, both
unilateral and standing execution may be used instead of
seated bilateral shoulder presses. However, unilateral exe-
cution was the more important destabilizing factor.
The significantly greater EMG activity in erector spinae
in standing unilateral versus bilateral shoulder presses,
support the hypotheses, while the results for the seated
bilateral versus unilateral did not. The increased neuro-
muscular activation in erector spinae for standing unilateral
versus bilateral presses was in all probability due to the
enhanced stability requirement of the core (Santana et al.
2007; Behm et al. 2005). The EMG activity in erector
spinae was only significantly greater for the exercise with
the greatest stability requirement. The degree of instability
was manipulated by the position (seated or standing) and
exercise (bilateral or unilateral). Using only one of these
factors did not increase the EMG activity in erector spinae.
This is in contrast to the results for rectus abdominis and
oblique external.
The results of the present study are supported from
researchers reported greater activation of the hip abductors
to stabilize the core in a single-leg stance (Gottshalk et al.
1989; Schmitz et al. 2002). Furthermore, Behm et al. (2005)
compared EMG activity in the core muscles during seated
unilateral and bilateral shoulder and chest presses. Unilat-
eral shoulder presses had greater EMG activity in erector
spinae (S1/L5), but not in upper erector spinae (L1–L2) or
lower-abdominal muscles. In contrast, unilateral chest
presses had greater EMG activity in upper and lower erector
spinae as well as lower-abdominal muscles. The results in
the shoulder and chest presses only partly support the
present study. However, these results are not directly
comparable to our study as we tested the seated shoulder
press with the upper torso pressed to the bench, while Behm
et al. (2005) did not have back support. Unfortunately, the
investigations by Behm et al. (2005) was limited by using
identical loads within the subjects, tested only in the seated
position, did not test the oblique muscles and did not report
intensity (% of 1RM) in the shoulder or chest presses
exercise. As the load increases for unilateral exercises,
greater contralateral muscle activation is needed to coun-
terbalance and diminish the destabilizing torque of the
single dumbbell on the core. It is also likely that increased
resistance load would result in greater muscle activation in
the core during standing versus seated shoulder presses.
Thus, it is therefore possible that low resistance in the
shoulder press exercises in the study by Behm et al. (2005)
caused similar EMG activation in the core.
Surprisingly few studies have investigated differences
in core muscle activation between exercises performed
seated and standing. The results of the present study are
partly supported by Santana et al. (2007) who demon-
strated increased EMG activity in erector spinae, rectus
abdominis, internal- and external oblique when perform-
ing standing unilateral chest press compared to supine
bilateral chest press. However, the results in Santana et al.
(2007) may be a result of (1) unilateral instead of bilat-
erally chest press, (2) standing instead of supine chest
press or a combination of 1 and 2. Furthermore, the force
direction of the standing unilateral chest press was hori-
zontal while the force direction in the supine position was
vertical. Producing force forward in the standing position
with no back-support in the horizontal force direction
naturally causes greater EMG-activity to maintain posi-
tion than a supine bench press with support in the force
direction.
Previous findings have suggested greater neuromuscular
activity in resistance exercises with greater instability in,
e.g. unstable surface compared to stable surface (Anderson
and Behm 2004; Kohler et al. 2010; Norwood et al. 2007).
However, with respect to sport activities and daily func-
tional tasks, a more beneficial training procedure may be to
employ standing ground-based free-weight exercises on a
stable surface (Behm et al. 2010; Hamlyn et al. 2007;
Nuzzo et al. 2008). To our knowledge, this is the first study
to investigate the effect of performing the same exercise
seated, standing, unilateral and bilateral on core muscle
activation. Many daily tasks involve movement of one or
several limbs and thereby activate core muscles which
serve to stabilize the spine (Cholewicki and van Vliet 2002;
Hodges and Richardson 1997). Coordination of core mus-
cles activation must be learned either for stability or
mobility (Schmidtbleicher 1992) and it may therefore be
Eur J Appl Physiol
123
more appealing to train the core muscles in a way that
mimics daily life activities (Sale 1988).
