Volume 89, Issue 7 , Pages 1305-1313, July 2008
Muscle Activation Changes After Exercise Rehabilitation for Chronic Low Back Pain
Article Outline
Abstract
Marshall PW, Murphy BA. Muscle activation changes after exercise rehabilitation for chronic low back pain.
Objective
To investigate the changes in 2 electromyographic measures, flexion relaxation (FR) response and feed-forward activation of the deep abdominals, associated with low back pain (LBP) after different rehabilitation interventions.
Design
A 2×2 factorial design with subjects' self-selecting treatment with randomization after 4 weeks to either the specific exercise group or exercise advice group for a further 12-week period.
Setting
General community practitioners and university training center.
Participants
Subjects with chronic nonspecific LBP were recruited for this study. A total of 112 people were initially screened, and 60 were recruited for the study, with 50 being available for long-term follow-up.
Intervention
Four weeks of treatment (manipulative or nonmanipulation) and 12 weeks of subsequent exercise (supervised Swiss ball training or exercise advice).
Main Outcome Measures
The Oswestry Disability Index, FR response measured at T12-L1 and L4-5, and feed-forward activation of the deep abdominal muscles.
Results
More rapid improvements in disability were identified for subjects who received the supervised exercise program. The FR response at L4-5 also increased more for those who received directly supervised exercise. Long-term follow-up showed that there was still a between-group difference in the FR response, despite no difference in self-rated disability. Long-term changes were observed for the feed-forward activation of the deep abdominals; however, no exercise or treatment effects were identified.
Conclusions
Supervised exercise rehabilitation leads to more rapid improvements in self-rated disability, which were associated with greater improvement in the low back FR response.
Key Words: Electromyography, Exercise, Low back pain, Muscle relaxation, Rehabilitation
List of Abbreviations: ANCOVA, analysis of covariance, ANOVA, analysis of variance, FR, flexion relaxation, LBP, low back pain, M-C, manipulation and control exercise, M-SB, manipulation and Swiss ball exercise, NM-C, nonmanipulation and control exercise, NM-SB, nonmanipulation and Swiss ball exercise, ODI, Oswestry Disability Index
IN THE LABORATORY-BASED assessment of LBP, much interest in the last 15 years has focused on motor control changes evident with this condition. Some research has presented evidence for altered recruitment patterns of the deep abdominal muscles during rapid limb movement and the inability to consciously activate these muscles during specific movement tasks.1, 2 Other research3 has investigated altered muscle reflex responses to rapid trunk unloading tasks. Furthermore, there has been continuing research into the electric silence of the back muscles during a trunk-bending task.4 What is unclear from this research is whether different types of physical interventions lead to differential changes in these measures when used in patients with chronic LBP.
The delayed feed-forward activation of the transversus abdominis muscle has given rise to a widely used clinical intervention of deep abdominal retraining performed by using a specific isometric task.5 What is interesting to note when reviewing the literature is that there is no evidence showing a change in the feed-forward measurement with deep abdominal retraining. Furthermore, no measure of spinal stability has been related to a normal or altered feed-forward activation of the transversus abdominis. The inference that the delayed activation of this musculature is indicative of impaired mechanical stability has not been supported by current research. The lack of evidence for whether this measurement changes means that clinical interventions based on this area lack support.
The measurement of the electric activity of the back extensor muscles during a trunk flexion task is commonly known as the FR response. First noticed by Allen in 1948,6 this measure was then investigated by Floyd and Silver7 in the 1950s. What this measure documents is the absence of electric activity at full trunk flexion compared with the activity measured during the flexion and extension movements of the trunk. The electric silence observed at full trunk flexion is thought to be invoked by a stretch inhibition reflex, reducing the active muscle contraction of the superficial erector spinae and allowing the passive spinal structures and some of the deeper back extensor musculature (eg, the quadratus lumborum) to provide the necessary tension required to maintain stability.8, 9 This measure has been able to discriminate people with back pain from healthy controls.10 There is some evidence showing a measurable decrease in the amount of activity during the relaxation phase of the movement after rehabilitation for LBP patients.4, 11
Commonly used physical intervention strategies often include a combination of both manual therapy and exercise modalities, and there is evidence that a combined approach is successful.12 The differential effects of individual and combined treatment approaches on measures of altered motor control have not been clearly delineated. This is an important area for investigations to increase the understanding of how people adapt to different types of treatment intervention. A particular manual therapy technique of interest is spinal manipulation (defined for the purpose of this article as a high-velocity/low-amplitude treatment thrust), which has documented effects on postural reflexes.13 There is also evidence to suggest that the FR response can be altered with exercise interventions.4, 11 However, it is not clear whether different types of physical intervention, especially manipulation in combination with exercise, lead to greater changes in the aforementioned feed-forward and FR measures.
