Trunk motor variability in patients with non-specific chronic low back pain

Fatigue and recovery-related changes in postural and core stability in sedentary employees: a study protocol

Prolonged sitting leads to a slumped posture, which indirectly influences spinal curvature and increases low back and hamstring stiffness. Active rather than passive recovery is an effective way to reduce the risks associated with such prolonged inactivity. However, it remains to be investigated which of the exercises frequently used for this purpose, the trunk stability and foam rolling exercise, is more beneficial. This protocol study will compare the effects of foam rolling exercises on the recovery of impaired core and postural stability induced by core muscle fatigue and hamstring muscle stiffness with those of trunk stabilization exercises in sedentary adults. Twenty sedentary adults ranging in age from 25 to 44 years old, comprising 50% men and 50% women, will participate in a modified Abt's trunk muscle fatigue protocol, then proceed with (1) active recovery in the form of trunk stabilization exercises, (2) active recovery in the form of foam rolling exercises, and (3) passive recovery, entails lying on a bed, respectively. Pre-fatigue, post-fatigue, and after all three recovery modalities, core and postural stability, and back and hamstring muscle flexibility will be evaluated using an inertial sensor system, and a posturography system. Muscle-fatigue conditions will be determined using electromyogram signals. Although the effects of foam rolling and trunk stabilization exercises can be attributed to different physiological mechanisms, the former releasing myofascial to improve flexibility and reduce muscle tension, the latter strengthening core muscles to stabilize posture, we hypothesize that both are equivalently effective in reducing the consequences of prolonged sitting.

Analysis of muscle synergies and muscle network in sling exercise rehabilitation technique

The study assessed motor control strategies across the four sling exercises of supine sling exercise (SSE), prone sling exercise (PSE), left side-lying sling exercise (LLSE), and right side-lying sling exercise (RLSE) positions base on the muscle synergies and muscle network analyses. Muscle activities of bilateral transversus abdominis (TA), rectus abdominis, multifidus (MF), and erector spinae (ES) were captured via surface electromyography. Muscle synergies were extracted through principal components analysis (PCA) and non-negative matrix factorization (NNMF). Muscle synergies number, muscle synergies complexity, muscle synergies sparseness, muscle synergies clusters and muscle networks were calculated. PCA results indicated that SSE and PSE decomposed into 2.88 ± 0.20 and 2.82 ± 0.15 synergies respectively, while the LLSE and RLSE positions decomposed into 3.76 ± 0.14 and 3.71 ± 0.11 muscle synergies, respectively, which were more complex (P = 0.00) but less sparse (P = 0.01). Muscle synergies clusters analysis indicated common muscle synergies among different sling exercises. SSE position demonstrated specific muscle synergies with a strong contribution of the bilateral TA. LLSE-specific synergy has a strong contribution of the left erector spinae (ES). The RLSE-specific synergy has significant contributions from the right ES and multifidus. Muscle networks were functionally organized, with clustering coefficient (F(1.5, 24) = 6.041, P = 0.01) and global efficiency of the undirected network (F(1.5, 24) = 6.041, P = 0.01), and betweenness-centrality of the directed network (F(2.7, 44) = 6.453, P = 0.00). Our research highlights the importance of evaluating muscle synergies and network adaptation strategies in individuals with neuromuscular disorders and developing targeted therapeutic interventions accordingly.

A Comparison of Contractile Properties and Acute Muscle Fatigue Response in Adult Females with Non-Specific Chronic Low Back Pain

This study examined the erector spinae contractile properties, trunk isokinetic strength, and differences in acute muscle fatigue response after exercise in young females with and without non-specific chronic low back pain (NSCLBP). This study evaluated participants using tensiomyography and isokinetic trunk strength tests. An independent t-test compared the control group and the NSCLBP group, while a two-way mixed ANOVA analyzed differences in the erector spinae's acute muscle fatigue response before and after exercise within and between groups. The results of the tensiomyography indicated that the NSCLBP group exhibited significantly lower Dm and Vc (p < 0.05) compared to the control group, while Tc showed no significant difference between groups. Significant differences in all variables were observed between the groups in the isokinetic trunk strength test (p < 0.05). Furthermore, the two-way mixed ANOVA revealed significant group main effects in Dm and Vc of the erector spinae (p < 0.05). This study found that non-specific chronic low back pain is linked to a decrease in Dm, Vc, and trunk isokinetic strength in both extensor and flexor muscles. It suggests that future research should further investigate the acute muscle fatigue response in individuals with and without NSCLBP.

