Relationship between muscle fiber composition and functional capacity of back muscles in healthy subjects and patients with back pain

Assessment of the paraspinal muscles of subjects presenting an idiopathic scoliosis: an EMG pilot study

Background

It is known that the back muscles of scoliotic subjects present abnormalities in their fiber type composition. Some researchers have hypothesized that abnormal fiber composition can lead to paraspinal muscle dysfunction such as poor neuromuscular efficiency and muscle fatigue. EMG parameters were used to evaluate these impairments. The purpose of the present study was to examine the clinical potential of different EMG parameters such as amplitude (RMS) and median frequency (MF) of the power spectrum in order to assess the back muscles of patients presenting idiopathic scoliosis in terms of their neuromuscular efficiency and their muscular fatigue.

Methods

L5/S1 moments during isometric efforts in extension were measured in six subjects with idiopathic scoliosis and ten healthy controls. The subjects performed three 7 s ramp contractions ranging from 0 to 100% maximum voluntary contraction (MVC) and one 30 s sustained contraction at 75% MVC. Surface EMG activity was recorded bilaterally from the paraspinal muscles at L5, L3, L1 and T10. The slope of the EMG RMS/force (neuromuscular efficiency) and MF/force (muscle composition) relationships were computed during the ramp contractions while the slope of the EMG RMS/time and MF/time relationships (muscle fatigue) were computed during the sustained contraction. Comparisons were performed between the two groups and between the left and right sides for the EMG parameters.

Results

No significant group or side differences between the slopes of the different measures used were found at the level of the apex (around T10) of the major curve of the spine. However, a significant side difference was seen at a lower level (L3, p = 0.01) for the MF/time parameter.

Conclusion

The EMG parameters used in this study could not discriminate between the back muscles of scoliotic subjects and those of control subject regarding fiber type composition, neuromuscular efficiency and muscle fatigue at the level of the apex. The results of this pilot study indicate that compensatory strategies are potentially seen at lower level of the spine with these EMG parameters.

Surface electromyography of the paravertebral muscles in patients with chronic low back pain

OBJECTIVE

To investigate the differences in the electromyographic signals of patients with chronic low back pain (CLBP) and healthy subjects.

DESIGN

Cross-sectional study with a matched-pair design.

SETTING

University hospital.

PARTICIPANTS

Thirty-one patients with CLBP and 31 healthy, matched-pair controls.

INTERVENTIONS

The mean rectified surface electromyographic amplitude and muscle strength were measured during maximal voluntary contraction (MVC). During an endurance test at 60% of MVC, the electromyographic parameters of the 2 groups were compared.Main outcome measure Electromyographic measuring of local fatigue, which can be described with changes in the median frequency or by a different parameter of the power spectrum called frequency banding.

RESULTS

The strength measurement revealed a deficiency of 40% in the patients and a deficit in the electromyographic amplitude of approximately 60%, compared with the control group. By pairwise comparison, the decrease in the median frequency during the endurance test was greater in the control group. In the frequency banding of the power spectrum, local fatigue was less pronounced in the CLBP patients in pairwise comparison.

CONCLUSIONS

The back muscles of CLBP patients appear to be less fatigable than those of controls. The results can be explained by morphologic changes, but influences such as pain, avoidance of pain, and deconditioning, need to be considered when the results are assessed.

Activation of lumbar paraspinal and abdominal muscles during therapeutic exercises in chronic low back pain patients11No 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(s) or upon any organization with which the author(s) is/are associated

OBJECTIVES

To assess the activities of paraspinal and abdominal muscles during therapeutic exercises for the treatment of patients with nonspecific chronic low back pain (CLBP), and to study the effects of active physical rehabilitation on these activities.

DESIGN

A cross-sectional study comparing muscle activities during 18 stabilization exercises, and a prospective follow-up of patients with CLBP during rehabilitation.

SETTING

Rehabilitation clinic in university hospital in Finland.

