Effects of a single session of posterior-to-anterior spinal mobilization and press-up exercise on pain response and lumbar spine extension in people with nonspecific low back pain.

Approximately 12% to 33% of e adult workforce is affected by low back pain each year, and it has been suggested that 70% to 95% of adults will have low back pain at some time during their lives. (1-6) The California Board of Worker Compensation ranks low back pain (and other, related ICD-9 diagnoses) as the primary reason for missed workdays and restricted-activity days. (7) Unlike the expenses associated with the management of other orthopedic disorders, the expenses associated with the management of back pain have increased over the last 20 to 30 years. (2, 3, 8)

People who report low back pain often have reduced spinal motion. (9-11) When motion is limited, spinal extension is frequently more restricted than flexion. (10, 12) Reduced spinal extension can be the result of pain or stiffness and can be classified as being either general (ie, total spine) or segmental (ie, one vertebral level). (9-11,13,14) Spinal mobilization techniques and range-of-motion exercises often are prescribed by physical therapists in an attempt to improve lumbar extension and ultimately reduce low back pain. (15-17)

Two commonly used methods for improving spinal extension are passive segmental mobilization and press-up exercises. Maitland et al (18) advocated the use of a segment-specific approach (ie, posterior-to-anterior [PA] mobilization), in which the intervention is focused on the specific vertebral levels that demonstrate restricted motion. In contrast, McKenzie and May (19) advocated a more general approach, in which a press-up exercise is used as a means of decreasing pain and increasing spinal motion.

A review of the literature revealed only 2 studies that have reported on the effects of PA mobilization on pain intensity and lumbar extension in people with nonspecific low back pain.(20,21) Although both of these investigations reported a reduction in pain following the mobilization procedure, neither study found that PA mobilization had an influence on lumbar extension. Similarly, the use of a press-up exercise has been shown to decrease symptoms in people with nonspecific low back pain in a number of studies. (22,25) Of these studies, only 2 quantified lumbar extension range of motion (22,24); however, these authors did not report an increase in motion following the press-up exercise.

One possible explanation for the lack of significant findings with respect to changes in lumbar extension following PA mobilization or press-up exercises may be related to the fact that the methods used to quantify spinal motion (ie, double inclinometers and an electromagnetic tracking system) were not sensitive enough to detect subtle, but perhaps clinically meaningful, changes in motion. Recently, we reported on the use of dynamic magnetic resonance imaging (MRI) to quantify segmental motion of the lumbar spine during a PA force application. (26-28) This modality appears to have an advantage over more conventional means of measuring spinal mobility because segmental motion can be assessed more precisely without the errors typically associated with skin movement and soft tissue bulk.

The purpose of this study was to assess the immediate effects of a single session of PA spinal mobilization and a press-up exercise on pain with standing extension and lumbar segmental extension (as quantified by dynamic imaging techniques) in people with low back pain. We sought to examine the immediate effects of each intervention because both Maitland et al (18) and McKenzie and May (19) advocated postintervention assessments to detect changes in pain and spinal motion. In addition, immediate changes in pain and motion have been shown to predict intervention outcomes. (29) We hypothesized that both interventions would be effective in reducing pain and increasing lumbar extension in people with nonspecific low back pain.

Method

Subjects

Thirty people (19 women and 11 men) who were 18 to 45 years of age and had a diagnosis of nonspecific low back pain participated in this study. People over the age of 45 years were excluded to control for the possible confounding effects of spine osteoarthritis. The number of subjects recruited was based on an a priori sample size calculation (see below).

Subjects were recruited from the Department of Physical Medicine and Rehabilitation and the Outpatient Physical Therapy Clinic at Stanford University Medical Center. Only people who reported a recent onset of low back pain (duration of <3 months) and the following signs and symptoms were admitted: localized low back pain at or above the waist level, decreased lumbar extension (assessed qualitatively while standing), and increased localized pain with lumbar extension during standing. The primary exclusion criteria were: spinal malignancy, cardiovascular disease, evidence of cord compression, aortic aneurysm, hiatal hernia, uncontrolled hypertension, spinal infection, severe respiratory disease, pregnancy, abdominal hernia, prior low back surgery, gross spinal deformity, spondylolisthesis, known rheumatic joint disease, and implanted devices that could interact with the magnetic field (eg, pacemakers, cochlear implants, or ferromagnetic cerebral aneurysm clips). In addition to these exclusion criteria, subjects were screened for any clinical evidence of lumbar disk pathology. Therefore, subjects who demonstrated any of the following were excluded: radiating pain below the level of the buttocks; sensation changes in the lower extremities; diminished reflexes; lower-extremity weakness, neurological signs, or both; urinary or fecal incontinence; and increased peripheral pain with repeated lumbar extension.

