PRONE KNEE FLEXION is often used to measure the

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1 1477 ORIGINAL ARTICLE Effects of the Abdominal Drawing-In Maneuver on Muscle Activity, Pelvic Motions, and Knee Flexion During Active Prone Knee Flexion in Patients With Lumbar Extension Rotation Syndrome Kyue-Nam Park, MS, PT, Heon-Seock Cynn, PhD, PT, Oh-Yun Kwon, PhD, PT, Won-Hwee Lee, MS, PT, Sung-Min Ha, MS, PT, Su-Jung Kim, MS, PT, Jong-Hyuck Weon, PhD, PT ABSTRACT. Park K-N, Cynn H-S, Kwon O-Y, Lee W-H, Ha S-M, Kim S-J, Weon J-H. Effects of the abdominal drawing-in maneuver on muscle activity, pelvic motions, and knee flexion during active prone knee flexion in patients with lumbar extension rotation syndrome. Arch Phys Med Rehabil 2011;92: Objective: To investigate the effects of performing an abdominal drawing-in maneuver (ADIM) during active prone knee flexion on the hamstrings and erector spinae muscle activity, the amounts of pelvic motion and knee flexion, and onset of pelvic movements. Design: Comparative, repeated-measures study. Setting: University research laboratory. Participants: Men patients (N 18) with lumbar extension rotation syndrome. Intervention: Subjects performed prone knee flexion in 2 conditions. Main Outcome Measures: To measure muscle activity, surface electromyogram (EMG) of both erector spinae and the medial and lateral hamstrings was performed. Kinematic data on the pelvic motion and knee flexion were measured using a 3-dimensional motion analysis system. Repeated 1-way analysis of variance was used for the statistical analysis. Results: Significantly decreased electromyographic activity in the right and left erector spinae and significantly increased electromyographic activity in the medial and lateral hamstrings activity were shown during prone knee flexion in ADIM condition using the pressure biofeedback unit. In addition, the amounts of anterior pelvic tilt, pelvic rotation, knee flexion, and perceived pain decreased significantly during prone knee flexion in the ADIM condition compared with the same maneuver in the non-adim condition. The onset of anterior pelvic tilt and pelvic rotation occurred significantly earlier in the non-adim condition, compared with the ADIM condition. Conclusions: ADIM effectively increased activation of knee flexors, decreased activation of back extensors, and reduced the From the Department of Rehabilitation Therapy, Graduate School, Yonsei University, Wonju, South Korea. Supported by the Korea Research Foundation Grant funded by the Korea Government (The Ministry of Education, Science and Technology, Basic Research Promotion Fund) (grant no. E00037). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Reprint requests to Heon-Seock Cynn, PhD, PT, Dept of Rehabilitation Therapy, Graduate School, Yonsei University, 1 Yonseidae-gil, Wonju, Gangwon-do , South Korea, cynn@yonsei.ac.kr /11/ $36.00/0 doi: /j.apmr pelvic motions and low back pain during prone knee flexion in patients with lumbar extension rotation syndrome. Key Words: Knee; Low back pain; Rehabilitation by the American Congress of Rehabilitation Medicine PRONE KNEE FLEXION is often used to measure the length of the rectus femoris muscle, to strengthen the hamstrings, and to test for upper lumbar radiculopathy. 1-3 In addition, active prone knee flexion is performed to classify movement impairment of the painful lumbar spine, because active movement of the limb may influence the symptoms. 3-6 While performing active knee flexion in the prone position, excessive lumbopelvic motion can occur. 4 Scholtes et al 7 reported that there was excessive lumbopelvic rotation at a smaller knee flexion angle in patients with low back pain (LBP) during knee flexion in the prone position compared with subjects without LBP. Previous research states that people with LBP report aggravated LBP with prone knee flexion and therefore advocated modification that involved manual and voluntary abdominal control during prone knee flexion. 4-9 Other researchers revealed that when the painful movement pattern was modified, such as by limiting lumbopelvic rotation, symptoms in people with LBP were reduced or eliminated One method to facilitate improved abdominal control is the abdominal drawing-in maneuver (ADIM) using a pressure biofeedback unit during lower-limb movements. Lumbar stabilization using a pressure biofeedback unit has been studied during hip extension in the prone position and hip abduction while lying on the side; these researches showed that excessive pelvic motions were prevented with significantly increased agonist activation in healthy subjects. 14,15 Sahrmann 4 and Harris-Hayes et al 5 stated that patients with lumbar extension rotation syndrome showed pelvic rotation and anterior tilt during active knee flexion in the prone position. Sahrmann 4 and Van Dillen et al 8 classified LBP into 5 subgroups: lumbar flexion syndrome, lumbar extension syndrome, lumbar rotation syndrome, lumbar flexion rotation syndrome, and lumbar extension rotation syndrome. Lumbar ex- ADIM CI EMG LBP RMS VAS List of Abbreviations abdominal drawing-in maneuver confidence interval electromyogram low back pain root mean square visual analog scale

