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

Convergent Validity between Electromyographic Muscle Activity, Ultrasound Muscle Thickness and Dynamometric Force Measurement for Assessing Muscle

Muscle fatigue is defined as a reversible decline in performance after intensive use, which largely recovers after a resting period. Surface electromyography (EMG), ultrasound imaging (US) and dynamometry are used to assess muscle activity, muscle morphology and isometric force capacity. This study aimed to assess the convergent validity between these three methods for assessing muscle fatigue during a manual prehension maximal voluntary isometric contraction (MVIC). A diagnostic accuracy study was conducted, enrolling 50 healthy participants for the measurement of simultaneous changes in muscle thickness, muscle activity and isometric force using EMG, US and a hand dynamometer, respectively, during a 15 s MVIC. An adjustment line and its variance (R²) were calculated. Muscle activity and thickness were comparable between genders (p > 0.05). However, men exhibited lower force holding capacity (p < 0.05). No side-to-side or dominance differences were found for any variable. Significant correlations were found for the EMG slope with US (r = 0.359; p < 0.01) and dynamometry (r = 0.305; p < 0.01) slopes and between dynamometry and US slopes (r = 0.227; p < 0.05). The sample of this study was characterized by comparable muscle activity and muscle thickness change between genders. In addition, fatigue slopes were not associated with demography or anthropometry. Our findings showed fair convergent associations between these methods, providing synergistic muscle fatigue information.

The dynamic postural steadiness and stabilization time between older adults with and without recurrent low back pain

BACKGROUND

Although postural control measures were reported to identify neuromuscular impairments, postural steadiness and stabilization time were not carefully investigated between subjects with and without recurrent low back pain (LBP). Research QuestionAre there group differences in the stabilization time, direction of sway, and dynamic postural steadiness index (DPSI) during one-leg standing?

METHODS

Thirty-four control subjects and 29 subjects with recurrent LBP participated in the study. Each subject stood upright on a single leg with and without visual input. The outcomes were measured for standing duration (sec), direction of sway, and the DPSI, which included the vertical steadiness index (VSI). The VSI assesses fluctuations to standardize the vertical ground reaction forces on the force plate.

RESULTS

The control group demonstrated significantly longer standing duration compared to the LBP group during the eyes-open condition (t = 3.55, p = 0.001). The LBP group demonstrated significantly faster stabilization time (t = 2.53, p = 0.01) in the sagittal plane. The DPSI demonstrated an excellent relationship with the VSI without visual input in the control group (r = 0.98, p = 0.001). The directions of sway demonstrated a significant interaction between groups (F = 9.29, p = 0.004).

SIGNIFICANCE

Although standing duration in the eyes-open condition decreased in the LBP group, a faster stabilization time in the sagittal plane was evident compared to the control group to adapt postural stability. These results indicated that vertical dynamic steadiness with visual input might be important to enhance compensatory postural control.

Investigation of the relationship between the clinical evaluation results of lumbar region muscles with cross-sectional area and fat infiltration

BACKGROUND

The relationship between the endurance of the lumbar paraspinal muscles and morphological changes needs to be clarified. In this context, the importance can be revealed of increasing the endurance level of the paraspinal muscles in the prevention and treatment of low back diseases.

OBJECTIVE

The aim of this study was to examine the relationship between the clinical evaluation results of the cross-sectional area (CSA) and fat infiltration of the lumbar deep paraspinal muscles.

METHODS

The study included 37 patients with mechanical low back pain (mechanical), 41 patients with lumbar hernia without root compression (discopathy) and 36 healthy individuals as a control group. The functional status of the lumbar deep paraspinal muscles was evaluated clinically with muscle endurance tests. The fat infiltration and CSA of the muscles were evaluated on axial MRI sections at the L3-S1 level.

RESULTS

The mean values of the prone bridge, Biering-Sorenson, and trunk flexion tests were seen to be highest in the control group and lowest in the discopathy group (p< 0.001). In all tests, the longest test period was obtained at < 10% fat infiltration and the shortest at > 50% fat infiltration. It was observed that as the amount of fat infiltration of the muscles increased, the test times were shortened. There was no significant relationship between the endurance level and the CSA of the groups.

CONCLUSION

The study results demonstrated that the endurance of the paraspinal muscles is associated with the fat infiltration of the muscles. In patients with chronic low back pain, information about muscle morphology and degeneration can be obtained with simple endurance tests without the need for further measurements. On clinical examination, a weak endurance level of the paraspinal muscles indicates the presence of a low back problem and an increase in the amount of fat infiltration.

Paraspinal strength and electromyographic fatigue in patients with sub-acute back pain and controls: Reliability, clinical applicability and between-group differences

BACKGROUND

Paraspinal muscle strength and fatigue are considered important in low back pain (LBP) prevention and rehabilitation. High reliability of paraspinal strength and electromyographic (EMG)-fatigue parameters has not been universally reported. Moreover, the discriminative validity of these parameters requires further exploration, under the threat of potentially poor reliability of the methods examined.

AIM

To investigate the reliability and discriminative validity of paraspinal strength and EMG-related fatigue in subjects with recurrent LBP and healthy participants.

METHODS

Test-retest measurements were performed in 26 healthy and 66 LBP volunteers, for reliability. Paraspinal isometric maximal and mean strength were determined with a maximum voluntary isometric contraction (MVIC) protocol, performed in a custom-made device. For the fatigue test, participants performed a 60% MIVC level continuous isometric contraction of the paraspinals, in conjunction with EMG analysis from 4 muscle sites of the lumbar spine. Initial median frequency (IMF), the median frequency slope (MFslope), as well as the root mean square (RMS) slope EMG parameters were used as fatigue measures. Data were analysed with repeated measures ANOVA for test-retest differences. For reliability, the intraclass correlation coefficient (ICC_3,1), standard error of the measurement (SEM) and the smallest detectable difference (SDD) were reported. Group-related differences for fatigue measures were analysed with a Multivariate Analysis of Covariance, with age, weight and strength as covariates.

RESULTS

Isometric strength presented statistically significant between-day differences (P < 0.01), however these did not exceed 10% (healthy: 7.2%/LBP-patients: 9.7%) and ICC reliability values were excellent, yet test-retest error was increased for the patient group (healthy: ICC_3,1: 0.92-0.96, SEM: 5.72-5.94 Hz, SDD: 18.51%-18.57%/LBP-patients: ICC_3,1: 0.91-0.96, SEM: 6.49-6.96, SDD: 30.75%-31.61%). For the frequency data, IMF reliability was excellent (healthy: ICC_3,1: 0.91-0.94, SEM: 3.45-7.27 Hz, SDD: 9.56%-20.14%/patients: ICC_3,1: 0.90-0.94, SEM: 6.41-7.59 Hz, SDD: 17.75%-21.02%) and of MF raw and normalised slopes was good (healthy: ICC_3,1: 0.78-0.82, SEM: 4.93-6.02 Hz, SDD: 13.66-16.67%/LBP-patients: ICC_3,1: 0.83-0.85, SEM: 6.75-7.47 Hz, SDD: 18.69%-20.69%). However, the reliability for RMS data presented unacceptably high SDD values and were not considered further. For discriminative validity, less MVIC and less steep MFslopes were registered for the patient group (P < 0.01).