[FIGURE 1 OMITTED]

All subjects were referred for the study by the same physician. As part of the routine examination process, subjects were screened through history, physical examination, and standard anterior-posterior, lateral, and oblique radiographs. Although disk pathology cannot be definitively diagnosed through physical examination or radiographs, subjects with disk herniation observed during MRI were dropped from the study and referred back to the physician for additional follow-up.

Instrumentation

As described in previous publications, (26-28) dynamic imaging of the lumbar spine was performed with a vertically opened (double-donut de sign) MRI system (0.5 T; Signa SP *). This system was equipped with a pulse sequence programming environment and real-time interactive MRI capability. Sagittal-plane imaging of the spine was performed with a receive-only surface coil and an ultra-fast spoiled GRASS (gradient-recalled acquisition in the steady state) pulse sequence. Images were obtained at a rate of one per second with the following parameters: repetition time, 200 milliseconds; echo time, 18 milliseconds; number of excitations, 1.0; matrix, 256 x 256; field of view, 28 x 21 cm; and a 7-mm section thickness with an interslice spacing of 1 mm. The surface coil was flexible so as not to limit spinal motion during the press-up maneuver.

Procedure

A flow diagram of the study design is shown in Figure 1. Subjects participated in pretreatment pain and MRI assessments, an intervention session, and then posttreatment pain and MR/ assessments. Prior to participation, all procedures were explained to each subject, and informed consent was obtained. Subjects signed a human subject consent form approved by the institutional review boards of Stanford University and the University of Southern California.

Pretreatment pain and MRI assessments. Prior to the pretreatment MRI assessment, each subject's initial pain level was assessed. Subjects were asked to stand, bend backward with their hands on their hips, and rate their low back pain with a visual analog scale.

In the pretreatment MRI assessment, sagittal-plane images of the lumbar spine were obtained with subjects at rest and performing a press-up maneuver. Subjects were placed on a sliding table in the prone position with a pillow under the abdomen. The sliding table was situated such that the spine and torso were within the opening of the MRI system. The surface coil was secured to the lumbar region with adhesive straps.

Following subject positioning within the MRI system, a series of sagittal-plane "localizers" were obtained to ensure that the image plane captured the vertebral bodies of all lumbar vertebrae. Once the image plane was determined, a static sagittal view of the lumbar spine was obtained in the resting position.

Each subject then performed a single press-up (to the subject's self-determined end range) and held the position for 3 seconds. A sagittal-plane image of the spine was obtained in the end-range position.

Intervention. Once the pretreatment pain and MRI evaluations were completed, each subject was randomly assigned to either a passive segmental mobilization (PA mobilization) group or an exercise (press-up) group. Both interventions were administered by a physical therapist with 18 years of manual therapy experience and certification as an Orthopaedic Clinical Specialist by the American Board of Physical Therapy Specialties. This investigator (RFL) was unaware of the findings of the baseline MRI and pain ratings.

Subjects assigned to the PA mobilization group (n=15; Tab. 1) were treated with the methods described by Maitland et al. (18) The premise behind this approach is that treatment should be focused on the specific lumbar segments that demonstrate restricted movement and in which pain is reproduced upon graded movements. (30-33) It is believed that the motion of the entire lumbar spine should improve when motion in the most limited or painful segment is increased.

The subject's position for the mobilization intervention was prone on a treatment table with a small pillow under the abdomen. First, the investigator applied PA pressure to the spinous process of each lumbar vertebra using 1 or 2 small-amplitude movements (grade I). (18) For each level, subjects were asked to report whether they perceived discomfort similar to that experienced while bending backward during standing. ff the subjects did not report any discomfort from the pressure at a particular vertebral level, then the investigator proceeded to the next higher grade of movement, using slightly larger amplitudes (grades IIIV). (18) Once the vertebral level at which the pressure reproducing lumbar discomfort with standing extension was identified, the intervention commenced.

