Physiotherapy Theory and Practice, 29(2):113–123, 2013
Copyright © Informa Healthcare USA, Inc.
ISSN: 0959-3985 print/1532-5040 online
DOI: 10.3109/09593985.2012.704492
RESEARCH REPORT
Electromyographic analysis of trunk and hip muscles
during resisted lateral band walking
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James W. Youdas, PT, MS,1 Brooke M. Foley, DPT,2 BreAnna L. Kruger, DPT,2 Jessica M.
Mangus, DPT,2 Alis M. Tortorelli, DPT,2 Timothy J. Madson, PT, MS, OCS,3 and
John H. Hollman, PT, PhD1
1
2
3
Associate Professor, Physical Therapy Program, Mayo Clinic, Rochester, MN, USA
Doctoral Student, Physical Therapy Program, Mayo Clinic, Rochester, MN, USA
Assistant Professor, Physical Therapy Program, Mayo Clinic, Rochester, MN, USA
ABSTRACT
The purpose of this study was to simultaneously quantify bilateral activation/recruitment levels (% maximum
voluntary isometric contraction [MVIC]) for trunk and hip musculature on both moving and stance lower limbs
during resisted lateral band walking. Differential electromyographic (EMG) activity was recorded in neutral,
internal, and external hip rotation in 21 healthy participants. EMG signals were collected with DE-3.1 doubledifferential surface electrodes at a sampling frequency of 1,000 Hz during three consecutive lateral steps.
Gluteus medius average EMG activation was greater ( p = 0.001) for the stance limb (52 SD 18% MVIC) than
moving limb (35 SD 16% MVIC). Gluteus maximus EMG activation was greater ( p = 0.002) for the stance limb
(19 SD 13% MVIC) than moving limb (13 SD 9% MVIC). Erector spinae activation was greater ( p = 0.007) in
hip internal rotation (30 SD 13% MVIC) than neutral rotation (26 SD 10% MVIC) and the moving limb (31 SD
15% MVIC) was greater ( p = 0.039) than the stance limb (23 SD 11% MVIC). Gluteus medius and maximus
muscle activation were greater on the stance limb than moving limb during resisted lateral band walking.
Therefore, clinicians may wish to consider using the involved limb as the stance limb during resisted lateral
band walking exercise.
INTRODUCTION
Rehabilitation professionals utilize hip abductor
strengthening exercises in patients with a variety of
musculoskeletal disorders including: 1) patellofemoral
pain syndrome (Bolgla, Malone, Umberger, and Uhl,
2008; Cichanowski, Schmitt, Johnson, and Niemuth,
2007; Ireland, Willson, Ballantyne, and Davis, 2003;
Piva, Goodnite, and Childs, 2005; Prins and van der
Wurff, 2009; Robinson and Nee, 2007); 2) iliotibial
band syndrome (Fairclough et al, 2006, 2007; Fredericson et al, 2000; Noehren, Davis, and Hamill, 2007);
3) total hip arthroplasty (Nilsdotter and Isaksson,
2010); 4) total knee arthroplasty (Chang et al, 2005;
Husby et al, 2009; Jensen, Aagaard, and Overgaard,
Accepted for publication 14 June 2012
Address correspondence to James W. Youdas, Physical Therapy
Program, Mayo Clinic, Rochester, MN, USA. E-mail: youdas.james@
mayo.edu
2011; Piva et al, 2011; Rasch, Byström, Dalen, and
Berg, 2007; Rasch, Dalen, and Berg, 2010; Trudelle-Jackson and Smith, 2004); and 5) chronic
ankle instability (Friel, McLean, Myers, and
Caceres, 2006; Nadler et al, 2000; Nicholas, Strizak,
and Veras, 1976). The clinical examples cited above
substantiate the usefulness of hip abductor muscle
strengthening in a variety of rehabilitation programs.
Strengthening exercises for the hip muscles can be
performed in either non-weight-bearing (NWB) or
weight-bearing positions (WB). The prudent clinician
who conscientiously uses evidence-based medicine
can assess the usefulness of a particular hip strengthening exercise procedure by reviewing the literature
and observing a muscle's activation level when
exposed to an external load under controlled conditions. One method to estimate a muscle's response
to an exercise is to record the peak electromyographic
(EMG) activation of the muscle with surface electrodes and then normalize this value to a subject's
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Youdas et al.
maximum voluntary isometric contraction (MVIC)
obtained during a manual muscle test. Investigators
report muscle activation as a percentage of the
MVIC (% MVIC). Investigators contend the
threshold value for promoting muscle strength gains
during therapeutic exercise requires muscle activation
greater than 50–60% MVIC (Anderson et al, 2006;
Ayotte, Stetts, Keenan, and Greenway, 2007). Therefore, clinicians can utilize EMG signal amplitude (%
MVIC) to help select the most appropriate strengthening exercise for the hip abductor muscles.