CONCLUSION

Reliability and discriminative ability of paraspinal strength and EMG-related frequency parameters were demonstrated in healthy participants and patients with LBP.

Chronic Pain Diagnosis Using Machine Learning, Questionnaires, and QST: A Sensitivity Experiment

In the last decade, machine learning has been widely used in different fields, especially because of its capacity to work with complex data. With the support of machine learning techniques, different studies have been using data-driven approaches to better understand some syndromes like mild cognitive impairment, Alzheimer’s disease, schizophrenia, and chronic pain. Chronic pain is a complex disease that can recurrently be misdiagnosed due to its comorbidities with other syndromes with which it shares symptoms. Within that context, several studies have been suggesting different machine learning algorithms to classify or predict chronic pain conditions. Those algorithms were fed with a diversity of data types, from self-report data based on questionnaires to the most advanced brain imaging techniques. In this study, we assessed the sensitivity of different algorithms and datasets classifying chronic pain syndromes. Together with this assessment, we highlighted important methodological steps that should be taken into account when an experiment using machine learning is conducted. The best results were obtained by ensemble-based algorithms and the dataset containing the greatest diversity of information, resulting in area under the receiver operating curve (AUC) values of around 0.85. In addition, the performance of the algorithms is strongly related to the hyper-parameters. Thus, a good strategy for hyper-parameter optimization should be used to extract the most from the algorithm. These findings support the notion that machine learning can be a powerful tool to better understand chronic pain conditions.

The influence of age on spinal and lower limb muscle activity during repetitive lifting

This study investigated the effects of age on upper erector spinae (UES), lower erector spinae (LES) and lower body (gluteus maximus; biceps femoris; and vastus lateralis) muscle activity during a repetitive lifting task. Twenty-four participants were assigned to two age groups: 'younger' (n = 12; mean age ± SD = 24.6 ± 3.6 yrs) and 'older' (n = 12; mean age = 46.5 ± 3.0 yrs). Participants lifted and lowered a box (13 kg) repetitively at a frequency of 10 lifts per minute for a maximum of 20 min. EMG signals were collected every minute and normalised to a maximum voluntary isometric contraction. A submaximal endurance test of UES and LES was used to assess fatigue. Older participants showed higher levels of UES and LES muscle activity (approximately 12-13%) throughout the task, but less fatigue compared to the younger group post-task completion. When lifting, lower-limb muscle activity was generally higher in older adults, although temporal changes were similar. While increased paraspinal muscle activity may increase the risk of back injury in older workers when repetitive lifting, younger workers may be more susceptible to fatigue-related effects. Education and training in manual materials handling should consider age-related differences when developing training programmes.

Effects of a Pilates protocol in individuals with non-specific low back pain compared with healthy individuals: Clinical and electromyographic analysis

BACKGROUND

Electromyography may be useful for assessing and understanding trunk muscle activation, and Pilates is commonly used as a treatment for low back pain. The objective of this study was to verify electromyography of trunk muscles after a Pilates protocol in individuals with non-specific low back pain and in healthy individuals.

METHODS

Volunteers were divided into two groups: non-specific low back pain (n = 19) and clinically healthy (n = 16) groups. Clinical assessments, classification of patients into subgroups, electromyography evaluations of the right lumbar extensor and right transverse abdominal/internal oblique muscle of the abdomen were performed before and after an 8-week Pilates protocol.

FINDINGS

Comparisons were made before and after the protocol and with the control group. There was significant improvement in pain, flexibility, resistance and strength of trunk muscles. In addition, after the Pilates, there was a decrease in the time elapsed between the onset and peak of lumbar muscle activation during the evaluation of trunk extension in the low back pain group, coming closer to the time of the abdominal muscle, as it also occurred in the control group.

INTERPRETATION

Pilates caused clinical improvement and balanced trunk muscle activation in the low back group, becoming similar to that of the control group. Furthermore, the effects of the proposed protocol were the same between the groups. Thus, Pilates may be indicated for management of non-specific low back pain.

Kinematic chain reactions on trunk and dynamic postural steadiness in subjects with recurrent low back pain

Although subjects with recurrent low back pain (LBP) demonstrate altered trunk control, the kinematic and kinetic responses of the trunk have not been carefully investigated. This study was conducted to compare the standing time, spine range of motion (ROM), and dynamic postural steadiness index (DPSI) based on visual condition between subjects with and without recurrent LBP during upright one leg standing. Sixty-three individuals participated in the study, including 34 control subjects and 29 subjects with recurrent LBP. The DPSI was a composite of the medio-lateral (MLSI), anterior-posterior (APSI), and vertical steadiness indices (VSI) on a force platform. The control group demonstrated longer standing time (s) during the eyes-open condition than the LBP group (26.82±6.03 vs. 19.87±9.36; t=2.96, p=0.01). Regarding spine ROM, visual condition was significantly different between groups (F=7.09, p=0.01) and demonstrated interactions with spine region and group (F=5.53, p=0.02). For the kinetic measures, there was a significant interaction between visual conditions and indices (F=25.30, p=0.001). In the LBP group, the DPSI was significantly correlated with the MLSI (r=0.59, p=0.002), APSI (r=0.44, p=0.03), and VSI (r=0.98, p=0.01) in the eyes-closed condition. Overall, the results of this study indicated that the LBP group decreased thorax and lumbar spine rotations during the eyes-closed condition. The LBP group also demonstrated positive correlations with the kinetic indices, enhancing dynamic postural steadiness in the eyes-closed condition in order to possibly avoid pain or further injury. This dynamic postural steadiness strategy is necessary to improve kinetic and kinematic chain reactions in the LBP group. This compensatory pattern supports the development of optimal postural correction strategies to prevent LBP recurrence and might represent a chain reaction to protect trunk control without visual input.

Are lumbar multifidus fatigue and transversus abdominis activation similar in patients with lumbar disc herniation and healthy controls? A case control study

PURPOSE

The aims of this study were to assess lumbar multifidus fatigue (LM) and transversus abdominis activation (TrA) in individuals with lumbar disc herniation associated with low back pain.

METHODS

Sixty individuals were divided into the lumbar herniation (LHG, n = 30) and control groups (CG, n = 30). Fatigue of the LM was assessed using surface electromyography during the Sorensen effort test, and activation of the TrA with a pressure biofeedback unit. Pain intensity was determined using a visual analog scale and the McGill pain questionnaire. The Oswestry disability questionnaire and the Borg scale for self-evaluating exertion were used to assess functional disability.

RESULTS

Fatigue was significantly more intense and the TrA activation was insufficient (p < 0.01) in individuals with disc herniation relative to the control group. The LHG had mild functional disability and moderate pain. There were differences in the initial exertion self-evaluation between groups, which were not observed in the final exertion evaluation.

CONCLUSION

Individuals with lumbar disc herniation associated with low back pain have increased fatigue of the LM and decreased activation of the TrA, when compared to the control group.

Validity and everyday clinical applicability of lumbar muscle fatigue assessment methods in patients with chronic non-specific low back pain: a systematic review

PURPOSE

This systematic literature review aimed at examining the validity and applicability in everyday clinical rehabilitation practise of methods for the assessment of back muscle fatiguability in patients with chronic non-specific low back pain (CNSLBP).