The present results are limited by only testing healthy
resistance trained men. For instance, Ballantyne et al. (1993)
reported different muscle activation patterns in subjects with
and without shoulder pain. Furthermore, using surface EMG
can only provide an estimate of neuromuscular activation.
EMG signals from rectus abdominis, external oblique and
erector spinae could have been affected by surrounding
muscle activation. Even if a small inter-electrode distance
was used, there is an inherent risk of cross-talk from
neighbouring muscles. Further research should focus on the
neuromuscular activation in the core performing exercises
standing instead of seated/supine and bilaterally instead of
unilaterally with low back pain patients.
In conclusion, the present study demonstrated greater
neuromuscular core activation when exercises were per-
formed standing compared to seated, and unilaterally
compared to bilaterally. We suggest that standing instead
of seated exercises, and unilateral instead of bilateral
exercises should be considered to increase core muscles
activation.
Ethics approval was obtained from the local research
ethics committee prior to the testing.
Acknowledgments We particularly thank the participants, and
Espen Krohn-Hansen and Mats Smaamo for assistance in participant
recruitment and data collection.
Conflict of interest None.
References
Adamson M, Macquaide N, Helgerud J, Hoff J, Kemi OJ (2008)
Unilateral arm strength training improves contralateral peak
force and rate of force development. Eur J Appl Phyisol
103:553–559
Arokoski J, Valta T, Airaksinen O (2001) Back and abdominal muscle
function during stabilization exercises. Arch Phys Med Rehabil
82:1089–1098
Anderson KG, Behm DG (2004) Maintenance of EMG activity and
loss of force output with instability. J Strength Cond Res
18:637–640
Baechle TR, Earle RW (2000) Resistance training. In: Baechle TR,
Earle RW (eds) Essentials of strength training and conditioning.
Human Kinetics, Champaign, pp 395–425
Ballantyne BT, O‘Hare SJ, Paschall JL, Pavla-Smith MM, Pitz AM,
Gillion JF, Soderberg GL (1993) Electromyographic activity of
selected shoulder muscles in commonly used therapeutic exer-
cises. Phys Ther 73:668–677
Behm DG, Leonard AM, Young WB, Andrew W, Bonsey C,
MacKinnon SN (2005) Trunk muscle electromyographic activity
with unstable and unilateral exercises. J Strength Cond Res 19:
193–201
Behm DG, Drinkwater EJ, Willardson JM, Cowley PM (2010)
Canadian society for exercise physiology position stand: the use
of instability to train the core in athletic and nonathletic
conditioning. Appl Physiol Nutr Metab 35:109–112
Bergmark A (1989) Stability of the lumber spine. A study in
mechanical engineering. Orthop Scand 230:1–54
Cholewicki J, van Vliet JJ (2002) Relative contribution of trunk
muscles to the stability of the lumbar spine during isometric
exertions. Clin biomech 17:99–105
Cresswell AG, Thorstensson A (1994) Changes in intra-abdominal
pressure, trunk muscle activation and force during isokinetic
lifting and lowering. Eur J Appl Physiol 68:315–321
Garhammer J (1981) Free weight equipment for the development of
athletic strength and power, part I. NSCA J 3:23–26
Goodman CA, Pearce AJ, Nicholes CJ, Gatt BM, Fairweather IH
(2008) No difference in 1RM strength and muscle activation
during the barbell chest press on a stable and unstable surface.
J Strength Cond Res 22:88–94
Goto K, Nagasawa M, Yanagisawa O, Kizuka T, Ishii N, Takamatsu
K (2004) Muscular adaptations to combinations of high- and low
resistance exercises. J Strength Cond Res 18:730–737
Gottshalk F, Kourosh S, Leveau B (1989) The functional anatomy of
tensor fasciae latae and gluteus medis and minus. J Anat 166:
179–189
Graham JF (2008) Exercise: dumbbell seated shoulder press.
