ArticlePDF Available

Influence of Pelvis Position on the Activation of Abdominal and Hip Flexor Muscles

Authors:

Abstract and Figures

A pelvic position has been sought that optimizes abdominal muscle activation while diminishing hip flexor activation. Thus, the objective of the study was to investigate the effect of pelvic position and the Janda sit-up on trunk muscle activation. Sixteen male volunteers underwent electromyographic (EMG) testing of their abdominal and hip flexor muscles during a supine isometric double straight leg lift (DSLL) with the feet held approximately 5 cm above a board. The second exercise (Janda sit-up) was a sit-up action where participants simultaneously contracted the hamstrings and the abdominal musculature while holding an approximately 45 degrees angle at the knee. Root mean square surface electromyography was calculated for the Janda sit-up and DSLL under 3 pelvic positions: anterior, neutral, and posterior pelvic tilt. The selected muscles were the upper and lower rectus abdominis (URA, LRA), external obliques, lower abdominal stabilizers (LAS), rectus femoris, and biceps femoris. The Janda sit-up position demonstrated the highest URA and LRA activation and the lowest rectus femoris activation. The Janda sit-up and the posterior tilt were significantly greater (p < 0.01 and p < 0.05, respectively) than the anterior tilt for the URA and LRA muscles. Activation levels of the URA and LRA in neutral pelvis were significantly (p < 0.01 and p < 0.05, respectively) less than the Janda sit-up position, but not significantly different from the posterior tilt. No significant differences in EMG activity were found for the external obliques or LAS. No rectus femoris differences were found in the 3 pelvis positions. The results of this study indicate that pelvic position had a significant effect on the activation of selected trunk and hip muscles during isometric exercise, and the activation of the biceps femoris during the Janda sit-up reduced the activation of the rectus femoris while producing high levels of activation of the URA and LRA.
Content may be subject to copyright.
INFLUENCE OF PELVIS POSITION ON THE ACTIVATION
OF ABDOMINAL AND HIP FLEXOR MUSCLES
JCHAD WORKMAN,
1
DAVID DOCHERTY,
2
KEVIN C. PARFREY,
1
AND DAVID G. BEHM
1
1
School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada;
2
School of Physical Education, University of Victoria, Victoria, British Columbia, Canada
ABSTRACT
Workman, JC, Docherty, D, Parfrey, KC, and Behm, DG. Influ-
ence of pelvis position on the activation of abdominal and hip
flexor muscles. J Strength Cond Res 22(5):1563–1569, 2008—A
pelvic position has been sought that optimizes abdominal
muscle activation while diminishing hip flexor activation. Thus,
the objective of the study was to investigate the effect of pelvic
position and the Janda sit-up on trunk muscle activation. Sixteen
male volunteers underwent electromyographic (EMG) testing of
their abdominal and hip flexor muscles during a supine
isometric double straight leg lift (DSLL) with the feet held
approximately 5 cm above a board. The second exercise (Janda
sit-up) was a sit-up action where participants simultaneously
contracted the hamstrings and the abdominal musculature
while holding an approximately 45°angle at the knee. Root
mean square surface electromyography was calculated for the
Janda sit-up and DSLL under 3 pelvic positions: anterior,
neutral, and posterior pelvic tilt. The selected muscles were the
upper and lower rectus abdominis (URA, LRA), external
obliques, lower abdominal stabilizers (LAS), rectus femoris,
and biceps femoris. The Janda sit-up position demonstrated the
highest URA and LRA activation and the lowest rectus femoris
activation. The Janda sit-up and the posterior tilt were
significantly greater (p ,0.01 and p,0.05, respectively)
than the anterior tilt for the URA and LRA muscles. Activation
levels of the URA and LRA in neutral pelvis were significantly (p
,0.01 and p,0.05, respectively) less than the Janda sit-up
position, but not significantly different from the posterior tilt. No
significant differences in EMG activity were found for the
external obliques or LAS. No rectus femoris differences were
found in the 3 pelvis positions. The results of this study indicate
that pelvic position had a significant effect on the activation of
selected trunk and hip muscles during isometric exercise, and
the activation of the biceps femoris during the Janda sit-up
reduced the activation of the rectus femoris while producing
high levels of activation of the URA and LRA.
KEY WORDS isometric exercise, muscle activation, electromy-
ography, rectus abdominis, rectus femoris
INTRODUCTION
Therapists, trainers, and coaches have emphasized
the importance of abdominal exercises for years.
Reasons have included sport performance, injury
prevention and rehabilitation (especially low back
pain), and aesthetics. Much of the interest has centered on the
perceived need to stabilize the ‘‘core,’’ which has generated
a variety of abdominal exercises designed to target specific
muscles. Several studies have examined the interplay between
the hip flexors and the abdominal muscles during a variety of
exercises (2,3,10,20). The general consensus has been that
high levels of hip flexor activity during abdominal strength-
ening exercises are undesirable. Ways in which the
abdominal muscles can be optimally activated while mini-
mizing activation of the hip flexors would seem to have practical
importance.
Abdominal muscle activity has been found to be very
dependent on the position of the pelvis during the
execution of the exercise. In particular, a posterior pelvic
tilthasbeenfoundtohaveamarkedinuenceonthe
activation of abdominal musculature (9,20,23). Shirado and
colleagues (21) reported that pelvic alignment could
influence the electromyographic (EMG) activity of the
trunk flexors and extensors during isometric trunk
exercises. Full flexion of the lumbar spine has been
reported to be unnecessary for maximum electrical activity
of the abdominal muscles, suggesting that it is the position
of the pelvis that influences the activation of the trunk
muscles (19). Although there are some studies that have
examined the effect of a posterior pelvic tilt on activation
of the trunk musculature, the effect of an anterior tilt or
neutral position of the pelvis has not been clearly
elucidated. Many therapists and exercise specialists
advocate the maintenance of a neutral spine and pelvis
(17,18) during abdominal exercises in order to facilitate
carryover into functional activities. In addition,
Address correspondence to Dr. David G. Behm, dbehm@mun.ca
22(5)/1563–1569
Journal of Strength and Conditioning Research
Ó2008 National Strength and Conditioning Association
VOLUME 22 | NUMBER 5 | SEPTEMBER 2008 | 1563
observation of people performing a variety of abdominal
exercises reveals that most do not prevent moving from
a neutral to an anterior tilt, which potentially changes the
purpose of the exercise and may predispose them to a risk
of low back problems (13). It would seem important to
define more clearly the effect of pelvic position, especially
neutral and anterior tilt positions, on the activation of the
trunk flexors.
The Janda sit-up (Figure 1), devised by Czech physician
Vladimir Janda and also referred to as a heels-press sit-up, has
received popularity in part because it is purported to decrease
hip flexor activity during the sit-up movement through
reciprocal inhibition (10). By actively contracting the ham-
strings muscles, an individual will theoretically deactivate the
hip flexors (10). However, there is little published evidence to
support or refute this theory.