METHODS

Extensive research was performed in MEDLINE, Cumulative Index of Nursing and Allied Health Literature (CINAHL), Embase, Physiotherapy Evidence Database (PEDro) and Cochrane Central Register of Controlled Trials (CENTRAL) databases from their inception to September 2014. Potentially relevant articles were also manually looked for in the reference lists of the identified publications. Studies examining lumbar muscle fatigue in people with CNSLBP were selected. Two reviewers independently selected the articles, carried out the study quality assessment and extracted the results. A modified Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) scale was used to evaluate the scientific rigour of the selected works.

RESULTS

Twenty-four studies fulfilled the selection criteria and were included in the systematic review. We found conflicting data regarding the validity of methods used to examine back muscle fatigue. The Biering-Sorensen test, performed in conjunction with surface electromyography spectral analysis, turned out to be the most widely used and comparatively, the most optimal modality currently available to assess objective back muscle fatigue in daily clinical practise, even though critical limitations are discussed.

CONCLUSIONS

Future research should address the identification of an advanced method for lower back fatigue assessment in patients with CNSLBP which, eventually, might provide physical therapists with an objective and reliable test usable in everyday clinical practise. Implications for Rehabilitation Despite its limitations, the Biering-Sorensen test is currently the most used, convenient and easily available fatiguing test for lumbar muscles. To increase validity and reliability of the Biering-Sorensen test, concomitant activation of synergistic muscles should be taken into account. Pooled mean frequency and half-width of the spectrum are currently the most valid electromyographic parameters to assess fatigue in chronic non-specific low back pain. Body mass index, grading of pain and level of disability of the study population should be reported to enhance research quality.

Postural strategy and trunk muscle activation during prolonged standing in chronic low back pain patients

Prolonged standing has been associated with development and aggravation of low back pain (LBP). However, the underlying mechanisms are not well known. The aim of the present study was to investigate postural control and muscle activation during and as a result of prolonged standing in chronic LBP (cLBP) patients compared to healthy controls (HCs). Body weight shifts and trunk and hip muscle activity was measured during 15 min standing. Prior and after the standing trial, strength, postural sway, reposition error (RE), flexion relaxation ratio (FRR), and pain were assessed and after the prolonged standing, ratings of perceived exertion. During prolonged standing, the cLBP patients performed significantly more body weight shifts (p<.01) with more activated back and abdominal muscles (p=.01) and similar temporal variability in muscle activation compared to HCs, while the cLBP patients reported more pain and perceived exertion at the end of prolonged standing. Moreover, both groups had a similar change in strength, postural sway, RE and FRR from before to after prolonged standing, where changes in HC were towards pre-standing values of cLBP patients. Thus, despite a more variable postural strategy, the cLBP patients did not have higher muscle activation variability, but a general increased muscle activation level. This may indicate a reduced ability to individually deactivate trunk muscles. Plausibly, due to the increased variable postural strategy, the cLBP patients could compensate for the relatively high muscle activation level, resulting in normal variation in muscle activation and normal reduction in strength, RE and FRR after prolonged standing.

The effects of bag style on muscle activity of the trapezius, erector spinae and latissimus dorsi during walking in female university students

Back pain is common in adolescents which has been associated with carrying a bag. However, there is little research examining the effects of bag style in female adolescents. The aim of the study was to investigate the effects of different bag conditions on muscle activity of the trapezius, erector spinae and latissimus dorsi muscles in female university students during walking. Twelve female university students walked on a treadmill for 5 minutes at 1.1 m/s during five conditions; control, 1 strapped rucksack, 2 strapped rucksack, ipsilateral shoulder strap and contralateral shoulder strap, each containing 10% bodyweight. Electromyography for the trapezius, erector spinae and latissimus dorsi was recorded for the last 30 s of each condition. Two-way ANOVA and paired t-tests were used to identify differences between right and left muscles and between bag conditions. Results showed that muscle activity of the left trapezius was significantly higher than the right trapezius during the 1 strap rucksack condition. For the left trapezius, the 2 strapped rucksack and the control condition had significantly lower muscle activity compared to the 1 strapped rucksack and the ipsilateral shoulder strap. For the left erector spinae muscle, there was significantly greater muscle activity when wearing the contralateral shoulder strap compared to the control. For the right erector spinae, significantly lower muscle activity was observed when wearing the 2 strapped rucksack compared to the ipsilateral shoulder strap and contralateral shoulder strap. There were no significant differences in muscle activity of the latissimus dorsi muscles between any of the bag conditions. These findings suggest that a two strapped rucksack should be used when carrying loads to reduce spinal muscle activity which may, in turn, reduce reports of back pain in female adolescents.

Age-related differences do affect postural kinematics and joint kinetics during repetitive lifting

BACKGROUND

Age is considered a risk factor for manual handling-related injuries and older workers incur higher injury-related costs than younger co-workers. This study investigated the differences between the kinematics and kinetics of repetitive lifting in two groups of handlers of different ages.

METHODS

Fourteen younger (mean 24.4 yr) and 14 older (mean 47.2 yr) males participated in the study. Participants repetitively lifted a box weighing 13 kg at a frequency of 10 lifts/min for a maximum of 20 min. Postural kinematics (joint and lumbosacral angles and angular velocities) and kinetics (joint moments) were measured throughout the lifting task using motion analysis and ground reaction forces. Muscle fatigue of the erector spinae was assessed using electromyography.

FINDINGS

Peak lumbosacral, trunk, hip and knee flexion angles differed significantly between age groups over the duration of the task, as did lumbosacral and trunk angular velocities. The younger group increased peak lumbar flexion by approximately 18% and approached 99% of maximum lumbosacral flexion after 20 min, whereas the older group increased lumbar flexion by 4% and approached 82% maximum flexion. The younger group had a larger increase in peak lumbosacral and trunk angular velocities during extension, which may be related to the increased back muscle fatigue observed among the younger group.

INTERPRETATION

Older participants appeared to control the detrimental effects of fatigue associated with repetitive lifting and limit lumbar spine range of motion. The higher rates of musculoskeletal injury among older workers may stem from a complex interaction of manual handling risk factors.

Properties of Force Output and Spectral EMG in Young Patients with Nonspecific Low Back Pain during Isometric Trunk Extension

[Purpose] To clarify the influence of nonspecific low back pain (NSLBP) on force fluctuation and the myoelectric data of back muscles during isometric trunk extension at low to high force levels. [Subjects] Fourteen male subjects with NSLBP and 14 healthy male control subjects participated in this study. [Methods] All participants extended their trunk isometrically maintaining 10 levels of target force [2, 5, 10, 15, 20, 30, 50, 70, 80 and 90% of maximal voluntary contraction (MVC) in a random order] for about 4 seconds with visual feedback. A force transducer and tri-axis force sensor were positioned at the 7th thoracic vertebra to measure force output and the direction of force. Myoelectric activities of the back muscles (longissimus thoracis, L2 level; multifidus, S1 level) were recorded by surface electromyography. [Results] Force output of NSLBP subjects fluctuated more than that of healthy subjects at 30% and 50%MVC. Higher median power frequency in the multifidus was observed in NSLBP subjects at moderate to high force levels. [Conclusion] These results show that the properties of force output in NSLBP subjects differ from those in healthy subjects, suggesting that the assessment of force fluctuation of back muscles at moderate force levels is a useful index for evaluating and discriminating NSLBP.