J Strength Cond Res 30:54–55
Hamlyn N, Behm DG, Young WB (2007) Trunk muscle activation
during dynamic weight-training exercises and isometric insta-
bility activities. J Strength Cond Res 21:1108–1112
Hermens HJ, Freriks B, Disselhorst-Klug C, Rau G (2000) Develop-
ment of recommendations for SEMG sensors and sensor
placement procedures. J Electromyo Kinesiol 10:361–374
Hodges PW, Richardson CA (1997) Contraction of the abdominal
muscles associated with movement of the lower limb. Phys Ther
77:132–142
Holm L, Reitelseder S, Pedersen TG, Doessing S, Petersen SG,
Flyvbjerg A, Andersen JL, Aagaard P, Kjaer M (2008) Changes
in muscle size and MHC composition in response to resistance
exercise with heavy and light loading intensity. J Appl Physiol
1005:1454–1461
Kohler JM, Flanagan SP, Whiting WC (2010) Muscle activation
patterns while lifting stable and unstable loads on stable and
unstable surfaces. J Strength Cond Res 24:313–321
Koyama Y, Kobayahi H, Suzuki S, Enoka RM (2010) Enhancing the
weight training experience: a comparison of limb kinematics and
EMG activity on three machines. Eur J Appl Physiol 109:
789–801
Lehman GJ, MacMillan B, MacIntyre I, Chivers M, Fluter M (2006)
Shoulder muscle EMG activity during push up variations on and
off a Swiss ball. Dyn Med 5:7
Liemohn W, Pariser G (2002) Core strength: Implications for fitness
and low back pain. ACSM Health Fitness J 6:10–16
Marshall PW, Murphy BA (2006) Increased deltoid and abdominal
muscle activity during Swiss ball bench press. J Strength Cond
Res 20:745–750
McCaw ST, Friday J (1994) A comparison of muscle activity between
a free weight and machine bench press. J Strength Cond Res
8:259–264
Munn J, Herbert RD, Hancock MJ, Gandevia SC (2005) Training with
unilateral resistance exercise increases contralateral strength.
J Appl Physiol 99:1880–1884
Norwood JT, Anderson GS, Gaetz MB, Twist PW (2007) Electro-
myographic activity of the trunk stabilizers during stable and
unstable bench press. J Strength Cond Res 21:343–347
Nuzzo JL, McCaulley GO, Cormie P, Cavill MJ, McBride JM (2008)
Trunk muscle activity during stability ball and free weight
exercises. J Strength Cond Res 22:95–102
Saeterbakken AH, Tillaar R, Seiler KS (2011) Effect of core stability
training on throwing velocity in female handball players.
J Strength Cond Res 25:712–718
Eur J Appl Physiol
123
Sale DG (1988) Neural adaptation to resistance training. Med Sci
Sports Exerc 20:135–145
Santana JC, Vera-Garcia FJ, McGill SM (2007) A kinetic and
electromyographic comparison of the standing cable press and
bench press. J Strength Cond Res 21:1271–1277
Schmidtbleicher D (1992) Training for power events. In: Komi PV
(ed) Strength and power in sport. Blackwll, Oxford, pp 381–395
Schmitz RJ, Riemann BL, Thompson T (2002) Gluteus medius
activity during isometric closed-chain hip rotation. J Sport
Rehabil 11:179–188
Schwanbeck S, Chilibeck PD, Binsted G (2009) A comparison of free
weight squat to Smith machine using electromyography.
J Strength Cond Res 23:2588–2591
Souza GM, Baker LL, Powers CM (2001) Electromyographic activity
of selected trunk muscles during dynamic spine stabilization
exercises. Arch Phys Med Rehabil 82:1551–1557
Struge B, Lærum E, Kirkesola G, Vøllestad N (2004) The efficacy of
a treatment program focusing on specific stabilizing exercises for
pelvic girdle pain after pregnancy. A randomized controlled trial.