Initially, the PA mobilization intervention consisted of graded oscillations applied to the most painful lumbar segment. Three bouts of 40-second oscillations were applied to this segment at a rate of approximately 1 to 2 Hz and at the highest amplitude tolerated without the reproduction of symptoms. Following mobilization of the most painful segment, 2 bouts of 40-second oscillations (up to grade IV but short of symptom reproduction) (18) were administered to each of the remaining lumbar vertebral levels. The total time for the PA mobilization intervention was approximately 10 minutes.

Of the 15 people treated, 4 reported pain at L5, 5 reported pain at L4, 2 reported pain at L3, and 1 reported pain at L2. Pain could not be localized to 1 segment in one subject, so each of the 5 lumbar segments was mobilized with 2 bouts of 40-second oscillations (grade IV). (18) The treated levels were not recorded in 2 subjects. Following the intervention, the subjects were asked to rate their pain with the procedure described for the preintervention assessment.

[FIGURE 2 OMITTED]

Subjects assigned to the press-up group (n=15; Tab. 1) were treated with the methods described by McKenzie and May.(19) As part of this intervention, subjects were asked to perform a press-up maneuver as far as possible without reproducing lumbar pain with standing extension.

The subject's initial position was the same as that used during MRI (ie, prone on a treatment table). In brief, the subject used the arms to press the top half of the body upward into spinal extension, while the pelvis was allowed to sag with gravity and remain on the treatment table. The subject was instructed to move from the prone position to maximum pain-free lumbar extension over the course of 5 seconds. The end-range position was held for 5 seconds before the subject returned to the starting position. A total of 10 repetitions were performed. During each repetition, the subject was encouraged to move slightly higher, within the limits of discomfort. If, at the completion of the 10 repetitions, the subject's level of pain was the same or lower, a second and third series of press-up maneuvers were performed. All subjects were able to successfully complete 30 repetitions. Each subject's treatment time was approximately 10 minutes.

Posttreatment pain and MRI assessments. Immediately following the intervention, pain and MRI assessments were repeated with the same procedures as those described above. The investigator coordinating the MRI assessment was unaware of each subject's treatment group assignment.

Image Analysis

Prior to analysis, all images were transferred from the MRI system con sole to a Macintosh G3 computer. ([dagger]) For the purposes of this study, only the images containing the vertebral segments at rest and at the end range of the press-up maneuver were analyzed.

Sagittal-plane intervertebral angles (lumbar spine) were measured with National Institutes of Health Image software.([double dagger]) The intervertebral angle was measured as the angle formed by lines defining the end-plates of adjacent vertebrae (Fig. 2). Segmental lumbar motion (ie, extension) was defined as the difference between the intervertebral angles measured on the resting and end-range images (Fig. 2).

Because it was not possible to replicate the exact resting position of the lumbar spine for the posttreatment MRI assessment, the pretreatment resting position was used to calculate motion during both pretreatment and posttreatment assessments. Therefore, the change in segmental extension following the intervention was defined as follows: (posttreatment end-range vertebral angle--pretreatment resting vertebral angle)--(pretreatment end-range vertebral angle--pretreatment resting vertebral angle).

As calculated with this equation, a positive value indicated an increase in extension for a particular functional spinal unit, whereas a negative value indicated a decrease in extension. Total lumbar extension was quantified by summing the inter-vertebral motion at each of the 5 functional units of the lumbar spine. The investigator doing all image analysis was unaware of each subject's treatment group assignment.

Measurement reliability. To establish the intratester reliability of the proposed measurements, dynamic MR images were obtained from 5 volunteers who were healthy on 2 separate occasions (1 week apart). Intraclass correlation coefficients were found to be excellent, ranging from .95 to .99 for all subjects. The standard error of measurement ranged from 0.40 to 0.66 degrees.

Determination of statistical power. Data from a previous publication (28) indicated that the inter-subject variability with respect to inter-segmental motion in people who were healthy was moderate. However, it was anticipated that the variability in the tested population would be 50% greater. Therefore, all power calculations took this increased variability into consideration. Furthermore, all power calculations were based on an alpha level of .05 for a one-tailed test. Given 15 subjects per treatment group, the chances of detecting a 25% decrease in pain response and a 25% increase in lumbar segmental extension were 85% and 98%, respectively, for both interventions.