The purpose of this study was to determine the influence of
pelvis position on therelative activity of selected abdominal and
hip musculature. A second purpose of the study was to
compare the relative muscle activity during anisometric hold at
approximately 45°of the Janda sit-up to the relative activity of
the muscle in the 3 pelvic positions. It was hypothesized that
the neutral and posterior pelvic tilt would increase the
activation of the anterior trunk muscles and that anterior
pelvic tilt would increase the activation of the rectus femoris
(reflecting the iliopsoas). In addition, it was hypothesized that
the Janda sit-up would produce high levels of activation in the
anterior trunk muscles while decreasing the activation of rectus
femoris.
METHODS
Experimental Approach to the Problem
Participants assumed a supine position and were fitted
unilaterally with surface EMG electrodes on the upper rectus
abdominis (URA), lower rectus abdominis (LRA), lower
abdominal stabilizers (LAS), external obliques, rectus femoris,
and biceps femoris muscles. Participants were asked to
perform a Janda sit-up (exercise 1) and hold a position during
the sit-up with the trunk at approximately 45°to the bench
while contracting the hamstrings. The second exercise
involved an isometric double straight leg lift (DSLL)
(exercise 2) in each of 3 pelvis positions: anterior tilt, neutral,
and posterior tilt. Each contraction was randomly allocated
and held for 5 seconds. Two trials of each exercise were
performed with a 30-second rest between trials and a
3-minute rest between each different exercise test position.
The EMG activity of each muscle was monitored across
each condition.
Subjects
A convenience sample of 15 subjects was selected to
participate in this study. All participants were male, with
a mean age of 25.9 68.4 years, mean height of 177.4 69.5 cm,
and mean weight of 78.9 611.9 kg. The participants were
instructed on the nature of the study and the equipment and
apparatus involved and were provided with the opportunity
to clarify this information. All subjects were either compet-
itive rugby players (n= 11) or recreational athletes (racquet
sports, running) (n= 4) who presently had no apparent or
known musculoskeletal injuries. All participants had exten-
sive experience with resistance training and performing
a variety of abdominal exercises throughout their training
career. Furthermore, they all scored in the excellent category
in the partial curl-up test of the Canadian Physical Activity,
Fitness, and Lifestyle appraisal. Fourteen participants were
able to complete the exercise movements correctly. One
participant was unable to maintain the pelvic tilt position
during the isometric portion of the leg raise activity. His data
were not included in the statistical analysis. Each subject was
required to read and sign a consent form before participation.
The Human Investigation Committee, Memorial University
of Newfoundland, approved this study.
Surface Electromyography Preparation and Placement
It has been suggested that a valid EMG signal is compromised
when the muscles of interest are performing a dynamic
contraction (4,8). As the joint moves through a range of
motion, the distance between the muscle and the detection
surface changes, which results in a change in the EMG
amplitude. It is recommended that isometric contractions be
used to control for movement during surface EMG testing.
Although this detracts from the ecological validity, it does
increase the validity and reliability of the EMG signal (8). An
effective start for analyzing the effect of pelvis position on
trunk muscle activity would be to use quantified and
controlled EMG procedures.
The electrode placement sites were prepared by shaving,
exfoliating with sandpaper, and wiped with isopropyl alcohol.
Participants were placed in a supine position on a plinth,
Figure 1. A Janda sit-up with resistance provided to the posterior ankle/
heel area so that the participant can contract the hamstrings while
attempting to curl the trunk/abdominal region.
1564
Journal of Strength and Conditioning Research
the
TM
Activation of Abdominals with Pelvic Position
providing support to the entire length and width of the body.
Electromyographic surface electrodes (Kendall Medi-trace
100 series; Kendall, Chikopee, MA) were placed in parallel
with the muscle fibers with an interelectrode distance of 2 cm.
A ground electrode was placed at the nearest bony
prominence for each pair of active electrodes. The 6 muscle
sites were the URA, LRA, external obliques, LAS (reported to
represent activation of the internal obliques and transversus
abdominis [1,5,6]), biceps femoris, and rectus femoris. The
rectus femoris was used to approximate the activity of the
deep hip flexors, namely, the iliopsoas muscle group (14).
Landmarking for the URA was achieved by measuring 3 cm
lateral to the midline and midway between the xiphoid
process and the umbilicus. The LRA was positioned 3 cm
lateral to the midline and 2 cm inferior to the umbilicus.
Additional electrodes were placed superior to the inguinal
ligament and 1 cm medial to the anterior superior iliac spine
for the lower abdominals. McGill et al. (14) reported that
surface electrodes adequately represent the EMG amplitude
of the deep abdominal muscle within a 15% root mean square
difference. However, Ng et al. (15) indicated that electrodes
placed medial to the anterosuperior iliac spine would receive
competing signals from the external obliques and transverse
abdominis with the internal obliques. Based on these
findings, the EMG signals obtained from this abdominal
location are described in the present study as the LAS, which
would be assumed to include EMG information from both
the transverse abdominis and internal obliques. The external
obliques were positioned superior to the anterior superior
iliac spine at an oblique angle, at the level of the umbilicus.
Biceps femoris electrodes were positioned at the midpoint
of the muscle belly of the biceps femoris. Rectus femoris
electrodes were positioned at the most proximal aspect of the
muscle belly. All muscle sites were measured on the right side
of the body only.
Exercise Instruction
The participants were instructed on proper technique to
complete a maximal anterior pelvic tilt and maximal posterior
pelvic tilt. The anterior pelvic tilt was achieved by asking the
participants to tilt the pelvis forward in order to create as
much space as possible between the plinth and the lower back
area. The posterior pelvic tilt was achieved by asking the
participants to flatten their lower back into the plinth. Manual
guidance was also provided during the instruction and
familiarization period to ensure proper technique and
understanding. The neutral position was described as the
participants’ normal, comfortable resting supine position. One
investigator was positioned by the side of each participant to
ensure proper pelvic positioning during data collection as well
as palpating the anterosuperior iliac spine as a way of
monitoring pelvic position. A second investigator was
positioned at each participant’s feet to ensure proper leg
lifting during the exercise. Participants were instructed to keep
their head resting on the plinth and to rest their hands by their
sides. Participants began in a supine position on the plinth
with their legs straight and their feet placed on a stable bench
15 cm in height. For the anterior pelvic tilt position,
participants were asked to assume the proper position. A
reference mark was placed on the lateral malleolus and the
bench supporting the feet. This mark would be used to ensure
the same starting position for the second trial of the exercise.
The participants were asked to raise their feet off the support 5
cm, hold the position for 5 seconds, and return to the support.
A 30-second rest period was provided before a second trial
was performed. The same procedure was followed for the
neutral and posterior pelvic tilt positions. A 3-minute rest
period was provided between the anterior, neutral, and
posterior tilt trials. The order of exercises was randomized.
If the position was not held properly, then the position and
the data acquisition was terminated and attempted again after
an appropriate rest period.