2 1478 ABDOMINAL DRAWING-IN MANEUVER DURING PRONE KNEE FLEXION, Park tension rotation syndrome is characterized by increased symptoms when the lumbar spine is positioned or moved into rotation and extension. Among the 5 subgroups of LBP, extension rotation syndrome occurs more frequently than other lumbar syndromes, 7-10 and 1 study 7 reported that people with lumbar extension rotation syndrome moved the hip and lumbopelvic region asymmetrically while performing movements such as prone knee flexion or lateral hip rotation. 7 Repeated lumbar extension rotation that occurs during knee flexion in the prone position or activities of daily living may cause tissue microtrauma, overuse syndrome, mechanical tissue failure, and the development of pain in the lumbopelvic region. 16 Van Dillen et al 10 proposed that an increase in the frequency of lumbopelvic motion imposes low-magnitude loading in the lumbar region leading to tissue stress accumulation and subsequently to LBP symptoms. It is recommended that patients with lumbar extension rotation syndrome perform prone knee flexion without excessive lumbopelvic motion. 4 However, no studies have investigated the electromyographic and kinematic data during prone knee flexion performed with the ADIM in people with lumbar extension rotation syndrome. The purpose of this study was to determine the effects of the ADIM on muscle activity of the erector spinae and hamstrings and on the kinematics of pelvic motion and knee flexion during active prone knee flexion in patients with lumbar extension rotation syndrome. Examining the effects of the ADIM using a pressure biofeedback unit while performing knee flexion in the prone position will shed light on evaluation procedures and on implementation of prone knee flexion exercises for subjects with LBP. We hypothesized that the ADIM using a pressure biofeedback unit during prone knee flexion could: (1) decrease erector spinae activity and increase hamstrings activity; (2) decrease anterior pelvic tilt in the sagittal plane, pelvic rotation in the horizontal plane, and knee flexion range; and (3) reduce perceived pain compared with prone knee flexion without performing the ADIM in patients with LBP. METHODS Participants For this study, 18 men ( y) with lumbar extension rotation syndrome were selected from 60 subjects diagnosed with work-related nonspecific chronic LBP at 3 workplacebased work-conditioning centers in South Korea. We defined chronic LBP as LBP with a duration exceeding 7 weeks. 9,17 The average intensity of the symptoms in the patients with chronic LBP in this study was above 6cm on a verbal pain scale ranging from 0 to 10 and measured in centimeters. 3 The subjects had all been injured at the workplace, and they had undergone physical therapy using mainly modalities at hospitals or clinics before participating in this study. The subjects were recruited from workers participating in a workplace workconditioning program at their entry to this study. Forty-two subjects were excluded from the study because they did not meet the selection criteria of lumbar extension rotation syndrome. The exclusion criteria included past or present neurologic or cardiopulmonary diseases, hip and knee joint contractures, specific LBP with radiating pain, and significant weakness of the hamstrings that would interfere with knee flexion in the prone position. The subjects with lumbar extension rotation syndrome were classified based on the evaluation method proposed by Sahrmann, 4 Harris-Hayes, 5 and Van Dillen 8 and colleagues. A standardized clinical examination consisted of alignment and movement tests. The assessments were made by the principal investigator using criteria suggested by Sahrmann. 4 In the initial primary test, the subject assumed a position or performed a movement. When the primary test provoked symptoms in the subject, a secondary test was performed with a modified movement pattern that decreased lumbar extension and rotation to determine whether the symptoms were decreased or eliminated. 9,12 Many tests (11 tests for extension and 10 tests for rotation) were used to make the classification rather than just a few tests. 