Alterations in magnitude and spatial distribution of erector spinae muscle activity in cyclists with a recent history of low back pain

PURPOSE

While cycling offers several health benefits, repetitive loading and maintenance of static postures for prolonged periods expose cyclists to low back pain (LBP). Despite high LBP prevalence in cyclists, underlying pathomechanics and specific lumbar region muscle activation patterns during cycling are unclear. Here, we compared lumbar erector spinae (ES) muscles activation and spatial distribution activity in cyclists with and without recent LBP history.

METHODS

Ten cyclists with recent LBP history (LBPG; Oswestry Disability Index score ~ 17.8%) and 11 healthy cyclists (CG) were recruited. After assessing the Functional Threshold Power (FTP), participants underwent an incremental cycling test with 4 × 3 min steps at 70%, 80%, 90%, and 100% of their FTP. High-density surface electromyography (HDsEMG) signals were recorded from both lumbar ES using two 64-channel grids. Information about ES activation levels (root-mean-square, RMS), degree of homogeneity (entropy), and cranio-caudal displacement of muscle activity (Y-axis coordinate of the barycenter of RMS maps) was extracted from each grid separately and then grand-averaged across both grids.

RESULTS

Repeated-measure 2-way ANOVAs showed a significant intensity by group interaction for RMS amplitude (p = 0.003), entropy (p = 0.038), and Y-bar displacement (p = 0.033). LBPG increased RMS amplitude between 70-100% (+ 19%, p = 0.010) and 80-100% FTP (+ 21%, p = 0.004) and decreased entropy between 70-100% FTP (- 8.4%, p = 0.003) and 80-100% FTP (- 8.5%, p = 0.002). Between-group differences emerged only at 100% FTP (+ 9.6%, p = 0.049) for RMS amplitude.

CONCLUSION

Our findings suggest that cyclists with recent LBP history exhibit higher ES muscles activation and less homogeneous activity compared to healthy controls, suggesting potential inefficient muscle recruitment strategy.

TRIAL REGISTRATION NUMBER

HEC-DSB/09-2023.

Reduced variability of erector spinae activity in people with chronic low back pain when performing a functional 3D lifting task

BACKGROUND

Chronic low back pain (LBP) is a leading cause of disability, which is exacerbated in some by repeated lifting. Electromyography (EMG) assessments of isolated erector spinae (ES) regions during lifting identified conflicting results. Here, high-density EMG comprehensively assesses the lumbar and thoracolumbar ES activity in people with and without LBP performing a multiplanar lifting task.

METHODS

Four high-density EMG grids (two bilaterally) and reflective markers were affixed over the ES and trunk to record muscle activity and trunk kinematics respectively. The task involved cyclical lifting of a 5 kg box for ∼7 min from a central shelf to five peripheral shelves, returning to the first between movements, while monitoring perceived exertion.

RESULTS

Fourteen LBP (26.9 ± 11.1 years) and 15 control participants (32.1 ± 14.6 years) completed the study. LBP participants used a strategy characterised by less diffuse and more cranially-focussed ES activity (P < 0.05). LBP participants also exhibited less variation in ES activity distribution between sides during movements distal to the central shelf (P < 0.05). There were few consistent differences in kinematics, but LBP participants reported greater exertion (P < 0.05).

CONCLUSION

In the presence of mild LBP, participants used a less variable motor strategy, with less diffuse and more cranially-focussed ES activity; this motor strategy occurred concomitantly with increased exertion while completing this dynamic task.

Task-dependent neuromuscular adaptations in low back pain: a controlled experimental study

Introduction

This study investigated the variability in lumbar neuromuscular adaptations to pain, the task dependency of pain adaptations and the effect of these adaptations on motor performance.

