Accepted Manuscript Effects of external pelvic compression on trunk and hip muscle EMG activity during prone hip extension in females with chronic low back pain Ji-Won Kim , PT, PhD Oh-Yun Kwon , PT, PhD Tae-Ho Kim , PT, PhD Duk-Hyun An , PT, PhD Jae-seop Oh , PT, PhD PII:
S1356-689X(14)00081-2
DOI:
10.1016/j.math.2014.04.016
Reference:
YMATH 1563
To appear in:
Manual Therapy
Received Date: 26 September 2013 Revised Date:
21 April 2014
Accepted Date: 28 April 2014
Please cite this article as: Kim J-W, Kwon O-Y, Kim T-H, An D-H, Oh J-s, Effects of external pelvic compression on trunk and hip muscle EMG activity during prone hip extension in females with chronic low back pain, Manual Therapy (2014), doi: 10.1016/j.math.2014.04.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Title Page
1. Title:
prone hip extension in females with chronic low back pain
2. Name and academic degree of each author
Oh-Yun Kwonb, PT, PhD ([email protected])
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Tae-Ho Kim c, PT, PhD ([email protected])
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Ji-Won Kima, PT, PhD ([email protected])
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Effects of external pelvic compression on trunk and hip muscle EMG activity during
Duk-Hyun An d, PT, PhD ([email protected]) Jae-seop Ohd, PT, PhD ([email protected])
Department of Physical Theraphy, NAMBU University, Gwangju, South Korea
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Department of Physical Therapy, YONSEI University, Wonju, South Korea
Department of Physical Therapy, DAEGU University, Daegu, South Korea
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Department of Physical Therapy, College of Biomedical Science and Engineering,
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3. Authors’ institutional affiliations
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INJE University, Gimhae, South Korea
4. The work should be attributed to Department of Physical Therapy, INJE University.
5. Corresponding author: JAE-SEOP, OH, PT, PhD Department of Physical Thearapy College of Biomedical Science and Engineering 1
ACCEPTED MANUSCRIPT INJE university 607 Obang-dong, Gimhae-si Gyeongsangnam-do, South Korea, 621-749
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[email protected]
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ABSTRACT
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Many studies have reported higher trunk and hip muscle activity in patients with
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chronic low back pain (CLBP). Increased trunk and hip muscle activity could contribute
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to pain. Previous studies have shown that external pelvic compression (EPC) decreased
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back and hip muscle activity during physical tasks.
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In this study, we assessed the effects of EPC on the electromyography (EMG)
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activity of the latissimus dorsi (LD), elector spinae (ES), gluteus maximus (GM), and
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biceps femoris (BF) in a CLBP group and a healthy group during prone hip extension
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(PHE).
Forty female volunteers (20 non-specific CLBP, 20 healthy) were recruited.
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Surface EMG data were collected from the LD, ES, GM, and BF muscles during a PHE
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task. Normalized EMG values were analyzed by separate repeated-measures analysis of
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variance (ANOVA) for each muscle.
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The normalized EMG activity in the left LD, bilateral ES, and right GM was
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significantly higher in the CLBP group than in the healthy group during PHE. In the
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CLBP group, the normalized EMG activity in the left LD, bilateral ES, and right GM
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was significantly lower with EPC than without (p < 0.05). This suggests that the
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application of EPC decreased trunk and hip extensor EMG activity in the CLBP group
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during PHE.
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Keywords:
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Chronic low back pain
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External pelvic compression
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Pelvic compression belt
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Prone hip extension
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1. INTRODUCTION
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Low back pain (LBP) is a major medical problem and makes a considerable
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contribution to disability (Freburger et al., 2009; Macfarlane et al., 2012). The
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prevalence of LBP was threefold higher in females than males, and females were more
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likely to suffer functional impairment because of LBP (Croft et al., 1998; Biglarian et
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al., 2012). Females with chronic LBP (CLBP) show less back and hip muscle strength
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than healthy females (Nadler, 2000; Bayramoğlu et al., 2001). Back and hip muscle
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strengthening exercises are important to prevent and treat CLBP because muscle
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weakness is a risk factor for LBP (Lee et al., 1999; Nadler, 2000; Bayramoğlu et al.,
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2001).
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Prone hip extension (PHE) is commonly used as a therapeutic exercise in
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patients with LBP to strengthen the trunk and hip extensors and lengthen the hip flexors.
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In the clinical setting, patients often perform exercises with difficulty due to increased
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pain and/or muscle weakness. A recent study showed higher trunk and hip muscle
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amplitudes in CLBP than in a healthy group during a PHE task (Arab et al., 2011).
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Although they did not measure spinal stability, the authors suggested the need for
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increased trunk and hip muscle activity to enhance trunk stability in the CLBP group
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(Arab et al., 2011). Many other studies have reported higher trunk muscle activity in
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patients with CLBP than in healthy subjects during various tasks, such as trunk bending
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and lifting tasks (Ambroz et al., 2000; Ferguson et al., 2004). It has been demonstrated
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that increased muscle activity is influenced by pain (Graven-Nielsen et al., 1997). Some
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researchers have suggested that increased trunk muscle activity could contribute to a
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vicious cycle of pain-spasm-pain and increase the load on the spine by co-contraction of
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the trunk muscles (Roland et al., 1986; Keir et al., 2004). Therefore, clinicians have
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emphasized reducing abnormally increased muscle activity during therapeutic exercises
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in patients with LBP (Fryer et al., 2004). To reduce abnormally increased muscle
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activity, some clinicians have used external pelvic compression (EPC) not only to
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decrease the pain but also to decrease the abnormally increased muscle activity during
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functional movements.