The purpose of this study was to evaluate changes in the feed-forward activation of the deep abdominal muscles and the FR response after different combinations of exercise and physical treatment modalities for patients with chronic LBP. The hypothesis of this study was that subjects who receive specific exercise and spinal manipulation will have greater improvements in the 2 neuromuscular measures used in this study: the FR response and the latency response of the deep abdominals to rapid limb movement.
Methods
Participants
Sixty men and women with chronic nonspecific LBP of at least 3 months in duration volunteered to participate in this study from a total of 112 people who were screened for participation (fig 1). This study was approved by our local ethics committee, and all subjects provided informed written consent before participation. Exclusion criteria included the presence of severe postural abnormality or neuromuscular disorder; previous diagnosis of pathology (confirmed by magnetic resonance imaging or radiography), which would contraindicate exercise or spinal manipulation; manipulative treatment in the last 3 months; or previous participation in a specific abdominal stabilization training program.
Fig 1.
Flowchart based on the CONSORT guidelines for participant flow through the study.
Sample Size
The calculation of the sample size was carried out with α equal to .05 (5% chance of type I error), 1 – β = .80 (power 80%), by using the results determined from the change in functional capacity (change in ODI score, 21% [n=27]) from a study evaluating the combined effects of spinal manipulation and exercise advice14 and from the results of a pilot study performed over the same 8-week time period (change in ODI score, 12.25% [n=20]15). The calculated effect size from these results was δ equal to .412. Based on the 2×2 factorial design of this study and allowing for a 15% dropout rate, this resulted in a sample size of 60 for this study.
Study Design
This study was a 16-week intervention with an initial 4-week period of self-selected treatment (manipulation- or non–manipulation-based providers) preceding a 12-week exercise period. Assessments were performed at baseline, 4 weeks (after the treatment period), 8 weeks (4-wk into the exercise period), and 16 weeks (at the end of the intervention period), with long-term follow-up 9 months later.
Subjects were recruited from local treatment providers who were classified as being either manipulative or nonmanipulative providers. The manipulative providers were by registered chiropractors and manipulative physiotherapists who agreed to participate in this study. Manipulations were applied to the lumbar and sacroiliac regions of the spine as well as to any other affected areas that the practitioner decided required treatment. The primary distinguishing factor of the manipulation intervention was that it had to include the high-velocity low-amplitude type of thrust applied to the lumbar and/or sacroiliac joints.16
Nonmanipulative treatment providers were classified as those professionals who administered treatment in the form of basic abdominal stabilization training and instruction in basic principles of ergonomics as well as treatment to any acute problems (not necessarily back related). Any form of passive pain-relieving treatment (ultrasound, electric stimulation, massage) was allowed. This treatment was performed by registered physical therapists and did not include spinal manipulation characterized by the high-velocity low-amplitude thrust.
The primary level of randomization in this study occurred after the initial 4-week treatment period. Subjects were prestratified according to age (>40y), sex, and treatment group (manipulative or nonmanipulative) and were then randomly assigned via a computer algorithm into one of two 12-week exercise programs. The first program involved weekly supervised training sessions with a suitably qualified exercise professional with the primary mode of training being the Swiss ball (exercise ball). This program was progressed every 4 weeks according to a traditional model in which the intensity of the exercise is increased by the sets and the repetitions are decreased (fig 2). The second program (fig 3) was the prescription of a home-based program based on some commonly recommended low back exercises with checkups on performance and technique taking place once every 4 weeks (the control exercise group).
Fig 2.
Photographs of the Swiss ball exercise program prescribed in this study.
Fig 3.
Photographs of the control exercise program prescribed in this study.