Spine 29:351–359
Vera-Garcia FJ, Grenier SG, McGill SM (2000) Abdominal muscle
response during curl-ups on both stable and labile surfaces. Phys
Ther 80(6):564–569
Eur J Appl Physiol
123
... Exercise protocols specifically targeting trunk muscles have been applied for both prevention and rehabilitation of low back pain [1,2], and the effects of this approach have been examined in several reviews over recent years [3][4][5]. Whereas initial regimens identified intra-pelvic, spine, and anterior abdominal muscles, that were proposed to exhibit a localised effect on proximal trunk stability via an enhanced feedforward mechanism at low levels (< 25%) of maximal voluntary contractions (MVC) [6], the concept of discrete trunk muscle training (TMT) has subsequently been deployed to improve physical fitness [7,8] as well as sport-specific performance. In this regard, earlier approaches defined a muscular cylinder within the trunk formed by a group of muscles, comprising the diaphragm, pelvic floor, abdominals, paraspinals, and gluteals [9][10][11]. ...
... However, the study included arm and shoulder muscles of the non-dominant arm in elite golfers. Still, unilateral resistance exercises have proven to increase the contralateral trunk muscles significantly in acute studies [8,102]. Isolated versus integrated trunk exercises (e.g., compound lifts like deadlift and squat) is an on-going debate regarding TMT. ...
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Background The role of trunk muscle training (TMT) for physical fitness (e.g., muscle power) and sport-specific performance measures (e.g., swimming time) in athletic populations has been extensively examined over the last decades. However, a recent systematic review and meta-analysis on the effects of TMT on measures of physical fitness and sport-specific performance in young and adult athletes is lacking. Objective To aggregate the effects of TMT on measures of physical fitness and sport-specific performance in young and adult athletes and identify potential subject-related moderator variables (e.g., age, sex, expertise level) and training-related programming parameters (e.g., frequency, study length, session duration, and number of training sessions) for TMT effects. Data Sources A systematic literature search was conducted with PubMed, Web of Science, and SPORTDiscus, with no date restrictions, up to June 2021. Study Eligibility Criteria Only controlled trials with baseline and follow-up measures were included if they examined the effects of TMT on at least one measure of physical fitness (e.g., maximal muscle strength, change-of-direction speed (CODS)/agility, linear sprint speed) and sport-specific performance (e.g., throwing velocity, swimming time) in young or adult competitive athletes at a regional, national, or international level. The expertise level was classified as either elite (competing at national and/or international level) or regional (i.e., recreational and sub-elite). Study Appraisal and Synthesis Methods The methodological quality of TMT studies was assessed using the Physiotherapy Evidence Database (PEDro) scale. A random-effects model was used to calculate weighted standardized mean differences (SMDs) between intervention and active control groups. Additionally, univariate sub-group analyses were independently computed for subject-related moderator variables and training-related programming parameters. Results Overall, 31 studies with 693 participants aged 11–37 years were eligible for inclusion. The methodological quality of the included studies was 5 on the PEDro scale. In terms of physical fitness, there were significant, small-to-large effects of TMT on maximal muscle strength (SMD = 0.39), local muscular endurance (SMD = 1.29), lower limb muscle power (SMD = 0.30), linear sprint speed (SMD = 0.66), and CODS/agility (SMD = 0.70). Furthermore, a significant and moderate TMT effect was found for sport-specific performance (SMD = 0.64). Univariate sub-group analyses for subject-related moderator variables revealed significant effects of age on CODS/agility ( p = 0.04), with significantly large effects for children (SMD = 1.53, p = 0.002). Further, there was a significant effect of number of training sessions on muscle power and linear sprint speed ( p ≤ 0.03), with significant, small-to-large effects of TMT for > 18 sessions compared to ≤ 18 sessions (0.45 ≤ SMD ≤ 0.84, p ≤ 0.003). Additionally, session duration significantly modulated TMT effects on linear sprint speed, CODS/agility, and sport-specific performance ( p ≤ 0.05). TMT with session durations ≤ 30 min resulted in significant, large effects on linear sprint speed and CODS/agility (1.66 ≤ SMD ≤ 2.42, p ≤ 0.002), whereas session durations > 30 min resulted in significant, large effects on sport-specific performance (SMD = 1.22, p = 0.008). Conclusions Our findings indicate that TMT is an effective means to improve selected measures of physical fitness and sport-specific performance in young and adult athletes. Independent sub-group analyses suggest that TMT has the potential to improve CODS/agility, but only in children. Additionally, more (> 18) and/or shorter duration (≤ 30 min) TMT sessions appear to be more effective for improving lower limb muscle power, linear sprint speed, and CODS/agility in young or adult competitive athletes.