The Janda sit-up was performed in a supine, crook-lying
position (Figure 1). A padded bar was placed at the back of
the lower leg and held in place manually by one of the
investigators. This bar provided an object against which each
participant was able to contract the hamstring muscles, by
attempting to perform bilateral knee flexion. This bar was
held manually by an investigator in order to ensure that
consistent hamstring contraction occurred throughout the
entire exercise trial. The participants were instructed to
contract the hamstring muscles, perform the sit-up, and hold
for 5 seconds at approximately 45°before returning to the
start position. A 30-second rest period was provided before
the second trial. The order of pelvic position and the Janda
sit-up was randomly assigned.
The isometric BSLL was used in this study to allow us to
maintain a relatively constant torso and leg position, while
changing only the pelvis position. We do acknowledge that
with any change in pelvis rotation there will be changes in the
rest of the kinetic chain, both above and below the pelvis.
However, this exercise would provide the most consistency in
the upper and lower body segments, allowing us to examine
the influence of the pelvis on abdominal muscle activity.
Electromyographic Data Collection
Electromyographic data were collected during the concentric
and isometric contractions of each exercise. The EMG signals
were amplified (MEC 100 amplifier; Biopac Systems Inc.,
Santa Barbara, CA), monitored, and directed through an
analog-digital converter (Biopac MP100) to be stored on the
computer (Sona, St. John’s, Newfoundland, Canada). The
EMG signals were collected over 15 seconds at 2000 Hz and
amplified (3500). The EMG activity was sampled at 2000 Hz
with a Blackman 61-dB band-pass filter between 10 and 500
Hz, amplified (Biopac Systems MEC bipolar differential 100
amplifier, Biopac Systems, Inc.; input impedance = 2 MV
common mode rejection ratio .110 dB minimum (50/60
Hz), noise .5 UV) and analog-to-digitally converted (12 bit)
and stored on personal computer for further analysis. The
VOLUME 22 | NUMBER 5 | SEPTEMBER 2008 | 1565
Journal of Strength and Conditioning Research
the
TM
|
www.nsca-jscr.org
EMG signal was rectified and integrated over the 5-second
static (isometric) contraction period of the movement. An
average of the 2 trials was obtained, and the mean integrated
value used for statistical analysis. Similar to previous
published research from this laboratory (6), absolute rather
than normalized EMG data were analyzed because it was a
repeated-measures design that was completed in a single
experimental session (no change in electrode position). Since
the focus was on changes in activation of individual muscles
and not between muscles or individuals, normalization of the
electromyogram was not considered necessary.
Statistical Analyses
A 1-way, repeated measures analysis of variance (GBStat;
Dynamic Microsystems, Silver Spring, MD) was performed to
detect differences in muscle activation for each muscle,
relative to pelvic position and Janda sit-up exercise. When
statistical significance was found, the Dunn’s (Bonferroni)
post hoc test was used to reveal the differences. Descriptive
statistics include mean 6SD.
RESULTS
Upper Rectus Abdominis
For the URA site, the Janda sit-up demonstrated the highest
EMG activity. Relatively, the anterior pelvic tilt position
showed 70.9% less activity in the URA (p,0.01). The EMG
activity in the neutral position was 52.1% less than that seen
in the Janda sit-up (p,0.01). There was no significant
difference between the Janda sit-up and the posterior pelvic
tilt position. The anterior position demonstrated 57% less
activity than the posterior pelvic tilt position (p,0.05)
(Figure 2).
Lower Rectus Abdominis
For the LRA site, the Janda sit-up elicited the highest EMG
activity. This was significantly different than the anterior
pelvic tilt position (p,0.01), which showed 68.4% less
activity, and the neutral position (p,0.05), which showed
46.3% less activity. There was no significant difference
between the Janda sit-up and the posterior pelvic tilt position
for LRA activity. The anterior pelvic tilt position showed
significantly less (56.6%) activity in the LRA than in the
posterior pelvic tilt position (p,0.05) (Figure 3).
Rectus Femoris
The rectus femoris site demonstrated the highest activity in
the anterior pelvic tilt position. This was significantly different
from the Janda sit-up (p,0.05), which showed 38.1% less
activity. There were no other significant rectus femoris
differences when compared to the other test positions. The
Janda sit-up was not significantly different from the posterior
pelvic tilt or neutral positions (Figure 4).
Biceps Femoris
In the biceps femoris site, the Janda sit-up provided the
highest EMG activity. This was significantly higher than all
other test positions (p,0.01). The neutral, anterior, and
posterior pelvic tilt positions demonstrated 91.1%, 88.6%, and
87.8% less biceps femoris activity, respectively. There were no
other significant differences in biceps femoris activity among
the pelvic tilt positions (Figure 5).
External Obliques
There were no statistically significant differences in external
obliques EMG activity when comparing the 4 test positions
(p= 0.09). The Janda sit-up and the neutral pelvis positions
showed the greatest difference
in EMG activity.
Lower Abdominal Stabilizers
There were no statistically sig-
nificant differences in LAS
EMG activity when comparing
the 4 test positions.
DISCUSSION
The major findings of this study
show that changing the posi-
tion of the pelvis significantly
changes the pattern of activa-
tion of the URA, LRA, and
rectus femoris. This is in agree-
ment with a study by Shields
and Heiss (20) who found that
the double straight leg lowering
exercise, while maintaining
posterior pelvic tilt, achieved
greater abdominal muscle acti-
vation compared to a typical
Figure 2. Upper rectus abdominis (URA) electromyographic activity in each pelvis position and the Janda sit-up.
Bars and accompanying lines represent mean electromyographic activity and SDs, respectively. *Significant
difference at the p,0.05 level; **significance level of p,0.01.
1566
Journal of Strength and Conditioning Research
the
TM
Activation of Abdominals with Pelvic Position
crunch exercise. Posterior pelvic tilting has also been found to
activate the rectus abdominis to a greater degree than in the
abdominal hollowing exercise (9). Other studies have
identified high levels of rectus abdominis activity during
the posterior pelvic tilt maneuver (24) and leg lifting exercise
(2). This differs from the results of Urquhart et al. (23) who
found the internal oblique mus-
cle more active than the rectus
abdominis during a posterior
pelvic tilt. In the Urquhart et al.
study, participants were asked
to gently and slowly rock their
pelvis backward. Urquhart et al.
(23) describe this as a gentle
effort, corresponding to a 2 on
the Borg scale. The present
methodology differed in that
the posterior pelvic tilt was
accompanied by the isometric
DSLL, a much more demand-
ing task. Our study was in
agreement, however, with the
authors’ conclusion that ab-
dominal muscle activity was
dependent on body position,
including lumbopelvic motion
or position.
There is general agreement
that an individual cannot pref-
erentially activate the URA
versus LRA (7,12) unless highly trained (19). The results of
the present study also found similar activation patterns for
the URA and LRA throughout the exercises. Moreover, it
has been found that no single exercise is able to optimally
recruit all the abdominal musculature simultaneously (3).