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External pelvic compression has been shown to facilitate or inhibit the EMG
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activity of the trunk and hip muscles and is an easy task to perform during the active
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straight leg raise (ASLR) (Mens et al., 1999; Hu et al., 2010). Mens et al. (1999)
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demonstrated that EPC improved the ASLR performance score. Hu et al. (2010)
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reported that EPC during ASLR resulted in reduced abdominal muscle activation.
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Although many studies assessing EPC have been conducted with subjects in the supine
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position, none has examined its effect on the activity of the trunk and hip extensors in
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the prone position, such as PHE. Thus, in this study we (1) compared the activity of the
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LD, ES, GM, and BF muscles bilaterally during hip extension in the prone position
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between a healthy group and a CLBP group and (2) examined the effects of EPC on the
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trunk and hip muscle extensor activity during PHE in a healthy group and a CLBP
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group. Based on previous findings, we hypothesized that (1) the trunk and hip extensor
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muscle activity would increase during PHE in a CLBP group compared with a healthy
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group, and (2) the application of EPC would result in decreased activity of the trunk and
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hip extensor muscles during PHE in the CLBP group.
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9 2. METHODS
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2.1. Subjects
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Forty female volunteers (20 with non-specific CLBP and 20 healthy females)
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participated. The patients with CLBP were recruited from two local outpatient
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orthopedic clinics and one spine hospital and the healthy females were recruited by
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word of mouth in Busan, South Korea. Care was taken to recruit participants of similar
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age, height, weight, and BMI into each group. Originally, 24 females with CLBP were
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tested, but four patients were excluded because they were unable to perform maximal
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voluntary contractions due to acute pain in the trunk and legs at the time of testing. The
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healthy group reported no history of LBP that required medical attention or resulted in
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limited function. Inclusion criteria for the CLBP group were LBP for more than 3
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months (pain felt between T12 and the gluteal fold). LBP intensity during the preceding
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week was scored using a numeric rating scale (NRS), from 0 to 10, where 0 denoted no
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pain and 10 the worst possible pain. The NRS has acceptable reliability and validity
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(Roach et al, 1997; Ferreira-Valente, 2011). Functional disability was measured using
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the Oswestry Disability Index (ODI). The ODI questionnaire is a reliable and valid
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instrument (Vianin, 2008). Patients had to have experienced LBP for at least 3 months,
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have NRS scores of at least 3, and ODI scores of at least 15% (Leitner, 2009; Marshall
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and Murphy, 2010). Exclusion criteria were specific conditions, such as neoplasms,
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spinal fractures, spondylolisthesis, spondylosis, spinal stenosis, ankylosing spondylitis,
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previous spinal surgery, lower extremity impairment, sacroiliac dysfunction, and
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pregnancy.
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The Inje University Faculty of Health Science Human Ethics Committee
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approved this study. All subjects provided written informed consent prior to
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participation.
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2.2. EMG Recording and Data Analysis
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Electromyography data were recorded and analyzed using the Delsys Trigno Wireless
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EMG system (Delsys, Boston, MA, USA). Before electrode placement, skin impedance
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was minimized by shaving off any body hair and cleaning the skin with 70% isopropyl
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alcohol. EMG data were collected bilaterally from the LD (4 cm below the inferior tip
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of the scapula and half the distance between the spine and lateral edge of the torso), ES
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(2 cm lateral to the spinous process of the L1 level and aligned parallel to the spine),
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GM (half the distance between the greater trochanter and second sacral vertebra and at
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an oblique angle at or slightly above the level of the trochanter), and BF (2 cm from the
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lateral border of the thigh and two-thirds the distance between the trochanter and back
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of the knee) muscles (Criswell, 2010). The signals were amplified and band-pass
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filtered (20-450 Hz) before being recorded digitally at 2000 samples/s, and then
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calculating the root mean square (RMS).
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We included two maneuvers to normalize the EMG activity: a maximum
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voluntary isometric contraction and submaximal voluntary isometric contraction
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(Pirouzi et al., 2006). In a pre-test, we verified that when both submaximal isometric
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contraction and maximal isometric contraction were applied, the values were measured
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at an even ratio. However, when maximal isometric contraction was used for ES and
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GM, the patients with lumbar pain developed acute pain. Therefore, the submaximal
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method was judged appropriate and so was used for ES and GM. This method of
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normalization for the trunk muscles has been shown to exhibit excellent within-day
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reliability for healthy controls and patients with CLBP (Dankaerts et al., 2004).