... The change may be attributed to a number of factors. As less core activation takes place during seating in comparison to standing (Saeterbakken & Fimland, 2012), one position could have offered better stabilisation for force generation than the other (Bampouras et al., 2017). Performance during the seated position was less familiar and consequently could have augmented the inter-limb difference (Palmer et al., 2018), even if it is unlikely that the sequential muscle activity would have been affected (Hirashima et al., 2002). ...
... Zemková et al. (Zemková et al., 2019) showed that trunk rotation power was different between rotation directions. Although in the present study, trunk rotation was not permitted, the trunk would still have been activated (Saeterbakken & Fimland, 2012). If this activation was different between positions, offering e.g., better stabilisation for force generation (Bampouras et al., 2017), the muscle strength and asymmetry scores are not reflecting purely the shoulder rotation from the shoulder and surrounding activated muscles (Yaghoubi et al., 2015), but rather the overall 'movement strength' and 'movement asymmetry' score. ...
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Water-polo players frequently perform overhead throws that could result in shoulder imbalances. For overhead throws, execution of the ‘eggbeater kick’ (cyclical movement of the legs) is required to lift the body out of the water. Although a symmetrical action, inter-limb differences in task execution could lead to knee frontal plane projection (FPPA) differences. The present study examined imbalances shoulder and knee FPPA in female players. Eighteen competitive female field players (24.1 ± 5.5 years, 1.68 ± 0.06 m, 72.9 ± 13.3 kg) had their shoulder strength assessed in a shot-mimicking position with a portable dynamometer, standing and seated (isolating the shoulder contribution). Anterior:posterior and shooting:non-shooting shoulder comparison were made. Additionally, players performed a drop jump. Knee FPPA was recorded from digitising and comparing the frames just before landing and at stance phase. During standing, players exhibited higher shooting:non-shooting asymmetry (p = 0.032) in the anterior contraction direction, while during seated the shooting shoulder anterior:posterior asymmetry was higher (p = 0.032). Interlimb knee FPPA asymmetry was higher in the stance phase (p = 0.02). Despite the overhead throwing and egg-beater demands impacting differently on each limb, considerable asymmetries do not develop, suggesting the overall training requirements (e.g. swimming, resistance training) were sufficient to maintain the asymmetry within desirable limits.
... In addition, due to the practically relevant nature of the training paradigm, it should be considered that global stabilizing musculature was highly involved during training. 44 This could imply global adaptations, especially in the lumbo-pelvic musculature, that contribute to transfer effects in tasks such as unilateral vertical jump that do not isolate a single muscle group. Although more research is needed to corroborate this, including functional exercises may be a key approach in the practical field to enhance the crosstransfer effect. ...
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... Halfkneeling is an anti-gravity position and has previously been used as a test for core stability [19]. In previous studies, trunk stabilizing exercises with unilateral isometric hip rotation in the supine position effectively activated ipsilateral internal obliques (IO) [20], while unilateral dumbbell lifting in the sitting position increased contralateral external obliques (EO) muscle activity [21]. These findings suggest that the load on the unilateral limb effectively promotes activity of the oblique muscles to counter the rotational moment acting on the trunk. ...