Self-Rated Disability
The measure used for self-reported LBP is version 2 of the ODI.17, 18 The ODI is a 10-item questionnaire regarding how a patient's LBP affects aspects of his/her life. Each item has 6 corresponding answers that are scored in severity from 0 to 5. The scores from the 10 items are summed (maximum total, 50) and expressed as a percentage. If a section is not filled in, then the maximum raw score of the ODI becomes the number of items answered multiplied by 5. Relative values are reported for the ODI score (total score/total possible score by 100%). The ODI is one of the most common forms of assessment for the functional capacity of LBP patients.18
Electromyographic Recordings
For the FR assessment, pairs of Ag/AgCl electrodesa with a surface diameter of 2cm and center-to-center distance of 3cm were applied to the right and left erector spinae at the level of L4-5 and T12-L1, approximately 3cm lateral to the midline of the body on the belly of the muscle. The electrodes were aligned longitudinally, parallel to the direction of the muscle fibers. For the feed-forward activation of the abdominal muscles, pairs of electrodes were applied to the right and left sides of a site previously described19 as representing the activity of the transversus abdominis and internal oblique muscles. Briefly, the medial electrode of each pair is located approximately 2cm medial and inferior to the anterior superior iliac spine. The deltoid prime movers for shoulder flexion, abduction, and extension were also prepared for the feed-forward muscle activation assessment.
Before applying the electrodes, the skin was lightly abraded with fine sandpaper and cleaned with an isopropyl alcohol swab to reduce skin impedance to below 5kΩ. Appropriate skin preparation was confirmed by using a digital multimeter after electrode application.
Electromyographic activity was recorded by using a data-acquisition systemb and digitized with a analog-to-digital cardc (common mode rejection ratio, 90dB at 60Hz; input impedance, 100MΩ; 16-bit analog-to-digital conversion), sampled at 2000Hz, and acquired by using a Pentium III computer system (2.5GHz processor, 512Mb RAM). The raw signal was band-pass filtered between 10 and 1000Hz. All signal analysis used the LabView software.c
Procedure and Analysis
FR assessmentFrom a standing position, subjects were required to bend forward as far as possible, pause at the bottom, and then return to the upright position. This was timed to an audio cadence so that each movement phase (flexion, relaxation, re-extension) was 3 seconds in duration for a total testing period for each trial of 9 seconds. Before recording data, the movement was practiced to confirm the maximal position reached during trunk flexion by sliding the hands down the outside of the legs. The feet were placed hip-width apart and marks were placed on the floor to confirm initial positioning. Three recorded trials were performed for each testing session.
The FR response was quantified by calculating the FR ratio. This is the ratio of muscle activity measured during the concentric re-extension phase divided by the activity measured during the paused relaxation phase. Muscle activity for each 3-second movement phase was calculated from the greatest 1-second root mean square (50ms). The mean of the 3 completed trials was used to quantify the FR response for each subject.
Feed-forward activation assessmentThe subject was required to stand in a position with the feet placed shoulder-width apart. Ten repetitions of right shoulder flexion, abduction, and extension were performed. The presentation of each shoulder movement direction was randomized for each collecting session. Each repetition was performed as fast as possible in response to a light signal that was preceded by a warning stimulus. A random time period was generated by the computer for the signal to move (green light) between 0.5 and 1.0 second after the warning stimulus (red light). Previous research20 has found no difference in limb movement speed between patients and control subjects. The subjects in this study were instructed to “breath and relax” between each trial. Between 5 and 10 seconds were allowed between each trial to ensure that a stable baseline was present. A trial was not performed if the subject was attempting to laugh, cough, talk, and so on. A time period of between 2 and 3 minutes was allowed between performances of each set of shoulder movements (1 set of 10 repetitions for each movement direction).
The latency between the onset of the abdominal muscles and the deltoid prime mover formed the basis of the analysis for this task. The mean latency for the right and left abdominal signals was calculated for the 10 trials performed for each movement. Before data analysis, the signals obtained during the feed-forward activation procedures were filtered by using a fourth-order, 100Hz low-pass Savitsky-Golay filter. The signals were visually inspected to determine that there was a detectable onset. Fewer than 5% of all trials were rejected because of an inability to discern a clear onset. For the visually accepted trials, the integrated profile method was used to determine the exact onset of each muscle signal. The integrated profile method involves comparing the normalized integral of the muscle signal to a time-normalized function to determine the point where there is a sudden increase in muscle activity.21 A visually determined window (150ms before and 200ms after the onset of deltoid) was used as the standard physiologic window for performing the integrated profile analysis to determine the relative abdominal muscle onset.