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All muscles were tested in the prone position. The maximum isometric
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contractions were performed against manual resistance for the LD and BF muscles
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(Kendall, 2005). The LD muscle was tested with the subject’s arms at her sides and
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shoulders internally rotated to create a palm-up position. Resistance was then applied to
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the forearm. The BF muscle was tested with the thigh and hip laterally rotated, knee
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flexed to approximately 20°, and resistance applied to the shank. For the submaximal
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voluntary isometric contraction of the ES and GM, the subject lifted both knees 5 cm
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off the examination table, with the knees flexed at 90°, and held them for 5 s (Dankaerts
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et al., 2004). Each maximum isometric contractions maneuver and submaximal
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voluntary isometric contraction was performed twice for 5 s, and the average muscle
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activity for the middle 3 s of the two trials was used for normalization. EMG results
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were normalized to the maximum and submaximum EMG RMS values calculated from
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the EMG signals obtained during voluntary isometric contraction test for each muscle.
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2.3 Application of EPC
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The EPC device (SI-LOC, OPTP, Canada) was applied below the anterior superior iliac
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spine (ASIS) (Damen et al., 2002) in the subjects and the strap was fastened firmly to
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the belt. This device was constructed of non-elastic material with Velcro ends and was 5
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cm wide at the front and back and 8 cm wide at the sides. The tightness was adjusted by
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a physiotherapist with experience in dealing with CLBP. EPC was applied without any
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pain or discomfort in the CLBP group.
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2.4 Experimental procedures
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Before the measurements, all of the individuals were instructed on active PHE and
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allowed 5 min of practice, which was sufficient familiarization for the investigation.
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The individuals were asked to lie prone with their arms at their side and head in the
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mid-line. An adjustable bar was placed over the experimental table in alignment with
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the back of knee, so that the popliteal region contacted the bar during the hip extension
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task. A target bar was set at 10° to provide tactile feedback. The individuals were told to
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extend their dominant leg from neutral to about 10° while keeping the knee extended.
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All individuals reported that they were right-leg dominant; i.e., they would use this leg
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to kick a ball (Willson et al., 2006). The subjects were asked to perform hip extension
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and maintain it for 5 s in this position (Fig. 1). The PHE tasks were performed under
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EPC and without EPC in randomized order. A 1-min rest was allowed between
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conditions.
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4 2.5 Statistical analyses
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The data used for the statistical analyses showed a normal distribution without
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substantial skew. The greatest skewness value was 1.85. Differences in demographic
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characteristics between the groups were examined using independent t-tests.
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Comparisons were made not only between groups (CLBP vs. healthy) to investigate the
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EMG activity of the back and hip extensor muscles but also within each group to
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examine the effect of EPC (EPC vs. no EPC) on the EMG activity of the back and hip
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extensor muscles during PHE. Separate repeated-measures analysis of variance
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(ANOVA) and the post hoc Bonferroni test were conducted for each muscle and for the
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four independent variables.
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3. RESULTS The demographics of both groups are summarized in Table 1. There was no significant difference between the groups (p > 0.05).
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Table 2 presents the analysis of the normalized RMS signal amplitudes for each muscle in the PHE with and without EPC for both groups. Analysis of PHE without
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EPC revealed that the signal amplitudes were higher in the CLBP group in the left LD,
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ES bilaterally, and right GM (all p < 0.05). There was no other between-group
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difference in the other muscles.
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Within the CLBP group, application of EPC resulted in significantly lower
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signal amplitudes in the left LD, the ES bilaterally, and the right GM versus the
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non-EPC condition (all p < 0.05; Table 2). Application of EPC resulted in no difference
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in signal amplitude in any muscle in the healthy group without back pain.
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4. DISCUSSION
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The results presented here support our hypotheses that the CLBP group had
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higher muscle activity of the left LD, ES bilaterally, and right GM than the healthy
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group during PHE. Increased trunk and hip extensor muscle activity may make it more
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difficult to perform the PHE task in the CLBP group than in the healthy group. These
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findings are consistent with those of Arab et al. (2011), who found higher bilateral ES
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muscle activity during PHE in a CLBP group than in a healthy group.
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Many factors may be associated with the higher trunk muscle activity patients with CLBP, such as pain and spinal instability, and difficulty in performing physical
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tasks (Silfies et al., 2005; Arab et al., 2011). Increased EMG activity in the trunk and
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hip extensor muscles during leg lifting in the prone position seems to compensate for
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the difficulty in performing physical tasks such as PHE and pain in the CLBP group.
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Previous studies have demonstrated that a painful area induces increased muscle
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activity, compared with a no-pain area (Graven-Nielsen et al., 1997). We considered
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that increased trunk and hip extensor muscle activity might subsequently affect muscle
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spasms, which, in turn, will cause pain (van Dieën et al., 2003). Additionally, increased
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trunk extensor muscle activity may lead to earlier muscle fatigue due to heightened
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muscle usage and may possibly increase spinal load, which is recognized to be harmful
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when attempting to reduce CLBP (Gadner-Morse and Stokers, 1998; Mannion, 1999).
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Thus, in patients with CLBP during PHE, care may be needed to avoid increased trunk
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and hip extensor muscle activity.