Therefore, a comprehensive, individualized program is
required to sufficiently chal-
lenge each of the abdominal
muscles (3) in different planes
of movement.
The anterior pelvic tilt posi-
tion provided the highest EMG
activity in the rectus femoris
and the lowest EMG record-
ings in both the URA and LRA.
The anterior tilt may place the
rectus femoris and underlying
iliopsoas muscle group in
a more optimal length position.
This will change the muscle
length–tension relationship and
produce higher contractile
forces. As the rectus femoris is
in an optimal position, the LRA
and URA will be placed in
a relatively lengthened position.
For the LRA and URA, the
change in length-tension rela-
tionship may place the muscles
in a disadvantageous position
and cause a reduction in
Figure 3. Lower rectus abdominis (LRA) electromyographic activity in each pelvis position and the Janda sit-up.
Bars and accompanying lines represent mean electromyographic activity and SDs, respectively. *Significant
difference at the p,0.05 level; **significance level of p,0.01.
Figure 4. Rectus femoris (RF) electromyographic activity in each pelvis position and the Janda sit-up. Bars and
accompanying lines represent mean electromyographic activity and SDs, respectively. *Significant difference at the
p,0.05 level.
VOLUME 22 | NUMBER 5 | SEPTEMBER 2008 | 1567
Journal of Strength and Conditioning Research
the
TM
|
www.nsca-jscr.org
contractile forces. Furthermore, several authors have cau-
tioned against the use of the BSLL because of the risk of low
back injury caused by increased shear and compressive forces
(3,9). Invariably, individuals may adopt an anterior pelvic tilt
position when performing sit-ups or leg raises that can be
considered contraindicated considering the increased shear
and compressive forces (3,9) placed on the lower back by
stronger hip flexors.
A secondary finding showed that the Janda sit-up produced
relatively high levels of URA and LRA activity and low levels
of rectus femoris activity; however, this was not significantly
different from the posterior pelvic tilt. Our results regarding
the inability of the Janda sit-up to significantly reduce hip
flexor activity in comparison to the posterior pelvic tilt are in
agreement with Juker et al. (10) who found no decrease in
psoas activity using the ‘‘press heels’’ sit-up. The Janda sit-up
is identical to a traditional bent-knee sit-up when considering
the trunk flexion component. The difference is in the
contraction of the hamstring muscles during the exercise. As
this is a sit-up movement, it is typically performed in
a posterior pelvic tilt start position (16). Participants were not
instructed regarding pelvis position before the Janda sit-up
trials. Therefore, pelvis position was not controlled during
this exercise. This may account for some of the similarities
between the Janda sit-up and the results from the posterior
pelvic tilt position. The contraction of the hamstrings during
the Janda sit-up purportedly reduces hip flexor activation
through reciprocal inhibition (10). Our data cannot conclude
whether the low rectus femoris activity can be attributed to
reciprocal inhibition through contraction of the hamstring
musculature. The Janda sit-up did demonstrate the highest
biceps femoris activity as antic-
ipated. However, the rectus
femoris activity was not signif-
icantly different from the pos-
terior pelvic tilt position.
Differences in the posterior
pelvic tilt and Janda sit-up are
seen when we examine their
relationship to the neutral pel-
vis position. For both the URA
and LRA sites, the Janda sit-up
demonstrated significant differ-
ences from the neutral position;
however, the posterior pelvic
tilt position did not. This may
be explained by the investiga-
tors’ definition of neutral pelvis.
The participants were asked to
maintain their normal, comfort-
able supine position. The dis-
crepancy of neutral for each
participant may have influ-
enced the results. In addition,
anatomically, the neutral posi-
tion may be closer in range of available motion to the
posterior tilt than the anterior direction. This may account for
the lack of significant difference in muscle activity when
comparing the neutral position to the posterior pelvic tilt
position.
When we examine the overall trend of muscle site activity,
a pattern emerges. As the participant moves from a posterior
pelvic tilt position through neutral to the anterior pelvic tilt
position, the relative activity of the URA, LRA, and rectus
femoris becomes reversed. During the posterior pelvic tilt and
Janda sit-up, there are high levels of activity in both the URA
and LRA and low activity in the rectus femoris. In the neutral
position, the level of activity of the URA and LRA decreases,
although this was shown to be only significantly different from
the Janda sit-up. The activity of the rectus femoris increased
slightly when mean EMG activity was examined; however, the
change was not significant. In the anterior pelvic tilt position,
the URA and LRA exhibited their lowest activity levels, while
the rectus femoris shows the highest level of activity.
There was no significant difference between the exercises in
the amount of EMG activity in the LAS or external obliques
muscle sites. This differs from Shields and Heiss (20), who
found varying levels of oblique muscle activity during their
isometric double straight leg lowering exercise. The finding
in the present study would suggest that the stabilizing role of
the LAS (24) was similar for all pelvic positions as well as the
Janda sit-up. As the DSLL is not a trunk flexion exercise,
a significant difference in the activity of a trunk flexor such as
the external obliques might not be expected. The Janda sit-
up, however, is a trunk flexion exercise, but it did not show
significant differences in external obliques activity compared
Figure 5. Biceps femoris (BF) electromyographic activity in each pelvis position and the Janda sit-up. Bars and
accompanying lines represent mean electromyographic activity and SDs, respectively. **Significance level of p,
0.05.
1568
Journal of Strength and Conditioning Research
the
TM
Activation of Abdominals with Pelvic Position
to the 3 different pelvis positions. During these exercises, the
external obliques probably also act as a stabilizer (2).
The biceps femoris muscle site was also unaffected by
a change in pelvis position. This hip extensor muscle may be
expected to have little activation during a hip flexion type of
activity. During the Janda sit-up, there was significantly
greater biceps femoris activity compared to the other test
positions. This is to be expected as the participant is instructed
to actively contract the hamstrings while performing the
Janda sit-up.
PRACTICAL APPLICATIONS
The results of this study will be of value when instructing
persons in correct posture during supine abdominal strength-
ening activities. There is evidence showing that specific
exercise instruction is important for a client to learn and retain
the proper technique and form of an exercise (11). Particular
attention should be given to individuals with increased
lumbar lordosis or very weak abdominal muscles. Several
authors have stressed the potential increase in lumbar
compression and shear force with some abdominal exercises.
The BSLL is not recommended for individuals who have
known lumbar pathologies or very weak abdominal mus-
culature (3,10). These individuals may be at risk of moving
into an anterior pelvic tilt position due to postural habit or
fatigue while exercising (9,22). By changing the rotation of
the pelvis, the focus of the strengthening exercise may shift
from the abdominals to the hip flexors. These results will add
to the existing and emerging scientific literature regarding the
relationship between the pelvis, hip, and lumbar spine and
the interplay of the supporting musculature.