10 The tests associated with lumbar extension signs included alignment in standing, return from forward bending in standing; trunk extension in sitting; alignment in supine position, hip and knee flexion in the supine position; alignment in prone position, knee flexion in prone, hip extension in prone; and alignment in quadruped, shoulder flexion in quadruped, and rock forward in quadruped. Tests related to lumbar rotation signs consisted of alignment in standing, side bending in standing; knee extension in supine, hip lateral rotation/abduction in partial hook lying; knee flexion in prone, hip lateral and medial rotation in prone; and alignment in quadruped, shoulder flexion in quadruped, and rock backward in quadruped. 4 The subject was diagnosed with lumbar extension rotation syndrome if (1) the lumbar spine tends to move in the direction of rotation and extension, (2) the lumbar spine alignment tends to be extended and rotated relative to the neutral position, (3) symptoms (often unilateral) are produced or increase with the lumbar spine positioned in or moved into rotation and extension, and (4) symptoms decrease or are eliminated with restriction of lumbar rotation and extension. 5,8 The reliability of examiner performance and patient classification were established in previous studies. 17,18 Specific procedures for determining the diagnosis of lumbar extension rotation syndrome have been described in detail elsewhere. 13 The average level of perceived pain while performing activities of daily living before entry to this study was measured using a visual analog scale (VAS) in millimeters. The subject characteristics are presented in table 1. Before the study, the principal investigator explained all of the procedures to the subjects in detail. All subjects signed an informed consent form approved by the university institutional review board. Electromyographic Recording and Data Analysis Electromyographic data were collected using a Noraxon Tele- Myo system, a and analyzed using Noraxon MyoResearch 1.06 XP software. a Skin preparation of the electrode sites involved shaving and cleaning with rubbing alcohol and sanding. Surface electrode pairs were positioned at an interelectrode distance of 2cm. The reference electrode was placed on the malleolus opposite the side to be tested. Electromyographic data were collected for both erector spinae (parallel to the spine, approximately 2cm lateral to the spinous process of L3, over the muscle belly), the medial hamstrings (3cm from the lateral border of the thigh and approx- Table 1: Subject Characteristics Parameter Age (y) Body mass (kg) Height (cm) VAS (0 100mm)* Duration of LBP (y) Active knee flexion with pelvis stabilized (deg) Modified Oswestry Disability Index (%) NOTE. Values are mean SD. Abbreviation: deg, degrees. *VAS was measured before entry to this study. Subjects (N 18)

3 ABDOMINAL DRAWING-IN MANEUVER DURING PRONE KNEE FLEXION, Park 1479 imately half the distance from the gluteal fold to the back of the knee), and the lateral hamstrings (2cm from the lateral border of the thigh, two-thirds the distance between the trochanter and the back of the knee). 19 The sampling rate was 1000Hz. A bandpass filter was used between 20 and 250Hz. The raw data were processed into the root mean square (RMS) with a window of 50 milliseconds. For normalization, the mean RMS of 3 trials of 3-second submaximal voluntary contraction was calculated for both the erector spinae and the medial and lateral hamstrings. While in the prone position, the subject raised both knees 5cm off the examination table while the knees were flexed at 90 and held them for 3 seconds. The normalization method for the submaximal voluntary contraction was used to minimize acute pain experienced during the standard maximal voluntary contraction normalization method. 20 The data for each trial were expressed as a percentage of the calculated mean RMS of the submaximal voluntary contraction, and the percentage of the calculated mean RMS of the submaximal voluntary contraction of the 3 trials was used for the data analysis. Kinematic Data A 3-dimensional ultrasonic motion analysis system, CMS-HS, b was used to measure the anterior pelvic tilt (anterior rotation of the pelvis in the sagittal plane), pelvic rotation (rotation of the pelvis in the horizontal plane), and angle of knee flexion between the femur and the tibia in the sagittal plane. One triple active marker was secured to the midline of the pelvis by fastening a strap passing around the pelvis at the level of both posterior superior iliac spines to measure pelvic motion as reported previously. 