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To inhibit EMG activity in trunk and hip muscles, researchers have used EPC
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(Sniders et al., 1998; Hu et al., 2010). In this study, we observed decreased left LD,
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bilateral ES, and right GM muscle activity with EPC, compared with no EPC, in the
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CLBP group during PHE. These results are consistent with a previous study of the
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active straight leg raise test. Hu et al. (2010) demonstrated that EPC reduced lower
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external oblique, internal oblique, and transverse abdominal muscle activity in
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asymptomatic subjects during ASLR. Previous studies also demonstrated that applying
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EPC can release pain and improve ASLR performance (Cogill et al., 1996; Mens et al.,
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1999). In this study, when EPC was applied in the CLBP group, pain was reduced,
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which may lead to decrease trunk and hip muscle activity. This finding suggests that
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EPC may be helpful in reducing pain and preventing intensified trunk and hip extensor
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muscle usage.
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We observed that in the healthy group, EPC did not influence trunk or hip extensor muscle activity during the PHE task. This is consistent with Park et al. (2013),
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who found no influence of EPC on abdominal activity in asymptomatic individuals
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during an ASLR task. Based on our results, the application of EPC may change the
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trunk and hip extensor muscle activity in only the CLBP group.
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4.1. Limitations
This study had several limitations. First, to apply EPC without overlap with the
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electrode of the GM, the pelvic belt was shifted upward. Although we attempted to
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avoid overlap of the EPC and the electrode of the GM as much as possible, we did not
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exclude this methodological limitation in the application of EPC. Second, because the
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dominant leg was chosen for the PHE task in this study, the side of pain may have
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affected the EMG activity of the back and leg muscles, especially in patients with
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unilateral back and buttock pain. Third, we did not quantify the EPC device tension.
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Fourth, although the EPC device was adjusted by a physical therapist with experience in
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dealing with females suffering from CLBP, it may have been applied with differing
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tightness. Finally, the standard deviation was large, indicating substantial
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interindividual variation in the CLBP group. Further studies are needed to assess the
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effects of EPC on lower extremity force in a CLBP group during PHE.
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5. CONCLUSIONS
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This study showed that the CLBP group had increased activation of the trunk extensor
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muscles compared with a healthy group during PHE. The application of EPC reduced
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trunk and hip extensor muscle activity in the CLBP group during PHE, whereas EPC
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did not change the activity of the trunk and hip extensor muscles in the healthy group.
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Further studies should investigate the effects of EPC on muscle strength in patients with
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CLBP during various tasks.
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biomechanical model on sacroiliac joint stability. Journal of Electromyography and
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Kinesiology 1998;8(4):205-14.
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van Dieën JH, Selen LP, Cholewicki J. Trunk muscle activation in low-back pain patients, an analysis of the literature. Journal of Electromyography and Kinesiology
3
2003;13(4):333-51.
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Index. Journal of Chiropractic Medicine. 2008;7(4):161-3.
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Vianin M. Psychometric properties and clinical usefulness of the Oswestry Disability
Willson JD, Ireland ML, Davis I. Core strength and lower extremity alignment during
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single leg squats. Medicine and Science in Sports and Exercise 2006;38(5):945-52.
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CLBP (n=20)
Age (years)
41.75 ± 8.64
43.7 ± 9
0.5
Weight (kg)
52 ± 7.94
55 ± 4.7
0.16
Height (cm)
158.5 ± 4.92
161 ± 3.88
0.15
BMI (kg/m2)
20.8 ± 3.7
21.33 ± 2.1
0.57
Pain onset (years)
NA
5.43
NA
Numeric rating scalea
NA
5.05
NA
Modified Oswestry scoreb
NA
30.4
NA
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Abbreviation: NA, not applicable.
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a
The numeric rating scale 0 to 10.
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The modified Oswestry score ranged from 0 to 100.
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p-value
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Table 2. Changes in the EMG amplitude of the trunk and hip extensor muscles during
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PHE with and without EPC. CLBP
EPC
No EPC
L LD (%MVIC)
6.83 ± 3.21
6.94 ± 2.98
13.62 ± 4.24a,b
10.77 ± 3.32
R LD (%MVIC)
7.74 ± 3.21
7.35 ± 4.26
9.75 ± 4.21
9.41 ± 4.55
L ES (%SMVC)
38.49 ± 6.76
37.01 ± 7.43
51.87 ± 11.69a,b
41.79 ± 8.08
R ES (%SMVC)
39.53 ± 6.29
39.58 ± 6.63
50.41 ± 18.12a,b
43.16 ± 14.13
L GM (%SMVC)
14.59 ± 4.67
14.43 ± 4.07
15.97 ± 9.41
15.13 ± 8.86
R GM (%SMVC)
23.44 ± 4.63
24.15 ± 5.22
33.31 ± 16.65a,b
27.24 ± 10.59
L BF (%MVIC)
7.01 ± 4.55
7.36 ± 4.54
5.21 ± 2.21
9.87 ± 2.11
R BF (%MVIC)
42.6 ±19.83
42.3 ± 22.39
44.17 ± 20.41
42.78 ± 16.97
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No EPC
EPC
Abbreviations: PHE, prone hip extension; CLBP, chronic low back pain; EPC, external
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Healthy Muscle
pelvic compression; L, left; R, right; LD, latissimus dorsi; ES, erector spinae;
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GM, gluteus maximus; BF, biceps femoris.
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Values are means ± SD.