Data Analysis
The SPSS statistical software analysis programd was used for the data analysis. Kolmogorov-Smirnov testing showed that the baseline FR and abdominal latency measurements were normally distributed. A repeated-measures ANOVA was used to determine differences between groups at baseline and to evaluate the changes over time throughout the intervention and long-term follow-up (exercise by treatment by time) for each measured variable. Global changes for the entire study over time were identified from the significance of the main effects of the repeated-measures ANOVA. Differences in the response for the groups over time were revealed by a significant interaction (time by exercise; time by treatment; time by exercise by treatment), and the location of the significant differences was identified by the performance of a priori repeated contrast analysis. A Bonferroni adjustment was used in the statistical analysis to control for multiple comparisons. For any variables identified as significantly changing over time, an ANCOVA was used to examine whether baseline values or disability scores were associated with the change in the tested variable. The statistical significance of this study was set at P less than .05. Unless otherwise stated, data are presented as mean ± SD throughout this study.
Results
The results from table 1 present the demographic information from the subjects separated by group.
Table 1. Baseline Physical Activity and Demographic Information for Subjects in Each Group
| Variable | M-C Group (n=13) | M-SB Group (n=12) | NM-C Group (n=13) | NM-SB Group (n=12) | P |
|---|---|---|---|---|---|
| Sex (% male) | 46 | 50 | 58 | 50 | |
| Age (y) | 35.8±10.4 | 34.3±9.2 | 41.7±10.7 | 33.9±9.6 | .77 |
| Height (cm) | 173±4 | 173±10 | 174±4 | 173±11 | .96 |
| Weight (kg) | 73.6±11.9 | 78.7±14.8 | 83.8±13.6 | 77.5±11.8 | .80 |
| BMI (kg/m2)⁎ | 24.6±3.6 | 26.2±2.9 | 27.5±4.1 | 26.4±6.5 | .54 |
| LBP duration (y) | 4.0±2.0 | 3.0±2.5 | 2.7±1.3 | 5.0±2.5 | .47 |
⁎Body mass index = weight (kg)/height (m)2. |
Changes in Self-Rated Disability
There were significant reductions over time in self-rated disability as measured by changes in the ODI (fig 4). There was a significant reduction in self-rated disability in the first 8 weeks of the intervention with both the 4- and 8-week assessments being significantly reduced from baseline. There were no exercise or treatment interaction effects identified over the first 8 weeks. A significant time by exercise interaction was found at the 16-week time point, with subjects who performed Swiss ball exercise (M-SB and NM-SB groups) differing significantly from the control exercise intervention (P=.023; mean difference 7.7; 95% confidence interval for mean difference, 1.2–14.3). There were no group or treatment effects identified at the 56-week time point. At long-term follow-up, there was still a significant reduction in self-rated disability compared with baseline for all the groups.
Fig 4.
Changes in ODI score over time for the 4 groups in the study. Note the significant difference between the Swiss ball (M-SB, NM-SB) exercise groups and the control exercise groups (M-C, NM-C) at the 16-week time point.
FR Response
There were significant changes over time identified for the FR ratio measured at the level of T12-L1 (table 2, fig 5). The mean ratio measured at the 56-week time point was significantly higher than the other time points. There were no treatment or exercise interactions identified in the analysis.
Table 2. Summary of the F Values From the Repeated-Measures ANOVA for Each Muscle Sites' FR Ratio Analysis
| Muscle | Time | Time by Treatment | Time by Exercise | Time by Treatment by Exercise |
|---|---|---|---|---|
| Right T12-L1 | 2.8⁎ | 2.5 | 2.1 | 0.62 |
| Left T12-L1 | 6.8‡ | 2.5 | 1.3 | 1.20 |
| Right L4-5 | 12.8‡ | 1.8 | 4.9† | 0.23 |
| Left L4-5 | 9.9‡ | 1.3 | 3.4⁎ | 0.43 |
⁎P<.05. |
†P<.01. |
‡P<.001. |
Fig 5.
FR responses measured for the right and left T12-L1 sites at each of the assessment time points.
There were significant increases in both the right and left L4-5 FR ratio over time for each group (fig 6). The exercise interaction was identified at the 8-, 16-, and 56-week time points, with subjects who used the Swiss ball having a significantly greater FR ratio compared with the control exercise group. The Swiss ball group did not change from the 16-week time point to the long-term follow-up. Subjects who performed the control exercise intervention did increase their FR ratio from 16 weeks to 56 weeks, but this was still significantly lower than the mean for those who received Swiss ball exercise during the intervention. There were no significant treatment interactions identified in the analysis. Results from the ANCOVA showed that neither baseline FR ratio nor disability levels were associated with the change in FR response.