Methods

Twenty-four healthy participants performed isometric back extension contractions at 45° and 90° trunk flexion under pain-free and experimental low back pain conditions induced by electrical stimulation. High-density surface electromyography recorded lumbar muscle activation strategies, and force steadiness was measured using a load cell.

Results

While considerable variability in neuromuscular adaptations to lumbar pain was observed among participants, consistent patterns were found between tasks. In the 90° trunk flexion position, both sides exhibited greater magnitudes of pain adaptations for muscle activity redistribution in the mediolateral axis (p < 0.05, 86% increase) and muscle activity amplitude (p < 0.001, 183% increase) compared to the 45° trunk flexion position. A significant negative correlation was found between the magnitude of the mediolateral spatial redistribution of muscle activity and force steadiness on the left side (p = 0.045).

Discussion

These findings highlight the intricate and task-dependent nature of neuromuscular adaptations to pain within lumbar muscles, and points toward a potential trade-off between pain adaptations and performance.

The effect of trunk position and pain location on lumbar extensor muscle recruitment strategies

The aim of this study was to investigate the effect of trunk position and experimental lumbar pain location on lumbar extensor muscle recruitment strategies. Nineteen healthy participants (10 men and 9 women), aged 25.3 ± 4.7 yr, performed isometric back extension contractions in three positions (neutral, 45°, and 90° trunk flexion) and under three conditions (no pain, caudal pain, and cranial pain). Lumbar muscle activation strategies were recorded using high-density surface electromyography. The effect of position and pain condition on muscle activity amplitude and spatial redistributions was assessed. Muscle activity amplitude was 43% higher in 45° trunk flexion than in neutral position on both sides (P < 0.05). In the 90° trunk flexion, participants showed a more lateral spatial distribution than in the 45° trunk flexion on the left side (P < 0.01, 5.4 mm difference) and the neutral position on both sides (P < 0.05, 8.2 mm difference). In the 45° trunk flexion, participants exhibited a more lateral spatial distribution compared with the neutral position on the right side (P < 0.05, 3.7 mm difference). A lateral spatial redistribution of muscle activity was observed in the caudal pain condition compared with the no pain condition on the right side (P < 0.05, 3.0 mm difference). Individual responses to pain varied across all variables. Different trunk positions result in different distributions of activation within the lumbar extensor muscles, possibly based on regional mechanical advantage. No clear indication of location-specific pain adaptation and no effect of task-dependent pain adaptation were found, whereas individual-specific adaptations were observed.NEW & NOTEWORTHY Changes in muscle activity amplitude and spatial redistribution of lumbar extensor muscles were observed in different trunk positions, potentially due to changes in their mechanical advantage. The results complement the current pain-adaptation theory by illustrating individual spatial redistributions of activation within lumbar extensor muscles during pain. The study found no clear indication of location-specific pain adaptation and no effect of task-dependent pain adaptation.

Acute neuromuscular and perceptual responses to blood flow restriction exercise in adults with severe haemophilia: A pilot study

INTRODUCTION

No previous studies have implemented a standard blood flow restriction (BFR) training session in people with severe haemophilia (PwH), where this type of training has been contraindicated.

AIMS

The purpose of this study was to evaluate the tolerability, adverse events, and neuromuscular and perceptual responses to an acute session of low load (LL) knee extensions with BFR in PwH under prophylaxis.

METHODS

Eight PwH performed one LL-BFR session with 40% arterial occlusion pressure (AOP). Perceptual responses and adverse effects were assessed, together with high-density surface electromyography of vastus medialis (VM) and lateralis (VL).

RESULTS

Significant normalized root mean square differences were found within each set, but not between sets. Spatial distribution (centroid displacement (p > .05), modified entropy (VM, set two, cycles three and five, p = .032) and coefficient of variation (VM, set two, cycles four and five lower than cycle three (p = .049; p = .036)) showed changes within each set. Median frequency showed a slight increase during cycle four of set four (p = .030). Rate of perceived exertion slightly increased with each set while tolerability slightly decreased in the last set and fear of training with BFR generally decreased after the session.

CONCLUSIONS

In PwH, a LL-BFR session at 40% AOP is safe and feasible. Our results suggest that potential muscle impairments may blunt neuromuscular adaptations induced by BFR.