PARTICIPANTS

Nine volunteers (5 men, 4 women) aged 27 to 58 years.

INTERVENTION

Three months of active outpatient rehabilitation (4 to 6 times in a rehabilitation clinic, supplemented with self-motivated exercise at home) supervised by a physiotherapist.

MAIN OUTCOME MEASURES

Surface electromyography was recorded bilaterally from L5 level paraspinal, rectus abdominis, and obliquus externus abdominis muscles. The recorded signal was averaged and normalized to the maximal electromyographic amplitude obtained during the maximal voluntary contraction. The measurements were taken before and after the exercise treatment period.

RESULTS

CLBP patients showed variable trunk muscle activity patterns during the different therapeutic exercises, similar to those that we reported earlier in healthy subjects. The maximal trunk isometric extension (pre, 147.3+/-75.9Nm; post, 170.1+/-72.3Nm) and flexion (pre, 72.0+/-37.9Nm; post, 93.5+/-42.5Nm) torques did not show a significant changes during the exercise period. However, trunk rotation-flexion torque (pre, 52.9+/-26.5Nm; post, 82.4+/-65.8Nm) increased significantly (35.8%) after the exercise period (P<.05). The corresponding maximal electromyographic amplitudes of back and abdominal muscles remained unchanged. Disability, as assessed by visual analog scale and Oswestry Disability Index, did not change.

CONCLUSIONS

The CLBP patients performed therapeutic exercises with similar abdominal and back extensor muscle activities in the same way as the healthy subjects in our earlier studies. In this study, active physical rehabilitation had no effect on the abdominal and back muscle activities or on pain and functional disability indices.

Lumbar muscle fatigue and recovery in patients with long-term low-back trouble--electromyography and health-related factors

OBJECTIVE

The aim was to explore the validity and reliability of EMG for assessing lumbar muscle fatigue.

DESIGN

Patients with long-term low-back trouble (n=57) were compared to a healthy reference group (n=55). Back muscle fatigue and recovery were studied in relation to health-related factors.

BACKGROUND

EMG spectral variables are important tools in the assessment of patients with low-back trouble. The influence of disability on these variables needs further investigation.

METHODS

EMG from the lower back muscles was recorded during a 45 s trunk extension at 80% of maximal voluntary contraction torque and during recovery. Disability was studied using questionnaires.

RESULTS

The reliability was high for maximal voluntary contraction torque and EMG initial median frequency, lower for the median frequency slope, and insufficient for median frequency recovery half-time. The patients had lower maximal voluntary contraction torque, higher initial median frequency at L5 level, flatter slope, and longer recovery half-time than the healthy subjects did. However, for subjects with significantly negative slope, indicating fatigue, there was no significant difference in slope between patients and healthy subjects, while, for subjects without such fatigue, patients showed significantly flatter slopes at L5. The sensitivity/specificity of the test was 86%/78%. The most significant variables selected with logistic regression were maximal voluntary contraction torque and initial median frequency at L5. Patients without significantly negative slopes during contraction and/or not exponential-like EMG recovery scored worse on several items concerning disability and self-efficacy.

CONCLUSIONS

EMG spectral variables in combination with torque might be used for classification. For patients with long-term low-back trouble, the ability to fatigue the lumbar muscles sufficiently to obtain a significantly negative slope during an 80% maximal voluntary contraction may be a sign of better functioning.

RELEVANCE

The ability to fatigue the back muscles during a test requiring a high force output might be achieved with back muscle training focused on increasing strength and self-efficacy.

Surface electromyography assessment of back muscle intrinsic properties

The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.