Fig 6.
FR responses measured for the right and left L4-5 sites at each of the assessment time points.
Feed-Forward Activation Measurements
There was a significant time effect identified in the analysis of the right transversus abdominis and internal oblique flexion movement latency response (F=11.6, P<.001) (fig 7). No significant treatment of exercise interactions were identified in the analysis. The mean latency time measured at the 56-week follow-up was significantly reduced compared with the values measured during the intervention period. There were no significant changes or interactions identified for the latency responses measured during the abduction and extension movements or for latency times measured from the left transversus abdominis and internal oblique. The ANCOVA analysis showed that baseline transversus abdominis and internal oblique latency times for the flexion movements were significantly associated with the amount of change measured (F=18.08, P<.001). Correlation analysis showed that high baseline latency times were significantly correlated with a greater decrease in latency time (change = postlatency time – prelatency time, a more negative number represents a greater change) measured over the course of the study (r=−.61, P<.05).
Fig 7.
Changes in the latency response measured from right transversus abdominis and internal oblique muscles for the shoulder flexion task. A significant time effect was identified from the repeated-measures ANOVA from 16 to 56 weeks only. No group effects were identified from the analysis. ANCOVA and correlation analysis found that subjects with higher baseline latency times had the greater improvements during the intervention.
Discussion
Summary of the Main Results
The results of this study do not support the hypothesis that spinal manipulation and exercise would lead to a greater change in the neuromuscular measures used in this study compared with the alternative treatment groups. However, the study results did provide support for the efficacy of supervised exercise in yielding a more rapid improvement in functional disability and the FR response.
Changes in FR Response
There is some research that has found improvements in the FR response after exercise, specifically manifest as decreased myoelectric activity during the full flexed position yielding a significantly elevated FR ratio over time.4, 15 The results of this study found improvements in the FR response, with a specific timely exercise effect identified only at L4-5 (T12-L1 only different at long-term follow-up). The improvement in the FR response after supervised exercise was manifest after the first 4 weeks of training, with a significant difference between the Swiss ball and control exercise groups identified at the 8-week point (4wk of treatment, 4wk of exercise).
It is well known that the early adaptations to an exercise program are because of neuromuscular changes.22, 23 What this study has shown through the measurement of the FR response are acute and chronic neuromuscular adaptations to different types of exercise programs. There are several trials that show both the short- and long-term advantages to supervised over unsupervised training for overall outcomes and compliance to the prescribed interventions.24, 25, 26, 27 Previous studies12, 14, 28, 29 that have combined exercise and treatment also used supervised training. Benefits from supervised training are from ensuring that a regular exercise workload is performed and the positive benefits from regular interaction with a treatment specialist (eg, expert advice, social interaction, support). Of the aforementioned studies, only the study performed by Mannion et al29 also used the FR response as an outcome measure and found no change. However, only subjective signal analysis was performed in the Mannion study to measure whether the FR response was present compared with the calculation of a ratio in this study. What the results of this study have shown is that a structured and supervised exercise program provides greater benefit over no supervision through eliciting a more rapid neuromuscular adaptation, which was maintained to the long-term follow-up.
The changes exhibited in the FR response can be explained within the context of the pain adaptation model described by Lund et al.30 This model describes dysfunctional characteristics of muscle as sometimes being a normal protective adaptation to avoid further pain and possible damage.30 Therefore, the heightened activity measured at full trunk flexion would be a normal protective response to maintain the stiffness of the spinal column. Without there being actual structural damage, this adaptation is not chronically required. These adaptations can also be explained with Panjabi's model of spinal stability, which describes 3 primary stabilizing systems (active musculature, passive ligaments and disks, central control unit) and suggests that dysfunction or adaptation in one will lead to changes in another.31, 32, 33 What this study has shown is that in LBP patients without diagnosed structural problems (an altered passive system), where there is altered muscle activity at full trunk flexion (altered active system and control unit) as a normal protective response, exercise is a positive factor in redressing these maladaptive stabilizing strategies. These results, including the improvement in the control exercise group at the long-term follow-up, also show that appropriate exercise models based on biomechanic principles that enhance spinal stability34 do work with or without supervision in eliciting neuromuscular adaptation. Therefore, programs that prescribe isolated muscle recruitment for low back exercise rehabilitation in an unsupervised context, in which the task itself may reduce spinal stability,35 cannot be justified on the basis of the ease of prescription.