One popular gluteal strengthening exercise used in
clinical practice is resisted lateral band walking,
whereby an elastic band is secured around the subject's ankles when standing with feet in neutral
shoulder width position. The band provides external
resistance to the hip muscles as the subject sidesteps
in a lateral direction. Recent reports described the usefulness of lateral band walking as a mechanical challenge to the hip abductors on the stance limb
(Youdas et al, 2006) as well as a strengthening exercise
in healthy young adults (Distefano, Blackburn,
Marshall, and Padua, 2009) and in patients at least
6-weeks status post unilateral primary total hip arthroplasty (Jacobs et al, 2009). However, the reports by
Distefano, Blackburn, Marshall, and Padua (2009)
and Jacobs et al (2009) do not address the simultaneous level of activation of the gluteal muscles on
the stance limb while the contralateral limb is
moving during resisted lateral band walking. On the
basis of personal experience when performing resisted
lateral band walking, the authors encountered greater
muscular demand from the hip muscles of the stance
limb than those of the moving limb. Clinically this
observation has also been confirmed by self-reports
from our patients who completed a series of standing
hip strengthening exercises using elastic tubing as external resistance. Furthermore, patients with anterior
cruciate ligament reconstruction performed elastictubing closed kinetic chain resistance exercises in
standing. The involved extremity was WB whereas
the elastic tubing was attached to the foot of the
healthy limb (Schulthies, Ricard, Alexander, and
Myer, 1998). EMG activity was recorded from the
knee extensors and flexors of the injured limb and
ranged from 25% to 50% MVIC for the four exercises.
Lastly, does hip joint transverse plane rotation influence the level of activation of the gluteal muscles
during resisted lateral sidestepping? For example,
during the lateral band walking exercise, the subject
is typically instructed to keep his or her toes of both
lower limbs pointed straight ahead (neutral hip
rotation) with knees over toes. Some clinicians
modify this lateral stepping technique by instructing
the subject to simultaneously externally rotate both
hips (toes pointed out) or internally rotate both hips
(toes pointed in) during the exercise. Presently, no
information exists in the literature to confirm the
benefits of lateral band walking with hip internal or external rotation vs. standard neutral hip rotation. It may
be posited there could be greater hip abductor muscle
activation during either internal or external rotation
conditions when compared to neutral hip rotation.
The length-tension relationship of skeletal muscle
reveals muscles develop less tension at shorter
lengths. If the gluteus medius muscles are functionally
reduced in length during hip internal or external
rotation conditions of resisted lateral band walking,
we would expect greater recruitment of motor units
from the gluteus medius muscle and hence a greater
amount of EMG activation (% MVIC) when compared to neutral rotation (Pasquet, Carpentier, and
Duchateau, 2005).
Trunk muscle activity is essential for stiffening the
lumbar spine and providing a stable base for lower
extremity movements (Hodges and Richardson,
1997). The use of muscles such as the abdominals
and lumbar extensors to stabilize the trunk within a
static posture amidst the presence of destabilizing
external loads is commonly referred to as “core stability” and ensures that limb muscles have a firm base
for the development of tension (Neumann, 2010a).
During resisted lateral band walking, the gluteal
muscles are pulling on the pelvis creating a trunk perturbation that needs to be balanced by muscular activation from the abdominal muscles and erector
spinae. Presently, no one has reported the activation
level (% MVIC) of the abdominal or back muscles
during resisted lateral band walking when the task on
the stance limb is less dynamic than running or
landing from a jump.
The purpose of this study was to simultaneously
quantify bilateral activation/recruitment levels (%
MVIC) for trunk and hip musculature on both
stance and moving lower limbs during resisted lateral
band walking during neutral, internal, and external
rotation of the hips. We offer the following three
hypotheses during resisted lateral band walking: 1)
during a resisted lateral sidestep, the stance limb
EMG activity of the gluteal muscles will be significantly greater than the EMG muscle activity
from the moving side; 2) during a resisted sidestep,
the stance limb EMG activity of the external oblique
and lumbar erector spinae will be significantly
greater than the external oblique and lumbar
erector spinae muscle activity from the moving limb;
and 3) sidestepping with bilateral hip internal or external rotation will yield significantly greater gluteal
muscle EMG activity than the neutral hip rotation
condition.