The effect of comprehensive group training on cross-sectional area, density, and strength of paraspinal muscles in patients sick-listed for subacute low back pain

The effect of exercise on back muscle cross-sectional area (CSA), density, and strength was evaluated in patients sick-listed for subacute low back pain. Twenty-four patients were randomized into an exercise (n = 11) or a control (n = 13) group. Patients in the exercise group followed a biweekly exercise protocol for 15 weeks. Control patients received usual care. Muscle CSA and density were measured by computed tomography before and after intervention. Isokinetic test of back extensors was conducted simultaneously. Results showed a tendency to increased muscle CSA and density in patients in the exercise group, a significant decrease in muscle CSA at L4-L5 in control group patients, and a significant difference in change between groups in muscle CSA at L4-L5. Back extension strength increased in patients in the exercise group, but the improvement was not significant compared with control group patients. In conclusion, there was a tendency for reversal of muscle atrophy after exercise.

Paraspinal denervation and the spinal degenerative cascade

BACKGROUND CONTEXT

The aging of the spine has been reported to follow a degenerative cascade described by Kirkaldy-Willis. This cascade does not take into account the paraspinal muscles. Substantial recent knowledge of the anatomy, physiology and pathophysiology of the paraspinal muscles suggests that they should play a role in the degenerative cascade. Pain relates to paraspinal denervation in a number of disorders. Using new needle electromyographic technique, MiniPM, we may be able to quantify the extent of paraspinal muscle denervation.

PURPOSE

To explore the potential interactions between paraspinal muscle denervation and the degenerative cascade.

STUDY DESIGN

Literature review, reanalysis of a blinded electromyographic study and case reports.

PATIENT SAMPLE

A previously reported group of 35 asymptomatic paid volunteers, ages 18 to 58 years. Two elderly volunteers with moderate to severe spinal stenosis on magnetic resonance imaging (MRI), one significantly disabled, one asymptomatic.

OUTCOME MEASURES

Blinded electromyographic testing, including MiniPM, a codified, quantified needle electromyography technique for the paraspinal muscles. In the two case reports, magnetic resonance imaging and 15-minute timed ambulation.

METHODS

The 35 volunteers were tested by a blinded electromyographer using the MiniPM technique. The two older subjects underwent MRI, MiniPM and extensive electrodiagnostic evaluations, functional testing, complete history and physical examination.

RESULTS

The patient with symptomatic stenosis had a MiniPM score of 6 on each side, and the asymptomatic volunteer had a score of 0. In the asymptomatic subject group, reproducible evidence for denervation was found in 20 subjects (57%), sparsely distributed, but more caudal than cranial (p<.0001). Based on conservative estimates of nerve regeneration rates, the population averaged a detected axonotemesis denervating event approximately once every 120 days.

CONCLUSIONS

Paraspinal denervation may be proven to be a better marker than MRI findings for symptomatic spinal stenosis. Subtle paraspinal muscle denervation occurs frequently in asymptomatic persons. Whether a cause or an effect, paraspinal denervation might lead to hypermobility and thus progression along the degenerative cascade.

Electromyographic assessment of back muscle weakness and muscle composition: reliability and validity issues

OBJECTIVE

To assess the reliability and construct validity of various electromyographic indices developed to assess back muscle weakness and muscle fiber composition.

DESIGN

A prospective study with repeated measures performed on 3 days along with comparisons of groups presenting different back strength and/or back muscle fiber composition.

SETTING

A biomechanics laboratory within a rehabilitation center.

PARTICIPANTS

Forty male volunteers (20 healthy, 20 with chronic low back pain) were assessed on 3 different days to assess reliability and to make group comparisons. Thirteen healthy women were also assessed once to obtain a third group with known lower strength and different back muscle fiber composition.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Surface electromyography was recorded for 4 pairs of homologous back muscles while the subjects performed, on a dynamometer, static trunk extension efforts. Electromyographic parameters were computed to assess muscle weakness and muscle fiber composition. The reliability of the data collected across the 3 sessions and comparisons between groups were determined.

RESULTS

Electromyographic parameters generally showed good to excellent reliability, but were insensitive to differences in back muscle strength and did not appear to be related to muscle composition. Some trends were observed in the electromyographic parameters across the force levels, but the large interindividual variability impeded statistical comparisons.