14,15 Three single markers were attached for measuring the knee joint angle: the first was located between the greater trochanter and lateral femoral condyle, the second marker was on the lateral femoral condyle, and the third was between the lateral femoral condyle and distal lateral malleolus of the fibula. The knee angle was measured relative to the thigh (the line connecting the first and second markers) and lower leg (the line connecting between the second and third markers). The measurement sensor consisting of 3 microphones was placed to the side of the subject so that it faced the markers. The prone position with the knee extended was calibrated to zero as a reference position. The sampling rate was 20Hz. The onset time of pelvic movements was determined visually with the aid of Win-data 2.19 software. b The time when the angle of pelvic or knee movement exceeded a threshold of 1 was defined as the onset of movement. 21 The mean value of the kinematic data was calculated for the last 5 seconds of isometric contraction. The mean value of the 3 trials was calculated to determine the onset of pelvic movements, the end range of pelvic motion, and the knee joint range of motion during active prone knee flexion. Procedure Active knee flexion without visible pelvic and hip motions. The length of the rectus femoris was measured because stiffness and/or shortness of the rectus femoris can affect the pelvic motion and knee flexion range of motion. The subject assumed the prone position on a treatment table with a neutral position of pelvis and hip joint. To determine which lower extremity to test, the subject was asked to flex the knee joint actively. A VAS was used to measure LBP during prone knee flexion. The lower extremity giving a greater VAS was deemed the lower extremity to be tested. Subjects were instructed to actively flex the knee to be tested toward the buttocks as much as they could while maintaining contact of the anterior pelvis, hip, and thigh with the treatment table. If visible pelvic movement or hip flexion was observed by the principal investigator during performance of prone knee flexion, the data were excluded. When the trunk, pelvis, hip, and thigh were straight based on observation by the principal investigator, the angle of active prone knee flexion was recorded. 22 The angle of this active knee flexion was recorded 3 times using a 3-dimensional ultrasonic motion analysis system (see table 1). Active prone knee flexion without the ADIM condition. The 3-chamber pressure cell of the pressure biofeedback unit. c (fig 1) was placed between the pad of the treatment table and the subject s lower abdomen and inflated to 70mmHg. The subject was asked to perform prone knee flexion comfortably without monitoring the change in the pressure gauge during a 15- second period (see fig 1). The subject performed knee flexion for 10 seconds, followed by a 5-second isometric contraction. A metronome was used to control the time and movement speed. The start signal was provided by beeper sound cue from the Noraxon TeleMyo system. B A C Fig 1. (A) Pressure biofeedback unit, (B) prone knee flexion without ADIM and (C) with ADIM.

4 1480 ABDOMINAL DRAWING-IN MANEUVER DURING PRONE KNEE FLEXION, Park Fig 2. Electromyographic signal amplitude during prone knee flexion with and without performing the ADIM. Abbreviations: ES, erector spinae; H, hamstrings; sub-mvc, submaximal voluntary contraction. *Significantly different (P<.05). RESULTS There were significant differences in the end range EMG signal amplitude between the 2 conditions. In the ADIM condition, the electromyographic activity decreased significantly in the right (mean difference, 18.04; 95% confidence interval [CI], ; P.001) and left erector spinae (mean difference, 20.02; 95% CI, ; P.002), and increased significantly in the medial (mean difference, 14.06; 95% CI, to 7.76; P.001) and lateral hamstrings (mean difference, 7.59; 95% CI, to 3.08; P.002) (fig 2). The end range angles of anterior pelvic tilt (mean difference, 4.79; 95% CI, ; P.001), pelvic rotation (mean difference, 2.66; 95% CI, ; P.001), and knee flexion (mean difference, 28.31; 95% CI, ; P.001) decreased more significantly under the ADIM condition than the non-adim condition (fig 3). The onset of anterior pelvic tilt was significantly earlier in the non-adim condition than the ADIM condition (mean difference, 5.83; 95% CI, 6.25 to 5.41; P.001) (fig 4). The onset of pelvic rotation was significantly earlier in the non-adim condition than the ADIM condition condition (mean difference, 1.02; 95% CI, 1.96 to.07; P.037) (see fig 4). The perceived pain level also decreased significantly in prone knee flexion in the ADIM condition (mean difference, 57.67; 95% CI, ; P.001) (fig 5). Active prone knee flexion with the ADIM condition. After recording the data without the ADIM, a 5-minute rest was allowed to minimize fatigue. Then, the subjects were familiarized with a method of performing the ADIM with a pressure biofeedback unit for approximately 30 minutes. Each subject was informed of the role and pressure monitoring mechanism of the pressure biofeedback unit. The 3-chamber pressure cell of the pressure biofeedback unit was inflated to 70mmHg, and the subject was instructed to draw in the abdomen and hold that position. The subject was asked to maintain a pressure of 60mmHg based on visual feedback from an analog pressure gauge during prone knee flexion. 