Original Research
Patients With Low Back Pain Demonstrate Increased Activity of the Posterior Oblique Sling Muscle During Prone Hip Extension Ji-Won Kim, PT, MSc, Min-Hyeok Kang, PT, MSc, Jae-Seop Oh, PT, PhD Objectives: To examine activation patterns of the myofascial chain in women experiencing chronic low back pain (CLBP) and women without CLBP during a prone hip extension (PHE) test. Design: Cross-sectional. Setting: Clinical research laboratory. Participants: Fifteen women experiencing CLBP and 15 women without CLBP. Methods: Surface electromyographic recordings from the posterior oblique sling during PHE. Main outcome measurements: Two-sample t-tests were used to compare demographic information and electromyographic signal amplitude of the posterior oblique sling between groups. Results: Women with CLBP exhibited significantly increased normalized electromyographic signal amplitudes in the contralateral latissimus dorsi (P ¼ .01), contralateral elector spinae (P < .01), ipsilateral elector spinae (P < .01), ipsilateral gluteus maximus (P ¼ .03), and ipsilateral biceps femoris (P ¼ .02) compared with women without CLBP. Conclusions: Women with CLBP had greater activity in the posterior oblique sling muscles than did women without CLBP during PHE. These findings suggest that an alteration can be made in posterior oblique sling muscle activities during PHE in women with CLBP. PM R 2014;-:1-6
INTRODUCTION Chronic low back pain (CLBP) is a common musculoskeletal problem in society today. CLBP affects up to 70%-80% of the population, who experience at least one episode during their lifetime, and 11%-12% of the population are disabled by it [1,2]. Women have a greater incidence of low back pain (LBP) than do men and are also more likely to have functional impairment caused by CLBP [3]. To improve functional restoration in women with CLBP, who typically show decreased trunk muscle strength, muscle-strengthening exercises are considered important [4]. Currently, core training in CLBP rehabilitation has become popular because it reduces pain and functional disability [5]. Core training is performed to strengthen the trunk and pelvic region and improve postural control [6]. The prone hip extension (PHE) test is an accepted test for measuring the motor pattern in the lumbopelvic area [7,8]. Ideally, in people performing the PHE test, the lumbopelvic region should be maintained in a neutral position, without rotation of the lumbar spine and/or pelvis [9] or excessive extension of the spine [9,10]. Altered lumbar spine and pelvic movement patterns have been shown to differentially activate lumbopelvic muscles during lower limb movement [11], which can contribute to lumbopelvic dysfunction [10]. In particular, a previous study of patients with LBP indicated increased electromyographic (EMG) activity in the trunk and hip muscles during various tasks, such as lifting and trunk rotation [12,13]. It seems that patients with LBP showed increased EMG activity of the trunk and hip muscles during these tasks because of abnormal motor recruitment patterns. The increased trunk and hip muscle activity also can be explained by postural disturbance and spinal instability in patients with LBP [14,15]. PM&R 1934-1482/13/$36.00 Printed in U.S.A.
J.-W.K. Department of Rehabilitation Science, Graduate School, INJE University, Gimhae, Republic of Korea Disclosure: nothing to disclose M.-H.K. Department of Rehabilitation Science, Graduate School, INJE University, Gimhae, Republic of Korea Disclosure: nothing to disclose J.-S.O. Department of Physical Therapy, College of Biomedical Science and Engineering, INJE University, 607 Obang-dong, Gimhae-si, Gyeongsangnam-do 621-749, Gimhae, Republic of Korea. Address correspondence to: J.-S.O.; e-mail: [email protected] Disclosure: nothing to disclose Submitted for publication December 24, 2012; accepted December 22, 2013.
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To evaluate muscular activation patterns during the PHE task, researchers have compared the EMG signals (in terms of amplitude) of the elector spinae (ES), gluteus maximus (GM), and hamstring muscle in subjects with and without CLBP [15,16]. However, studies have reported inconsistent muscle activation patterns in patients with CLBP [15,16]. For example, Arab et al [15] evaluated EMG amplitudes during PHE in women with and without CLBP and found increased ES, GM, and biceps femoris (BF) muscle activities in women with CLBP, which these investigators suggested was attributable to reduced spinal stability. In contrast, Guimaraes et al [16] found no difference in the trunk or hip muscles between groups and suggested that assessment of muscle activation patterns in the PHE task cannot be used to discriminate between persons with and without LBP. When the GM fails to control the pelvis, the contralateral latissimus dorsi (LD) may become dominant because the LD and GM, along with the thoracolumbar fascia, work synergistically to control the lumbopelvic region [17]. The BF, GM, ES, and LD muscles create the posterior oblique sling, one of the myofascial slings involved in extension during normal activities for postural control [18]. Such a myofascial sling is a chain of anatomically interconnected muscles [19]. Muscle slings are thought to facilitate the transfer force through the trunk, particularly from the lower to the upper body [18]. Page et al [18] described 3 muscle slings (the posterior oblique sling, anterior oblique sling, and longitudinal sling) that are activated differently based on the load applied. Similarly, Myers [19] explained that 3 major lines (the superficial back line, superficial front line, and lateral line) were made of myofascial or connective tissue units. The superficial back line consists of the nuchal ligament, trapezius, LD, ES, thoracolumbar fascia, hamstrings, gastrocnemius, and plantar fascia, aligned similarly to the elements of the posterior oblique sling [19]. Although in clinical practice the myofascial sling has been considered in strengthening programs, it is being promoted in the clinical literature without any scientific underpinning [19,20]. Muscle slings in the trunk are necessary for rotational trunk movements, such as reciprocal gait pattern, active straight leg raising (ASLR), and hip extension in a prone position [18]. To the best of our knowledge, no study has been performed to evaluate the posterior oblique sling muscular pattern during PHE in women with CLBP. Gaining an understanding of the activity of the myofascial sling in clinical tests may have clinical significance. Thus in the present study we assessed the EMG signal amplitude (muscle activity) of the posterior oblique sling muscles during PHE in women with and without CLBP. Based on findings of previous studies, we hypothesized that the activity of the posterior oblique sling muscles would be greater during PHE in women with CLBP than in women without CLBP. Investigating the differences between the groups should provide beneficial information for clinicians who design rehabilitation exercises.