CONCLUSIONS

The assessment of muscle weakness and muscle fiber composition through electromyographic analysis does not appear feasible, at least on an individual basis, for the muscles of the back.

Comparative histochemical composition of muscle fibres in a pre- and a postvertebral muscle of the cervical spine

References to histochemistry are extensive for human limb muscles but occur less frequently in relation to vertebral muscle. Most vertebral muscle literature has been concerned with muscle fibre characteristics in the lumbar and thoracic spine, due in large part to the incidence of low back pain and idiopathic scoliosis. However few studies have investigated the histochemical composition of neck muscles in humans: and, to our knowledge, no previous study has examined the antagonistic longus colli and multifidus muscle pair. In addition, while age-related segmental degeneration is most prominent between C5 and C7, it is not known whether these osteoligamentous changes are paralleled by changes in muscle fibre ratio. Tissue blocks comprising muscle and bone from C5-C7 segments were harvested at autopsy from 16 subjects with ages ranging from 4 to 77 years. The prevertebral longus colli and postvertebral multifidus muscle pairs were randomly selected from one or other side in each subject. The tissue was frozen, sectioned and histochemically stained for myofibrillar adenosine triphosphatase. Analysis of muscle fibre types was performed by light microscopy. Wilcoxon paired t-tests were used to ascertain whether intramuscular and intermuscular differences in fibre composition were significant. In addition, correlation and regression analyses were used to determine whether fibre type proportions changed in either muscle with increasing age. The present study has revealed histochemical differences between longus colli and multifidus at the level of the C5-C7 vertebral segments. Multifidus comprises a significantly greater proportion of type I than type II fibres. Longus colli comprises a significantly greater proportion of type II fibres than multifidus. Further there were no changes in fibre type proportion in either muscle with increasing age. These observations suggest that longus colli responds equally to postural and phasic demands, whereas multifidus is predominantly postural. Also it would appear that age-related structural alterations in lower cervical segments are not paralleled by changes in muscle fibre ratio.

Median frequency of the electromyographic signal: effect of time-window location on brief step contractions

The purpose of this study was to determine, for different back muscles, if the median frequency (MF) of the electromyographic (EMG) power spectrum changes according to the position of the time window during a 5 s step contraction. Twenty males with no known back problems were standing upright in a dynamometer allowing lower limb and pelvis stabilization. Trunk extension efforts were performed by pushing on a force platform positioned at the T4 level while the extension moment at L5/S1 was displayed as visual feedback. The EMG signals from four homologous back muscles (multifidus at L5, ilicostalis lumborum at L3, and longissimus at L1 and T10) were collected using active surface electrodes during two 5 s static step contractions performed at five force levels (10, 20, 40, 60 and 80% of the maximal voluntary contraction). The root mean square (RMS) and MF values of the EMG signals corresponding to three 250 ms time windows (beginning, middle and end of each step contraction) were computed. The RMS values of several back muscles increased from the first to the third time window for contractions performed at high force levels only. However, a concomitant decrease in the MF values was observed only for the left multifidus muscle. It was concluded that muscle fatigue does not generally manifest itself during 5 s step contractions through the EMG signal. However, it is recommended to use step contractions lasting less than 5 s and to choose a time window located in the first 1-3 s to completely eliminate the possible effects of fatigue.

Histochemistry and morphology of the multifidus muscle in lumbar disc herniation: comparative study between diseased and normal sides

STUDY DESIGN

This comparative study was conducted on 19 patients (13 men and 6 women) with lumbar disc herniation (LDH). The histologic and histochemical differences and changes in the back muscles of the diseased and normal sides were evaluated.

OBJECTIVES

To determine the histologic differences in the back muscles between the diseased and normal sides in lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

The morphologic changes of back muscles between the diseased and normal sides in lumbar disc herniation were examined using histologic and histochemical methods. Few studies have reported the difference in these changes based on quantitative analyses.