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METHODS
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Subjects
Twenty-one healthy subjects, 10 men and 11 women,
volunteered to participate. Subjects had a mean age,
height, body mass, body mass index, and days per
week of participation in physical activity of: 25.0 SD
3.1 years; 1.8 SD 0.1 m; 82.2 SD 7.9 kg; 25.0 SD
2.6 kg/m2; 3.9 SD 1.2 days/week, respectively, for
men, and 24.5 SD 1.4 years; 1.7 SD 0.1 m; 69.1
SD 4.9 kg; 23.8 SD 2.4 kg/m2; 3.1 SD 1.7 days/
week, respectively, for women. Subjects comprised a
sample of convenience and were recruited primarily
from the Mayo Clinic School of Health Sciences. To
be included in the study volunteers needed to range
in age between 20 and 30 years because of their ease
of accessibility within our institution's School of
Health Sciences. At the time of testing, volunteers
had no complaints of injury to the low back or lower
limbs within the last 6-months. Subjects were
excluded if they had a recent history (within the past
2 years) of lower limb surgery. A sample size of 21 subjects was required to detect a mean difference in EMG
activation of 10% MVIC (effect size = 0.33) between
conditions with a statistical power (1 − β) equal to
0.90 at α = 0.05 (Faul, Erdfelder, Lang, and
Buchner, 2007). Written informed consent was
obtained prior to the start of data collection and procedures were approved by the Mayo Clinic School of
Health Sciences Institutional Review Board, Rochester, MN, USA.
Instrumentation
Raw EMG signals were collected with Bagnoli™ DE
3.1 double-differential surface EMG sensors (Delsys
Inc., Boston, MA, USA). The sensor contacts were
made from 99.9% pure silver bars 10 mm in length,
spaced 10 mm apart, and encased within preamplifier
assemblies measuring 41 × 20 × 5 mm. The preamplifier gain was 10 v/v. The combined preamplifier and
main amplifier permitted a gain from 100 to 10,000.
The common-mode rejection ratio was 92 dB at
60 Hz, and input impedance was greater than
1,015 Ω at 100 Hz. Data were sampled at a frequency
of 1,000 Hz. Raw EMG signals were processed with
EMG works® Data Acquisition and Analysis software
(Delsys Inc., Boston, MA, USA).
Three-dimensional motion analysis was performed
with a computer-aided Vicon MX motion analysis
system with five high-resolution MX20+ infrared
digital cameras (Vicon Motion Systems, Oxford,
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UK). Kinematic data were sampled at 50 Hz.
Cameras were positioned so each marker was detected
by a minimum of two cameras throughout the task.
Vicon Nexus software was used to record the timing
of the steps taken during the lateral band walking.
Testing procedure
Data were collected in a research laboratory at the
Mayo Clinic School of Health Sciences. All subjects
wore appropriate clothing to permit correct placement
of the EMG electrodes. Using a technique described
by Criswell (2011), surface electrodes were positioned
bilaterally over the muscle belly of the following four
muscles: 1) gluteus medius (middle fibers); 2)
gluteus maximus (middle to posterior fibers); 3) external oblique; and 4) lumbar erector spinae. The skin
over each muscle belly was prepared by shaving any
hair from the vicinity and cleansing with isopropyl
alcohol wipes. Surface electrodes were attached to
the cleansed area with adhesive interfaces (Delsys
Inc., Boston, MA, USA) and secured with 3M™
Transpore™ medical tape (St. Paul, MN, USA).
The electrodes were configured in parallel with the
muscle fibers. A common ground electrode was
placed on the skin over-lying the right medial malleolus. Wires from electrodes were connected to a small
transmitter attached to the participant's back. Next,
subjects performed a series of resistance tests using
2- to 3-second hold times to: 1) set the gain on the
Delsys EMG instrumentation for each muscle; and
2) provide subjects several practice trials so they
were familiar with the muscle test procedure. Specific
muscle test procedures were previously described by
Hislop and Montgomery (2007). For the gluteus
medius, the subject was positioned in side-lying with
the tested lower extremity uppermost. Both thigh
and leg were in extension and the lower extremity
maintained in line with the trunk. The untested
lower extremity was flexed at the hip and knee for stability. The subject was instructed to abduct the uppermost lower extremity about 30° from midline
whereupon the examiner applied manual resistance
just proximal to the malleolus. The gluteus maximus
was tested with the subject prone and a pillow placed
under the pelvis to provide 10°–15° of hip flexion.