LBP AND INCREASED POSTERIOR OBLIQUE SLING ACTIVITY
METHODS Subjects A total of 30 female volunteers (15 control subjects and 15 patients with nonspecific CLBP) aged between 22 and 58 years were included in the study. The women with and without CLBP were matched in terms of age, height, weight, and body mass index (BMI); characteristics of the participants are shown in Table 1. Women with CLBP were recruited from 3 local orthopedic clinics in South Korea. Eighteen patients with CLBP were originally tested, but 3 were excluded because their symptoms were provoked at the time of testing (ie, acute back, hip, and/or posterior thigh pain when performing a PHE task and/or maximal voluntary isometric contraction). Participants were recruited to the CLBP group if they had nonspecific LBP, defined as pain lasting at least 3 months without a clear, specific cause (eg, infection, tumor, osteoporosis, ankylosing spondylitis, fracture, inflammatory process, radicular syndrome, or cauda equine syndrome), with or without referral of pain to the leg [21]. Inclusion also required pain in the lumbar or lumbosacral region with restricted activity and a minimum modified Oswestry Disability Index score of 15% at baseline [22]. The pain must have been present for at least the previous 12 weeks (mean SD, 5.93 4.72 years). Exclusion criteria for the CLBP group were pregnancy, spinal surgery, neoplasm, fractures, spondylolisthesis, spondylolysis, spinal stenosis, ankylosing spondylitis, a BMI of 30 or higher (because of the potential influence of fat tissue on our ability to measure surface activity), and not being able to perform the PHE task because of weakness in the GM. For descriptive purposes, data regarding the disability and pain of patients with CLBP were assessed with the modified Oswestry Disability Index and a visual analog scale, Table 1. Demographic and clinical characteristics of participants (N ¼ 30), mean SD Group
Characteristic Age, y Weight, kg Height, cm BMI, kg/m2 Pain onset. y Visual analogue scale score* Modified Oswestry scorey
Control Subjects (n [ 15)
CLBP (n [ 15)
42.87 11.28 44.33 10.75 57.20 6.53 58.06 7.97 161.66 5.38 161.40 6.23 22.21 2.96 22.32 3.08 (range: 19.2-27.8) (range: 18.3-27.3) NA 5.93 4.72 NA 5.13 1.84 NA
47.00 10.17
P Value .72 .74 .9 .85 NA NA NA
CLBP ¼ chronic low back pain; BMI ¼ body mass index; NA ¼ not applicable. *The visual analog scale score ranged from 0 to 10. y The Modified Oswestry score ranged from 0 to 100.
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respectively. To be eligible for the control group, participants were required to have no history of LBP, with no restricted function or any respiratory or neurologic disorder or pain elsewhere in the spine or lower limbs. Women without LBP were recruited from the local community via word of mouth. The Inje University Faculty of Health Science Human Ethics Committee granted approval for this study. All subjects provided written informed consent before participating.
Instrumentation The activity levels of the posterior oblique sling muscles were measured with a wireless EMG system (Delsys, Inc, Boston, MA). Before placement of the EMG electrodes, the skin at the anatomic landmarks was shaved (if required) and cleaned with alcohol. Pairs of surface electrodes were positioned bilaterally well within the muscle borders and aligned with the muscle orientation of the posterior oblique sling muscles. The electrodes for LD were placed 4 cm below the inferior tip of the scapula and half the distance between the spine and the lateral edge of the torso [23]. For ES, the electrodes were placed approximately 2 cm lateral to the spinous process at the L1 level and aligned parallel to the spine [23]. For GM, electrodes were placed at half the distance between the greater trochanter and second sacral vertebra and at an oblique angle at, or slightly above, the level of the trochanter [23]. For the BF, the electrodes were placed 2 cm from the lateral border of the thigh and at two thirds the distance between the trochanter and the back of the knee [23]. A single examiner attached all the electrodes. The signals were amplified and band-pass filtered (20-450 Hz) before being recorded digitally at 2000 samples per second, and then the root mean square (RMS) was calculated. To normalize individual muscle contraction levels, we used 2 maneuvers of voluntary contractions [13]. For the submaximal contraction of ES and GM, the subject lifted both knees 5 cm off the examination table while the knees were flexed at 90 and held them for 5 seconds in a prone position. Maximal contractions were avoided for the ES and GM muscles, because reproduction of pain on testing would have possibly invalidated the use of the RMS values for normalization [24]. This method of normalization for the trunk muscles has been shown to exhibit excellent within-day reliability for healthy control subjects and patients with CLBP [24]. Maximal voluntary isometric contractions against manual resistance were used for the LD and HS muscles [25]. Two maneuvers of voluntary contractions were performed twice, and the average muscle activity for the middle 3 seconds of the 2 trials was used for normalization. The average RMS of the EMG signal during each PHE task trial was calculated and expressed as a percentage of the normalized value. The mean percent normalized value of three repetitions was determined for EMG data analysis.