Data Analysis

Differences between the treatment groups in pain and total lumbar extension were compared over time by use of a 2x2 analysis of variance (ANOVA) (group x time) with repeated measures. If significant inter actions were observed, then the individual main effects were considered separately. Statistical analyses were performed with SPSS software, version 11.0. ([section]) All significance levels were set at P<.05.

Results

The ANOVA results for average pain scores revealed a significant main effect for time (F=23.274; df=l,14; P<.O01; Tab. 2). When averaged across both treatment groups, average pain scores (SD) were lower after intervention than before intervention (2.6 [+ or -] 1.7 versus 4.0 [+ or -] 1.9). No significant group effect or group x time interaction was observed. On average, subjects in the PA mobilization group reported a posttreatment pain score of 2.4[+ or-] 1.8, which did not differ significantly from the posttreatment pain score of 2.8 [+ or -] 1.5 reported by subjects in the press-up group.

The ANOVA results for average total lumbar extension revealed a significant main effect for time (F = 11.764; df = 1,14; P=.004; Tab. 3). When averaged across both treatment groups, average lumbar extension was greater after intervention than before intervention (24.3[degrees] [+ or -] 6.1[degrees] versus 21.2[degrees] + 4.7[degrees]). No significant group effect or group x time interaction was observed. On average, subjects in the PA mobilization group demonstrated 23.8[+ or -]6.5 degrees of lumbar extension, which did not differ significantly from the posttreatment lumbar extension of 24.9 [+ or -] 6.0 demonstrated by subjects in the press-up group.

Discussion

Spinal mobilization and press-up exercises arc common interventions used by physical therapists to decrease back pain and increase lumbar motion. The results of the present study found both interventions to be equally effective in reducing pain with standing extension and increasing lumbar extension following a single treatment session. On average, subjects reported a 41% reduction in pain following PA mobilization and a 30% reduction in pain following the press-up exercise. The pain reduction achieved following both interventions (PA mobilization=l.7 [+ or -] 2.1; press-up exercise=1.2 [+ or -] 1.4) was statistically significant, but the clinical meaningfulness of these changes is questionable. (34)

The 41% reduction in pain following lumbar PA mobilization in the present study is consistent with that reported in previous investigations.(20,21) For example, Chiradejnant et al[degrees] reported a 36% reduction in pain following two 1-minute bouts of spinal mobilization in subjects with nonspecific low back pain. Goodsell et a121 also studied the effects of PA mobilization on nonspecific low back pain and reported an average pain reduction of 33%. The 30% reduction in pain following the press-up intervention in the present investigation is slightly below the range reported previously (33%-88%). (22-25) However, this difference is likely attributable to the fact that the subjects in previous studies performed press-up exercises over multiple sessions and the follow-up time for pain reassessment ranged from 2 to 6 weeks following the initiation of treatment.

On average, total lumbar extension motion increased 3.6 degrees following PA mobilization and 2.7 degrees following the press-up exercise. Although these changes are statistically significant, the clinical relevance of such small changes in motion is questionable. However, when viewed as a percent change in lumbar extension, respective gains of 17.8% and 11.7% with PA mobilization and the press-up exercise were observed. This finding is in contrast to those of Chiradejnant et al (20) and Goodsell et al, (21) who did not find a significant increase in extension following PA mobilization. Our results support the work of McCollam and Benson, (35) who reported a 7.1% increase in lumbar extension, as measured with 2 fluid-based inclinometers. However, there are several important differences between the study of McCollam and Benson (35) and the present study. First, in the former study, PA mobilization was applied to an asymptomatic population. Second, in the former study, the intervention consisted of three 1-minute bouts of PA mobilization applied to L3, L4, and L5 (9 minutes total). In contrast, subjects in the present study typically received 2 minutes of PA mobilization at one vertebral level.

The effects of the press-up intervention on spinal extension in the present study differed from those in previous investigations. (22,24) Using a magnetic tracking device, Elnaggar et a1 (22) found no changes in total lumbar sagittal-plane motion following a press-up exercise. Separate measurements of spinal extension were not reported. Because magnetic tracking systems detect spinal motion via sensors attached to the skin overlying the spinous processes, the reliance on surface contact to detect angular displacement and the sliding of skin over the spinous processes may have prevented the detection of changes in angular motion.