With the knee maintained at 90° of flexion, the
subject was instructed to extend the thigh of the
tested side through the available hip extension rangeof-motion. The examiner applied manual resistance
at the distal thigh. The external oblique muscle was
tested with the subject supine with lower extremities
straight and hands clasped behind the head. The
examiner instructed the subject to flex the neck and
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Youdas et al.
thoracolumbar spine and rotate the elbow of the test
side toward the opposite knee so the scapula cleared
the support surface. Lastly, the lumbar erector
spinae were tested with the subject positioned prone
and hands clasped behind the head. The examiner instructed the subject to extend the lumbar spine until
the thorax cleared the surface of the table. The examiner stabilized the subject's lower extremities just distal
to the malleoli. After establishing the gain for each
EMG amplifier and familiarizing the subject with the
muscle tests, MVICs of each muscle were obtained
using a 5-second manual muscle test procedure. For
each subject, an examiner provided verbal encouragement to help the subject produce maximum effort
during the MVIC.
Sixteen spherical motion analysis reflective markers
were placed bilaterally on specific anatomic landmarks
as follows: a) anterior superior iliac spine; b) posterior
superior iliac spine; c) lateral mid-thigh; d) lateral epicondyle of knee; e) lateral mid-shank; f) lateral malleolus; g) calcaneal tuberosity; and h) dorsal surface
of fourth metatarsal (Figure 1). With the subject
standing in anatomic position, a 10-second static
trial was recorded to establish baseline measurements
for processing the kinematic data. The kinematic data
were used to identify the timing of the stance and
moving lower extremities during the lateral stepping
procedure.
Each subject performed a series of three lateral
steps against a 30.5 cm (12-inch) long by 1.3 cm
(0.5-inch) wide elastic band (SPRI Products Inc.,
Westchester, OH, 45069, USA). The exercises were
performed under three hip rotation conditions: 1)
neutral rotation-toes pointing straight ahead; 2) hips
internally rotated-toes pointed inwards; and 3) hips
externally rotated-toes pointed outwards (Figure 2).
Regardless of hip rotation condition, the lateral sidestep was always initiated by the dominant lower limb
defined as the preferred limb used to kick a soccer
ball. Nineteen subjects (91%) were right lower limb
dominant. Hip rotation conditions were counterbalanced to account for order effects.
To standardize repetition speed before data collection, each subject practiced resisted lateral band walks
to the beat of a metronome (45 b·minute−1) (Bolgla
and Uhl, 2005; Distefano, Blackburn, Marshall, and
Padua, 2009). Each subject practiced several trials
for each condition (neutral, internal rotation, and
external rotation) for familiarity with the exercise.
Successful performance of lateral band walking was
ultimately judged by the examiners. A fresh elastic
band was positioned around each subject's ankles at
the level of the malleoli while he or she stood
upright with feet spaced shoulder width apart as
seen in Figure 2. Participants stood hands on hips
with knees and hips in about 30° of flexion. For the
FIGURE 1 Placement of the EMG electrodes and the spherical motion analysis reflective markers. (a) Anterior view illustrating the
bilateral EMG electrode placement for recording from the external oblique and gluteus medius muscles. (b) Lateral view illustrating
EMG electrode placement for recording from the external oblique, gluteus medius, and lumbar erector spinae muscles. (c) Posterior
view illustrating bilateral EMG electrode placement for recording from the lumbar erector spinae. The electrode placement sites for the
gluteus maximus muscles are obscured by the participant's shorts.
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FIGURE 2 Hip rotation positions during resisted lateral band walking using the SPRI elastic band. A fresh band was positioned
around each subject's ankles at the level of the medial malleoli while he or she stood upright with feet spaced at shoulder width (indicated by floor markings). Participants stood hands on hips with knees and hips in about 20°–30° of flexion. (a) Neutral hip rotation,
(b) internal hip rotation, and (c) external hip rotation.
leading (moving) lower limb, each subject performed
a lateral step, a distance of 160% of his or her shoulder
width (indicated with floor markings [Distefano,
Blackburn, Marshall, and Padua, 2009]), until a
single-limb stance was assumed. The trailing or
stance limb followed with hip adduction to reproduce
the starting position of feet at shoulder width. For
neutral hip rotation, each participant kept his or her
toes pointed straight ahead with knees over toes. For
internal rotation both feet toed inward whereas for
external rotation both feet toed outward. For each
hip rotation condition subjects performed a series of
three successive steps. To avoid fatigue, subjects
were allowed to rest between hip rotation conditions
(30–45 seconds). Mean elastic band tension at
shoulder width starting position was 3.5 SD 0.54 kg,
whereas mean elastic band tension at the completion
of the lateral step (160% shoulder width) was 5.7
SD 0.61 kg.