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Procedures Before testing, all subjects were instructed about active PHE and given a sufficient familiarization period to practice before the investigation. All procedures for EMG measurements were performed with the subjects in the prone position on a therapeutic table with a firm mattress. The subjects were asked to lie prone with their arms at their side and with a neutral position of the pelvis and hip joint. We set the target angle at 10 to control the amount of hip extension. A goniometer was used to determine when the leg was at 10 extension, and an adjustable bar was placed at this level and provided feedback. Feedback information at 10 of hip extension also was given to the subjects by verbal instruction. The participant was instructed to extend the leg of his or her dominant side (the preferred leg for kicking a ball) from neutral to about 10 while keeping the knee straight [15,26]. When the hip was placed at 10 of extension, the participant was asked to hold this position for 5 seconds (Figure 1). The positions of the pelvis and limb were supervised visually during the PHE task to ensure that the subject maintained a neutral pelvis position, hip extension, and knee extension. If visible hip rotation movement or pelvic rotation was observed, the data were excluded. A 1-minute rest period was provided between each trial.
Statistical Analysis Differences in descriptive measures (ie, age, height, weight, and BMI) and task for the magnitude of the posterior oblique sling activities between women with and without CLBP were compared by using the independent t-test. Statistical analyses were performed with SPSS software (version 18.0; SPSS
Figure 1. The start (A) and end (B) positions of the prone hip extension task.
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Inc, Chicago, IL). P values < .05 were considered to indicate statistical significance.
RESULTS Descriptive Statistics No significant differences in physical characteristics (ie, age, height, weight, and BMI) were found between the women with and without CLBP (Table 1).
EMG Activity of the Posterior Oblique Sling EMG activity in the posterior oblique sling during hip extension in the prone position in women with and without CLBP is shown in Table 2 and Figure 2. The EMG amplitudes in the contralateral LD (P ¼ .01), contralateral ES (P ¼ .01), ipsilateral ES (P ¼ .01), ipsilateral GM (P ¼ .03), and ipsilateral BF (P ¼ .02) were significantly greater in women with CLBP than in women without CLBP.
DISCUSSION Evaluation of the muscle activation pattern in the lumbopelvic region during active PHE has been proposed to be a clinical tool for assessing lumbopelvic disease [7,8]. The muscle sling system provides lumbopelvic stability during various activities [17,19]. However, to date no study has been performed to investigate the posterior oblique sling muscles (LD, ES, GM, and BF) during PHE. In the present study, we examined the recruitment pattern of the posterior oblique sling in women with and without CLBP during PHE. Greater muscular activation patterns of the contralateral LD were found in women with CLBP (14.04 8.42) compared with women who did not have CLBP (6.83 2.91) during the PHE test. One possible explanation is that women without CLBP stabilize their lumbopelvic region more effectively, whereas women with CLBP need more activity of the contralateral LD muscle to achieve the same task. According to Norris [27], if the GM fails to control the pelvis, rotation of the thoracolumbar spine may occur
toward the contralateral side during PHE. We suggest that to compensate for faulty movements, such as rotation of the thoracolumbar spine, overactivity of the contralateral LD may occur in women with CLBP during PHE. As a result the contralateral LD can become dominant in maintaining a lumbopelvic neutral position because of insufficiency in the GM to control the lumbopelvic region [17]. Bruno and Murphy [28] found greater activity in the upper trapezius in persons with abnormal spine patterns versus normal spine patterns during PHE because the upper trapezius is part of a chain system (superficial back line), and an abnormal spine pattern may compensate for a motor control deficit in the lumbopelvic region. Our findings are in line with those of Janda [18], who indicated that muscle slings are necessary to facilitate reciprocal patterns between the upper and lower extremities and for rotational lumbopelvic stability. The posterior oblique sling is one of the muscle slings, and the contralateral LD, thoracolumbar fascia, ipsilateral GM, and ipsilateral BF create lumbopelvic stability during load transfer tasks [29,30]. During the PHE test, the optimal movement pattern is for the pelvis to remain neutral and to be controlled by the abdominal musculature; however, in patients with lumbopelvic dysfunction, the lumbopelvic region can show excessive extension and rotational patterns [9,10]. In women with CLBP, the lack of pelvic postural control during PHE may reflect increased activity of the contralateral LD for pelvic control, which can be related to changes in the motor control pattern of the myofascial sling. It seems that increased activity of the ipsilateral GM may produce posterior tilt of the pelvis; to provide a neutral position, increased muscle activity of the contralateral LD is required for a counterbalancing effect, which causes anterior tilt of the pelvis. These results are consistent with those of previous studies involving sacroiliac joint pain. Subjects with sacroiliac joint pain display greater activity of the contralateral LD than do healthy subjects [31]. Like patients with LBP, patients with sacroiliac joint dysfunction experience difficulty in load transfer in clinical tests [32]. Significantly greater EMG activity of the ipsilateral GM also was found in women with CLBP (29.31 9.60)
Table 2. Electromyographic activity of muscles during prone hip extension in subjects with and without chronic low back pain Amount of Activation CLD (% MVIC) ILD (% MVIC) CES (% SMVC) IES (% SMVC) CGM (% SMVC) IGM (% SMVC) CBF (% MVIC) IBF (% MVIC)
Control Subjects 6.83 7.71 38.95 34.37 12.87 20.64 4.93 34.50
(2.91) (5.80) (10.82) (10.20) (8.45) (10.95) (2.58) (15.35)
CLBP 14.04 11.75 58.34 51.72 16.30 29.31 5.49 48.25
(8.42) (9.64) (11.75) (10.72) (8.02) (9.60) (2.52) (14.85)
Confidence Interval
P Value
12.05 to 2.35 9.98 to 1.91 27.83 to 10.94 25.18 to 9.53 9.59 to 2.74 16.37 to 0.95 2.23 to 1.11 25.50 to 2.45
.01* .22 .00* .00* .26 .03* .89 .02*
CLBP ¼ chronic low back pain; CLD ¼ contralateral latissimus dorsi; MVIC ¼ maximal voluntary isometric contraction; ILD ¼ ipsilateral latissimus dorsi; CES ¼ contralateral erector spinae, SMVC ¼ submaximal voluntary contraction; IES ¼ ipsilateral erector spinae; CGM ¼ contralateral gluteus maximus; IGM ¼ ipsilateral gluteus maximus; CBF ¼ contralateral biceps femoris; IBF ¼ ipsilateral biceps femoris. *P < .05.
