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1454 ORIGINAL ARTICLE Effects of Lumbar Stabilization Using a Pressure Biofeedback Unit on Muscle Activity and Lateral Pelvic Tilt During Hip Abduction in Sidelying Heon-Seock Cynn, PT, MA, Jae-Seop Oh, PT, MSc, Oh-Yun Kwon, PT, PhD, Chung-Hwi Yi, PT, PhD ABSTRACT. Cynn H-S, Oh J-S, Kwon O-Y, Yi C-H. Effects of lumbar stabilization using a pressure biofeedback unit on muscle activity and lateral pelvic tilt during hip abduction in sidelying. Arch Phys Med Rehabil 2006;87:1454-8. Objective: To assess the effects of lumbar spine stabilization using a pressure biofeedback unit on the electromyographic activity and angle of lateral pelvic tilt during hip abduction in a sidelying position. Design: Comparative, repeated-measures study. Setting: University research laboratory. Participants: Eighteen able-bodied volunteers (9 men, 9 women) with no history of pathology. Intervention: Subjects were instructed to perform hip abduction in a sidelying position in both the preferred hip abduction (PHA) and hip abduction with lumbar stabilization (HALS). A pressure biofeedback unit was used for lumbar stabilization. Main Outcome Measures: Surface electromyography was recorded from the quadratus lumborum, gluteus medius, internal oblique, external oblique, rectus abdominis, and multifidus muscles. Kinematic data for lateral pelvic tilt angle were measured using a motion analysis system. Dependent variables were examined with 2 (PHA vs HALS) ⫻ 2 (men vs women) analysis of variance. Results: Significantly decreased electromyographic activity in the quadratus lumborum (PHA, 60.39%⫾15.62% of maximum voluntary isometric contraction [MVIC]; HALS, 27.90%⫾13.03% of MVIC) and significantly increased electromyographic activity in the gluteus medius (PHA, 25.03%⫾ 10.25% of MVIC; HALS, 46.06%⫾21.20% of MVIC) and internal oblique (PHA, 24.25%⫾18.10% of MVIC; HALS, 44.22%⫾20.89% of MVIC) were found when the lumbar spine was stabilized. Lateral pelvic tilt angle (PHA, 13.86°⫾4.66°; HALS, 5.55°⫾4.16°) was decreased significantly when the lumbar spine was stabilized. In women the electromyographic activity (percentage of MVIC) in gluteus medius, external oblique, and rectus abdominis was significantly higher than that observed in men. Conclusions: With lumbar stabilization, the gluteus medius and internal oblique activity was increased significantly, and the quadratus lumborum activity was decreased significantly, causing reduced lateral pelvic tilt in a sidelying position. These results suggest that hip abduction with lumbar stabilization is useful in excluding substitution by the quadratus lumborum. From the Department of Rehabilitation Therapy, Graduate School, Yonsei University, Wonju, South Korea. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to Oh-Yun Kwon, PT, PhD, Dept of Rehabilitation Therapy, Graduate School, Yonsei University, 234 Maji-li, Hungob-myon, Wonju, Kangwon-do 222-710, Republic of Korea, e-mail: [email protected]. 0003-9993/06/8711-10804$32.00/0 doi:10.1016/j.apmr.2006.08.327 Arch Phys Med Rehabil Vol 87, November 2006 Key Words: Electromyography; Muscle; Rehabilitation; Spine. © 2006 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation URING THE PAST DECADE, in the field of physical D therapy, the concept of lumbar stabilization has emerged to prevent musculoskeletal injuries, to rehabilitate, and to improve performance. Lumbar stabilization refers to internal stabilization achieved by the isometric contraction of abdominal and lumbar muscles to maintain stability.1 It has also been referred to in the literature as core strengthening, motor control training, and dynamic stabilization.2 Panjabi3 theorized that spine stability is dependent on 3 subsystems: passive (spinal column), active (spinal muscles), and control (neural control) subsystems. Panjabi4 also defined a neutral zone as being a midrange position with minimal resistance to displacement owing to minimal tension in the passive subsystem. In this midrange position, deep intersegmental muscle contraction should be provided to control excessive motion and to compensate for instability because passive restraints cannot control the spinal movement. Two deep muscles, the transversus abdominis and lumbar multifidus, are important for this spinal segment stabilization. It was also suggested that cocontraction of these deep muscles must be performed without involvement of the rectus abdominis or external oblique muscles, which are overactive in patients with low back pain.5 A pressure biofeedback unit,a originally developed for assessing the ability of abdominal muscles to actively stabilize the lumbar spine, has been used to examine lumbar stabilization