Data reduction
Kinematic data and EMG recruitment data were analyzed during the side-stepping tests. Regarding kinematic data, three-dimensional coordinates of the
retro-reflective markers were collected during the
tests. Marker displacement trajectories were sampled
at 50 Hz and filtered with a Woltring quintic spline
filter at a mean square error of 20 mm. The dependent
variable was the normalized peak EMG activity (%
MVIC) for each of the eight muscles. MVICs were
collected to normalize data and permit meaningful
comparisons among study subjects. Raw EMG data
collected during the tests were band-pass filtered
between 20 and 450 Hz and subsequently processed
with a root-mean-square algorithm using moving
windows with 125-ms time constants. EMG data collected during the side-stepping tests were normalized
to their muscles' respective MVIC trials and therefore
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expressed as a percentage of the MVIC (% MVIC).
The room dimensions (4.3 × 6.1 m) and the positions
of the cameras permitted a maximum of three lateral
steps for each of the three hip rotation conditions. Kinematic data were used to determine the time in which
the second lateral step of each condition occurred
(from abducting limb heel-off to heel-contact of the
trailing limb [stance limb]). The second lateral step
time was then used to determine % MVIC for each
of the eight muscles sampled during the lateral
stepping procedure.
Statistical analysis
For each muscle, EMG levels were compared using a
three (hip angle) × 2 (limb factor) ANOVA with
repeated measures on muscle. If interactions were
significant, post-hoc comparisons were made. When
main effects were significant pair-wise comparisons
were examined with Bonferroni adjustments to alpha
( p = 0.05). All data were analyzed with SPSS 15.0
for Windows software (SPSS Inc, Chicago, IL, USA).
RESULTS
Table 1 illustrates the mean peak EMG values for all
levels of each factor. The gluteus medius and lumbar
erector spinae muscles demonstrated peak EMG activation (% MVIC) for both moving and stance limbs
during resisted hip internal rotation. In contrast the
gluteus maximus muscle demonstrated peak EMG
activation for both moving and stance limbs during
external rotation. For the external oblique muscle
peak EMG activation for the moving limb occurred
during resisted external rotation whereas for the
stance limb EMG activation was relatively equivalent
for both resisted internal and external hip rotation.
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Youdas et al.
TABLE 1 Descriptive statistics for the mean peak values of muscle activation (% MVIC) from hip and trunk muscles of stance and
moving limbs under three conditions of hip transverse plane rotation during resisted lateral band walking.
Hip angle condition
Muscle
Gluteus medius
Gluteus maximus
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Lumbar erector spinae
External oblique
Limb condition
Neutral
Internal rotation
External rotation
Stance
Moving
Stance
Moving
Stance
Moving
Stance
Moving
49.9 ± 21.9
32.8 ± 21.9
18.1 ± 14.2
12.1 ± 8.4
23.5 ± 11.4
28.2 ± 13
14.2 ± 16.9
12.2 ± 7.9
57.8 ± 24.3
43.8 ± 27
17.5 ± 10.3
13 ± 9.1
24.1 ± 12.4
35.3 ± 18.9
16.5 ± 23.1
12.3 ± 8.3
47.6 ± 21.5
27.3 ± 18.1
20.5 ± 14.7
14.8 ± 10.7
22.4 ± 11.5
28.7 ± 14
16 ± 19.5
15.7 ± 11.5
Note: Values are means and standard deviations.
Gluteus medius
The interaction between the hip angle and limb factor
was not significant (F2,38 = 0.45, p = 0.64). Hip angle
main effect was significant (F2,38 = 4.1, p = 0.02) as
was the limb main effect (F1,19 = 16.1, p = 0.001).
Despite the significant hip angle effect, none of the
pair-wise comparisons between hip rotation conditions were significant. Regarding the limb main
effect (Figure 3), gluteus medius activation was
greater in the stance limb than in the moving limb
(mean difference = 17.1% MVIC, p = 0.001).
pair-wise comparisons between hip rotation conditions
were significant. Gluteus maximus activation was
greater in the stance limb (Figure 4) than the moving
limb (mean difference = 5.4% MVIC, p = 0.002).