Neuromuscular fatigue during high-intensity intermittent exercise in individuals with intellectual disability

This study examined neuromuscular fatigue after high-intensity intermittent exercise in 10 men with mild intellectual disability (ID) in comparison with 10 controls. Both groups performed three maximal voluntary contractions (MVC) of knee extension with 5 min in-between. The highest level achieved was selected as reference MVC. The fatiguing exercise consists of five sets with a maximal number of flexion-extension cycles at 80% of the one maximal repetition (1RM) for the right leg at 90° with 90 s rest interval between sets. The MVC was tested again after the last set. Peak force and electromyography (EMG) signals were measured during the MVC tests. Root Mean Square (RMS) and Median Frequency (MF) were calculated. Neuromuscular efficiency (NME) was calculated as the ratio of peak force to the RMS. Before exercise, individuals with ID had a lower MVC (p<0.05) and a lower RMS (p<0.05). No significant difference between groups in MF and NME. After exercise, MVC decreases significantly in both groups (p<0.001). Individuals with ID have greater force decline (p<0.001 vs. p<0.01). RMS decreased significantly (p<0.001) whereas the NME increased significantly (p<0.05) in individuals with ID, but both remained unchanged in controls. The MF decreased significantly in both groups (p<0.001). In conclusion, individuals with ID presented a lower peak force than individuals without ID. After a high-intensity intermittent exercise, individuals with ID demonstrated a greater force decline caused by neural activation failure. When rehabilitation and sport train ID individuals, they should consider this nervous system weakness.

Association of back pain with hypovitaminosis D in postmenopausal women with low bone mass

Background

Back pain is a major public health problem due to its high frequency, to the resulting activity constraint, and the need for surgery in many cases. Back pain is more frequent in women than men, mainly in postmenopausal women. High prevalence of hypovitaminosis D has been detected in postmenopausal women, and it is associated with decreased bone mass, sarcopenia, vertebral fractures, and inflammation, which can be related to back pain.

Methods

The relation between back pain and hypovitaminosis D was evaluated in this study, as well the difference regarding the number of bedridden days, number of days away from work, and daily activities limitation between women with and without hypovitaminosis D. This study reviewed baseline data from an interventional phase III multicenter trial in low bone mass postmenopausal women. The study included demographic data, 25OHD determinations, Newitt/Cummings questionnaire on back pain, and vertebral fracture identified thought X-ray evaluation.

Results

The trial included 9354 participants, but only 9305 underwent all the evaluations. The age median was 67 (60 - 85 years old) and age at menopause was 49 (18 - 72 years). Hypovitaminosis D was found in 22.5% of the subjects, 15.3% of them had vertebral fractures, 67.5% with back pain, and 14.8% reduced their daily activities in the previous six months. Subjects with hypovitaminosis D, compared to those without hypovitaminosis D, reported more back pain (69.5 v 66.9%, p: 0.022), more cases of severe back pain (8.5% v 6.8%, p: 0,004), higher limitation in their daily activities (17.2 v 14.0%, p: 0.001), and more fractures (17.4 v 14.6%, p: 0,002); also, they had more trouble to perform daily activities addressed in the Newwit/Cummings questionnaire.

Conclusion

Hypovitaminosis D was related to back pain, to its severity, and to difficulty in perform daily activities.

Trial registration

ClinicalTrial.gov: NCT00088010

Disability and back muscle fatigability changes following two therapeutic exercise interventions in participants with recurrent low back pain

Background

The level of disability and endurance of back muscles have been investigated, but there is conflicting evidence following specific exercise interventions for participants with recurrent low back pain (LBP). The purpose of this study was to compare the level of disability and slope of median frequency (MF) of thoracic and lumbar erector spinae (ES) muscles following core stabilization exercise (CSE) and spinal flexibility exercise (SFE).

Material/Methods

In total, 46 individuals participated in this study. There were 25 participants in the CSE intervention group (average age of 47.7±8.9 years) and 21 participants in the SFE group (average age of 53.1±9.0 years). Each group participated in the specific exercise intervention program for 4 weeks while maintaining their current activity and/or exercise levels. The Oswestry Disability Index (ODI) was used to measure the level of disability changes. The fatigability of the ES back muscles was measured by the slope of MF, using a modified Sorensen test.

Results

The disability level decreased significantly following CSE intervention (t=2.23, p<0.05). However, there was no significant difference in muscle fatigability changes in the 4-week intervention period for either group.

Conclusions

The CSE intervention reduced disability level following the 4-week intervention period. Further studies are needed to investigate the effectiveness of specific back muscle exercises in longer intervention periods for back muscle fatigability.

The effect of continuous ultrasound on chronic non-specific low back pain: a single blind placebo-controlled randomized trial

BACKGROUND

Non-specific chronic low back pain (NSCLBP) is one of the most common musculoskeletal disorders around the world including Iran. One of the most widely used modalities in the field of physiotherapy is therapeutic ultrasound (US). Despite its common use, there is still inconclusive evidence to support its effectiveness in patients with NSCLBP. The objective of this study was to evaluate the effect of continuous US compared with placebo US additional to exercise therapy for patients with NSCLBP.

METHODS

In this single blind placebo controlled study, 50 patients with NSCLBP were randomized into two treatment groups: 1) continuous US (1 MHz &1.5 W/cm2) plus exercise 2) placebo US plus exercise. Patients received treatments for 4 weeks, 10 treatment sessions, 3 times per week, every other day. Treatment effects were assessed in terms of primary outcome measures: 1) functional disability, measured by Functional Rating Index, and 2) global pain, measured by a visual analog scale. Secondary outcome measures were lumbar flexion and extension range of motion (ROM), endurance time and rate of decline in median frequency of electromyography spectrum during a Biering Sorensen test. All outcome variables were measured before, after treatment, and after one-month follow-up. An intention to treat analysis was performed. Main effects of Time and Group as well as their interaction effect on outcome measures were investigated using repeated measure ANOVA.

RESULTS

Analysis showed that both groups had improved regarding function (FRI) and global pain (VAS) (P < .001). Lumbar ROM as well as holding time during the Sorensen test and median frequency slope of all measured paravertebral muscles did not change significantly in either group (P > .05). Improvement in function and lumbar ROM as well as endurance time were significantly greater in the group receiving continuous US (P < .05).

CONCLUSIONS

The study showed that adding continuous US to a semi supervised exercise program significantly improved function, lumbar ROM and endurance time. Further studies including a third group of only exercise and no US can establish the possible effects of placebo US.

TRIAL REGISTRATION

NTR2251.

Spectral analysis of EMG using intramuscular electrodes reveals non-linear fatigability characteristics in persons with chronic low back pain

Greater fatigability across lumbar extensors has been reported in persons with chronic low back pain (LBP), however, extensor atrophy tends to be local to the site of pain. Therefore, specific ultrasound guided local and remote intramuscular electromyographic recordings were undertaken during an isometric horizontal trunk hold in two carefully matched cohorts; persons with and without LBP. The test was performed to self-determined maximal hold time, and the control group held the horizontal position longer (P < 0.001). A power spectral analysis was performed to calculate the normalized median frequency (NMF) slope for both the first and last 30s of the fatigue test due to the group difference in hold times. There were no significant group differences in NMF slope at the first 30s of testing (P = 0.650). The NMF slope for the first and last 30s was not different in healthy subjects (P = 0.688), but was different in persons with LBP, illustrated by shallowing of the slope at the last 30s of the test (P = 0.008). A between muscle comparison in the LBP group showed greater non-linear behavior in the deep multifidus (painful region) in contrast to T10 longissimus thoracis (nonpainful region) (P = 0.013). Possible explanations for these findings are discussed.