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a
Significant between group differences in the non-EPC condition
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b
Significant differences between the non-EPC and EPC conditions in the CLBP group
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(B)
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Figure 1. Target bar and the two PHE tasks: (A) starting position; (B) PHE with EPC.
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Abbreviations: PHE, prone hip extension; EPC, external pelvic compression.
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Ethics approval was obtained from the Inje University Ethics Committee for Human Investigations,
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and written informed consent was obtained from all participants.
S1356-689X(14)00081-2
DOI:
10.1016/j.math.2014.04.016
Reference:
YMATH 1563
To appear in:
Manual Therapy
Received Date: 26 September 2013 Revised Date:
21 April 2014
Accepted Date: 28 April 2014
Please cite this article as: Kim J-W, Kwon O-Y, Kim T-H, An D-H, Oh J-s, Effects of external pelvic compression on trunk and hip muscle EMG activity during prone hip extension in females with chronic low back pain, Manual Therapy (2014), doi: 10.1016/j.math.2014.04.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Title Page
1. Title:
prone hip extension in females with chronic low back pain
2. Name and academic degree of each author
Oh-Yun Kwonb, PT, PhD ([email protected])
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Tae-Ho Kim c, PT, PhD ([email protected])
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Ji-Won Kima, PT, PhD ([email protected])
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Effects of external pelvic compression on trunk and hip muscle EMG activity during
Duk-Hyun An d, PT, PhD ([email protected]) Jae-seop Ohd, PT, PhD ([email protected])
Department of Physical Theraphy, NAMBU University, Gwangju, South Korea
b
c
Department of Physical Therapy, YONSEI University, Wonju, South Korea
Department of Physical Therapy, DAEGU University, Daegu, South Korea
d
Department of Physical Therapy, College of Biomedical Science and Engineering,
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3. Authors’ institutional affiliations
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4. The work should be attributed to Department of Physical Therapy, INJE University.
5. Corresponding author: JAE-SEOP, OH, PT, PhD Department of Physical Thearapy College of Biomedical Science and Engineering 1
ACCEPTED MANUSCRIPT INJE university 607 Obang-dong, Gimhae-si Gyeongsangnam-do, South Korea, 621-749
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[email protected]
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ABSTRACT
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Many studies have reported higher trunk and hip muscle activity in patients with
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chronic low back pain (CLBP). Increased trunk and hip muscle activity could contribute
4
to pain. Previous studies have shown that external pelvic compression (EPC) decreased
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back and hip muscle activity during physical tasks.
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In this study, we assessed the effects of EPC on the electromyography (EMG)
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activity of the latissimus dorsi (LD), elector spinae (ES), gluteus maximus (GM), and
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biceps femoris (BF) in a CLBP group and a healthy group during prone hip extension
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(PHE).
Forty female volunteers (20 non-specific CLBP, 20 healthy) were recruited.
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Surface EMG data were collected from the LD, ES, GM, and BF muscles during a PHE
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task. Normalized EMG values were analyzed by separate repeated-measures analysis of
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variance (ANOVA) for each muscle.
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The normalized EMG activity in the left LD, bilateral ES, and right GM was
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significantly higher in the CLBP group than in the healthy group during PHE. In the
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CLBP group, the normalized EMG activity in the left LD, bilateral ES, and right GM
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was significantly lower with EPC than without (p < 0.05). This suggests that the
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application of EPC decreased trunk and hip extensor EMG activity in the CLBP group
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during PHE.
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Keywords:
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Chronic low back pain
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External pelvic compression
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Pelvic compression belt
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Prone hip extension
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1. INTRODUCTION
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Low back pain (LBP) is a major medical problem and makes a considerable
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contribution to disability (Freburger et al., 2009; Macfarlane et al., 2012). The
4
prevalence of LBP was threefold higher in females than males, and females were more
5
likely to suffer functional impairment because of LBP (Croft et al., 1998; Biglarian et
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al., 2012). Females with chronic LBP (CLBP) show less back and hip muscle strength
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than healthy females (Nadler, 2000; Bayramoğlu et al., 2001). Back and hip muscle
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strengthening exercises are important to prevent and treat CLBP because muscle
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weakness is a risk factor for LBP (Lee et al., 1999; Nadler, 2000; Bayramoğlu et al.,
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2001).
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Prone hip extension (PHE) is commonly used as a therapeutic exercise in
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patients with LBP to strengthen the trunk and hip extensors and lengthen the hip flexors.
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In the clinical setting, patients often perform exercises with difficulty due to increased
14
pain and/or muscle weakness. A recent study showed higher trunk and hip muscle
15
amplitudes in CLBP than in a healthy group during a PHE task (Arab et al., 2011).
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Although they did not measure spinal stability, the authors suggested the need for
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increased trunk and hip muscle activity to enhance trunk stability in the CLBP group
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(Arab et al., 2011). Many other studies have reported higher trunk muscle activity in
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patients with CLBP than in healthy subjects during various tasks, such as trunk bending
2
and lifting tasks (Ambroz et al., 2000; Ferguson et al., 2004). It has been demonstrated
3
that increased muscle activity is influenced by pain (Graven-Nielsen et al., 1997). Some
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researchers have suggested that increased trunk muscle activity could contribute to a
5
vicious cycle of pain-spasm-pain and increase the load on the spine by co-contraction of
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the trunk muscles (Roland et al., 1986; Keir et al., 2004). Therefore, clinicians have
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emphasized reducing abnormally increased muscle activity during therapeutic exercises
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in patients with LBP (Fryer et al., 2004). To reduce abnormally increased muscle
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activity, some clinicians have used external pelvic compression (EPC) not only to
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decrease the pain but also to decrease the abnormally increased muscle activity during
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functional movements.