External oblique
The interaction between the hip angle and limb factor
for the external oblique was not significant (F2,38 = 1.1,
p = 0.35). Neither hip angle main effect (F2,38 = 2.1, p
= 0.13) nor limb main effect (F1,19 = 0.34, p = 0.57)
were significant (Figure 5).
Gluteus maximus
Lumbar erector spinae
The interaction between the hip angle and limb factor
was not significant (F2,36 = 0.39, p = 0.68). Hip angle
main effect was significant (F2,36 = 3.5, p = 0.04) as
was the limb main effect (F1,18 = 13, p = 0.002).
Despite a significant hip angle effect, none of the
The interaction between the hip angle and limb factor
was not significant (F2,38 = 2.5, p = 0.10). Hip angle
main effect was significant (F2,38 = 5.35, p = 0.01) as
was the limb main effect (F1,19 = 4.9, p = 0.04). Pair-
FIGURE 3 Mean normalized EMG activity from the gluteus
medius muscle obtained during resisted lateral band walking
(sidestepping). EMG activity (% MVIC) is significantly
greater on the stance limb than the moving limb ( p = 0.001)
when collapsed across hip angles. The error bars represent standard error.
FIGURE 4 Mean normalized EMG activity from the gluteus
maximus muscle obtained during resisted lateral band walking
(sidestepping). EMG activity (% MVIC) is significantly
greater on the stance limb than the moving limb ( p = 0.002)
when collapsed across hip angles. The error bars represent standard error.
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FIGURE 5 Mean normalized EMG activity from the external
oblique muscle obtained during resisted lateral band walking
(sidestepping). EMG activity (% MVIC) is not different
between the stance and moving limbs when collapsed across
hip angles. The error bars represent standard error.
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trunk and hip musculature on both stance and
moving lower limbs during resisted lateral band
walking during neutral, internal, and external rotation
of the hips. Data supported our first hypothesis
whereby during resisted lateral band walking EMG
activity of the gluteal muscles from the stance limb
would be significantly greater than gluteal EMG activation from the moving limb. Data did not support
our second hypothesis that stated during a resisted
sidestep stance limb EMG activity of the external
oblique and lumbar erector spinae would be significantly greater than external oblique and lumbar
erector spinae muscle activity from the moving limb.
Lastly, our third hypothesis was partially supported
by the data. Hip rotation during resisted sidestepping
had no effect on EMG activity of the gluteal muscles.
However, lateral band walking with internal rotation
produced significantly greater EMG activity of the
erector spinae on the moving limb when compared
to resisted sidestepping in neutral hip rotation.
Gluteus medius
FIGURE 6 Mean normalized EMG activity from the erector
spinae muscle obtained during resisted lateral band walking
(sidestepping). Pair-wise comparison analysis for hip angles revealed erector spinae EMG activity (% MVIC) is significantly
greater in the internal rotation condition when compared to
neutral hip rotation ( p = 0.007). Pair-wise comparison analysis
for side revealed erector spinae recruitment is significantly
greater on the moving limb than the stance limb ( p = 0.04).
wise comparison analysis for hip angles (Figure 6)
revealed erector spinae recruitment was greater in
the internal rotation condition when compared to
neutral hip rotation (mean difference, 3.9% MVIC,
p = 0.007). Pair-wise comparison analysis for limb
revealed erector spinae recruitment was greater on
the moving limb than the stance limb (mean difference = 7.4% MVIC, p = 0.04).
DISCUSSION
Our study's aim was to simultaneously quantify bilateral activation/recruitment levels (% MVIC) for
Physiotherapy Theory and Practice
The primary finding of this study revealed significantly
greater gluteus medius muscle activation on the stance
limb compared to the moving limb during resisted
lateral band walking. Our results are supported by
Neumann (2010a) with regard to frontal plane stability of the pelvis during walking. WB is more demanding on the stance limb during resisted sidestepping
because the gluteus medius muscle must overcome
band resistance in addition to the contralateral pelvic
drop on the moving NWB limb due to 83% body
mass. In contrast, the moving limb must overcome
band resistance and the mass (16%) of the limb.
With respect to the gluteus medius muscle, results
from the present study and those from previous investigators also reported WB exercises produced levels of
muscle activation that exceeded 50% MVIC: (singlelimb squat [47.8 SD 22.8%] [Krause et al, 2009]);
(left pelvic drop [57 SD 32%] and right WB with
left hip abduction against a cuff mass equal to 3%
body mass [46 SD 34%] [Bolgla and Uhl, 2005]);
(single-limb squat [64 SD 24%] [Distefano, Blackburn, Marshall, and Padua, 2009]); and (WB standing
abduction against an external load of 1% body weight–
height [67 SD 56%] [Jacobs et al, 2009]).