Spinal kinematic variability is increased in people with chronic low back pain during a repetitive lifting task

Changes in spinal kinematic variability have been observed in people with chronic non-specific LBP (CNSLBP) during the performance of various repetitive functional tasks. However, the direction of these changes (i.e., less or more kinematic variability) is not consistent. This study aimed to assess differences in kinematic variability of the 3D angular displacement of thoracic and lumbar spinal segments in people with CNSLBP compared to asymptomatic individuals during a repetitive lifting task. Eleven people with CNSLBP and 11 asymptomatic volunteers performed 10 cycles of multi-planar lifting movements while spinal kinematics were recorded. For the three planes of motion, point-by-point standard deviations (SDs) were computed across all cycles of lifting and the average was calculated as a measure of kinematic variability for both segments. People with CNSLBP displayed higher thoracic (F = 8.00, p = 0.010, ηp2 = 0.286) and lumbar kinematic variability (F = 5.48, p = 0.030, ηp2 = 0.215) in the sagittal plane. Moreover, group differences were observed in the transversal plane for thoracic (F = 7.62, p = 0.012, ηp2 = 0.276) and lumbar kinematic variability (F = 5.402, p = 0.031, ηp2 = 0.213), as well as in the frontal plane for thoracic (F = 7.27, p = 0.014, ηp2 = 0.267) and lumbar kinematic variability (F = 6.11, p = 0.022, ηp2 = 0.234), all showing higher variability in those with CNSLBP. A significant main effect of group was not detected (p > 0.05) for spinal range of motion (ROM). Thus, people with CNSLBP completed the lifting task with the same ROM in all three planes of motion as observed for asymptomatic individuals, yet they performed the lifting task with higher spinal kinematic cycle-to-cycle variation.

High-density surface electromyography allows to identify risk conditions and people with and without low back pain during fatiguing frequency-dependent lifting activities

Low back pain (LBP) is a leading cause of disability in the workplace, often caused by manually lifting of heavy loads. Instrumental-based assessment tools are used to quantitatively assess the biomechanical risk of lifting activities. This study aims to verify that, during the execution of fatiguing frequency-dependent lifting, high-density surface electromyography (HDsEMG) allows the discrimination of healthy controls (HC) versus people with LBP and biomechanical risk levels. Fifteen HC and eight people with LBP performed three lifting tasks with a progressively increasing lifting index, each lasting 15 min. Erector spinae (ES) activity was recorded using HDsEMG and amplitude parameters were calculated to characterize the spatial distribution of muscle activity. LBP group showed a less ES activity than HC (lower root mean square across the grid and of the activation region) and an involvement of the same muscular area across the task (lower coefficient of variation of the center of gravity of muscle activity). The results indicate the usefulness of HDsEMG parameters to classify risk levels for both HC and LBP groups and to determine differences between them. The findings suggest that the use of HDsEMG could expand the capabilities of existing instrumental-based tools for biomechanical risk classification during lifting activities.

Not all movements are equal: Differences in the variability of trunk motor behavior between people with and without low back pain-A systematic review with descriptive synthesis

BACKGROUND

Differences in variability of trunk motor behavior between people with and without low back pain (LBP) have been reported in the literature. However, the direction and consistency of these differences remain unclear. Understanding variability of trunk motor behavior between individuals with LBP and those without is crucial to better understand the impact of LBP and potentially optimize treatment outcomes. Identifying such differences may help tailor therapeutic interventions.

OBJECTIVE

This systematic review aims to answer the question: Is variability of trunk motor behavior different between people with and without LBP and if so, do people with LBP show more or less variability? Furthermore, we addressed the question whether the results are dependent on characteristics of the patient group, the task performed and the type of variability measure.

METHODS

This study was registered in PROSPERO (CRD42020180003). A comprehensive systematic literature search was performed by searching PubMed, Embase, Cinahl, Cochrane Central Register of Controlled Trials, Web of Science and Sport Discus. Studies were eligible if they (1) included a LBP group and a control group, (2) included adults with non-specific low back pain of any duration and (3) measured kinematic variability, EMG variability and/or kinetic variability. Risk of Bias was evaluated and a descriptive synthesis was performed.