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External pelvic compression has been shown to facilitate or inhibit the EMG
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activity of the trunk and hip muscles and is an easy task to perform during the active
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straight leg raise (ASLR) (Mens et al., 1999; Hu et al., 2010). Mens et al. (1999)
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demonstrated that EPC improved the ASLR performance score. Hu et al. (2010)
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reported that EPC during ASLR resulted in reduced abdominal muscle activation.
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Although many studies assessing EPC have been conducted with subjects in the supine
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position, none has examined its effect on the activity of the trunk and hip extensors in
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the prone position, such as PHE. Thus, in this study we (1) compared the activity of the
2
LD, ES, GM, and BF muscles bilaterally during hip extension in the prone position
3
between a healthy group and a CLBP group and (2) examined the effects of EPC on the
4
trunk and hip muscle extensor activity during PHE in a healthy group and a CLBP
5
group. Based on previous findings, we hypothesized that (1) the trunk and hip extensor
6
muscle activity would increase during PHE in a CLBP group compared with a healthy
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group, and (2) the application of EPC would result in decreased activity of the trunk and
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hip extensor muscles during PHE in the CLBP group.
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2.1. Subjects
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Forty female volunteers (20 with non-specific CLBP and 20 healthy females)
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participated. The patients with CLBP were recruited from two local outpatient
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orthopedic clinics and one spine hospital and the healthy females were recruited by
15
word of mouth in Busan, South Korea. Care was taken to recruit participants of similar
16
age, height, weight, and BMI into each group. Originally, 24 females with CLBP were
17
tested, but four patients were excluded because they were unable to perform maximal
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voluntary contractions due to acute pain in the trunk and legs at the time of testing. The
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healthy group reported no history of LBP that required medical attention or resulted in
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limited function. Inclusion criteria for the CLBP group were LBP for more than 3
3
months (pain felt between T12 and the gluteal fold). LBP intensity during the preceding
4
week was scored using a numeric rating scale (NRS), from 0 to 10, where 0 denoted no
5
pain and 10 the worst possible pain. The NRS has acceptable reliability and validity
6
(Roach et al, 1997; Ferreira-Valente, 2011). Functional disability was measured using
7
the Oswestry Disability Index (ODI). The ODI questionnaire is a reliable and valid
8
instrument (Vianin, 2008). Patients had to have experienced LBP for at least 3 months,
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have NRS scores of at least 3, and ODI scores of at least 15% (Leitner, 2009; Marshall
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and Murphy, 2010). Exclusion criteria were specific conditions, such as neoplasms,
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spinal fractures, spondylolisthesis, spondylosis, spinal stenosis, ankylosing spondylitis,
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previous spinal surgery, lower extremity impairment, sacroiliac dysfunction, and
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pregnancy.
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The Inje University Faculty of Health Science Human Ethics Committee
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approved this study. All subjects provided written informed consent prior to
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participation.
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2.2. EMG Recording and Data Analysis
2
Electromyography data were recorded and analyzed using the Delsys Trigno Wireless
3
EMG system (Delsys, Boston, MA, USA). Before electrode placement, skin impedance
4
was minimized by shaving off any body hair and cleaning the skin with 70% isopropyl
5
alcohol. EMG data were collected bilaterally from the LD (4 cm below the inferior tip
6
of the scapula and half the distance between the spine and lateral edge of the torso), ES
7
(2 cm lateral to the spinous process of the L1 level and aligned parallel to the spine),
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GM (half the distance between the greater trochanter and second sacral vertebra and at
9
an oblique angle at or slightly above the level of the trochanter), and BF (2 cm from the
10
lateral border of the thigh and two-thirds the distance between the trochanter and back
11
of the knee) muscles (Criswell, 2010). The signals were amplified and band-pass
12
filtered (20-450 Hz) before being recorded digitally at 2000 samples/s, and then
13
calculating the root mean square (RMS).
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We included two maneuvers to normalize the EMG activity: a maximum
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voluntary isometric contraction and submaximal voluntary isometric contraction
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(Pirouzi et al., 2006). In a pre-test, we verified that when both submaximal isometric
17
contraction and maximal isometric contraction were applied, the values were measured
18
at an even ratio. However, when maximal isometric contraction was used for ES and
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GM, the patients with lumbar pain developed acute pain. Therefore, the submaximal
2
method was judged appropriate and so was used for ES and GM. This method of
3
normalization for the trunk muscles has been shown to exhibit excellent within-day
4
reliability for healthy controls and patients with CLBP (Dankaerts et al., 2004).