METHODS

All samples were harvested bilaterally from the multifidus muscle at the level of L4-L5 or L5-S1 in patients with lumbar disc herniation and then were examined by histologic and histochemical methods (hematoxylin-eosin, Gomori trichrome, NADH-TR, and ATPase stains). The percentage, cross-sectional area (CSA), and lesser diameter (LD) of muscle fibers were measured using computerized image analysis. The Wilcoxon, paired t, Kruskal Wallis, and Fisher tests were used for statistical analysis.

RESULTS

Both Type I and II fibers in the diseased side were significantly smaller than those from the normal side. In the diseased side, the potential strength of Type II fibers was weakened. Some pathologic changes (fiber type grouping, small angulated fibers, group atrophy, moth-eaten appearance, and internal nuclei, etc.) in the diseased side were more obvious than those in the normal side. When the straight leg raising test results were abnormal, both Type I and II fibers in the diseased side were smaller than those in the normal side. The Type I fibers of the diseased side were significantly smaller when the patients had symptoms of central low back pain. The size of the Type I fibers as well as of the Type II fibers did not differ between the diseased and normal sides in patients with unilateral and bilateral low back pain.

CONCLUSIONS

The present study indicated that there were differences in the characteristics of the multifidus muscle between the diseased and normal sides in patients with lumbar disc herniation. The changes in muscle characteristics primarily were related to the disc protrusion. In addition, different locations of the low back pain seemed to cause different secondary effects on the muscle characteristics.

The comparison of trunk muscles EMG activation between subjects with and without chronic low back pain during flexion-extension and lateral bending tasks

The purpose of the study was to compare the electromyographic (EMG) activity of the trunk muscles between normal subjects and chronic low back pain (CLBP) patients during standardized trunk movements. Thirty-three male subjects (18 normals, 15 suffering from non specific CLBP) aged between 35 and 45 yr participated. A biomechanical analysis involving the recording of EMG signals from 12 trunk muscles, the kinematics of trunk segments and the computation of L5/S1 moments was performed. The subjects performed flexion-extension and lateral bending (left and right) tasks (three complete cycles) with and without a 12 kg load. Between group comparisons were performed on the full cycle average pattern of all biomechanical variables for each task. The reliability of EMG variables was evaluated for 10 subjects (5 normals and 5 CLBP) who performed the tasks on three different days. The reliability of EMG amplitude values was generally excellent for agonist muscles but poor to moderate for antagonists. The EMG amplitude analysis revealed significant differences between groups for some muscles (left lumbar and thoracic erector spinae). The abnormal (asymmetric) EMG patterns detected among CLBP patients were not explained by postural asymmetries.

Toward a better prescription of the prone back extension exercise to strengthen the back muscles

This study investigated the level of resistance and the level of muscle activation of the prone back exercise. Fifteen male subjects with no previous history of low back injury performed two repetitions of seven exercises. These consisted of four maximal isometric voluntary contractions (MVC) and three prone back extension (PBE) exercises. The subject was lying prone on a table, the upper body was suspended off the end of the table and the legs and thighs were secured to the table with straps. Three starting positions from the horizontal were investigated, 0 degree, 30 degrees and 60 degrees, and were compared with MVC to quantify the level of effort needed to perform the task. The results showed that the three PBE exercises require a level of resistance and a level of muscle activation generally under 40% of the maximum capacity of healthy subjects. Muscle activity of the erector spinae (ES) was slightly greater when the exercise started at 60 degrees, compared to 0 degree and 30 degrees. During the static phase of the PBE exercises, the level of resistance remained at 40% relative to the peak reaction moment of the MVC, but muscular activity of ES tended to work at a lower activity level. In conclusion, since for healthy subjects PBE exercises are low resistance exercises, they seem to be more specifically designed to develop muscular endurance of the back muscles.