in various studies.6-10 It is a reliable and valid clinical instrument for assessing deep abdominal muscle function, and has been used to develop a method for the careful monitoring of lumbar stabilization.11,12 The pressure biofeedback unit consists of an inflatable cushion connected to a pressure gauge and an inflation device. When the pressure biofeedback unit is placed and inflated, the subject is required to maintain the desired pressure and a constant lumbar position during lowerextremity movement under external loads. Changes in the pressure during hip movement reflect an inability to maintain isometric contraction of the abdominal muscles, resulting in uncontrolled movement and instability of the lumbar spine. According to Janda,13 hip abduction has failed if hip flexion, hip external rotation, or lateral pelvic tilt is observed before 40° of abduction is achieved. Lateral pelvic tilt can occur when the quadratus lumborum substitutes for a weakened gluteus medius.14 The lateral portion of the quadratus lumborum originates on the lateral ilium and inserts into the 12th rib without attachment to any vertebrae and produces primarily a lateral bending moment, whereas the medial portion of the muscle provides segmental stability through its segmental attachments.5 Substitution by the lateral portion of the quadratus lumborum leads to pelvic obliquity LUMBAR STABILIZATION DURING HIP ABDUCTION, Cynn (lateral pelvic tilt), and the lumbar spine undergoes lateral flexion resulting in lateral instability and impaired movement.15 Although many studies assessing lumbar stabilization have been conducted with subjects in the supine position,7,10 no studies on lumbar stabilization with subjects in the sidelying position were found in the literature. In addition, we know of no study confirming the effect of lumbar stabilization on the selective recruitment of the gluteus medius and the inhibition of the quadratus lumborum in the sidelying position. Given that hip abduction in the sidelying position is the appropriate movement for testing the range of motion and strength of the gluteus medius and is commonly prescribed as an exercise, investigating the role of lumbar stabilization during sidelying will provide the clinician with useful information for designing and implementing exercise protocols. Based on published reports and clinical experience, we hypothesized that increased gluteus medius activity and reduced quadratus lumborum activity would result in decreased ipsilateral lateral tilt during hip abduction in the sidelying position while the lumbar spine is stabilized with a pressure biofeedback unit. The aims of this study were to assess the effect of lumbar stabilization using a pressure biofeedback unit on the electromyographic activity and angle of lateral pelvic tilt and to investigate the difference of muscle activation between men and women during hip abduction in the sidelying position. METHODS Participants We recruited 18 able-bodied young subjects (9 men, 9 women) from university students who volunteered to participate in this study. Subjects’ characteristics are shown in table 1. The exclusion criteria were past or present neurologic, musculoskeletal, or cardiopulmonary diseases that could interfere with hip abduction. Each subject signed informed consent approved by the university institutional review board before entering the study. Surface Electromyographic Recording and Data Analysis We collected electromyographic data using a data acquisition system (Biopac MP100WSWb) and a Bagnoli electromyography system.c The skin was cleansed with rubbing alcohol, and disposable Ag-AgCl surface electrodes were positioned at an interelectrode distance of 2cm. The reference electrode was attached to the styloid process of the ulna on the dominant upper extremity. Electromyographic data were collected for the following muscles on the same side as the dominant lower extremity: quadratus lumborum (⬇4cm lateral from the vertebral ridge or belly of the erector spinae muscle, and at a slightly oblique angle at half the distance between the 12th rib and the iliac crest), gluteus medius (parallel to the muscle fibers, over the proximal one third of the distance between the iliac crest and the greater trochanter), external oblique (on the inferior edge of the 8th rib, superolateral to the costal margin), internal oblique (in the horizontal plane, 2cm medial to the anterior superior iliac spine), rectus abdominis (2cm lateral to the umbricus),16,17 and Table 1: Subject Characteristics Parameters Subjects (N⫽18) Age (y) Weight (kg) Height (cm) 23.5⫾3.5 59.3⫾5.1 167.7⫾4.3 NOTE. Values are mean ⫾ standard deviation (SD). 