5
All muscles were tested in the prone position. The maximum isometric
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contractions were performed against manual resistance for the LD and BF muscles
7
(Kendall, 2005). The LD muscle was tested with the subject’s arms at her sides and
8
shoulders internally rotated to create a palm-up position. Resistance was then applied to
9
the forearm. The BF muscle was tested with the thigh and hip laterally rotated, knee
10
flexed to approximately 20°, and resistance applied to the shank. For the submaximal
11
voluntary isometric contraction of the ES and GM, the subject lifted both knees 5 cm
12
off the examination table, with the knees flexed at 90°, and held them for 5 s (Dankaerts
13
et al., 2004). Each maximum isometric contractions maneuver and submaximal
14
voluntary isometric contraction was performed twice for 5 s, and the average muscle
15
activity for the middle 3 s of the two trials was used for normalization. EMG results
16
were normalized to the maximum and submaximum EMG RMS values calculated from
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the EMG signals obtained during voluntary isometric contraction test for each muscle.
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2.3 Application of EPC
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The EPC device (SI-LOC, OPTP, Canada) was applied below the anterior superior iliac
3
spine (ASIS) (Damen et al., 2002) in the subjects and the strap was fastened firmly to
4
the belt. This device was constructed of non-elastic material with Velcro ends and was 5
5
cm wide at the front and back and 8 cm wide at the sides. The tightness was adjusted by
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a physiotherapist with experience in dealing with CLBP. EPC was applied without any
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pain or discomfort in the CLBP group.
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2.4 Experimental procedures
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Before the measurements, all of the individuals were instructed on active PHE and
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allowed 5 min of practice, which was sufficient familiarization for the investigation.
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The individuals were asked to lie prone with their arms at their side and head in the
13
mid-line. An adjustable bar was placed over the experimental table in alignment with
14
the back of knee, so that the popliteal region contacted the bar during the hip extension
15
task. A target bar was set at 10° to provide tactile feedback. The individuals were told to
16
extend their dominant leg from neutral to about 10° while keeping the knee extended.
17
All individuals reported that they were right-leg dominant; i.e., they would use this leg
18
to kick a ball (Willson et al., 2006). The subjects were asked to perform hip extension
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and maintain it for 5 s in this position (Fig. 1). The PHE tasks were performed under
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EPC and without EPC in randomized order. A 1-min rest was allowed between
3
conditions.
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The data used for the statistical analyses showed a normal distribution without
7
substantial skew. The greatest skewness value was 1.85. Differences in demographic
8
characteristics between the groups were examined using independent t-tests.
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Comparisons were made not only between groups (CLBP vs. healthy) to investigate the
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EMG activity of the back and hip extensor muscles but also within each group to
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examine the effect of EPC (EPC vs. no EPC) on the EMG activity of the back and hip
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extensor muscles during PHE. Separate repeated-measures analysis of variance
13
(ANOVA) and the post hoc Bonferroni test were conducted for each muscle and for the
14
four independent variables.
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3. RESULTS The demographics of both groups are summarized in Table 1. There was no significant difference between the groups (p > 0.05).
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Table 2 presents the analysis of the normalized RMS signal amplitudes for each muscle in the PHE with and without EPC for both groups. Analysis of PHE without
3
EPC revealed that the signal amplitudes were higher in the CLBP group in the left LD,
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ES bilaterally, and right GM (all p < 0.05). There was no other between-group
5
difference in the other muscles.
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Within the CLBP group, application of EPC resulted in significantly lower
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signal amplitudes in the left LD, the ES bilaterally, and the right GM versus the
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non-EPC condition (all p < 0.05; Table 2). Application of EPC resulted in no difference
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in signal amplitude in any muscle in the healthy group without back pain.
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4. DISCUSSION
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The results presented here support our hypotheses that the CLBP group had
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higher muscle activity of the left LD, ES bilaterally, and right GM than the healthy
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group during PHE. Increased trunk and hip extensor muscle activity may make it more
15
difficult to perform the PHE task in the CLBP group than in the healthy group. These
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findings are consistent with those of Arab et al. (2011), who found higher bilateral ES
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muscle activity during PHE in a CLBP group than in a healthy group.
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Many factors may be associated with the higher trunk muscle activity patients with CLBP, such as pain and spinal instability, and difficulty in performing physical
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tasks (Silfies et al., 2005; Arab et al., 2011). Increased EMG activity in the trunk and
4
hip extensor muscles during leg lifting in the prone position seems to compensate for
5
the difficulty in performing physical tasks such as PHE and pain in the CLBP group.
6
Previous studies have demonstrated that a painful area induces increased muscle
7
activity, compared with a no-pain area (Graven-Nielsen et al., 1997). We considered
8
that increased trunk and hip extensor muscle activity might subsequently affect muscle
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spasms, which, in turn, will cause pain (van Dieën et al., 2003). Additionally, increased
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trunk extensor muscle activity may lead to earlier muscle fatigue due to heightened
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muscle usage and may possibly increase spinal load, which is recognized to be harmful
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when attempting to reduce CLBP (Gadner-Morse and Stokers, 1998; Mannion, 1999).