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Figure 2. Comparison of the activity of the posterior oblique sling during prone hip extension in female subjects with and without chronic low back pain (CLBP). RMS ¼ root mean square; CLD ¼ contralateral latissimus dorsi; ILD ¼ ipsilateral latissimus dorsi; CES ¼ contralateral erector spinae; IES ¼ ipsilateral erector spinae; CGM ¼ contralateral gluteus maximus; IGM ¼ ipsilateral gluteus maximus; CBF ¼ contralateral biceps femoris; IBF ¼ ipsilateral biceps femoris. *P < .05.
compared with women without CLBP (20.64 10.95). These changes, like the significantly increased EMG signal amplitude of the hip extensor during lifting of the leg, seem to indicate that CLBP makes it difficult to lift a leg. This supposition is supported by recent research that showed greater activation of hip flexor muscles in patients with pregnancy-related LBP compared with healthy control subjects during ASLR [33]. The pregnancy-related LBP was correlated with increased laxity of the pelvic girdle [34]. Thus women with pregnancy-related LBP may need more muscle activity to overcome the laxity and may need to exert more effort during ASLR. Similarly, it is commonly believed that lumbopelvic instability is an important component in persons with CLBP [15]. In our study, trunk and hip muscle activities were increased in women with CLBP compared with women without CLBP. One explanation may be that women with CLBP attempt to stabilize the lumbopelvic region more than healthy women need to. Our results are similar to the findings of Arab et al [15], who investigated the activation pattern of the trunk and hip muscles in women with and without CLBP. These investigators found increased activity of the ES, GM, and BF in patients with CLBP. The patients with CLBP showed decreased activity of deep muscles such as the multifidus, which suggests that co-contraction of trunk and hip muscles could be used to compensate for lumbar segment stability [35]. In many studies, increased muscle activity of the ES, GM, and BF has been demonstrated in patients with CLBP compared with patients without CLBP during various tasks [12,36,37]. We found differences in the activation pattern of the posterior oblique sling during PHE in women with and without CLBP. For effective evaluation and therapeutic exercises with the PHE in patients with LBP, researchers and therapists should consider the posterior oblique sling
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system. When performing a PHE evaluation, researchers should assess not only the muscular pattern of the ES, GM, and BF but also the contralateral LD to evaluate lumbopelvic region dysfunction. In the clinical field, the therapist should consider an effective intervention strategy based on modification of the altered posterior oblique sling muscular pattern in persons with CLBP. We suggest that internal lumbopelvic stabilization methods (eg, the abdominal drawing-in maneuver) or external lumbopelvic stabilization methods (eg, use of a lumbopelvic belt) may be useful to modify the altered muscular pattern during the PHE task [38,39], because these interventions assist load transfer and provide normal movement patterns during lower extremity exercises [38,39]. The results of this study will help guide the evaluation of tools and the design of PHE exercise programs specifically for patients with LBP. This study has several limitations. First, the experimental group consisted only of women, and thus this study cannot be generalized to the entire population of patients with CLBP. Second, we supervised the movements of the hip and pelvis by visual judgment during the PHE task. Although visual judgment is used in most clinical settings, a motion analysis system would be useful to provide objective validity. Third, we used the submaximal contraction for EMG normalization, which made it difficult to completely exclude the potential error of measurement when comparing subjects with use of the submaximal normalization method. Finally, we did not measure the timing of muscle activity during PHE. Further study is needed to quantify the muscle onset times of the LD, ES, GM, and BF in patients during the PHE task to evaluate lumbopelvic stability.
CONCLUSIONS Posterior oblique sling muscle activity was greater in women with CLBP than in women without CLBP. The findings of this study suggest the presence of altered posterior oblique sling muscle activity during PHE in women with CLBP. Future work should assess the activity pattern of posterior oblique sling muscles in subjects with CLBP during functional activities, such as standing on one leg or walking.