1455 multifidus (parallel to the muscle fibers, 2cm lateral to the midline running through the L5 spinal process).18 We amplified and digitized the electromyographic signals with AcqKnowledge software (version 3.7.2).b Bandpass (20⫺450Hz) and bandstop filters (60Hz) were used. The raw data were processed into the root mean square (RMS) and were converted to ASCII files for analysis. For normalization, the mean RMS of 3 trials of maximal voluntary isometric contraction (MVIC) was calculated for each muscle. The manual muscle testing position was used, as described by Kendall et al.19 The electromyographic signals collected during hip abduction were expressed as a percentage of the calculated mean RMS of the MVIC (% MVIC). Kinematic Study of Lateral Pelvic Tilt We used a 3-dimensional ultrasonic motion analysis system (CMS-HSd) to measure the lateral pelvic tilt during hip abduction in sidelying. One triplet bearing 3 active markers that emit an ultrasonic signal was secured to the pelvis on the side of the lower extremity to be lifted. Three markers were positioned to face the measuring sensor by a fastening belt passing around at the level of anterior superior iliac spines. The measuring sensor consisting of 3 microphones was positioned in front of the subject to record the ultrasonic signal from the markers. The measuring plane was set and aligned according the markers. The angle of the lateral pelvic tilt measured before hip abduction was calibrated to 0° as a reference position, and the relative angle of the lateral pelvic tilt during hip abduction was calculated from this reference position.20,21 The sampling rate was 20Hz. After data collection angular displacements for lateral pelvic tilt were low-pass filtered with a cutoff frequency of 8Hz. The kinematic data were analyzed by the Windata software (version 2.19).d The mean angle of 3 trials was determined for comparison. Procedure Each subject was required to assume a sidelying position with the nondominant lower extremity contacting a firm mattress. The upper trunk, pelvis, and dominant lower extremity were aligned in a straight line. The nondominant lower extremity could be flexed at both the hip and knee joints for comfort and stability. While sidelying, the subject was asked to perform hip abduction with the dominant lower extremity in both the preferred condition and the stabilized-lumbar condition, in random order. An inclinometer was used to determine when the hip was in 35° of abduction. A bar was placed at this level and provided feedback to the subject as they were instructed to abduct their hip until the side of their knee touched the bar and to hold the position for 5 seconds. The electromyographic signal was recorded during this 5-second period. In the stabilized-lumbar condition, the pressure biofeedback unit was placed between the firm mattress and the subject’s lumbar spine in the sidelying position. The elastic bag was inflated until the lumbar curve was straight, at which point the target pressure was determined. The spinous processes in lumbar region were palpated and a rigid ruler was used to visually establish that the lumbar curve was straight. Subjects were instructed to use the visual feedback provided by the analog gauge of the pressure biofeedback unit in order to maintain the determined target pressure during hip abduction. A researcher monitored the pressure fluctuations. Pressure changes of ⫾5mmHg from the target pressure were allowed to accommodate changes induced by breathing. Prior to testing all subjects were familiarized with the standard position and movement and with the use of the pressure biofeedback unit and felt comfortable at the time of data collection. Arch Phys Med Rehabil Vol 87, November 2006 1456 LUMBAR STABILIZATION DURING HIP ABDUCTION, Cynn Statistical Analysis The data are expressed as the mean ⫾ standard deviation (SD). A 2⫻2 analysis of variance with 1 within-subject factor (condition) and 1 between-factor (sex) was used to determine the main effects and their interaction in each muscle with the significance level set at P equal to or less than .05. RESULTS The electromyographic activity and the angle of lateral pelvic tilt during preferred hip abduction (PHA) and hip abduction with lumbar stabilization (HALS) is shown in table 2. There were significant main effects for condition (PHA vs HALS) in quadratus lumborum (F1,16⫽54.51, P⫽.000), gluteus medius (F1,16⫽46.29, P⫽.000), internal oblique (F1,16⫽23.92, P⫽.000), and for angle of the lateral pelvic tilt (F1,16⫽73.79, P⫽.000). There were significant main effects for sex in gluteus medius (F1,16⫽4.98, P⫽.040), external oblique (F1,16⫽20.10, P⫽.000), and rectus abdominis (F1,16⫽14.25, P⫽.002). There were also significant condition by sex interactions in