Although our study did not address the mechanism by which pain and motion were influenced by the 2 interventions, it is interesting to consider what changes may have occurred during both treatment procedures. Both mechanical and neurophysiological mechanisms have been described to explain pain reduction and improved mobility following joint motion or mobilization, and it is conceivable that both mechanisms played a role in the findings of the present study. For example, passive motion has been reported to selectively stretch contracted tissues without damaging healthy adjacent tissues. (1) In addition, repetitive movements are thought to distribute synovial fluid over the articular cartilage and disk, resulting in less resistance to motion. (36) With less resistance to motion, subjects may have felt free to move and thus may have experienced less pain.

In addition to the mechanical explanation as to how mobilization and exercise may influence pain and motion, recent studies have suggested a neurophysiological explanation. For example, dorsal horn activation (as measured with functional MRI) from a painful stimulus has been shown to decrease following joint mobilization. (37) This finding could explain the observations of several authors who have reported that passive movements applied to either the spine (38, 39) or the extremities (40-42) elevated pain thresholds to various mechanical stimuli. In addition, a study of the Hoffman reflex demonstrated a transient attenuation of alpha motor neuron excitability following mobilization. (43) If the motion produced by the press-up maneuver during the pretreatment MRI assessment was limited by protective muscle guarding, then a reduction in alpha motor neuron excitability may have decreased the guarding response and thus allowed more movement during the posttreatment MRI assessment.

In order to explore the relationship between changes in pain and changes in lumbar extension motion for subjects enrolled in the present study, a post hoc correlation analysis was performed. When participants in both groups were combined, a statistically significant relationship was found (r=-.37, P=.04). The negative correlation indicated that greater decreases in pain were associated with greater increases in lumbar extension. Although this finding supports the link between pain and joint motion, the strength of this relationship was relatively weak. It also should be noted that cause-and-effect relationships cannot be inferred by such an analysis.

Several limitations of our study need to be acknowledged. First, the relatively small change in total lumbar extension following PA mobilization and the press-up exercise in the present study may have been related to the age and activity level of the subjects. Our participants were young and physically active. Because spinal motion is known to decrease with age, mobilization applied to a population with less spinal motion may have resulted in greater increases in spinal motion after intervention. Second, the strict inclusion criteria used in the present study limit the generalizability of the results to all low back pain populations. For example, subjects who have both back pain and leg pain and who report centralization of symptoms with extension exercises may have responded more favorably to the press-up intervention. (44-46) Third, only the immediate effects of the 2 interventions were considered in the present study; therefore, long-term gains in motion and pain reduction cannot be assumed. Fourth, our study design lacked a sham group to account for any potential placebo effect that may have occurred with either of the interventions. In addition, a sham group would have controlled for any potential improvements in pain or motion attributable to the testing procedure itself and would have been useful in establishing the test-retest stability of the MRI measurements. Last, the inability to exactly reproduce the pretreatment resting position for the post-treatment MRI assessment may have influenced the results of the present study. These limitations should be considered in the design of future investigations in this area.

Conclusion

The immediate effects of PA mobilization and a press-up exercise were examined in people with nonspecific low back pain. Following the intervention, subjects in both groups reported significantly less pain with standing extension. Additionally, both PA mobilization and the press-up exercise resulted in a significant increase in lumbar extension. There were no significant differences in pain and lumbar extension between the 2 interventions studied. Our findings suggest that both PA mobilization and press-up exercises can have an immediate effect on symptoms and lumbar motion in people with nonspecific low back pain.

This article was submitted March 1, 2007, and was accepted December 11, 2007.

DOI: 10.2522/ptj.20070069

References

(1) Frank C, Akeson WH, Woo SL, et al. Physiology and therapeutic value of passive joint motion. Clin Orthop. 1984;185: 113-115.

(2) Frank JW, Brooker AS, DeMaio SE, et al Disability resulting from occupational low back pain, part II: what do we know about secondary prevention? A review of the scientific evidence on prevention after disability begins. Spine. 1996;21:2918-2929.

(3) Frank JW, Kerr MS, Brooker AS, et al. Disability resulting from occupational low back pain, part I: what do we know about primary prevention? A review of the scientific evidence on prevention before disability begins. Spine. 1996;21:2908-2917.

(4) Scientific approach to the assessment and management of activity-related spinal disorders: a monograph for clinicians. Report of the Quebec Task Force on Spinal Disorders. Spine. 1987;12(7 suppl):S1-S59.