Lumbar muscle fatigue and subjective health measurements in patients with lumbar disc herniation 2 years after surgery

INTRODUCTION

In this prospective study the purpose was to evaluate patients with lumbar-disc herniation regarding changes in back-muscle fatigue and subjective health measurements 2 years after surgery.

METHODS

Endurance time, EMG median frequency and ratings of lumbar-muscle fatigue and pain were measured before surgery, 4 weeks after and 2 years after surgery in 26 patients (19 men and 7 women) with lumbar-disc herniation. A modified Sørensen test was performed with concurrent recordings of electromyography from the lumbar muscles at four recording sites. The questionnaires Oswestry disability index, Roland-Morris disability questionnaire, Self-efficacy scale, SF-36, Back beliefs questionnaire, Odom and a 6-grade physical activity scale were used.

RESULTS

Two years after surgery the patients had longer endurance times (increase from 178 s to 231 s, p < 0.001), a non-significant tendency for flatter L5 slopes (decrease from -0.20 to -0.16 Hz/s, p < 0.066), higher initial median frequency (L1 increase from 58 to 64 Hz p < 0.001, L5 increase from 76 to 84 Hz p = 0.001) and improved questionnaire scores. The questionnaires Oswestry, Roland-Morris and SF-36 physical functioning correlated with the endurance time 0.69-0.93 and with L5 slope 0.01-0.93 and the highest correlations were found in women.

CONCLUSION

Both EMG and endurance time measurements are needed for evaluating fatigue in lumbar-disc herniation.

Needle EMG Response of Lumbar Multifidus to Manipulation in the Presence of Clinical Instability

A proposed mechanism for the persistence of low back pain due to clinical instability is a decrease in control of local spinal musculature, more specifically decreased recruitment of multifidus. Altered segmental mechanoreceptor input has been proposed as a contributing factor responsible for a decrease in local muscle recruitment. In this case report, immediate changes in the recruitment of the deep multifidus following manipulation were examined using needle EMG and isometric testing of trunk rotational force. Trunk rotational force appeared to improve while the multifidus demonstrated a decrease in activity as measured by needle EMG. No specific conclusions can be drawn from this report; however, the results do suggest that immediate multifidus function may be influenced with manipulation, resulting in improved muscular control of the trunk.

Reliability of measurements of endurance time, electromyographic fatigue and recovery, and associations to activity limitations, in patients with lumbar disc herniation

BACKGROUND

Electromyographic (EMG) spectral parameters and endurance tests for back muscles have long been used to estimate low-back muscle fatigue.

PURPOSE

The present purpose was to evaluate the test-retest reliability of a fatigue-testing protocol and to investigate associations between activity limitations and fatigue in patients with lumbar disc herniation.

METHODS

To evaluate the reliability, endurance time, EMG spectral parameters and ratings of lumbar muscle fatigue and back pain were measured three times in 15 patients with lumbar disc herniation. The patients performed a modified Sørensen test with concurrent recordings of electromyography from the lumbar muscles at four recording sites. Ratings of their perceived fatigue and pain on a Borg scale were collected simultaneously. Recovery over five minutes was recorded. Questionnaires about activity, participation, self-efficacy and health were also used.

RESULTS

Endurance time had an ICC of 0.85 indicating good reliability. Initial, end and median frequency recovery had intraclass correlation coefficients (ICCs) over 0.6 that is acceptable but with large standard errors of measurement. The median frequency slopes for the four recording sites had ICCs of 0.19-0.48. Agreement coefficients for the Borg ratings ranged between 0.78 and 0.97. Moderate correlation was found between activity limitations and endurance time.

CONCLUSIONS

Endurance time measurement and Borg ratings may be recommended for evaluating intervention both with groups of patients, i.e. for research purposes, and for individuals. The median frequency parameters may be recommended for groups only. The study shows the importance of establishing the reliability of the patient category if the results are to be used to evaluate intervention.

Time to task failure of trunk extensor muscles differs with load type

Time to task failure of trunk extensor muscles during seated submaximal isometric exertions was assessed in 18 healthy participants using 2 different load types. One required supporting an inertial load (position-matching task) whereas the 2nd required maintaining an equivalent torque against a rigid restraint (force-matching task). Time to task failure was significantly longer for position-matching tasks compared to the force-matching tasks. This finding is opposite to that reported for the appendicular muscles. A subset of 4 individuals completed a 2nd experiment to test the time to task failure of the elbow flexors in the position- and force-matching tasks. Time to task failure of the elbow flexors was significantly longer for the force-matching tasks compared to position matching. Thus, the same population shows that the effects of load type on time to task failure are opposite for the appendicular and axial muscles. This could be an important issue in understanding the mechanisms of task failure, and the endurance capacity of the trunk extensor muscles.

Análise espectral do sinal eletromiográfico do músculo eretor da espinha obtido do teste de Sorensen

INTRODUÇÃO: A fadigabilidade excessiva dos músculos lombares é um achado comum em pacientes portadores de dor lombar. Por isso, a avaliação da resistência isométrica desses músculos tem sido recomendada nessa população. OBJETIVO: O objetivo deste estudo foi identificar e analisar objetivamente o comportamento da fadiga do músculo eretor da espinha em um teste de resistência isométrica realizado até a exaustão. METODOLOGIA: Nove sujeitos saudáveis realizaram o teste de Sorensen modificado com contrações em intensidades correspondentes a 5%, 10%, 15% e 20% da contração voluntária máxima. A fadiga muscular foi identificada pela análise do comportamento da frequência mediana (FM) em função do tempo. RESULTADOS: O tempo de resistência isométrica foi inversamente correlacionado com a intensidade da contração. Contudo, a intensidade da contração não demonstrou efeito sobre a taxa de declínio da FM. A fadiga muscular foi significante em todas as porções do músculo eretor da espinha. Comparações entre os músculos eretor da espinha direito e esquerdo não revelaram diferenças significantes, enquanto que comparações entre porções do músculo eretor da espinha localizadas em diferentes níveis lombares revelaram maiores níveis de fadiga em L4-L5 bilateralmente. CONCLUSÃO: A análise espectral do sinal eletromiográfico foi eficaz para idenficação da fadiga do músculo eretor da espinha. Também foi possível identificar diferenças funcionais entre as diferentes porções desse músculo. O conhecimento dessas particularidades permite intervir de forma mais específica na prevenção e reabilitação dos distúrbios da coluna lombar.

The eccentric, concentric strength relationship of the hamstring muscles in chronic low back pain

OBJECTIVE

The objective of this study was to measure hamstring muscle eccentric and concentric strength in individuals with and without low back pain (LBP). Two composite scores for the relative balance of eccentric to concentric strength at the different movement velocities were calculated (the DEC and SEC), to determine whether or not self perceived pain, disability, or fear avoidance measures were associated with hamstring strength characteristics.

DESIGN

Cross-sectional repeated measures design.

SETTING

University laboratory.

PARTICIPANTS

Fifteen individuals with chronic LBP and 15 matched controls.