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24. Dankaerts W, O’Sullivan PB, Burnett AF, Straker LM, Danneels LA. Reliability of EMG measurements for trunk muscles during maximal and sub-maximal voluntary isometric contractions in healthy controls and CLBP patients. J Electromyogr Kinesiol 2004;14:333-342. 25. Kendall FP, McCreary EK, Provance PG, et al. Muscles: Testing and Function with Posture and Pain. 5th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2005. 26. Willson JD, Ireland ML, Davis I. Core strength and lower extremity alignment during single leg squats. Med Sci Sports Exerc 2006;38: 945-952. 27. Norris CM. Spinal stabilisation: Muscle imbalance and the low back. Physiotherapy 1995;81:127-137. 28. Bruno PA, Murphy DR. An investigation of neck muscle activity in asymptomatic participants who show different lumbar spine motion patterns during prone hip extension. J Manipulative Physiol Ther 2011; 34:525-532. 29. Vleeming A, Pool-Goudzwaard AL, Stoeckart R, van Wingerden JP, Snijders CJ. The posterior layer of the thoracolumbar fascia. Its function in load transfer from spine to legs. Spine (Phila Pa 1976) 1995;20: 753-758. 30. Carvalhais VO, Ocarino Jde M, Araújo VL, Souza TR, Silva PL, Fonseca ST. Myofascial force transmission between the latissimus dorsi and gluteus maximus muscles: An in vivo experiment. J Biomech 2013; 46:1003-1007. 31. Mooney V, Pozos R, Vleeming A, Gulick J, Swenski D. Exercise treatment for sacroiliac pain. Orthopedics 2001;24:29-32. 32. Pool-Goudzwaard AL, Vleeming A, Stoeckart R, Snijders CJ, Mens JM. Insufficient lumbopelvic stability: A clinical, anatomical and biomechanical approach to ‘a-specific’ low back pain. Man Ther 1998;3: 12-20. 33. de Groot M, Pool-Goudzwaard AL, Spoor CW, Snijders CJ. The active straight leg raising test (ASLR) in pregnant women: Differences in muscle activity and force between patients and healthy subjects. Man Ther 2008;13:68-74. 34. Mens J, Vleeming A, Snijders CJ, Stam HJ, Ginai AZ. The active straight leg raising test and mobility of the pelvic joints. Eur Spine J 1999;8: 468-473. 35. Danneels LA, Vanderstraeten GG, Cambier DC, Witvrouw EE, De Cuyper HJ. CT imaging of trunk muscles in chronic low back pain patients and healthy control subjects. Eur Spine J 2000;9:266-272. 36. Roland M. A critical review of the evidence for a pain-spasm-pain cycle in spinal disorders. Clin Biomech 1986;1:102-109. 37. van Dieën JH, Cholewicki J, Radebold A. Trunk muscle recruitment patterns in patients with low back pain enhance the stability of the lumbar spine. Spine 2003;28:834-841. 38. Oh JS, Cynn HS, Won JH, Kwon OY, Yi CH. Effects of performing an abdominal drawing-in maneuver during prone hip extension exercises on hip and back extensor muscle activity and amount of anterior pelvic tilt. J Orthop Sports Phys Ther 2007;37:320-324. 39. Park KM, Kim SY, Oh DW. Effects of the pelvic compression belt on gluteus medius, quadratus lumborum, and lumbar multifidus activities during side-lying hip abduction. J Electromyogr Kinesiol 2010;20: 1141-1145.
Patients With Low Back Pain Demonstrate Increased Activity of the Posterior Oblique Sling Muscle During Prone Hip Extension Ji-Won Kim, PT, MSc, Min-Hyeok Kang, PT, MSc, Jae-Seop Oh, PT, PhD Objectives: To examine activation patterns of the myofascial chain in women experiencing chronic low back pain (CLBP) and women without CLBP during a prone hip extension (PHE) test. Design: Cross-sectional. Setting: Clinical research laboratory. Participants: Fifteen women experiencing CLBP and 15 women without CLBP. Methods: Surface electromyographic recordings from the posterior oblique sling during PHE. Main outcome measurements: Two-sample t-tests were used to compare demographic information and electromyographic signal amplitude of the posterior oblique sling between groups. Results: Women with CLBP exhibited significantly increased normalized electromyographic signal amplitudes in the contralateral latissimus dorsi (P ¼ .01), contralateral elector spinae (P < .01), ipsilateral elector spinae (P < .01), ipsilateral gluteus maximus (P ¼ .03), and ipsilateral biceps femoris (P ¼ .02) compared with women without CLBP. Conclusions: Women with CLBP had greater activity in the posterior oblique sling muscles than did women without CLBP during PHE. These findings suggest that an alteration can be made in posterior oblique sling muscle activities during PHE in women with CLBP. PM R 2014;-:1-6
INTRODUCTION Chronic low back pain (CLBP) is a common musculoskeletal problem in society today. CLBP affects up to 70%-80% of the population, who experience at least one episode during their lifetime, and 11%-12% of the population are disabled by it [1,2]. Women have a greater incidence of low back pain (LBP) than do men and are also more likely to have functional impairment caused by CLBP [3]. To improve functional restoration in women with CLBP, who typically show decreased trunk muscle strength, muscle-strengthening exercises are considered important [4]. Currently, core training in CLBP rehabilitation has become popular because it reduces pain and functional disability [5]. Core training is performed to strengthen the trunk and pelvic region and improve postural control [6]. The prone hip extension (PHE) test is an accepted test for measuring the motor pattern in the lumbopelvic area [7,8]. Ideally, in people performing the PHE test, the lumbopelvic region should be maintained in a neutral position, without rotation of the lumbar spine and/or pelvis [9] or excessive extension of the spine [9,10]. Altered lumbar spine and pelvic movement patterns have been shown to differentially activate lumbopelvic muscles during lower limb movement [11], which can contribute to lumbopelvic dysfunction [10]. In particular, a previous study of patients with LBP indicated increased electromyographic (EMG) activity in the trunk and hip muscles during various tasks, such as lifting and trunk rotation [12,13]. It seems that patients with LBP showed increased EMG activity of the trunk and hip muscles during these tasks because of abnormal motor recruitment patterns. The increased trunk and hip muscle activity also can be explained by postural disturbance and spinal instability in patients with LBP [14,15]. PM&R 1934-1482/13/$36.00 Printed in U.S.A.
J.-W.K. Department of Rehabilitation Science, Graduate School, INJE University, Gimhae, Republic of Korea Disclosure: nothing to disclose M.-H.K. Department of Rehabilitation Science, Graduate School, INJE University, Gimhae, Republic of Korea Disclosure: nothing to disclose J.-S.O. Department of Physical Therapy, College of Biomedical Science and Engineering, INJE University, 607 Obang-dong, Gimhae-si, Gyeongsangnam-do 621-749, Gimhae, Republic of Korea. Address correspondence to: J.-S.O.; e-mail: [email protected] Disclosure: nothing to disclose Submitted for publication December 24, 2012; accepted December 22, 2013.