(5) Volinn E. The epidemiology of low back pain in the rest of the world. Spine. 1997; 22: 1798.

(6) Walker B. The prevalence of low back pain: a systematic review of the literature from 1966 to 1998. J Spinal Disord. 2000;13:205-217.

(7) California Department of Industrial Relations. Division of Labor Statistics & Research. 2005 nonfatal occupational injuries and illnesses in California: case and demographic tables. Available at: http://www.dir. ca.gov/dlsr/Injuries/Demographics/2005 / Menu.htm.

(8) Frymoyer JW, Durette CL. The economics of spinal disorders. In: Frymoyer JW, ed. Adult Spine: Principles and Practice. Philadelphia, Pa: Lippincott-Raven; 1997: 143-150.

(9) McGregor A, Anderton L, Gedroyc W. The assessment of intersegmental motion and pelvic tilt in elite oarsmen. Med Sci Sports Exerc. 2002;34:1143-1149.

(10) Burton AK, Battie MC, Gibbons L, et al. Lumbar disc degeneration and sagittal flexibility. J Spinal Disord. 1996;9:418-424.

(11) Latimer J, Lee M, Adams R, Moran CM. An investigation of the relationship between low back pain and lumbar posteroanterior stiffness. J Manipulative Physiol Ther. 1996;19:587-591.

(12) Troup JD, Foreman TK, Baxter CE, Brown D. 1987 Volvo award in clinical sciences: the perception of back pain and the role of psychophysical tests of lifting capacity. Spine. 1987;12:645-657.

(13) Mellin G. Decreased joint and spinal mobility associated with low back pain in young adults. J Spinal Disord. 1990;3: 238 -243.

(14) Pearcy M, Portek I, Shepherd J. The effect of low-back pain on lumbar spinal movements measured by three-dimensional X-ray analysis. Spine. 1985;10:150-153.

(15) Koes BW, Bouter LM, Beckerman H, et al. Physiotherapy exercises and back pain: a blinded review. BMJ. 1991;302:1572-1576.

(16) Koes BW, Bouter LM, van Mameren H, ct al. Randomiscd clinical trial of manipulative therapy and physiotherapy for persistent back and neck complaints: results of one-year follow-up. BMJ 1992;304:601-605.

(17) Koes BW, Bouter LM, van der Heijden GJ. Methodological quality of randomized clinical trials on treatment efficacy in low back pain. Spine. 1995;20:228-235.

(18) Maitland GD, Hengeveld E, Banks K, English K. Maitland's Vertebral Manipulation. Oxford, United Kingdom: Butterworth-Heinemann; 2001.

(19) McKenzie R, May S. The Lumbar Spine: Mechanical Diagnosis & Therapy. Waikanae, New Zealand: Spinal Publications New Zealand Ltd; 2003.

(20) Chiradejnant A, Latimer J, Maher CG, Stepkovitch N. Does the choice of spinal level treated during posteroanterior (PA) mobilisation affect treatment outcome? Pbysiotber Theory Pract. 2002:18:165-174.

(21) Goodsell M, Lee M, Latimer J. Short-term effects of lumbar posteroanterior mobilization in individuals with low-back pain. J Manipulative Physiol Ther. 2000;23: 332-342.

(22) Elnaggar IM, Nordin M, Sheikhzadch A, et al. Effects of spinal flexion and extension exercises on low-back pain and spinal mobility in chronic mechanical low-back pain patients. ,Spine. 1991;16:967-972.

(23) Long A, Donclson R, Fung T. Does it matter which exercise? A randomized control trial of exercise fur low back pain. Spine. 2004; 29:2593-2602.

(24) Nwuga G, Nwuga V. Relative therapeutic efficacy of the Williams and McKenzie protocols in back pain management. Physiother Pract. 1985;1:99-105.

(25) Ponte J. Jensen GJ, Kent BE. A preliminary report on the use of the McKenzie protocol versus Williams protocol in the treatment of low back pain. J Orthop Sports Phys Ther. 1984;6:130-138.

(26) Beneck G J, Ktdig K, Landel RF, Powers CM. The relationship between lumbar segmental motion and pain response produced by a posterior-to-anterior force in persons with nonspecific low back pain. J Orthop Sports Phys Ther. 2005;35:203-209.