From these data, we can conclude that a change in pelvis
position demonstrates significant differences in URA, LRA
and rectus femoris muscle activity, as measured by surface
electromyography. When considering pelvis position in-
dependently, the highest abdominal muscle activity occurs in
the posterior pelvic tilt position. The Janda sit-up also seems
to be effective in producing significant activation of the rectus
abdominis.
ACKNOWLEDGMENTS
The National Science and Engineering Research Council of
Canada supported this research.
REFERENCES
1. Anderson, K and Behm, DG. Trunk muscle activity increases
with unstable squat movements. Can J Appl Physiol 30: 33–45, 2005.
2. Andersson, EA, Nilsson, J, Ma, Z, and Thorstensson, A. Abdominal
and hip flexor muscle activation during various training exercises.
Eur J Appl Physiol 75: 115–123, 1997.
3. Axler, CT and McGill, SM. Low back loads over a variety of
abdominal exercises: searching for the safest abdominal challenge.
Med Sci Sports Exerc 29: 804–811, 1997.
4. Basmaijan, JV and De Luca, CJ. Muscles Alive: Their Functions
Revealed by Electromyography (5th ed.). Baltimore: Williams &
Wilkins, 1985.
5. Behm, DG, Burry, SM, Greeley, GED, Poole, AC, and Mackinnon,
SN. An unstable base alters limb and abdominal activation strategies
during the flexion-relaxation response. J Sports Sci Med 5: 323–332,
2006.
6. Behm, DG, Leonard, A, Young, W, Bonsey, A, and MacKinnon, S.
Trunk muscle EMG activity with unstable and unilateral exercises.
J Strength Cond Res 19: 193–201, 2005.
7. Clark, KM, Laurence, EH, and Sinyard, J. Electromyographic
comparison of the upper and lower rectus abdominis during
abdominal exercises. J Strength Cond Res 17: 475–483, 2003.
8. De Luca, CJ. The use of surface electromyography in biomechanics.
J Appl Biomech 13: 135–163, 1997.
9. Drysdale, CL, Earl, JE, and Hertel, J. Surface electromyographic
activity of the abdominal muscles during pelvic-tilt and abdominal-
hollowing exercises. J Athletic Train 39: 32–36, 2004.
10. Juker, D, McGill, S, Kropf, P, and Steffen, T. Quantitative
intramuscular myoelectric activity of lumbar portions of psoas and
the abdominal wall during a variety of tasks. Med Sci Sports Exerc 30:
301–310, 1998.
11. Karst, GM and Willett, GM. Effects of specific exercise instructions
on abdominal muscle activity during trunk curl exercises. J Orthop
Sports Phys Ther 34: 4–12, 2004.
12. Lehman, GJ and McGill, SM. Quantification of the differences in
electromyographic activity magnitude between the upper and lower
portions of the rectus abdominis muscle during selected trunk
exercises. Phys Ther 81: 1096–1101, 2001.
13. McGill, SM. The biomechanics of low back injury: implications on
current practice in industry and in the clinic. J Biomech 30: 465–475,
1997.
14. McGill, SM, Juker, D, and Kropf, P. Appropriately placed surface
EMG electrodes reflect deep muscle activity (psoas, quadratus
lumborum, abdominal wall) in the lumbar spine. J Biomech 29: 1503–
1507, 1997.
15. Ng, JK, Kippers, V, and Richardson, CA. Muscle fiber orientation of
abdominal muscles and suggested surface EMG electrode positions.
Electromyogr Clin Neurophysiol 38: 51–58, 1998.
16. Norris, CM. Abdominal muscle training in sport. Br J Sports Med 27:
19–26, 1993.
17. Panjabi, MN. The stabilizing system of the spine. Part 1. Function,
dysfunction, adaptation, and enhancement. J Spine Disord 5: 383–389,
1992.
18. Panjabi, MN. The stabilizing system of the spine. Part 2. Neutral
zone and stability hypothesis. J Spine Disord 5: 390–397,
1992.
19. Sarti, MA, Monfort, M, Fuster, MA, and Villaplana, LA.
Muscle activity in upper and lower rectus abdominis during
abdominal exercises. Arch Phys Med Rehabil 77: 1293–1297, 1996.
20. Shields, RK and Heiss, DG. An electromyographic comparison of
abdominal muscle synergies during curl and double straight leg
lowering exercises with control of the pelvic position. Spine 22:
1873–1879, 1997.
21. Shirado, O, Toshikazu, I, Kaneda, K, and Strax, TE.
electromyographic analysis of four techniques of isometric
trunk muscle exercises. Arch Phys Med Rehabil 76: 225–229,
1995.
22. Shirazi-Adl, A, Sadouk, S, Parnianpour, M, Pop, D, and
El-Rich, M. Muscle force evaluation and the role of
posture in human lumbar spine under compression. Eur Spine J
11: 519–526, 2002.
23. Urquhart, DM, Hodges, PW, Allen, TA, and Story, IH. Abdominal
muscle recruitment during a range of voluntary exercises. Manual
Ther 10: 144–153, 2005.
24. Vezina, MJ and Hubley-Kozey, CL. Muscle activation in therapeutic
exercises to improve trunk stability. Arch Phys Med Rehabil 81:
1370–1379, 2000.
VOLUME 22 | NUMBER 5 | SEPTEMBER 2008 | 1569
Journal of Strength and Conditioning Research
the
TM
|
www.nsca-jscr.org
... Erector spinae At 2 cm laterally from the vertebra L3 (Gottschall et al., 2013) Cyclists were strapped in a prone position on a bench with their trunks unsupported. Manual resistance was applied by downward pressure at the mid-thoracic vertebrae level, as cyclists maintained a constant position with their trunk parallel to the floor (Caldwell et al., 2003) External oblique Above the anterior superior iliac spine at an oblique angle, at the level of the umbilicus (Workman et al., 2008) Cyclists were supine in a hook-lying position with their feet flat on the floor. The trunk was maximally flexed and rotated to the left, with manual resistance at the shoulders applied in the direction of trunk extension and proper rotation (Vera-Garcia et al., 2000) Anterior rectus abdominis At 3 cm laterally to the midline and midway between the xiphoid process and the umbilicus (Workman et al., 2008) Cyclists were required to perform a resisted curl-up exercise (Vera-Garcia et al., 2000) Appendix B ...
... Manual resistance was applied by downward pressure at the mid-thoracic vertebrae level, as cyclists maintained a constant position with their trunk parallel to the floor (Caldwell et al., 2003) External oblique Above the anterior superior iliac spine at an oblique angle, at the level of the umbilicus (Workman et al., 2008) Cyclists were supine in a hook-lying position with their feet flat on the floor. The trunk was maximally flexed and rotated to the left, with manual resistance at the shoulders applied in the direction of trunk extension and proper rotation (Vera-Garcia et al., 2000) Anterior rectus abdominis At 3 cm laterally to the midline and midway between the xiphoid process and the umbilicus (Workman et al., 2008) Cyclists were required to perform a resisted curl-up exercise (Vera-Garcia et al., 2000) Appendix B ...