Despite a significant hip angle main effect we failed
to detect a meaningful difference in EMG activation of
the gluteus medius among the three hip positions.
Change in hip position during resisted lateral band
walking does not appear to have differential effects
upon the activation of the gluteus medius muscle.
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Gluteus maximus
In the present study gluteus maximus muscle activation during resisted lateral band walking was
greater on the stance limb than the moving limb and
this mean difference was statistically significant.
Nevertheless, we observed reduced activation of the
gluteus maximus muscle during resisted lateral sidestep walking on the stance limb when compared to
the gluteus medius muscle. We attribute this difference to the limited amount (20°–30°) of trunk-onthigh flexion during WB so the gluteus maximus was
not needed as a strong hip extensor. Moreover, the
hamstrings potentially supplied the necessary internal
force to control trunk flexion (Fischer and Houtz,
1968; Pohtilla, 1969). Stance limb gluteus maximus
muscle activation provided frontal (hip abduction)
and transverse (hip external rotation) plane stabilization to the hip to protect the stance knee joint from
valgus collapse during WB (Powers, 2010). Regarding
the moving limb, the gluteus maximus has minimal
potential to abduct the hip joint during the lateral sidestep because the muscle's fiber orientation (Delp,
Hess, Hungerford, and Jones, 1999; Dostal, Soderberg, and Andrews, 1986; Neumann, 2010b) is
more medial relative to the anterior–posterior axis of
motion within the femoral head (Neumann, 2010a).
Only one other report (Distefano, Blackburn, Marshall, and Padua, 2009) examined muscle activation
of the gluteus maximus during resisted lateral band
walking. Investigators reported greater muscle activation of the gluteus maximus muscle (27 SD 16%)
on the dominant limb during resisted lateral band
walking when compared to the present study (13.3
SD 9.1%). However, EMG activity was measured
during both moving and single-limb support phases
of the dominant limb from participants in the earlier
reported study (Distefano, Blackburn, Marshall, and
Padua, 2009).
Despite a significant hip angle effect, none of the
pair-wise comparisons between hip rotation conditions were significant. Because of a modest external rotation moment arm of 2.1 cm (Delp, Hess,
Hungerford, and Jones, 1999; Dostal, Soderberg,
and Andrews, 1986; Neumann, 2010b) we expected
the middle/posterior fibers of the gluteus maximus
muscle to be more active electromyographically
during resisted lateral band walking in hip external
rotation when compared to neutral rotation. Nonetheless, our data did not support this hypothesis
presumably because the less powerful external rotators of the thigh (quadratus femoris, obturator
externus and internus, and piriformis) were activated before the gluteus maximus. We were
unable to record the electrical activity of these
small muscles because they were overlapped by
the more superficial gluteus maximus.
External oblique
External oblique muscle activation was larger on the
stance limb than the moving limb, but this mean
difference was not statistically significant. We attribute
the absence of a limb factor effect for the external
oblique because subjects were instructed to maintain
a vertical trunk during resisted lateral band walking.
By reducing lateral trunk lean toward the moving
side, subjects may have minimized activation of the
external oblique muscles as trunk stabilizers.
Lumbar erector spinae
In contrast to the pattern of muscle activation for the external oblique, lumbar erector spinae muscle activation
on the moving limb was of greater magnitude than the
value recorded on the stance limb and this mean difference was statistically significant. When performing
lateral band walking subjects stood hands on hips
with knees and hips in about 20°–30° of flexion with
the trunk held upright. The erector spinae were activated bilaterally in response to the forward trunk lean.
Greater erector spinae muscle activation on the
moving limb reflects the need for additional pelvic
control in the frontal plane and we believe this was
accomplished through a force couple between the
erector spinae on the moving limb and the gluteus
medius on the stance limb (Neumann, 2010a).
Although the muscle pull of the erector spinae and
gluteus medius muscles occurred in opposite linear directions, their resulting torque was in the same rotary
direction and served to keep the pelvis of the moving
limb from dropping due to the effects of gravity as the
moving thigh was abducted against the external load
provided by the elastic band. Lastly, we observed
significantly greater erector spinae recruitment in the
internal rotation condition when compared to neutral
hip rotation. From a kinesiologic perspective, we
believe the erector spinae of the moving limb were
required to work harder to prevent pelvic rotation
when the limb was internally rotated.