MAIN OUTCOME MEASURES

Isokinetic eccentric and concentric strength at 30 degrees s(-1) and 120 degrees s(-1)(.) Composite scores (DEC and SEC) based on peak torque were calculated to evaluate the relationship between the different muscle actions across the test velocities. Self report measures included the Oswestry disability index, general health and well being, fear avoidance, and pain.

RESULTS

Eccentric/concentric strength ratio at 30 degrees s(-1) was higher for the LBP group (F(1,58)=4.81, p=0.032). The SEC was also higher for the LBP (F(1,58)=5.97, p=0.018). Fear avoidance beliefs and mental well-being were significantly associated with the SEC only in the LBP group (adjusted r(2)=0.26, (F(2,27)=5.8, p=.008). For the control group both the DEC and SEC were associated with self report measures. Matched differences between groups' for the SEC were best explained by fear avoidance beliefs about work (adjusted r(2)=0.12, F(1,28)=5.1, p=0.03).

CONCLUSION

Reduced concentric relative to eccentric strength is best identified by the SEC. The SEC was significantly associated with impaired self report measures of fear avoidance and mental well being in individuals with LBP. Differences between groups for the SEC were best explained by fear avoidance beliefs about work.

Postural control during prolonged standing in persons with chronic low back pain

Prolonged standing has been associated with the onset of low back pain symptoms in working populations. So far, it is unknown how individuals with chronic low back pain (CLBP) behave during prolonged unconstrained standing (PS). The aim of the present study was to analyze the control of posture by subjects with CLBP during PS in comparison to matched healthy adults. The center of pressure (COP) position of 12 CLBP subjects and 12 matched healthy controls was recorded in prolonged standing (30min) and quiet stance tasks (60s) on a force plate. The number and amplitude of COP patterns, the root mean square (RMS), speed, and frequency of COP sway were analyzed. Statistical analyses showed that CLBP subjects produced less postural changes in the antero-posterior direction with decreased postural sway during the prolonged standing task in comparison to the healthy group. Only CLBP subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS, COP speed and COP frequency in the quiet standing trial after the prolonged standing task in comparison to the pre-PS trial. The present study provides additional evidence that individuals with CLBP might have altered sensory-motor function. Their inability to generate responses similar to those of healthy subjects during prolonged standing may contribute to CLBP persistence or an increase risk of recurrent back pain episodes. Moreover, quantification of postural changes during prolonged standing could be useful to identify CLBP subjects prone to postural control deficits.

Different parts of erector spinae muscle fatigability in subjects with and without low back pain

BACKGROUND CONTEXT

There is conflicting evidence regarding erector spinae muscle fatigability because previous studies have not considered the thoracic and lumbar components separately. These muscles have very different mechanical responses and, therefore, would be recruited differentially for the chosen task.

PURPOSE

The present study was conducted to compare whether fatigability differences exist in the thoracic and lumbar parts of the erector spinae muscles in subjects with and without low back pain (LBP).

STUDY DESIGN

This cross-sectional study was conducted in the Motion Analysis Lab at Cleveland State University.

PATIENT SAMPLE

The study sample included 40 subjects with LBP and 40 subjects without LBP.

OUTCOME MEASURES

The fatigability of the erector spinae muscles was compared based on median frequency of electromyography (EMG) versus time. The level of pain of each subject was also compared using the Oswestry Disability Index.

METHODS

Fatigue measurements were evaluated between groups based on the assessed sides as well as the thoracic and lumbar parts of the erector spinae muscles using surface EMG. A modified version of the isometric fatigue test as introduced by Sorensen was used to test the endurance of the erector spinae muscles.

RESULTS

There were significant median EMG frequency (F((1, 78))=28.82, p=.001) differences in the thoracic and lumbar parts of the erector spinae muscles between subjects with and without LBP. The thoracic part had a significantly lower median EMG frequency than the lumbar part in subjects with LBP. The thoracic and lumbar parts of the erector spinae muscles had interactions with group (F((1, 78))=47.88, p=.01] and age (F((1, 78))=16.51, p=.01).

CONCLUSIONS

The results of this study suggested that subjects with LBP demonstrated higher fatigability of the erector spinae muscles at the thoracic part than at the lumbar part. The increased fatigability of the thoracic part needs to be emphasized in rehabilitation strategies for subjects with LBP. In addition, as age increased, the median frequency of the lumbar part of the erector spinae muscles significantly decreased. Understanding the anatomical and biomechanical characteristics of the erector spinae muscle may enhance clinical outcomes and rehabilitation strategies for subjects with LBP.

The assessment of back muscle capacity using intermittent static contractions. Part I – Validity and reliability of electromyographic indices of fatigue

INTRODUCTION

Back muscle capacity is impaired in chronic low back pain patients but no motivation-free test exists to measure it. The aims of this study were to assess the reliability and criterion validity of electromyographic indices of muscle fatigue during an intermittent absolute endurance test.

METHODS

Healthy subjects (44 males and 29 females; age: 20-55 yrs) performed three maximal voluntary contractions (MVC) and a fatigue test while standing in a static dynamometer. Surface EMG signals were collected from four pairs of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). The fatigue test, assessing absolute endurance (90-Nm torque), consisted in performing an intermittent extension task to exhaustion. Strength was defined as the peak MVC whereas our endurance criterion was defined as the time to reach exhaustion (Tend) during the fatigue test. From the first five min (females) or ten min (males) of EMG data, frequency and time-frequency domain analyses were applied to compute various spectral indices of muscle fatigue.

RESULTS

The EMG indices were more reliable when computed from the time-frequency domain than when computed from the frequency domain, but showed comparable correlation results (criterion validity) with Tend and Strength. Some EMG indices reached moderate to good correlation (range: 0.64-0.69) with Tend, lower correlations (range: 0.39-0.55) with Strength, and good to excellent between-day test-retest reliability results (intra-class correlation range: 0.75-0.83). The quantification of the spectral content more locally in different frequency bands of the power spectrum was less valid and reliable than the indices computed from the entire power spectrum. Differences observed among muscles were interpreted in light of specific neuromuscular activation levels that were observed during the endurance test. These findings supported the use of an intermittent and time-limited (5-10min) absolute endurance test, that is a practical way to assess the back capacity of chronic low back pain subjects, to assess absolute endurance as well as strength with the use of electromyographic indices of muscle fatigue.

Back and hip extensor muscles fatigue in healthy subjects: task-dependency effect of two variants of the Sorensen test

Paraspinal muscle fatigability during various trunk extension tests has been widely investigated by electromyography (EMG), and its task-dependency is established recently. Hip extensor muscle fatigability during the Sorensen test has been reported. The aim of the present experiments was to evaluate the task-dependency of back and hip extensor muscle fatigue during two variants of the Sorensen test. We hypothesized that the rate of muscular fatigue of the hip and back extensor muscles varies according to the test position. Twenty healthy young males with no history of low back pain volunteered to participate in this cross-sectional study. They were asked to perform two body weight-dependent isometric back extension tests (S1 = Sorensen test; S2 = modified Sorensen on a 45 degrees Roman chair). Surface EMG activity of the paraspinal muscles (T10 and L5 levels) and hip extensor muscles (gluteus maximus; biceps femoris) was recorded, and muscular fatigue was assessed through power spectral analysis of the EMG data by calculating the rate of median power frequency change. We observed hip extensor muscle fatigue simultaneously with paraspinal muscle fatigue during both Sorensen variants. However, only L5 level EMG fatigue indices showed a task-dependency effect between S1 and S2. Hip extensor muscles appear to contribute to load sharing of the upper body mass during both Sorensen variants, but to a different extent because L5 level fatigue differs between the Sorensen variants. Our findings suggest that task-dependency has to be considered when EMG variables are compared between two types of lumbar muscle-fatiguing tasks.