Article
Cycling is a sport where cyclists predominantly adopt a sitting posture, with the trunk tilted forward. This posture requires a high volume of training and duration in several intensities of effort. This study aims to: 1) evaluate the behaviour of the thoracic and lumbar spine flexion and sacral inclination in the sagittal plane, the thoracic and lumbar spine flexion in the frontal plane, and the trunk torsion in the transverse plane; 2) compare the activation of the core muscles as the intensity of effort increases during an incremental test in cycling, and 3) identify which core muscle has a greater activation in each intensity zone. The spinal posture and the activation of the eight core muscles were evaluated in twelve competitive cyclists during incremental cycling intensities. Thoracic and lum-bar spine flexion and sacral inclination statistically increased as the intensity of effort increased (Start < VT1 < VT2 < VO2max). A significant increase in muscle activation was observed in all core muscles evaluated as the intensity increased. The rectus abdominis showed statistically significant greater muscle activation than the other core muscles evaluated. In conclusion, as the intensity of effort in cycling increases, cyclists significantly increase the thoracic and lumbar spine flexion, the sacral inclination in the sagittal plane, the thoracic and lumbar spine flexion in the frontal plane, trunk rotation in the transverse plane, as well as the activation of the core muscles.
... asyon programlarının bir parçası olarak yer almaktadır (Yoo, 2014). Dinamik omurga stabilitesini sürdürmek için nöromüsküler kontrolü, dayanıklılığı ve kasların gücünü geliştirmeyi amaçlayan PPT hareketinde rektus abdominis, internal ve eksternal abdominal oblik kaslar ile transversus abdominis kaslarında aktivasyon elde edillir (Drysdale vd., 2004., Workman vd., 2008, Urquhart vd 2005, Blackburn ve Portney, 1981. Aktive olan bu kaslar omurganın hem yüzeyel hem de derin stabilizasyonunda rol alırlar. Son yıllarda yayınlanan metaanaliz ve klinik rehberlerde kronik bel ağrılı hastalarda gövde stabilizasyonunun önemi vurgulanmış ve dizabiliteyi azalttığı yönünde bulgular sunulmuştur (Oliveira vd., 2018, ...
... Bu nedenle tedavi programlarına eklenen PPT egzersizi karın kaslarını kuvvetlendirmeyi hedefler ayrıca gövde stabilizasyonuna yardım eder (Wang vd., 2012). Daha önce yapılan çalışmalarda PPT hareketi sırasında rektus abdominis, eksternal abdominal oblik, internal abdominal oblik ve transversus abdominis kaslarında aktivite artışı olduğunu, servikal, torakal veya lomber erektör spina kaslarında aktivite artışı olmadığını göstermektedir (Drysdale vd., 2004;Workman vd., 2008;Urquhart vd., 2005;Blackburn ve Portney, 1981). Kuciel ve ark tarafından yakın zamanda yapılan bir çalışmada PPT hareketi sırasında rektus abdominis ile transversus abdominis/internal abdominal oblik kasların yüzeyel EMG sinyalinde anlamlı derecede artış olduğunu gösterdi (Kuciel. ...
... Considering the most active muscle during SLR exercise (Soderberg & Cook, 1983), we expected to see an increase in RF muscle activity with AE, especially during SLR exercises. RF activity increases with anterior pelvic tilt as it shortens RF muscle length (Workman, Docherty, Parfrey, & Behm, 2008), so decreasing anterior pelvic tilt with AE may compensate the improvement in RF activity that was seen in VMO and VL. Similar to our finding, Barbosa et al. (2017) found no change in RF muscle activity with AD technique during 60-degree-squat exercise. ...
Article
The purpose of this study was to investigate the effect of Abdominal Enhancement (AE) on the muscle activation of vastus medialis obliquus (VMO), vastus lateralis (VL) and rectus femoris (RF) muscle activation levels during eccentric, isometric and concentric phases of single leg raise (SLR), single leg wall squat (SLWS) and forward lunge (FL) exercises. Sixteen healthy individuals (Age: 24.6 ± 1.7 years) were included in the study. Internal Obliques/Transversus Abdominis (IO/TA), VMO, RF and VL muscle activation levels were measured by surface EMG during the exercises in two conditions: with and without AE. The abdominal drawing-in technique was used for AE. Repeated-measures analysis of variance was performed for statistical analysis. With AE, the average of IO/TA muscle activation level was 28.9%. VMO and VL muscle activation levels were significantly greater with AE during SLR (p = .02), SLWS (p < .001) and FL (VMO, p = .008, VL, p = .04) exercises. The effect of AE on VMO muscle activation level ranged from 2.5% to 5% (Effect size range: 0.54 to 0.91) and VL muscle activation level ranged from 2.1% to 5.5% (Effect size range: 0.35-1.24). RF muscle activation level did not change with AE (p > .05). The results of this study showed that AE increased VMO and VL muscle activities during SLR, SLWS and FL exercises but the corresponding changes were small. Even if this is not enough for muscle strengthening, exercises with AE may be used to enhance knee joint stability while controlling lumbopelvic stability.
... 1. Transverse abdominal/internal oblique muscle: 2 cm below the anterior superior iliac spine, in the lower medial direction [13]. ...
... Cables were fixed to the skin with tape to minimize the movement of electrodes. Electrodes were placed bilaterally in supine position in the following sites: 1) Transverse/internal oblique abdominal muscle (TrA/IO) -2 cm below the anterior superior iliac spine, in the inferomedial direction [31] 2) Lower rectus abdominis (RA) muscle -midpoint between the umbilicus and the pubic symphysis, 3 cm to the side [3]. ...
Article
Full-text available
Purpose: Exercises after pregnancy can reduce the severity and risk of postnatal locomotor system disorders and muscular dysfunctions. The aim of the study was to evaluate electromyographic activity of abdominal muscles in women who gave birth naturally and via a caesarean section, and to compare it to a group of women who have never given birth. Methods: 27 women were included into the study after completing the personal questionnaire and functional examination. The surface electromyography during abdominal bracing and posterior pelvic tilt was used to test rectus abdominis muscles and internus oblique/ transversus abdominis muscles bilaterally. After normalization test, patients were asked to perform abdominal bracing and posterior pelvic tilt exercises. Results: Activity of rectus abdominis muscle is higher in posterior pelvic tilt compared to abdominal bracing. It should be noted that the internus oblique/transversus abdominis muscle activity in both exercises is similar. Conclusions: In women after natural birth and after a cesarean section who experienced no locomotor system symptoms, no statistically significant differences in abdominal muscle activity in both exercises were observed. In each group being studied, posterior pelvic tilt activated rectus abdominis muscles to a greater extent than just bracing.
... This imbalance is expressed by an anterior tilt of the pelvis by the quadriceps muscles and iliopsoas muscles, while the posterior tilt is caused by the hamstrings muscle pulling posteriorly [34]. Accordingly, for those who have LBP with lumbar hyperlordosis, correcting muscle flexibility and strength on abdominal and hip joint is necessary to improve anterior pelvic tilt [35,36]. ...