Clinical implications
Previous research has indicated muscle activation levels
should fall in the 40–60% range to be used for strengthening purposes (Andersen et al, 2006; Ayotte, Stetts,
Keenan, and Greenway, 2007). Since gluteus medius
activation levels on the stance limb were significantly
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Physiotherapy Theory and Practice
greater than the moving limb and in the 50–60% range
(52 ± 18%), the clinician can confidently use resisted
lateral band walking for strengthening stance limb hip
abductors provided the band's elastic tension is sufficient. Because resisted lateral band walking produced
EMG signal amplitudes of less than 40% for the
gluteus maximus, external oblique, and lumbar erector
spinae on both stance and moving limbs, we would not
recommend physical therapists prescribing this exercise
to strengthen these muscles in healthy subjects
(Ekstrom, Donatelli, and Carp, 2007). However,
resisted lateral band walking would be expected to
promote endurance or motor control training in the
muscles of the trunk and gluteus maximus (Ekstrom,
Donatelli, and Carp, 2007). Overall the gluteus
maximus and external oblique muscles displayed
greater EMG activity on the stance limb than moving
limb although the difference was not significant.
Perhaps this observation reflects the muscles' low level
of activation for stabilization purposes.
Based upon data from this study, subjects who performed resisted lateral band walking in hip internal or
external rotation do not selectively augment muscle
activation of the gluteal or trunk muscles when compared to conventional sidestepping in neutral hip
rotation. Furthermore, resisted lateral band walking
with the hips internally rotated may contribute to
faulty lower extremity kinematics such as excessive
hip adduction and internal rotation and therefore
would not be recommended as a component of a hip
strengthening program (Powers, 2010).
Limitations
Due to the possibility of signal artifact a potential limitation of this study was the use of peak EMG amplitude
rather than the average peak amplitude for a specific
window of time. The proximity between the surface
electrodes for the gluteus maximus and gluteus
medius muscles may have allowed for some crosstalk. We attempted to minimize this from happening
by using standardized electrode placement sites for
the gluteal muscles and recording EMG signals
during resisted side-step walking (Criswell, 2011).
Another study limitation was the inability to record
muscle activation signals using surface electrodes
from the gluteus minimus and posterior fibers of the
gluteus medius because both muscles are deep to the
gluteus medius and gluteus maximus muscles, respectively. Our results regarding the effects of hip joint
rotation on the recruitment of hip abductor muscles
may have been different had we been able to record
EMG activity from the gluteus minimus during simultaneous hip internal rotation and posterior fibers of the
Physiotherapy Theory and Practice
121
gluteus medius during simultaneous hip external
rotation. In the present study, subjects were constrained to three successive sidesteps due to the
room's dimensions and placement of the cameras
used to identify the timing of the stance and moving
extremities. Clinically, during resisted lateral band
walking subjects typically make a series of repeated
steps that exceeds single digits. Lastly, results from
the present study were obtained from healthy subjects
so care is necessary when a physical therapist applies
these findings to people with lower extremity pathology.
Future research needs to be performed on subjects with
lower extremity dysfunction to examine the effect of
resisted lateral band walking on both the stance and
moving lower limbs.
CONCLUSION
Resisted lateral band walking generated significantly
greater muscle activation in the gluteus medius
muscle on the stance limb than the moving limb.
Muscle recruitment of the gluteus medius on the
stance limb during resisted lateral band walking
would be sufficient to produce a strengthening effect
(>50% MVIC). Therefore, it may be advantageous to
place the weaker limb as the stance limb when performing resisted lateral band walking. Likewise, activation of
the gluteus maximus muscle was significantly greater
on the stance limb than the moving limb. Nevertheless,
lateral band walking against elastic resistance as performed in the present study would not be expected to
produce a strengthening effect in the gluteus
maximus muscles because the activation level for
both sides was too low (<50% MVIC). External
oblique muscle activation was larger on the stance
than the moving limb although this mean difference
was not statistically significant. In contrast, lumbar
erector spinae muscle activation on the moving limb
was of significantly greater magnitude than the value
recorded on the stance limb. Resisted lateral band
walking as performed in this study would not be
expected to generate a strengthening effect in the external oblique and lumbar erector spinae. Finally, no
significant differences were found in hip muscle activation levels between the three hip rotation conditions:
1) neutral; 2) internal rotation; and 3) external rotation.
Acknowledgment
Funding was provided by the authors' Program in
Physical Therapy.
122
Youdas et al.
Declaration of interest: The authors report no
conflicts of interest. The authors alone are responsible
for the content and writing of the paper.
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