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The importance of an interaction between trunk stability muscles and hip muscle function has been suggested. However, reported exercises rarely act on the trunk and hip muscles simultaneously. Here, we devised an abdominal oblique and hip muscle exercise, the Self-oblique exercise (SOE). We examined whether SOE activated abdominal and hip muscles in the supine and half-kneeling positions, compared with abdominal crunch (AC) and plank exercises; and whether participants could modulate the exercise load. Participants were 20 healthy males with some sports experience such as football and baseball on average 10.5 ± 4.0 years. Participants applied self-pressure to their right thighs using the contralateral upper limb with 40% or 70% of the maximum force in Supine SOE and Half- kneeling SOE. The following abdominal and hip muscles were measured using surface electromyography: bilateral external obliques (EO), bilateral internal obliques (IO), right rectus abdominis, right gluteus medius (GMed), and right adductor longus (ADD). All evaluated muscle groups showed significant differences between exercises (p < 0.001). Supine SOE-70% showed 80.4% maximal voluntary contraction (MVC) for left EO (p < 0.017), 61.4% MVC for right IO (p < 0.027), 24.3% MVC for GMed (p < 0.002), and 42.4% MVC for ADD (p < 0.004); these were significantly greatest among all exercises. Muscle activity during Supine SOE-70% was greater than that during Supine SOE-40%. Similarly, Half-kneeling SOE-40% promoted abdominal and hip muscle exertion, and showed more significant activity in GMed (p < 0.006) and ADD (p < 0.001) than AC and plank. SOE could activate abdominal and hip muscles depends on the pressure applied by upper limb. Also, SOE allows participants to modulate the exercise load in a self-controlled step by step manner. Modulation of the exercise load is difficult in AC or plank compared to SOE, and AC or plank cannot obtain simultaneous oblique and hip muscle activity. SOE could be practiced anywhere, in various positions, without any tools.
... The electrode from latissimus dorsi was placed approximately 4 cm below the interior border of scapula, half the distance between the spine and the lateral edge of the torso. All electrodes were placed on the dominate side (i.e., the preferred throwing arm) of the body [36]. ...
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... Specifically, global and local muscles (e.g., lower limbs and spinal muscles) could have counterbalanced the body sway induced by the gymnastic balls. Researchers contended that data on the activation of core muscles during tasks performed on unstable surfaces [21] or in a seated position (in addition to a standing one) [22] are needed. As far as we are concerned, our study is the first to investigate muscle activation while performing the same exercise with different gymnastic balls. ...
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... The EMG signals were converted to root mean square (RMS) signals using a hardware circuit network (frequency response 450 kHz, averaging constant 12 ms, total error ± 0.5 %). The mean EMG amplitudes of the three whole repetitions (eccentric and concentric phases) in the dynamic tests were used for the calculation of the RMS values used in the analyses (Saeterbakken and Fimland, 2012). ...
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Thesis
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The aim of the study was to compare the kinematics and the timing and amount of electromyographic (EMG) activity during the lat-pull down exercise performed on machines that afforded one, two, or three degrees of freedom for the movement. Seven healthy men (age 29.4 +/- 5.6 years) participated in the study. The exercise was performed with a 30% 1-RM load. Three types of machines with varying degrees of freedom were used: Type 1, the conventional device that restricted the movement to a frontal plane; Type 2, the addition of forearm supination-pronation; Type 3, the addition of forearm supination-pronation and horizontal extension-flexion about the shoulder. All exercises involved a technique known as beginning movement load (BML) training in which light loads are lifted with a relaxation-lengthening-shortening sequence of muscle activation. The Type-3 machine showed: (1) the greatest vertical displacement of the wrist (p < 0.05); (2) the greatest abduction-adduction displacement about the shoulder (p < 0.01); (3) the least flexion-extension displacement about the elbow joint (p < 0.01); (4) a peak vertical velocity for the shoulder that preceded (p < 0.01) those for the elbow and then wrist during the pull-down phase; (5) a progressive proximal-to-distal sequence of EMG activation involving the serratus anterior, posterior deltoid, latissimus dorsi, and triceps brachii muscles; (6) a reversal of the roles for biceps and triceps brachii during the pull-down phase. These results suggest that BML exercises with greater degrees of freedom can enhance the association between training actions and functional activities.