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Thus, in patients with CLBP during PHE, care may be needed to avoid increased trunk
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To inhibit EMG activity in trunk and hip muscles, researchers have used EPC
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(Sniders et al., 1998; Hu et al., 2010). In this study, we observed decreased left LD,
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bilateral ES, and right GM muscle activity with EPC, compared with no EPC, in the
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CLBP group during PHE. These results are consistent with a previous study of the
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active straight leg raise test. Hu et al. (2010) demonstrated that EPC reduced lower
2
external oblique, internal oblique, and transverse abdominal muscle activity in
3
asymptomatic subjects during ASLR. Previous studies also demonstrated that applying
4
EPC can release pain and improve ASLR performance (Cogill et al., 1996; Mens et al.,
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1999). In this study, when EPC was applied in the CLBP group, pain was reduced,
6
which may lead to decrease trunk and hip muscle activity. This finding suggests that
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EPC may be helpful in reducing pain and preventing intensified trunk and hip extensor
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muscle usage.
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We observed that in the healthy group, EPC did not influence trunk or hip extensor muscle activity during the PHE task. This is consistent with Park et al. (2013),
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who found no influence of EPC on abdominal activity in asymptomatic individuals
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during an ASLR task. Based on our results, the application of EPC may change the
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trunk and hip extensor muscle activity in only the CLBP group.
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4.1. Limitations
This study had several limitations. First, to apply EPC without overlap with the
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electrode of the GM, the pelvic belt was shifted upward. Although we attempted to
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avoid overlap of the EPC and the electrode of the GM as much as possible, we did not
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exclude this methodological limitation in the application of EPC. Second, because the
2
dominant leg was chosen for the PHE task in this study, the side of pain may have
3
affected the EMG activity of the back and leg muscles, especially in patients with
4
unilateral back and buttock pain. Third, we did not quantify the EPC device tension.
5
Fourth, although the EPC device was adjusted by a physical therapist with experience in
6
dealing with females suffering from CLBP, it may have been applied with differing
7
tightness. Finally, the standard deviation was large, indicating substantial
8
interindividual variation in the CLBP group. Further studies are needed to assess the
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effects of EPC on lower extremity force in a CLBP group during PHE.
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5. CONCLUSIONS
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This study showed that the CLBP group had increased activation of the trunk extensor
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muscles compared with a healthy group during PHE. The application of EPC reduced
14
trunk and hip extensor muscle activity in the CLBP group during PHE, whereas EPC
15
did not change the activity of the trunk and hip extensor muscles in the healthy group.
16
Further studies should investigate the effects of EPC on muscle strength in patients with
17
CLBP during various tasks.
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ACCEPTED MANUSCRIPT Table 1. Demographic and clinical characteristics of the participants (N=40), mean ± SD. Characteristics Healthy (n=20)
CLBP (n=20)
Age (years)
41.75 ± 8.64
43.7 ± 9
0.5
Weight (kg)
52 ± 7.94
55 ± 4.7
0.16
Height (cm)
158.5 ± 4.92
161 ± 3.88
0.15
BMI (kg/m2)
20.8 ± 3.7
21.33 ± 2.1
0.57
Pain onset (years)
NA
5.43
NA
Numeric rating scalea
NA
5.05
NA
Modified Oswestry scoreb
NA
30.4
NA
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Abbreviation: NA, not applicable.
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a
The numeric rating scale 0 to 10.
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The modified Oswestry score ranged from 0 to 100.
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p-value
Group
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Table 2. Changes in the EMG amplitude of the trunk and hip extensor muscles during
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PHE with and without EPC. CLBP
EPC
No EPC
L LD (%MVIC)
6.83 ± 3.21
6.94 ± 2.98
13.62 ± 4.24a,b
10.77 ± 3.32
R LD (%MVIC)
7.74 ± 3.21
7.35 ± 4.26
9.75 ± 4.21
9.41 ± 4.55
L ES (%SMVC)
38.49 ± 6.76
37.01 ± 7.43
51.87 ± 11.69a,b
41.79 ± 8.08
R ES (%SMVC)
39.53 ± 6.29
39.58 ± 6.63
50.41 ± 18.12a,b
43.16 ± 14.13
L GM (%SMVC)
14.59 ± 4.67
14.43 ± 4.07
15.97 ± 9.41
15.13 ± 8.86
R GM (%SMVC)
23.44 ± 4.63
24.15 ± 5.22
33.31 ± 16.65a,b
27.24 ± 10.59
L BF (%MVIC)
7.01 ± 4.55
7.36 ± 4.54
5.21 ± 2.21
9.87 ± 2.11
R BF (%MVIC)
42.6 ±19.83
42.3 ± 22.39
44.17 ± 20.41
42.78 ± 16.97
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EPC
Abbreviations: PHE, prone hip extension; CLBP, chronic low back pain; EPC, external
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Healthy Muscle
pelvic compression; L, left; R, right; LD, latissimus dorsi; ES, erector spinae;
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GM, gluteus maximus; BF, biceps femoris.
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Values are means ± SD.
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a
Significant between group differences in the non-EPC condition
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b
Significant differences between the non-EPC and EPC conditions in the CLBP group
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(A)
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(B)
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Figure 1. Target bar and the two PHE tasks: (A) starting position; (B) PHE with EPC.
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Abbreviations: PHE, prone hip extension; EPC, external pelvic compression.
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ACCEPTED MANUSCRIPT Ethical approval statement
Ethics approval was obtained from the Inje University Ethics Committee for Human Investigations,
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and written informed consent was obtained from all participants.