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To evaluate muscular activation patterns during the PHE task, researchers have compared the EMG signals (in terms of amplitude) of the elector spinae (ES), gluteus maximus (GM), and hamstring muscle in subjects with and without CLBP [15,16]. However, studies have reported inconsistent muscle activation patterns in patients with CLBP [15,16]. For example, Arab et al [15] evaluated EMG amplitudes during PHE in women with and without CLBP and found increased ES, GM, and biceps femoris (BF) muscle activities in women with CLBP, which these investigators suggested was attributable to reduced spinal stability. In contrast, Guimaraes et al [16] found no difference in the trunk or hip muscles between groups and suggested that assessment of muscle activation patterns in the PHE task cannot be used to discriminate between persons with and without LBP. When the GM fails to control the pelvis, the contralateral latissimus dorsi (LD) may become dominant because the LD and GM, along with the thoracolumbar fascia, work synergistically to control the lumbopelvic region [17]. The BF, GM, ES, and LD muscles create the posterior oblique sling, one of the myofascial slings involved in extension during normal activities for postural control [18]. Such a myofascial sling is a chain of anatomically interconnected muscles [19]. Muscle slings are thought to facilitate the transfer force through the trunk, particularly from the lower to the upper body [18]. Page et al [18] described 3 muscle slings (the posterior oblique sling, anterior oblique sling, and longitudinal sling) that are activated differently based on the load applied. Similarly, Myers [19] explained that 3 major lines (the superficial back line, superficial front line, and lateral line) were made of myofascial or connective tissue units. The superficial back line consists of the nuchal ligament, trapezius, LD, ES, thoracolumbar fascia, hamstrings, gastrocnemius, and plantar fascia, aligned similarly to the elements of the posterior oblique sling [19]. Although in clinical practice the myofascial sling has been considered in strengthening programs, it is being promoted in the clinical literature without any scientific underpinning [19,20]. Muscle slings in the trunk are necessary for rotational trunk movements, such as reciprocal gait pattern, active straight leg raising (ASLR), and hip extension in a prone position [18]. To the best of our knowledge, no study has been performed to evaluate the posterior oblique sling muscular pattern during PHE in women with CLBP. Gaining an understanding of the activity of the myofascial sling in clinical tests may have clinical significance. Thus in the present study we assessed the EMG signal amplitude (muscle activity) of the posterior oblique sling muscles during PHE in women with and without CLBP. Based on findings of previous studies, we hypothesized that the activity of the posterior oblique sling muscles would be greater during PHE in women with CLBP than in women without CLBP. Investigating the differences between the groups should provide beneficial information for clinicians who design rehabilitation exercises.
LBP AND INCREASED POSTERIOR OBLIQUE SLING ACTIVITY
METHODS Subjects A total of 30 female volunteers (15 control subjects and 15 patients with nonspecific CLBP) aged between 22 and 58 years were included in the study. The women with and without CLBP were matched in terms of age, height, weight, and body mass index (BMI); characteristics of the participants are shown in Table 1. Women with CLBP were recruited from 3 local orthopedic clinics in South Korea. Eighteen patients with CLBP were originally tested, but 3 were excluded because their symptoms were provoked at the time of testing (ie, acute back, hip, and/or posterior thigh pain when performing a PHE task and/or maximal voluntary isometric contraction). Participants were recruited to the CLBP group if they had nonspecific LBP, defined as pain lasting at least 3 months without a clear, specific cause (eg, infection, tumor, osteoporosis, ankylosing spondylitis, fracture, inflammatory process, radicular syndrome, or cauda equine syndrome), with or without referral of pain to the leg [21]. Inclusion also required pain in the lumbar or lumbosacral region with restricted activity and a minimum modified Oswestry Disability Index score of 15% at baseline [22]. The pain must have been present for at least the previous 12 weeks (mean SD, 5.93 4.72 years). Exclusion criteria for the CLBP group were pregnancy, spinal surgery, neoplasm, fractures, spondylolisthesis, spondylolysis, spinal stenosis, ankylosing spondylitis, a BMI of 30 or higher (because of the potential influence of fat tissue on our ability to measure surface activity), and not being able to perform the PHE task because of weakness in the GM. For descriptive purposes, data regarding the disability and pain of patients with CLBP were assessed with the modified Oswestry Disability Index and a visual analog scale, Table 1. Demographic and clinical characteristics of participants (N ¼ 30), mean SD Group
Characteristic Age, y Weight, kg Height, cm BMI, kg/m2 Pain onset. y Visual analogue scale score* Modified Oswestry scorey
Control Subjects (n [ 15)
CLBP (n [ 15)
42.87 11.28 44.33 10.75 57.20 6.53 58.06 7.97 161.66 5.38 161.40 6.23 22.21 2.96 22.32 3.08 (range: 19.2-27.8) (range: 18.3-27.3) NA 5.93 4.72 NA 5.13 1.84 NA
47.00 10.17
P Value .72 .74 .9 .85 NA NA NA
CLBP ¼ chronic low back pain; BMI ¼ body mass index; NA ¼ not applicable. *The visual analog scale score ranged from 0 to 10. y The Modified Oswestry score ranged from 0 to 100.
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respectively. To be eligible for the control group, participants were required to have no history of LBP, with no restricted function or any respiratory or neurologic disorder or pain elsewhere in the spine or lower limbs. Women without LBP were recruited from the local community via word of mouth. The Inje University Faculty of Health Science Human Ethics Committee granted approval for this study. All subjects provided written informed consent before participating.