Changes in Feed-Forward Measurements
This study is the first we know of that has investigated changes in the feed-forward response of the deep abdominal muscles after exercise or treatment over a period of time. There was a significant improvement in the latency response from the end of the intervention to the long-term follow-up. No significant treatment or exercise effects were observed. It is interesting to note that the only measurement that changed over time was for the latency time of the right transversus abdominis and internal oblique muscle site during right shoulder flexion. Furthermore, it is interesting to note that the amount of change in the latency time is associated with people who had a more delayed response at the baseline measurement.
As previously discussed, because sample size was based on changes in disability, we cannot discount that there are statistical differences between the treatment modalities that this thesis did not have the power to detect. Popular therapeutic interventions designed for chronic nonspecific LBP are based on altered motor control of the transversus abdominis.5 Therefore, it is reasonable to expect that types of treatment other than manipulation, such as mobilization-based techniques, may also have a positive effect on the measured latency response. Recent evidence36 investigating a spinal mobilization technique found some alterations in abdominal muscle activity in LBP patients after an acute treatment, although no changes in transversus abdominis function were noted.
There are important considerations for the changes in the feed-forward response that require future investigation. First, the adaptation over time was side and direction specific (right transversus abdominis and internal oblique during right shoulder flexion). Previous research20, 37, 38 has primarily identified the delayed activation of the transversus abdominis during shoulder flexion, but only the contralateral abdominal response has been measured. Future research using fine-wire electromyography needs to be performed to corroborate the findings of this study. This will help establish whether the side and direction findings are specific to the function of the transversus abdominis or if they are simply a marker of impaired lumbopelvic nervous system activity that the surface electromyography method can detect. Second, the relationship between initial baseline latency times and the measured change requires future research. This finding suggests that not all people with LBP have a delayed latency response. Therefore, based on the Panjabi model of spinal stability, it is reasonable to believe that the alteration in the neural system may be caused by a change in the active or passive system. Future research should look to identify patients with a delayed latency response and attempt to investigate a clinical prediction rule such as that shown by Fritz and colleagues39, 40 to improve our subclassification and treatment of chronic LBP.
Finally, the lack of an identified effect for either the treatment or exercise modality (not discounting the chance of a type II error) while showing improvement in all groups over time may indicate that this particular measurement does not need specific treatments designed for it. As previously suggested, the utility of this measure may be as a general marker of impaired neuromuscular function in the lumbopelvic region rather than a measure of a specific instability requiring tailored intervention.
Study Limitations
Two main limitations that may affect overall conclusions about this study relate to the sample size and a possible floor effect on the primary disability measure. The sample-size calculation was based on changes in ODI scores. This introduces a possible type II error in the analysis of the neuromuscular measures used in this study because of the power calculation not being based on an expected change in these outcome variables. This issue can be observed in the time by treatment results for the T12-L1 FR ratio (see table 2), where the measured F value of 2.5 provides a P value of .06, which is not significant but suggestive of the possibility that a type II error exists. A floor effect on the change in ODI score may explain why there is no long-term difference between the groups for this measure, although there are still between-group differences manifest in the L4-5 FR response. Previous research41, 42 suggests that the ODI is not accurate with very low scores. Therefore, this measure may not have been sensitive enough to track any long-term disability related changes in the exercise group. Although the Swiss ball was the mode of exercise used for the specific training group, it should not be inferred from this study that this form of training is more superior to another. The main aspect to the exercise group underlying the positive result is the supervised and periodized nature of the program used in this group rather than the use of the Swiss ball.
Conclusions
Supervised exercise was a more rapid means of eliciting neuromuscular improvement, manifest by an increased FR response. The unsupervised exercise program also showed chronic neuromuscular improvement. No treatment effects were identified for either neuromuscular improvements or disability, although there is a possibility of type II error because sample-size calculations were based on changes in disability. This study has provided data that can be used for future sample size calculations in which changes and differences in these particular measurements are of interest. This is the first study to document chronic changes in the latency of the deep abdominal muscles, which may indicate that this measure is an appropriate marker of general nervous system dysfunction in the low back region. Lund's pain adaptation model and Panjabi's model of spinal stability provide a useful context to understand the nature of the changes measured in this study.
Suppliers
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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.
PII: S0003-9993(08)00275-X
doi:10.1016/j.apmr.2007.11.051
© 2008 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.
Volume 89, Issue 7 , Pages 1305-1313, July 2008