(27) Kulig K, Landel R, Powers CM. Assessment of lumbar spine kinematics using dynamic MRI: a proposed mcchanism of sagittal plane motion indt, ced by manual posterior-to-anterior mobilization. J Orthop Sports Phys Ther. 2004;34:57-64.

(28) Powers CM, Kulig K, Harrison J, Bergman G. Segmental mobility of the lumbar spine during a posterior to anterior mobilization: assessment using dynamic MRI. Clin Biomech (Bristol, Avon). 2003; 18:80-83.

(29) Hahne AJ, Keating JL, Wilson SC. Do within-sessinn changes in pain intensity and range of motion predict between session changes in patients with low back pain? Aust J Physiother. 2004;50:17-23.

(30) Lee M, Kelly DW, Steven GP. A model of spine, ribcage and pelvic responses to a specific lumbar manipulative force in relaxed subjects. J Biomech. 1995;28: 1403-1408.

(31) Lee M, Liversidgc K. Posteroanterior stiffness at three locations in the lumbar spine. J Manipulative Physiol Ther. 1994;17: 511-516.

(32) Lee M, Steven GP, Crosbie J, Higgs RJ. Variations in posteroanterior stiffness in the thoracolumbar spine: preliminary nbservations and proposed mechanisms. Phys Tber. 1998;78:1277-1287.

(33) Lee R, Evans J. Towards a better understanding of spinal posterioanterior mubilisation. Physiotherapy. 1994;80:68-73.

(34) Childs JD, Piva SR, Fritz JM. Responsiveness of the numeric pain rating scale in patients with low back pain. Spine. 2005;30:1331-1334.

(35) McCollam RL, Benson C. Effects of postero-anterior mobilization on lumbar extension and flexion. Journal of Manual and Manipulative Therapy. 1993;1:134-141.

(36) Twomey L, Taylor J. Exercise and spinal manipulation in the treatment of low back pain. Spine. 1995;20:615-619.

(37) Malisza KL, Stroman PW, Turner A, et al. Functional MRI of the rat lumbar spinal cord involving painful stimulation and the effect of peripheral joint mobilization. J Magn Reson Imaging. 2003; 18:152-159.

(38) Paungmali A, O'Leary S, Souvlis T, Vicenzino B. Naloxone fails to antagonize initial hypoalgesic effect of a manual therapy treatment for lateral epicondylalgia. J Manipulative Physiol Ther. 2004;27:180-185.

(39) Dhondt W, Willaeys T, Verbruggen LA, et al. Pain threshold in patients with rheumatnid arthritis and effect of manual oscillations. Scand J Rheumatol. 1999;28:88-93.

(40) Moss P, Sluka K, Wright A. The initial effects of knee joint mobilization on osteoarthritic hyperalgcsia. Matt Ther: 2007; 12:109-118.

(41) Panngmali A, O'Leary S, Souvlis T, Vicenzino B. Hypoalgesic and sympathoexcitatory effects of mobilization with movement for lateral epicondylalgia. Phys Ther. 2003;83:374 -383.

(42) Vicenzino B, Paungmali A, Buratowski S, Wright A. Specific manipulative therapy treatment for chronic lateral cpicondylalgia produces uniquely characteristic hypoalgesia. Man Ther. 2001;6:205-212.

(43) Dishman JD, Bulbulian R. Spinal reflex attenuation associated with spinal manipulation. Spine. 2000;25:2519-2524; discussion 2525.

(44) Long AL. The centralization phenomenon: its usefulness as a predictor or outcome in conservative treatment of chronic low back pain (a pilot study). Spine. 1995;20: 2513-2520; discussion 2521.

(45) Werneke M, Hart DL. Centralization phenomenon as a prognostic factor for chronic low back pain and disability. Spine. 2001 ;26:758 -764; discussion 765.

(46) Werneke M, Hart DL, Cook D. A descriptive study of the centralization phenomenon: a prospective analysis. Spine. 1999; 24:676-683.

* General Electric Medical Systems, 2421 N Fairview Rd, Milwaukee, WI 53226.

([dagger]) Apple, 1 Infinite Loop, Cupertino, CA 95014.

([double dagger]) National Institutes of Health, 900 Rockville Pike, Bethesda, MD 20892.

([section]) Pss Inc, 233 s Wacker Dr, Chicago, IL 60606.