23 As it is difficult for patients with LBP to maintain a pressure of 60mmHg using the biofeedback pressure unit, a 2-week training period consisting of 3 sessions per week (approximately 30min/d) was conducted before testing. When the subject was able to perform the ADIM within pressure changes of 5mmHg 3 times consecutively during active prone knee flexion, the familiarization period was considered completed. No subject reported discomfort or fatigue after familiarization. After familiarization, prone knee flexion with the ADIM was performed. This condition was not different from active prone knee flexion without ADIM, except that the subject was asked to monitor the pressure gauge and maintain a pressure of 60mmHg based on visual feedback from an analog pressure gauge (see fig 1). 23 The muscle activity, kinematics of pelvic motions and knee flexion, and onset time of pelvic motions under both conditions were measured on the same day after the training period. The level of perceived LBP was measured under both conditions. The VAS was a 100-mm line with 0 representing no pain and 100 representing the worst pain imaginable. Statistical Analysis Data are expressed as the mean SD. The significance of the difference between the 2 conditions (ADIM condition vs non-adim condition) was assessed using a 1-way repeated analysis of variance with the level of statistical significance set at.05. Fig 3. Angle of anterior pelvic tilt and pelvic rotation and knee flexion with and without performing the ADIM. *Significantly different (P<.05).

5 ABDOMINAL DRAWING-IN MANEUVER DURING PRONE KNEE FLEXION, Park 1481 DISCUSSION Pelvic motions such as anterior pelvic tilt and pelvic rotation are often observed in patients with LBP while they are performing active prone knee flexion. 4,5,7 Active prone knee flexion is often used as a test to identify movement impairment syndromes of the lumbar spine such as lumbar extension rotation syndrome. 3-6 We believe that ours is the first study to confirm the beneficial effects of the ADIM using a pressure biofeedback unit on muscle activity and related pelvic motions in people with lumbar extension rotation syndrome during prone knee flexion. When prone knee flexion was performed without the ADIM, anterior pelvic tilt of 7.48 and pelvic rotation of 4.50 occurred, and these results concur with a previous explanation that excessive pelvic motion occurs in people with lumbar extension rotation syndrome. 5 In our study, performing the ADIM during active prone knee flexion reduced the kinematic data significantly: a 64% decrease in anterior pelvic tilt and a 58.9% decrease in pelvic rotation. These findings support the role of abdominal control in preventing greater pelvic motion. According to Sahrmann, 4 insufficient abdominal control may contribute to excessive pelvic motion during prone knee flexion in the non-adim condition. Hence, the greater pelvic motion in our study may be attributed to a lack of abdominal muscle control. 4 When the kinematics of anterior pelvic tilt, pelvic rotation, and knee flexion were plotted as a function of time during active prone knee flexion to examine the onset time between the ADIM and non-adim conditions, the onset of anterior pelvic tilt and pelvic rotation were delayed more significantly in the ADIM condition than the non-adim condition. This implies that the early onset of anterior pelvic tilt and rotation are attributed to a lack of control by the abdominal muscles. This finding concurs with the results of previous research that reported early lumbopelvic rotation in some people with LBP. 10,12,13 Although we did not measure the electromyographic activity of the abdominal muscles directly during the ADIM, previous studies have reported that performing the ADIM can increase the stability of the spine while in the prone position, and the thickness of the transversus abdominis increased when the ADIM was performed in the prone position. 24 Therefore, it is plausible that the ADIM may help improve abdominal muscle control during active prone knee flexion in people with lumbar extension rotation syndrome. The ADIM also reduced the knee flexion angle significantly, by 24.4% with the ADIM. Two mechanisms may Fig 4. Comparison of the movement onset of pelvic motions during knee flexion with and without ADIM conditions. (A) Knee flexion, (B) anterior pelvic tilt, (C) pelvic rotation. Vertical solid line indicates the onset time without ADIM, and vertical dotted line indicates the onset time with ADIM. *Significantly different (P<.05). Error bars represent the SD. Fig 5. VAS with and without performing the ADIM. *Significantly different (P<.05).