Electromyography for assessment of pain in low back muscles

BACKGROUND AND PURPOSE

Pain is currently evaluated with "subjective" methods (eg, patient self-report). This study aimed to test whether fatigue indexes are able to accurately discriminate between subjects with and subjects without low back pain.

SUBJECTS

Sixty subjects separated into 2 groups--a group with low back pain (n=30) and a group without low back pain (n=30)--participated in this study.

METHODS

Electromyographic (EMG) and force data were obtained during a muscle fatigue test. The same test was repeated to monitor recovery. Linear regression analysis was used to obtain fatigue indexes.

RESULTS

Subjects with pain produced significantly lower force values than those without pain. The use of fatigue indexes and force values permitted accurate classification in 89.5% of cases.

DISCUSSION AND CONCLUSION

The results confirm that subjects with pain show early myoelectrical manifestations of muscle fatigue and that EMG can be a useful tool in the evaluation of low back pain.

Comparação da fadiga eletromiográfica dos músculos paraespinhais e da cinemática angular da coluna entre indivíduos com e sem dor lombar

Indivíduos com dor lombar têm redução na força e na resistência dos músculos paraespinhais. A avaliação da fadiga e da resistência dos músculos paraespinhais é importante, uma vez que tem sido reportado que indivíduos com lombalgia desenvolvem um déficit no condicionamento físico que influencia na força e na função do tronco. Além disso, ainda é incerto a relação da fadiga dos paraespinhais e o ângulo de flexão anterior de tronco. Os objetivos deste estudo foram comparar a fadiga em indivíduos com e sem dor lombar e correlacionar a fadiga com o ângulo de flexão anterior de tronco. O grupo lombalgia foi composto por dez indivíduos com diagnóstico médico exclusivo de lombalgia. O grupo controle foi composto por dez indivíduos que possuíam características físicas semelhantes. Inicialmente avaliou-se a flexão anterior de tronco dos indivíduos pelo método angular de Whistance. A fadiga dos músculos paraespinhais foi avaliada nas alturas de L1 e L5 por meio da eletromiografia de superfície em duas cargas: 50 e 75% da contração isométrica voluntária máxima. Os resultados do estudo indicaram que o grupo lombalgia apresentou menor força durante os testes de contração isométrica voluntária máxima (P < 0,004). Embora o grupo lombalgia tenha apresentado maior valor de fadiga, não houve diferença estatisticamente significante entre os dois grupos para as alturas de L1 e L5 nas duas cargas. As correlações entre a fadiga e o ângulo de flexão anterior de tronco mostraram-se de fracas a moderadas (valores entre r = -0,58 a 0,51). Estes achados indicam que ambos os grupos fadigam, entretanto o grupo lombalgia apresentou maior fadiga. Além disso, não se pode predizer a fadiga por meio do ângulo de flexão anterior de tronco.

Gender specific activation patterns of trunk muscles during whole body tilt

Gender specific differences as evidenced in both anthropometric data and physical performance of healthy persons have been broadly demonstrated. Recently advancements in surface electromyography (SEMG) have shown possible differences in men's and women's muscle coordination patterns. However, quantitative information about gender related muscle co-ordination patterns are rare. This investigation was carried out to both verify if trunk muscle SEMG amplitude-force relationship differs between men and women and refine techniques of measurement and data analysis using SEMG. Thirty-one healthy volunteers (16 women, 15 men) were investigated during whole body tilt at angles from 5 degrees to 90 degrees (from quasi vertical to horizontal position). Subjects had to maintain body in body axis while their lower body was fixed and the upper body remained unsupported. SEMG was taken from five different trunk muscles of both sides simultaneously. At corresponding tilt angles women exhibited higher amplitude levels of their abdominal muscles in comparison to men, who were characterized by higher back muscle amplitudes. Abdominal muscles showed a non-linear SEMG amplitude-force relationship but differed between genders with more linearity in women. Back muscles showed a linear amplitude-force relationship with no differences between genders. Women were characterized by higher levels of co-contraction of all investigated muscles. The data are in accordance with histological investigations, which already proved specific fiber distribution patterns in both abdominal and back muscles and gender related differences in relative area of Type 1 fibers of back muscles. The observed differences in SEMG-force relationship for the abdominal muscles remain hypothetical because of lack of histological information.

Impaired neck motor function and pronounced pain-related fear in helicopter pilots with neck pain - a clinical approach

There is recognition that neck pain is a significant clinical problem in military aviation. In the present trial, the objectives were to explore neck motor function and pain-related fear in pilots with differing progression of neck pain. Seventy-two military helicopter pilots were enrolled: 20 had acute ongoing neck pain, 27 had subacute pain, and 25 were pain-free controls. Neck-flexor electromyography activity (root-mean-square) during staged active craniocervical flexion, median power frequency during sustained neck-flexor contraction, cervical range of motion, rating of perceived exertion after sustained flexor contraction, and rated fear-avoidance beliefs about physical activity were estimated. Main effects emerged for flexor activity, fear-avoidance and range of motion, but not for median frequency variables or perceived exertion. Post hoc testing showed that, compared to controls, both pain groups had greater flexor activity at higher stages of craniocervical flexion while the acute group had higher fear-avoidance and less range of motion in axial rotation and flexion-extension, all P<0.01. Discriminant regression revealed a sensitivity/specificity of 87%/71% (neck-pain/controls), with the flexor activity superior. The results indicate that altered neuromotor synergies are present at different progressions of pain. The tracing of such aberrant activity and fear-avoidance beliefs is suggested in future screening and neck intervention research.

Task dependency in back muscle fatigue--correlations between two test methods

BACKGROUND

Various test methods which engage the back muscles in different tasks have been used in studies of back muscle fatigue with electromyography. The present objective was to study task dependency in lumbar muscle fatigue by comparing two test methods.

METHODS

In this cross-sectional study, 22 healthy subjects performed a seated (45s) and a prone test (to the limit of endurance) of back muscle fatigue in randomised order. Fatigue of the lumbar muscles was assessed using electromyography spectral variables and ratings of back muscle fatigue (Borg scale). Linear regression of the median frequency during contraction, and conventional statistical tests of group differences and correlations were used.

FINDINGS

Significant differences (P<0.001) between the seated and the prone test were found for the initial median frequency, the slope, the median frequency decrease during the whole contraction, and for the ratings. However, correlation coefficients between the seated and the prone test were low for the median frequency decrease (r=0.42), absent for the slopes of median frequency (r=-0.08), higher for the Borg ratings (r(s)=0.51; P<0.05) and highest for the initial median frequency (r=0.69; P<0.05). Within each test, correlations between the Borg ratings and the electromyography variables were essentially absent (r<0.19).

INTERPRETATION

Electromyography variables assessed in one type of task in a fatiguing test may not be valid for other types of fatiguing tasks, for example in daily life work situations. Thus task dependency has to be considered when using surface electromyography in determining lumbar muscle fatigue. Ratings of fatigue, however, seem to be less task dependent than the electromyography variables.