Article
Full-text available
Background: LBP is a common and serious problem affecting vast populations of the world. However, only few studies on LBP in sub-Saharan Africa have been conducted. Studies report that LBP and pelvic angle are interrelated, and African residents have a high pelvic tilt. The strategy to prevent LBP should focus on activities that promote holistic health. For that purpose, it is important to grasp the state of LBP and how it affects people's lifestyle in Tanzania to clarify the direction of implementation of physiotherapy treatment and reduce the incidences of LBP among adults. This study aimed to investigate the prevalence and presentation of low back pain (LBP) and the relationship between anthropometric measurements and LBP among people in Moshi city, Kilimanjaro region Tanzania. Methods: Following signing consent forms, participants were given questionnaires regarding LBP and then grouped accordingly into either asymptomatic or symptomatic cohorts. Anthropometric measurements of participants' height, weight, curvature of the spine, and pelvic angle were obtained. Results: A Mann-Whitney U test analysis showed a significant difference in pelvic angle, body mass index (BMI), and thoracic kyphosis angle between the asymptomatic group and the symptomatic group. No significant differences in lumbar lordosis angle or abdominal muscle strength were found between the two groups. Conclusions: A person with symptomatic LBP in Tanzania has a large anteversion of the pelvic tilt and a thoracic kyphotic posture. This study shows a relationship between sagittal spinal alignment and LBP in Tanzania, which could allow for prospective identification of subjects prone to developing LBP in the future.
... PIVETTA; BADARÓ, 2014). A literatura destaca uma estreita correlação interfuncional entre a pelve, o MAP e as outras estruturas desta (BO, 2001;CHEN et al, 2005;WORKMAN, 2018;GAMEIRO, 2013). ...
Article
Introduction: Hip osteoarthritis (OA) with acetabular dysplasia negatively affects pelvic alignment and muscle function. We aimed to investigate the changes in muscle atrophy and fatty infiltration of the hip and trunk muscles 1 year after total hip arthroplasty (THA) in patients with hip OA with acetabular dysplasia. Methods: This study included 51 female patients who underwent THA for unilateral hip OA with acetabular dysplasia. The cross-sectional area (CSA) and muscle density of the gluteus maximus, gluteus medius, gluteus minimus, piriformis, iliopsoas, rectus abdominis, and abdominal oblique muscles using computer tomography and pelvic inclination angle using radiographs were assessed before and 1 year after THA. Results: At the 1-year follow-up, the CSA and muscle density of the gluteus medius (2,078 to 2,522 mm2 and 30.3 to 39.4 hounsfield units [HU]), iliopsoas (715 to 901 mm2 and 40.3 to 50.8 HU), and rectus abdominis (336 to 363 mm2 and 28.6 to 30.6 HU) of the affected limb had increased significantly (P < 0.05). The CSA and muscle density of the gluteus maximus (2,429 versus 2,884 mm2 and 23.7 versus 32.6 HU), gluteus minimus (636 versus 785 mm2 and 14.3 versus 37.1 HU), piriformis (505 versus 607 mm2 and 23.4 versus 31.6 HU), and iliopsoas (901 versus 997 mm2 and 50.8 versus 54.5 HU) in the affected limb were lower than those in the unaffected limb (P < 0.01). Postoperatively, the CSA and muscle density of the rectus abdominis were not significantly different between the limbs, and the pelvic inclination angle (35.2° to 32.1°, P < 0.01) was significantly decreased. Discussion: Compared with the nonoperated limb, substantial atrophy and fatty infiltration of most hip muscles persisted in the operated limb 1 year after THA in patients with acetabular dysplasia; asymmetry in the rectus abdominis muscle fully resolved. In patients with acetabular dysplasia, the surgical technique and postoperative rehabilitation should be further considered to optimize hip muscle recovery.
Article
Overhead throwing by cricketers when fielding with different approaches has been described using two-dimensional analysis. Currently, the three-dimensional kinematic and kinetic characteristics of an overhead throw performed by cricketers following a run-up is unknown. Fifteen South African cricketers performed six overhead throws, from a stationary position and with a run-up over 15-20 m prior to fielding a ball, respectively. Kinematic data and ground reaction forces were collected throughout the throwing trials. Joint kinetics were calculated using inverse dynamics. An independent t-test or Mann-Whitney U test was used to determine joint kinetic differences between throwing approaches. Differences between the kinematic waveforms for stationary and run-up throwing approaches were assessed using one-dimensional statistical parametric mapping ANOVA (P<0.05). The shoulder, elbow and thoraco-lumbar joints displayed similar kinematics between throwing approaches. The run-up approach displayed increased hip flexion between 0-34% and 57-100% (F(1, 28) = 6.726;P=0.01) of the throwing cycle; and lumbo-pelvic flexion between 57-65% (F(1, 28) = 6.823;P=0.02) of the throwing cycle; greater shoulder compression (F(1, 28) = 1.036;P=0.02) and posterior force (F(1, 28) = 1.052;P=0.009) at maximum external rotation; yet less superior shoulder force (F(1, 28) = 1.744;P=0.005) and elbow compression (F(1, 28) = 4.331;P=0.03), superior (F(1, 28) = 1.212;P=0.002) and medial (F(1, 28) = 1.370;P=0.03) elbow forces at ball release, when compared to a stationary position. Cricketers maintain similar upper limb kinematics between overhead throwing approaches. However, throwing with a run-up approximately doubles the forces exerted on the shoulder at maximum external rotation, which is most likely caused by the greater dominant hip and lumbo-pelvic flexion noted. This may amplify the potential risk for shoulder injury when throwing.
Article
Full-text available
The flexion-relaxation phenomenon consisting of an erector spinae silent period occurring with trunk flexion can place considerable stress upon tissues. Since individuals often flex their trunks while unstable, the purpose of the study was to examine the effect of an unstable base on the flexion-relaxation response. Fourteen participants flexed at the hips and back while standing on a stable floor or an unstable dyna-disc. Hip and trunk flexion were repeated four times each with one-minute rest. Electromyographic (EMG) electrodes were placed over the right lumbo-sacral erector spinae (LSES), upper lumbar erector spinae (ULES), lower abdominals (LA), biceps femoris and soleus. In addition to the flexion-relaxation phenomenon of the ES, a quiescence of biceps femoris and a burst of LA EMG activity was observed with the majority of stable trials. There was no effect of instability on the flexion-relaxation phenomenon of the ULES or LSES. The incidence of a biceps femoris silent period while stable was diminished with an unstable base. Similarly, the incidence of a LA EMG burst was curtailed with instability. Soleus EMG activity increased 29.5% with an unstable platform. An unstable base did not significantly affect LSES and ULES EMG flexion-relaxation, but did result in more persistent lower limb and LA activity. Key PointsAn unstable base did not affect the flexion relaxation response of the erector spinae.An unstable base decreased the incidence of biceps femoris quiescent period.An unstable base diminished the incidence of the lower abdominals EMG burst.