6 1482 ABDOMINAL DRAWING-IN MANEUVER DURING PRONE KNEE FLEXION, Park possibly produce the reduced angle of knee flexion in the ADIM condition. First, the pelvic stabilization in the ADIM condition increased the stiffness of abdominal muscles, leading to a substantial decrease in the angle of knee flexion under the ADIM condition. However, it is not clear that a few-degree decrease in anterior pelvic tilt under the ADIM condition due to only muscle stiffness across the hip joint would result in an 18 to 64 decrease in knee flexion. Because the anterior pelvic tilt and pelvic rotation motions were initiated before reaching the end range of knee flexion in this study, the altered movement strategy may contribute to the change in anterior pelvic tilt during knee flexion in the prone position. Scholtes et al 7 reported that people with LBP had an excessive maximum lumbopelvic rotation angle and earlier lumbopelvic rotation during active knee flexion and hip lateral rotation compared with people without LBP. They attributed their findings to both biomechanical restriction and a result of a learned movement strategy. Therefore, altered movement strategy is another possible mechanism for the decreased angle of knee flexion under the ADIM condition in our study. Evidence suggests that patients with lumbar extension rotation syndrome exhibit preferential movements into anterior pelvic tilt during active knee flexion in the prone position. 7 Limiting the amount of active knee flexion may have helped restrict anterior pelvic tilt in the ADIM condition by avoiding the end ranges of knee motion where greater passive tension on the rectus femoris muscle can cause further increases in anterior pelvic tilt. Therefore, both flexibility exercise and motor control training for pelvic stabilization should be considered when prone knee flexion exercise is implemented for altering the movement patterns in patients with lumbar extension rotation syndrome. Without the ADIM, the right erector spinae muscle activity was 23.36% submaximal voluntary contraction, and the left erector spinae was 25.78% submaximal voluntary contraction. Previous research demonstrated an increased anterior pelvic tilt angle and lumbopelvic rotation in the LBP group compared with a group without LBP. 7 The erector spinae muscle acts in lumbar extension and anterior pelvic tilt in the non-adim condition. Therefore, increased erector spinae muscle activity induced anterior pelvic tilt in people with lumbar extension rotation syndrome in this study. Greater relative flexibility of the lumbar spine compared with the rectus femoris can cause greater pelvic motion. Sahrmann 4 suggested that directional susceptibility to movement secondary to excessive flexibility in the lumbar spine contributes to exaggerated anterior pelvic tilt with lumbar extension in prone knee flexion. The increased activity of both erector spinae muscles with exaggerated anterior pelvic tilt in the non-adim condition of our study may be another causative factor. We observed a 77.2% decrease in electromyographic activity in the right erector spinae and a 77.7% decrease in electromyographic activity in the left erector spinae EMG when subjects performed prone knee flexion with the ADIM compared with prone knee flexion without the ADIM. The ADIM with a pressure biofeedback unit may have facilitated the contraction of the abdominal muscles, which counteract the erector spinae muscles. This is a possible reason for the decrease in the erector spinae muscle activity under the ADIM condition. This result indicates that the ADIM can alter motor control and change the movement strategies in people with lumbar extension rotation syndrome during prone knee flexion. 