Low levels of physical activity in back pain patients are associated with high levels of fear-avoidance beliefs and pain catastrophizing

BACKGROUND AND PURPOSE

Fear-avoidance beliefs are important determinants for disability in patients with non-specific low-back pain (LBP). The association with self-reported level of physical activity is less known. The aim of the present study was to describe the level of physical activity in patients with chronic non-specific LBP and its relation to fear-avoidance beliefs and pain catastrophizing.

METHOD

A cross-sectional study on 64 patients with chronic non-specific LBP in primary healthcare. The variables measured and the questionnaires used were: level of physical activity (six-graded scale); activity limitations (Roland Morris Disability Questionnare (RDQ)); fear-avoidance beliefs (Tampa Scale of Kinesiophobia (TSK) 13-item and sub-scales 'activity avoidance' and 'somatic focus'); and pain catastrophizing (Pain Catastrophizing Scale (PCS)). The level of physical activity was dichotomised into low and high physical activity. Individual median scores on the TSKandPCSscales were used to group the patients into different levels offear-avoidance beliefs and pain catastrophizing. Univariate logistic regressions were used to calculate odds ratios for having low physical activity.

RESULTS

Patients with low physical activity had significantly higher scores in fear-avoidance beliefs and pain catastrophizing (p < 0.05). Odds ratios for low level of physical activity were between 4 and 8 (p < 0.05) for patients with high fear-avoidance beliefs or medium/high pain catastrophizing.

CONCLUSIONS

This study indicates that it seems important for physiotherapists in primary care to measure levels of fear-avoidance beliefs or pain catastrophizing. In particular, the two subscales of the TSK could be of real value for clinicians when making treatment decisions concerning physical exercise therapy for patients with chronic LBP.

A proposta biomecânica para a avaliação de sobrecarga na coluna lombar: efeito de diferentes variáveis demográficas na fadiga muscular

OBJETIVOS: Analisar a fadiga de músculos lombares e determinar as variáveis demográficas relacionadas com a fadiga destes músculos. MÉTODOS: A atividade eletromiográfica (EMG) dos músculos iliocostal direito (IL-D), iliocostal esquerdo (IL-E), multífido direito (MU-D) e multífido esquerdo (MU-E) de 18 voluntários foi captada durante contrações isométricas sub-máximas. Valores de root mean square (RMS) e freqüência mediana (FM) foram correlacionados com o tempo de resistência isométrica (TRI). Slopes de RMS positivos e de FM negativos indicaram a ocorrência da fadiga muscular. Procedimentos de regressão múltipla foram realizados para verificar as variáveis demográficas relacionadas com a fadiga muscular. RESULTADOS: A fadiga foi identificada em todos os músculos e intensidades de contração (p<0.01), exceto no MU-E em 5% na análise do slope de RMS. Diferenças significantes foram encontradas entre o TRI de 5% e 15% (p=0.01), 5% e 20% (p=0.0002). Níveis de fadiga mais elevados estiveram bilateralmente presentes nos músculos multífidos na análise do slopes de FM. A associação do TRI, da idade e da massa corporal dos voluntários foi identificada como fator determinante para a ocorrência da fadiga nos músculos avaliados. CONCLUSÕES: Intervenções destinadas ao tratamento de problemas na coluna lombar devem considerar os vários fatores responsáveis pela fadiga dos músculos desta região.

A Meta-Analytic Review of Surface Electromyography Among Persons With Low Back Pain and Normal, Healthy Controls

Significant differences in surface electromyography (SEMG) have been reported between persons with low back pain (LBP) and normal, healthy controls. This manuscript presents a systematic meta-analytic review of studies examining SEMG differences between these groups. Forty-four articles were identified using MEDLINE and a review of reference lists in articles. For static SEMG, the largest effect size was observed for SEMG while standing, with subjects having LBP demonstrating higher SEMG. The effect size for flexion/relaxation measures was found to be very high (d = -1.71). Studies examining SEMG during isometric exercise or muscle recovery following exercise produced inconsistent findings. Sensitivity and specificity of SEMG for dynamic SEMG measures averaged 88.8% and 81.3%. Most classification schemes were statistically determined and utilized a combination of measures. Only one published study prospectively validated a classification scheme. SEMG measures of flexion-relaxation appear to distinguish LBP subjects from controls with good accuracy, and the sensitivity and specificity of SEMG can be increased by using multiple measures. Further research is needed to determine the combination of measures that are cost-effective, reliable, valid and discriminate with a high degree of accuracy between healthy persons and those with LBP.

PERSPECTIVE

SEMG is a simple and noninvasive measure of muscle activity. SEMG measures hold promise as an objective marker of LBP.

Back extensor muscle fatigue in patients with lumbar disc herniation. Pre-operative and post-operative analysis of electromyography, endurance time and subjective factors

We investigated back muscle fatigue and endurance in patients with lumbar disc herniation before and after surgery, and established the degree of association between perceived fatigue and objectively measured fatigue. Additionally, the relationships between muscle fatigue and endurance time on the one hand, and activity, participation, self-efficacy and health on the other, were investigated to clarify the grades of association between these factors. Forty-three consecutive patients with lumbar disc herniation were tested before surgery and 4 weeks after surgery. The protocol comprised an isometric endurance test (modified Sørensen's test) with concomitant measures of electromyography, and Borg ratings of pain and fatigue. To measure activity, participation, self-efficacy and health, the patients also filled in questionnaires. Results showed a post-operatively significant improvement in lumbar muscle fatigue expressed as a flatter L5 slope for the men. No significant improvement was found for endurance times or for Borg ratings. Endurance time correlated with questionnaire answers on physical activity, the Roland-Morris, the Oswestry, self-efficacy and some items of the SF-36 with correlation coefficients ranging from 0.52 to 0.91. The L5 slope correlated with the Roland-Morris, the Oswestry and some items of the SF-36 only in women with correlation coefficients between 0.53 and 0.77. We conclude that the effects of surgery reduced muscle fatigue for the men. There is an association between muscle fatigue and endurance with activity limitations, participation restrictions, self-efficacy and health in patients undergoing surgery for lumbar disc herniation.

Effects of evoked pain on the electromyogram and compound muscle action potential of the brachial biceps muscle

Muscle pain is often accompanied by a feeling of muscle fatigue and weakness. We examined the effect of experimental muscle pain on the electromyogram (EMG) during maximal voluntary contraction (MVC), and on the compound muscle action potential (CMAP) of the brachial biceps muscle. Twenty-one healthy subjects were injected intramuscularly with 0.1 ml/30 microg of the vanilloid receptor agonist (capsaicin) or 0.2 ml of 5% hypertonic saline. A Teflon-coated cannulated EMG needle was used to record the EMG interference pattern (IP) at MVC. The CMAP of the brachial biceps muscle was obtained by stimulation of the musculocutaneous nerve at the axilla using surface electrodes. Amplitude, mean frequency of the power spectrum, and turns/s of the interference pattern were reduced after pain induced by capsaicin or hypertonic saline. Latency, amplitude, and area-under-curve of the CMAP did not change after injection of either substance. Acute stimulation of muscle nociceptors thus produced a fatiguelike change in the interference pattern during MVC, possibly due to a decrease in motoneuron firing rate and increased muscle fatigability.