gluteus medius (F1,16⫽7.30, P⫽.016), external oblique (F1,16⫽11.55, P⫽ .004), and multifidus (F1,16⫽10.37, P⫽.005). With lumbar spine stabilization, the electromyographic activity was decreased significantly in the quadratus lumborum and increased significantly in the gluteus medius and internal oblique. The angle of lateral pelvic tilt was decreased significantly with lumbar spine stabilization. In women the electromyographic activity in gluteus medius, external oblique, and rectus abdominis was higher than that observed in men. Table 2: Electromyographic Activity in Muscles and Angle of Lateral Pelvic Tilt During Preferred Hip Abduction and Hip Abduction With Lumbar Stabilization Parameters Muscle activity (% MVIC) Quadratus lumborum Men Women All Gluteus medius Men Women All Internal oblique Men Women All External oblique Men Women All Rectus abdominis Men Women All Multifidus Men Women All Angle of lateral pelvic tilt (deg) Men Women All PHA HALS 56.08⫾21.46 64.70⫾9.78 60.39⫾15.62 32.23⫾15.34 23.57⫾10.72 27.90⫾13.03 22.37⫾10.67 27.73⫾9.83 25.03⫾10.25 36.98⫾18.05 55.14⫾24.35 46.06⫾21.20 20.26⫾17.34 28.24⫾18.86 24.25⫾18.10 31.15⫾25.70 57.29⫾16.08 44.22⫾20.89 19.93⫾8.24 39.67⫾19.74 29.80⫾13.99 16.94⫾12.54 50.08⫾34.04 33.51⫾23.29 14.53⫾7.60 30.97⫾22.82 22.75⫾15.21 12.57⫾9.18 32.93⫾26.96 22.75⫾18.07 41.19⫾16.51 43.29⫾23.97 42.24⫾20.74 25.42⫾15.20 40.82⫾24.75 33.12⫾19.99 11.99⫾4.15 15.73⫾4.58 13.86⫾4.66 4.36⫾3.14 6.73⫾4.87 5.55⫾4.16 NOTE. Values are mean ⫾ SD. Arch Phys Med Rehabil Vol 87, November 2006 DISCUSSION Lumbar stabilization can be achieved by the cocontraction of the transversus abdominis and lumbar multifidus. When the transversus abdominis contracts, the intra-abdominal pressure (IAP) increases, and the tension of the thoracolumbar fascia increases. Consequently, stabilization of the spine is maintained by the IAP in the abdominal cavity and the stiffness of the lumbar spine.22 Furthermore, the activation of the transversus abdominis is independent of the direction of limb movement and is continuous throughout lower limb movement,23,24 suggesting a stabilizing function of the abdominal pressure. Panjabi4 determined that the lumbar multifidus acts as a stabilizer in the lumbar spine because it is a deep, segmentally attached muscle. The role of the multifidus as a segmental stabilizer has been also demonstrated previously.25-27 We found significantly increased internal oblique activities with lumbar stabilization. The internal oblique was thought to enhance the stability of the spine in previous studies,23,28,29 and this is consistent with our results, suggesting that increased internal oblique muscle activity contributed to lumbar stabilization. In this study, however, the activity of the external oblique, rectus abdominis, and multifidus did not show significant changes with the use of a pressure biofeedback unit. Lumbar stabilization during hip abduction in sidelying does not seem to affect the activity of these muscles. Unlike the internal oblique muscle, the external oblique and rectus abdominis do not blend at the lateral raphe of the thoracolumbar fascia,1 so that the external oblique does not contribute to lumbar stabilization. The rectus abdominis runs longitudinally from pubic crest and symphysis to costal cartilages and sternum. Thus, this muscle could have led to sagittal plane stabilization with the multifidus that runs relatively longitudinally. Our findings are consistent with those of Arokoski et al18 who reported that it was difficult to contract the paraspinal muscles independently from the external oblique during stabilization exercise in the sidelying position. In addition, Jull et al7 found no RMS amplitude difference in rectus abdominis and the lumbar erector spinae with abdominal setting action during leg lifting in supine position. In women a higher percentage of MVIC in gluteus medius, external oblique, and rectus abdominis was observed. This higher percentage of MVIC in women is thought to result from the need to maintain lumbopelvic stability required during hip abduction in sidelying position. The sex-dependent differences exist affecting the lumbopelvic stability between men and women, even though we did not measure the differences. First, less skeletal muscle mass, thickness of lateral abdominal muscles, and physiologic cross-sectional area of abdominal region in women were reported from the previous studies.30-32 As muscle mass increases, so does amount of titin. Passive muscle stiffness will increase as amount of titin increases, because titin contribute to passive muscle stiffness.15 Thus, passive muscle stiffness in women will be lower than that in men. This lower passive stiffness can result in less lumbopelvic stability