Instrumentation The activity levels of the posterior oblique sling muscles were measured with a wireless EMG system (Delsys, Inc, Boston, MA). Before placement of the EMG electrodes, the skin at the anatomic landmarks was shaved (if required) and cleaned with alcohol. Pairs of surface electrodes were positioned bilaterally well within the muscle borders and aligned with the muscle orientation of the posterior oblique sling muscles. The electrodes for LD were placed 4 cm below the inferior tip of the scapula and half the distance between the spine and the lateral edge of the torso [23]. For ES, the electrodes were placed approximately 2 cm lateral to the spinous process at the L1 level and aligned parallel to the spine [23]. For GM, electrodes were placed at half the distance between the greater trochanter and second sacral vertebra and at an oblique angle at, or slightly above, the level of the trochanter [23]. For the BF, the electrodes were placed 2 cm from the lateral border of the thigh and at two thirds the distance between the trochanter and the back of the knee [23]. A single examiner attached all the electrodes. The signals were amplified and band-pass filtered (20-450 Hz) before being recorded digitally at 2000 samples per second, and then the root mean square (RMS) was calculated. To normalize individual muscle contraction levels, we used 2 maneuvers of voluntary contractions [13]. For the submaximal contraction of ES and GM, the subject lifted both knees 5 cm off the examination table while the knees were flexed at 90 and held them for 5 seconds in a prone position. Maximal contractions were avoided for the ES and GM muscles, because reproduction of pain on testing would have possibly invalidated the use of the RMS values for normalization [24]. This method of normalization for the trunk muscles has been shown to exhibit excellent within-day reliability for healthy control subjects and patients with CLBP [24]. Maximal voluntary isometric contractions against manual resistance were used for the LD and HS muscles [25]. Two maneuvers of voluntary contractions were performed twice, and the average muscle activity for the middle 3 seconds of the 2 trials was used for normalization. The average RMS of the EMG signal during each PHE task trial was calculated and expressed as a percentage of the normalized value. The mean percent normalized value of three repetitions was determined for EMG data analysis.
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Procedures Before testing, all subjects were instructed about active PHE and given a sufficient familiarization period to practice before the investigation. All procedures for EMG measurements were performed with the subjects in the prone position on a therapeutic table with a firm mattress. The subjects were asked to lie prone with their arms at their side and with a neutral position of the pelvis and hip joint. We set the target angle at 10 to control the amount of hip extension. A goniometer was used to determine when the leg was at 10 extension, and an adjustable bar was placed at this level and provided feedback. Feedback information at 10 of hip extension also was given to the subjects by verbal instruction. The participant was instructed to extend the leg of his or her dominant side (the preferred leg for kicking a ball) from neutral to about 10 while keeping the knee straight [15,26]. When the hip was placed at 10 of extension, the participant was asked to hold this position for 5 seconds (Figure 1). The positions of the pelvis and limb were supervised visually during the PHE task to ensure that the subject maintained a neutral pelvis position, hip extension, and knee extension. If visible hip rotation movement or pelvic rotation was observed, the data were excluded. A 1-minute rest period was provided between each trial.
Statistical Analysis Differences in descriptive measures (ie, age, height, weight, and BMI) and task for the magnitude of the posterior oblique sling activities between women with and without CLBP were compared by using the independent t-test. Statistical analyses were performed with SPSS software (version 18.0; SPSS
Figure 1. The start (A) and end (B) positions of the prone hip extension task.
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Inc, Chicago, IL). P values < .05 were considered to indicate statistical significance.
RESULTS Descriptive Statistics No significant differences in physical characteristics (ie, age, height, weight, and BMI) were found between the women with and without CLBP (Table 1).
EMG Activity of the Posterior Oblique Sling EMG activity in the posterior oblique sling during hip extension in the prone position in women with and without CLBP is shown in Table 2 and Figure 2. The EMG amplitudes in the contralateral LD (P ¼ .01), contralateral ES (P ¼ .01), ipsilateral ES (P ¼ .01), ipsilateral GM (P ¼ .03), and ipsilateral BF (P ¼ .02) were significantly greater in women with CLBP than in women without CLBP.
DISCUSSION Evaluation of the muscle activation pattern in the lumbopelvic region during active PHE has been proposed to be a clinical tool for assessing lumbopelvic disease [7,8]. The muscle sling system provides lumbopelvic stability during various activities [17,19]. However, to date no study has been performed to investigate the posterior oblique sling muscles (LD, ES, GM, and BF) during PHE. In the present study, we examined the recruitment pattern of the posterior oblique sling in women with and without CLBP during PHE. Greater muscular activation patterns of the contralateral LD were found in women with CLBP (14.04 8.42) compared with women who did not have CLBP (6.83 2.91) during the PHE test. One possible explanation is that women without CLBP stabilize their lumbopelvic region more effectively, whereas women with CLBP need more activity of the contralateral LD muscle to achieve the same task. According to Norris [27], if the GM fails to control the pelvis, rotation of the thoracolumbar spine may occur