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Objective To determine whether gluteus medius (GM) activity increases in response to isometric closed-chain external hip rotation. Design Subjects performed single-leg stances in 3 different conditions: 0° knee flexion, 0° hip flexion (C1); 0° knee flexion, 20° hip flexion (C2); and knee flexed 20–30°, 20° hip flexion (C3). Posteriorly directed forces of 8.9 N (F1), 17.8 N (F2), and 26.7 N (F3) were applied at the lateral pelvis of the nonstance side during each condition. Subjects 20 college students. Measurements Surface EMG RMS amplitude from the GM and kinematic data from the trunk, hip, and knee. Results Statistical analyses revealed a significant Condition 3 Force interaction and significant increases of EMG activity from C1F1 and C1F2 to C1F3 and from C3F1 to C3F2 and C3F3. F2 and F3 of C2 were significantly less than F2 and F3 of both C1 and C3. Conclusions GM activity increases in response to isometric, closed-chain, external hip-rotation forces, and forward movement of the upper body with respect to the base of support decreases GM activity.
Article
The exercise technique of the dumbbell seated shoulder press is described and demonstrated in this column.
Article
Learning Objective: To (1) develop an understanding of the concept of core strength and stabilty, (2) explain why this concept is important to spine health, and (3) evaluate trunk training activities with respect to their contribution to core strength and stability. (C) 2002 American College of Sports Medicine
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Objectives: To assess the paraspinal and abdominal muscle activities during different therapeutic exercises and to study how load increment produced by varying limb movements and trunk positions could affect these muscle activities. Design: A cross-sectional study comparing muscle activities between men and women. Setting: Rehabilitation clinic in university hospital. Participants: Twenty-four healthy volunteers (14 women, 10 men) aged 21 to 39 years. Interventions: Subjects performed 16 different therapeutic exercises commonly used to treat low back pain. Main outcome measures: Surface electromyography was recorded from the paraspinal (T9, L5) and abdominal (rectus abdominis, obliquus externus) muscles during these exercises. Average electromyographic amplitudes obtained during the exercises were normalized to the amplitude in maximal voluntary contraction (% MVC) to produce interindividually comparable muscle activity assessments. Results: Mean average normalized electromyographic amplitudes (% MVC) of the exercises were below 50% MVC. At L5 level, the multifidus muscle activities were significantly higher (p <.05) in women than in men, whereas no significant difference was found at T9 level. Similarly, rectus abdominis and obliquus externus activities were significantly higher (p <.001, p <.05) in women than in men. Load increment in hands or unbalanced trunk and limb movements produced higher paraspinal and abdominal muscle activities (p <.05). Conclusions: Simple therapeutic exercises are effective in activating both abdominal and paraspinal muscles. By changing limb and trunk positions or unbalancing trunk movements, it is possible to increase trunk muscle activities. Women were better able to activate their stabilizing trunk muscles than men; but it is also possible that men, having a much higher degree of strength on maximal contraction, only need to activate a smaller amount of that maximum to perform a similar activity.
Article
The purpose was to study the effect of a sling exercise training (SET)-based core stability program on maximal throwing velocity among female handball players. Twenty-four female high-school handball players (16.6 ± 0.3 years, 63 ± 6 kg, and 169 ± 7 cm) participated and were initially divided into a SET training group (n = 14) and a control group (CON, n = 10). Both groups performed their regular handball training for 6 weeks. In addition, twice a week, the SET group performed a progressive core stability-training program consisting of 6 unstable closed kinetic chain exercises. Maximal throwing velocity was measured before and after the training period using photocells. Maximal throwing velocity significantly increased 4.9% from 17.9 ± 0.5 to 18.8 ± 0.4 m·s in the SET group after the training period (p < 0.01), but was unchanged in the control group (17.1 ± 0.4 vs. 16.9 ± 0.4 m·s). These results suggest that core stability training using unstable, closed kinetic chain movements can significantly improve maximal throwing velocity. A stronger and more stable lumbopelvic-hip complex may contribute to higher rotational velocity in multisegmental movements. Strength coaches can incorporate exercises exposing the joints for destabilization force during training in closed kinetic chain exercises. This may encourage an effective neuromuscular pattern and increase force production and can improve a highly specific performance task such as throwing.