Article
Full-text available
The neutral zone is a region of intervertebral motion around the neutral posture where little resistance is offered by the passive spinal column. Several studies--in vitro cadaveric, in vivo animal, and mathematical simulations--have shown that the neutral zone is a parameter that correlates well with other parameters indicative of instability of the spinal system. It has been found to increase with injury, and possibly with degeneration, to decrease with muscle force increase across the spanned level, and also to decrease with instrumented spinal fixation. In most of these studies, the change in the neutral zone was found to be more sensitive than the change in the corresponding range of motion. The neutral zone appears to be a clinically important measure of spinal stability function. It may increase with injury to the spinal column or with weakness of the muscles, which in turn may result in spinal instability or a low-back problem. It may decrease, and may be brought within the physiological limits, by osteophyte formation, surgical fixation/fusion, and muscle strengthening. The spinal stabilizing system adjusts so that the neutral zone remains within certain physiological thresholds to avoid clinical instability.
Article
This lecture explores the various uses of surface electromyography in the field of biomechanics. Three groups of applications are considered: those involving the activation timing of muscles, the force/EMG signal relationship, and the use of the EMG signal as a fatigue index. Technical considerations for recording the EMG signal with maximal fidelity are reviewed, and a compendium of all known factors that affect the information contained in the EMG signal is presented. Questions are posed to guide the practitioner in the proper use of surface electromyography. Sixteen recommendations are made regarding the proper detection, analysis, and interpretation of the EMG signal and measured force. Sixteen outstanding problems that present the greatest challenges to the advancement of surface electromyography are put forward for consideration. Finally, a plea is made for arriving at an international agreement on procedures commonly used in electromyography and biomechanics.
Article
Objective: To compare the intensity of the upper versus lower rectus abdominis (RA) muscle activity provoked by each of two different abdominal exercises and to contrast the intensity of contraction elicited by two different abdominal exercises on each RA muscle portion. Design: Nonrandomized control trial. Setting: Kinesiology laboratory in a university medicine faculty. Participants: Convenience sample of 33 healthy volunteers. Subjects who had practiced endurance or strength training activities (1.5 hours 3 days a week for 3 years) and those who had not accomplished that criterion comprised a high and a low physical activity group, respectively. Each of these two groups was divided by the ability to perform the exercises into two subgroups: correct and incorrect performers (cp, ic). Main outcome measure: Average surface iEMG was compared between upper and lower RA and on each muscle portion performing curl-up (CU) and posterior pelvic tilt (PT) exercises. The coefficient of variation, a two-way analysis of variance, and the t test were calculated. Results: The upper RA showed significantly greater activity during performance of CU exercise by the cp subgroups of both high (t = 2.14302, 95%) and low (t = 2.35875, 95%) activity groups. Only the cp subgroup of the high activity group showed that PT was significantly more strenuous than CU exercise on lower RA (t = -2.06467, 95%). Conclusions: Among correct performers, CU produces greater activity on upper RA. For persons who have a high level of activity, PT is more strenuous than CU on lower RA. Among incorrect performers, either exercise indistinctly activates the muscle portions.
The ability of surface electrodes to accurately detect the activity of a particular muscle relies not only on their being placed over the muscle but also on their position in relation to muscle fibre orientation. For optimal pick-up of electromyographic (EMG) signals, surface electrodes are best aligned in parallel with the fibre orientation of the underlying muscle. This study aimed to measure muscle fibre orientation and other parameters of muscle morphology of the abdominal muscles in relation to palpable bony landmarks. Thirty-seven embalmed cadavers (19 males and 18 females) were examined. Results showed that the fibres of obliquus externus abdominis were about 4 degrees more vertical than the lower edge of the eighth rib. Below the rib cage, the muscle fibres of obliquus externus abdominis were approximately 5 degrees closer to vertical than a reference line between the most inferior point of the costal margin and the contralateral pubic tubercle. In the anterolateral abdominal wall area below the anterior superior iliac spine (ASIS), the obliquus internus abdominis was superficial being covered only by the aponeurosis of obliquus externus abdominis. At the level of ASIS, the muscle fibres of obliquus internus abdominis were almost horizontally orientated but at 2 cm below ASIS were aligned about 6 degrees inferomedially to the horizontal. The muscle fibres of upper rectus abdominis were 2 degrees inferolateral to the midline while the lower rectus abdominis muscle fibres deviated inferomedially from the midline by about 8 degrees. The appropriate surface electrode placements which follows the muscle fibre orientation of the obliquus externus abdominis, obliquus internus abdominis and rectus abdominis have been suggested.
Article
Since most previous reports of EMG activation profiles from psoas and the abdominal wall have been qualitative, the objective of this work was to document myoelectric activity from these deep muscles. This knowledge is required to assist in choosing specific training exercises and for making rehabilitation decisions that require knowledge of normalized and calibrated muscle activation levels in different tasks. Intramuscular EMG was collected from five men and three women, in whom amplitudes were normalized to maximum contraction efforts and reported over a wide variety of clinical and rehabilitation tasks. Electrodes were inserted into vertebral portions of psoas and the three layers of the abdominal wall. Normalized signal amplitudes were reported as peak levels and time histories. All forms of sit-ups activated psoas (15-35% MVC) more than the curl-up (<10%); psoas was not highly activated during barbell lifting of loads up to 100 kg (< 16% MVC); psoas was most active during maximal hip flexion efforts; push-ups activated psoas up to 25% MVC. Several isometric abdominal exercises were evaluated using the criteria of maximizing abdominal activation while minimizing psoas activity: the side (bridge) support exercise proved the best training method for the abdominal wall. Consideration of deep muscle activity, provided in this report, is important for choosing the most appropriate rehabilitation and training program for an individual. Specific guidance is provided for choosing the best abdominal exercise, together with activation profiles during lifting, during twisting, and during hip rotation.
Cortical average evoked potentials were simulated by summing five damped sinusoids. The characteristics of these "evoked" responses could be manipulated by changing parameters of the sinusoids. The synthesized signals were mixed with noise processes whose power and band-width were manipulated. Thus data were generated to stimulate a variety of conditions which could conceivably occur in an experiment on evoked potentials. Stepwise discriminant analysis (BMD07M) has been applied to these simulated data in an attempt to determine the degree to which the program identifies, in a sensible manner, the differences we introduced into the synthesized evoked responses. The simulation results indicate that stepwise discriminant analysis can indeed be an efficacious tool in research on evoked potentials. The program does detect differences in evoked potentials. It can be used, with some reservations, to identify the components of an evoked potential which the experimental variables have affected. In a special set of simulations we have attempted to determine the degree to which stepwise discriminant analysis could serve to detect the presence or absence of an evoked potential. These simulations show that the score of an average evoked potential in the data. The implications of this finding to the use of evoked potentials in sensory sensitivity testing were evaluated in studies for the effect on them of stimulus intensity.