toward the contralateral side during PHE. We suggest that to compensate for faulty movements, such as rotation of the thoracolumbar spine, overactivity of the contralateral LD may occur in women with CLBP during PHE. As a result the contralateral LD can become dominant in maintaining a lumbopelvic neutral position because of insufficiency in the GM to control the lumbopelvic region [17]. Bruno and Murphy [28] found greater activity in the upper trapezius in persons with abnormal spine patterns versus normal spine patterns during PHE because the upper trapezius is part of a chain system (superficial back line), and an abnormal spine pattern may compensate for a motor control deficit in the lumbopelvic region. Our findings are in line with those of Janda [18], who indicated that muscle slings are necessary to facilitate reciprocal patterns between the upper and lower extremities and for rotational lumbopelvic stability. The posterior oblique sling is one of the muscle slings, and the contralateral LD, thoracolumbar fascia, ipsilateral GM, and ipsilateral BF create lumbopelvic stability during load transfer tasks [29,30]. During the PHE test, the optimal movement pattern is for the pelvis to remain neutral and to be controlled by the abdominal musculature; however, in patients with lumbopelvic dysfunction, the lumbopelvic region can show excessive extension and rotational patterns [9,10]. In women with CLBP, the lack of pelvic postural control during PHE may reflect increased activity of the contralateral LD for pelvic control, which can be related to changes in the motor control pattern of the myofascial sling. It seems that increased activity of the ipsilateral GM may produce posterior tilt of the pelvis; to provide a neutral position, increased muscle activity of the contralateral LD is required for a counterbalancing effect, which causes anterior tilt of the pelvis. These results are consistent with those of previous studies involving sacroiliac joint pain. Subjects with sacroiliac joint pain display greater activity of the contralateral LD than do healthy subjects [31]. Like patients with LBP, patients with sacroiliac joint dysfunction experience difficulty in load transfer in clinical tests [32]. Significantly greater EMG activity of the ipsilateral GM also was found in women with CLBP (29.31 9.60)
Table 2. Electromyographic activity of muscles during prone hip extension in subjects with and without chronic low back pain Amount of Activation CLD (% MVIC) ILD (% MVIC) CES (% SMVC) IES (% SMVC) CGM (% SMVC) IGM (% SMVC) CBF (% MVIC) IBF (% MVIC)
Control Subjects 6.83 7.71 38.95 34.37 12.87 20.64 4.93 34.50
(2.91) (5.80) (10.82) (10.20) (8.45) (10.95) (2.58) (15.35)
CLBP 14.04 11.75 58.34 51.72 16.30 29.31 5.49 48.25
(8.42) (9.64) (11.75) (10.72) (8.02) (9.60) (2.52) (14.85)
Confidence Interval
P Value
12.05 to 2.35 9.98 to 1.91 27.83 to 10.94 25.18 to 9.53 9.59 to 2.74 16.37 to 0.95 2.23 to 1.11 25.50 to 2.45
.01* .22 .00* .00* .26 .03* .89 .02*
CLBP ¼ chronic low back pain; CLD ¼ contralateral latissimus dorsi; MVIC ¼ maximal voluntary isometric contraction; ILD ¼ ipsilateral latissimus dorsi; CES ¼ contralateral erector spinae, SMVC ¼ submaximal voluntary contraction; IES ¼ ipsilateral erector spinae; CGM ¼ contralateral gluteus maximus; IGM ¼ ipsilateral gluteus maximus; CBF ¼ contralateral biceps femoris; IBF ¼ ipsilateral biceps femoris. *P < .05.
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Figure 2. Comparison of the activity of the posterior oblique sling during prone hip extension in female subjects with and without chronic low back pain (CLBP). RMS ¼ root mean square; CLD ¼ contralateral latissimus dorsi; ILD ¼ ipsilateral latissimus dorsi; CES ¼ contralateral erector spinae; IES ¼ ipsilateral erector spinae; CGM ¼ contralateral gluteus maximus; IGM ¼ ipsilateral gluteus maximus; CBF ¼ contralateral biceps femoris; IBF ¼ ipsilateral biceps femoris. *P < .05.
compared with women without CLBP (20.64 10.95). These changes, like the significantly increased EMG signal amplitude of the hip extensor during lifting of the leg, seem to indicate that CLBP makes it difficult to lift a leg. This supposition is supported by recent research that showed greater activation of hip flexor muscles in patients with pregnancy-related LBP compared with healthy control subjects during ASLR [33]. The pregnancy-related LBP was correlated with increased laxity of the pelvic girdle [34]. Thus women with pregnancy-related LBP may need more muscle activity to overcome the laxity and may need to exert more effort during ASLR. Similarly, it is commonly believed that lumbopelvic instability is an important component in persons with CLBP [15]. In our study, trunk and hip muscle activities were increased in women with CLBP compared with women without CLBP. One explanation may be that women with CLBP attempt to stabilize the lumbopelvic region more than healthy women need to. Our results are similar to the findings of Arab et al [15], who investigated the activation pattern of the trunk and hip muscles in women with and without CLBP. These investigators found increased activity of the ES, GM, and BF in patients with CLBP. The patients with CLBP showed decreased activity of deep muscles such as the multifidus, which suggests that co-contraction of trunk and hip muscles could be used to compensate for lumbar segment stability [35]. In many studies, increased muscle activity of the ES, GM, and BF has been demonstrated in patients with CLBP compared with patients without CLBP during various tasks [12,36,37]. We found differences in the activation pattern of the posterior oblique sling during PHE in women with and without CLBP. For effective evaluation and therapeutic exercises with the PHE in patients with LBP, researchers and therapists should consider the posterior oblique sling
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system. When performing a PHE evaluation, researchers should assess not only the muscular pattern of the ES, GM, and BF but also the contralateral LD to evaluate lumbopelvic region dysfunction. In the clinical field, the therapist should consider an effective intervention strategy based on modification of the altered posterior oblique sling muscular pattern in persons with CLBP. We suggest that internal lumbopelvic stabilization methods (eg, the abdominal drawing-in maneuver) or external lumbopelvic stabilization methods (eg, use of a lumbopelvic belt) may be useful to modify the altered muscular pattern during the PHE task [38,39], because these interventions assist load transfer and provide normal movement patterns during lower extremity exercises [38,39]. The results of this study will help guide the evaluation of tools and the design of PHE exercise programs specifically for patients with LBP. This study has several limitations. First, the experimental group consisted only of women, and thus this study cannot be generalized to the entire population of patients with CLBP. Second, we supervised the movements of the hip and pelvis by visual judgment during the PHE task. Although visual judgment is used in most clinical settings, a motion analysis system would be useful to provide objective validity. Third, we used the submaximal contraction for EMG normalization, which made it difficult to completely exclude the potential error of measurement when comparing subjects with use of the submaximal normalization method. Finally, we did not measure the timing of muscle activity during PHE. Further study is needed to quantify the muscle onset times of the LD, ES, GM, and BF in patients during the PHE task to evaluate lumbopelvic stability.
CONCLUSIONS Posterior oblique sling muscle activity was greater in women with CLBP than in women without CLBP. The findings of this study suggest the presence of altered posterior oblique sling muscle activity during PHE in women with CLBP. Future work should assess the activity pattern of posterior oblique sling muscles in subjects with CLBP during functional activities, such as standing on one leg or walking.
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