while assuming hip abduction in sidelying position. Second, the wider pelvic size in women,31 as an anthropometric difference, may be one of the causes inducing lower lumbopelvic stability in women. The center of gravity in sidelying position in women would be positioned relatively higher than men secondary to the wider pelvis, possibly threatening the lumbopelvic stability of maintaining hip abduction in sidelying position. For these possible reasons, it is presumed that the higher percentage of MVIC in gluteus medius, external oblique, and rectus abdominis was required in women to overcome the lower lumbopelvic stability during hip abduction in sidelying position. Further LUMBAR STABILIZATION DURING HIP ABDUCTION, Cynn studies should address the relation between the neuromuscular control in the lumbopelvic region during hip abduction in sidelying position and the sex-specific differences. Janda13 also identified an abnormal recruitment sequence for hip abduction in symptomatic subjects compared with nonsymptomatic subjects. In patients with low back pain, gluteus medius activity was delayed, whereas gluteus medius activity was observed before the ipsilateral quadratus lumborum in normal subjects. The recruitment imbalance between the gluteus medius and quadratus lumborum can induce movement impairment. For this reason, the gluteus medius and quadratus lumborum should be closely monitored for lumbar stability and joint support.15 Clinicians often report overactivity and trigger points for the quadratus lumborum with gluteus medius insufficiency in patients with back pain.14 In addition, increased tension in the quadratus lumborum was implicated in pelvic upward movement and rotational malalignment.33 Care should be taken to prevent an overactive quadratus lumborum from substituting for the gluteus medius. Our results confirm the hypothesis that lumbar stabilization during hip abduction in sidelying can reduce quadratus lumborum activity and ipsilateral pelvic tilt and can recruit the gluteus medius and internal oblique. Previous studies have recommended a treatment protocol that included relaxation to decrease the activity of the quadratus lumborum and exercise to facilitate the recruitment of the gluteus medius.5,14 The lumbar stabilization method used here could stabilize the pelvis and recruit the gluteus medius muscle without substitution by the quadratus lumborum. Therefore, we suggest that lumbar stabilization during sidelying is useful in treatment protocols designed to prevent motor control dysfunction by reducing quadratus lumborum activity and strengthening the gluteus medius. Our study showed that lumbar stabilization using a pressure biofeedback unit significantly increased gluteus medius and internal oblique activity, while decreasing quadratus lumborum activity and ipsilateral pelvic tilt in hip abduction during sidelying. We used surface electromyography to investigate muscle activity and assumed that the detected signal represented each muscle in its entirety; however, there are potential signal alterations caused by muscle movements below the surface electrode or cross-talk from adjacent muscles. We established the predetermined hip abduction at 35° of verticality to assure hip abduction in the frontal plane and to prevent possible hip or pelvis movement in other planes that might affect the targeted muscle activities. Our results cannot be generalized to other populations because all the subjects participating in the study were young and able-bodied. Therefore, the benefits of lumbar stabilization used in this study should be confirmed in other populations. The activity of the transversus abdominis was not measured in our study. Therefore, further studies are warranted to assess deep muscle activity during hip abduction training while sidelying with lumbar stabilization and to determine the direct benefit and selective muscle facilitation associated with lumbar stabilization. CONCLUSIONS This study showed that the activity of the gluteus medius and internal oblique increased significantly, the activities of the quadratus lumborum decreased significantly, and the lateral pelvic tilt was reduced significantly during sidelying with lumbar stabilization achieved using a pressure biofeedback unit. Therefore, hip abduction with lumbar stabilization during sidelying can be recommended as a more effective method for excluding unwanted substitution by the quadratus lumborum and to facilitate gluteus medius muscle activity. 1457 References 1. Kisner C, Colby LA. Therapeutic exercise: foundations and techniques. 4th ed. Philadelphia: FA Davis; 2002. 2. Akuthota V, Nadler SF. Core strengthening. 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