CM Powers, PT, PhD, is Associate Professor, Division of Biokinesiology and Physical Therapy at the School of Dentistry, University of Southern California, 1540 E Alcazar St, CHP-155, Los Angeles, CA 90089-9006 (USA). Address all correspondence to Dr Powers at: [e-mail].

GJ Beneck, PT, MS, OCS, is a PhD student, Division of Biokinesiology and Physical Therapy at the School of Dentistry, University of Southern California, and Lecturer, Department of Physical Therapy, California State University at Long Beach, Long Beach, Calif.

K Kulig, PT, PhD, is Associate Professor of Clinical Physical Therapy, Division of Biokinesiology and Physical Therapy at the School of Dentistry, University of Southern California.

RF Landel, PT, DPT, OCS, CSCS, is Associate Professor of Clinical Physical Therapy, Division of Biokinesiology and Physical Therapy at the School of Dentistry, University of Southern California.

M Fredericson, MD, is Associate Professor, Department of Orthopaedic Surgery, Division of Sports Medicine, Stanford University, Stanford, Calif, and Director of Stanford Physical Medicine and Rehabilitation Clinics.

[Powers CM, Beneck GJ, Kulig K, et al. Effects of a single session of posterior-to-anterior spinal mobilization and press-up exercise on pain response and lumbar spine extension in people with nonspecific low back pain. Phys Ther. 2008;88:485-493.]

Dr Powers, Dr Kulig, and Dr Landel provided concept/idea/research design. Dr Powers, Mr Beneck, and Dr Landel provided writing. Dr Powers, Dr Kulig, Dr Landel, and Dr Fredericson provided data collection. Dr Powers, Mr Beneck, and Dr Kulig provided data analysis. Dr Powers provided fund procurement and facilities/equipment. Dr Fredericson provided subjects. Dr Powers and Dr Fredericson provided institutional liaisons. Dr Powers and Dr Kulig provided project management and consultation (including review of manuscript before submission).

This study was approved by the institutional review boards of Stanford University and the University of Southern California.

Data from this study were presented at the Combined Sections Meeting of the American Physical Therapy Association; February 12-16, 2003; Tampa, Fla.

This research was funded by a grant from the Foundation for Physical Therapy.

Table 1.
Characteristics of the Study Participants in Each of
the Intervention Groups

Characteristic    [bar.X] [+ or -] SD for the Following          P
                  Group:

                  PA Mobilization (n=75;   Press-up (n=15;
                  8 Women, 7 Men)          11 Women, 4 Men)

Age (y)            30.2 [+ or -] 7.9        32.3 [+ or -] 9.6    .523

Height (cm)       175.7 [+ or -] 11.3      171.2 [+ or -] 8.4    .224

Weight (kg)        71.6 [+ or -] 14.5       68.1 [+ or -] 12.3   .477

Body mass index    23.0 [+ or -] 3.0        23.3 [+ or -] 4.0    .846
(kg/[m.sup.2])

Table 2. Pain Scores

Group or          Pain Score, [bar.X] [+ or -] SD
Parameter

                  Before             After
                  Intervention       Intervention

PA mobilization   4.1 [+ or -] 1.7   2.4 [+ or -] 1.8

Press-up          4.0 [+ or -] 2.1   2.8 [+ or -] 1.5

Collapsed         4.0 [+ or -] 1.9   2.6 [+ or -] 1.7 (a)
group average

Group or          Average Change
Parameter

PA mobilization   1.7 [+ or -] 2.1

Press-up          1.2 [+ or -] 1.4

Collapsed         1.4 [+ or -] 1.8
group average

(a) Significant main effect for time (P<.001).

Table 3.
Total Lumbar Extension

Group or          Total Lumbar Extension ([degrees]),
Parameter         [bar.X] [+ or -] SD

                  Before              After
                  Intervention        Intervention

PA mobilization   20.2 [+ or -] 5.2   23.8 [+ or -] 6.5

Press-up          22.2 [+ or -] 3.9   24.9 [+ or -] 6.0

Collapsed         21.2 [+ or -] 4.7   24.3 [+ or -] 6.1 (a)
group average

Group or          Average Change
Parameter

PA mobilization   3.6 [+ or -] 5.0

Press-up          2.7 [+ or -] 5.1

Collapsed         3.1 [+ or -] 4.9
group average

(a) Significant main effect for time (P=.004).