4,7 Activity in the medial hamstrings was 33.63% submaximal voluntary contraction and that in the lateral hamstrings was 34.76% submaximal voluntary contraction without the ADIM during prone knee flexion. With the ADIM, the muscle activity increased by 41.9% in the medial hamstrings and by 21.8% in the lateral hamstrings. The hamstrings flex the knee and cause posterior pelvic tilt. It can also be postulated that under the ADIM condition, increased medial and lateral hamstrings activity prevents undue anterior pelvic tilt. Another explanation is that the increased hamstrings muscle activity was influenced by the position of the knee at end range. That is, greater hamstring muscle activity was required to maintain the knee flexed in midrange against gravity (with the ADIM, ) than in a reduced-gravity position with the lower leg resting against the back of the thigh (without the ADIM, ). This result indicates that the ADIM can be used to activate the hamstrings effectively in people with lumbar extension rotation syndrome to provide pelvic stability. Another explanation is that the hamstrings may have had to increase activation in the ADIM condition to work against the stiffness of the anterior musculature. The perceived level of pain determined using the VAS was 64.39mm without the ADIM and decreased to 6.72mm under the ADIM condition. This decrement in LBP can be explained by 2 mechanisms. First, the reduced pain may be associated with less compressive stress induced by decreased erector spinae muscle activity during prone knee flexion with the ADIM. Second, people with lumbar extension rotation syndrome tend to move in extension and rotation of the lumbar spine during lower-extremity movements. When repetitious movement occurs in a specific direction, increased stress accumulates, eliciting microtrauma, tissue failure, and LBP. 16,25 Reducing the anterior pelvic tilt and pelvic rotation using the ADIM might result in less pain during prone knee flexion than without the ADIM. This suggests that the ADIM should be recommended for minimizing LBP while performing prone knee flexion in people with lumbar extension rotation syndrome. Study Limitations This study has several limitations. First, because we recruited only men with a low disability level with lumbar extension rotation syndrome (15.6% Oswestry Disability Index) at 3 industrial work-conditioning centers, the findings cannot be generalized to all patients with LBP syndrome. Second, we did not measure the activity of the abdominal muscles because the test was performed in the prone position. Further studies are required to investigate the effects of the ADIM using a pressure biofeedback unit on the deep abdominal muscles. The long-term effect of prone knee flexion with the ADIM on LBP and muscle activity and the pelvic motions in subjects with lumbar extension rotation syndrome should be determined. Third, because the subjects participated in a 2-week training period for the ADIM before testing active prone knee flexion, the training period could have influenced not only hamstring or abdominal muscle activity but also pain provocation under the non-adim condition. Fourth, although the surface electrodes were located precisely to minimize the crosstalk in our study, there may have been possible crosstalk between the medial and lateral hamstrings. 26 Koh and Grabiner 26 reported that conventional bipolar electrode recordings showed crosstalk involving the medial and lateral hamstrings and recommended a doubledifferential technique for reducing crosstalk. Fifth, we studied the effect of the ADIM during a standardized movement test. However, it is not known whether the effects of performing the ADIM observed in this study will carry over to the performance of other functional activities such as upright postures and movements during daily activities in subjects with lumbar extension rotation syndrome. The training effects of the ADIM should be examined in a prospective study. Further study is required to confirm whether the prone knee flexion exercises

7 ABDOMINAL DRAWING-IN MANEUVER DURING PRONE KNEE FLEXION, Park 1483 with the ADIM can carry over to reduce repeated lumbar extension rotation stress in daily activities. CONCLUSIONS The study examined the effects of performing the ADIM using a pressure biofeedback unit during prone knee flexion on the hamstrings and erector spine muscle activity and on the amounts of pelvic motions and knee flexion. The findings suggest that the ADIM using a pressure biofeedback decreased the activity of both erector spinae muscles and increased the medial and lateral hamstrings muscle activity. The amounts of anterior pelvic tilt, pelvic rotation, knee flexion, and perceived pain also decreased more significantly in prone knee flexion with the ADIM than in the same maneuver without the ADIM. References 1. Butler DS. The sensitive nervous system. Adelaide: Noigroup Publications; Nadler SF, Malanga GA, Stitik TP, Keswani R, Foye PM. 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