RESULTS

Thirty-nine studies were included, thirty-one of which were included in the descriptive synthesis. In most studies and experimental conditions, variability did not significantly differ between groups. When significant differences were found, less variability in patients with LBP was more frequently reported than more variability, especially in gait-related tasks.

CONCLUSIONS

Given the considerable risk of bias of the included studies and the clinical characteristics of the participants with low severity scores for pain, disability and psychological measures, there is insufficient evidence to draw firm conclusions.

The Role of Back Muscle Dysfunctions in Chronic Low Back Pain: State-of-the-Art and Clinical Implications

Changes in back muscle function and structure are highly prevalent in patients with chronic low back pain (CLBP). Since large heterogeneity in clinical presentation and back muscle dysfunctions exists within this population, the potential role of back muscle dysfunctions in the persistence of low back pain differs between individuals. Consequently, interventions should be tailored to the individual patient and be based on a thorough clinical examination taking into account the multidimensional nature of CLBP. Considering the complexity of this process, we will provide a state-of-the-art update on back muscle dysfunctions in patients with CLBP and their implications for treatment. To this end, we will first give an overview of (1) dysfunctions in back muscle structure and function, (2) the potential of exercise therapy to address these dysfunctions, and (3) the relationship between changes in back muscle dysfunctions and clinical parameters. In a second part, we will describe a framework for an individualised approach for back muscle training in patients with CLBP.

Diaphragmatic breathing exercises in recovery from fatigue-induced changes in spinal mobility and postural stability: a study protocol

Prolonged periods of sitting at work can increase trunk muscle fatigue from the continuous contraction of deep trunk muscles. Insufficient activity of these muscles can decrease muscular support to the spine and increases stress on its passive structures. This can lead to reduced spinal mobility and impaired postural stability. It may also stimulate nociceptor activity leading to pain. However, frequently used recovery modalities such as muscle strengthening and stretching exercises, can be time-consuming, impractical, and difficult to implement in the workplace. Diaphragmatic breathing exercises, which increase the activity of the deep trunk muscles by raising intra-abdominal pressure, seem to be a suitable alternative. However, little is known as to what extent diaphragmatic breathing exercises contribute to the reduction of fatigue induced by prolonged sitting. This paper presents a study protocol that aims to investigate the acute effect of diaphragmatic breathing exercises on recovery of fatigue-induced changes in spinal mobility and postural stability in sedentary middle-aged adults at risk of developing non-specific low back pain. Twenty sedentary adults aged between 25 and 44 years will perform Abt's fatigue protocol, followed by 1) active recovery using diaphragmatic breathing exercises and 2) passive recovery in the form of lying on the bed, respectively. There will be 1 week of rest in-between. Pre-fatigue, post-fatigue, and after the active and passive recovery, spinal mobility and postural stability will be evaluated using the spinal mouse device and a posturography system, respectively. The electromyography will be used to determine the muscle-fatigue conditions. We hypothesize that active recovery in a form of diaphragmatic breathing exercises would be more effective in restoring spinal mobility and postural stability followed by the fatigue of back and hamstring muscles compared to passive recovery in sedentary adults. Increasing core and respiratory muscle strength via these exercises could be beneficial for overall mobility and stability of the spine. Reducing compressive stress on the passive structures of the spine may be also beneficial for lowering low back pain. Therefore, we believe that diaphragmatic breathing exercises have the possibility to be incorporated into the workplace and contribute to better back health in sedentary middle-aged adults. Clinical Trial Registration: [https://www.irct.ir/trial/67015], identifier [IRCT20221126056606N1].

Understanding Discrepancies in a Person's Fear of Movement and Avoidance Behavior: A Guide for Musculoskeletal Rehabilitation Clinicians Who Support People With Chronic Musculoskeletal Pain

BACKGROUND: Generic self-report measures do not reflect the complexity of a person's pain-related behavior. Since variations in a person's fear of movement and avoidance behavior may arise from contextual and motivational factors, a person-centered evaluation is required-addressing the cognitions, emotions, motivation, and actual behavior of the person. CLINICAL QUESTION: Most musculoskeletal rehabilitation clinicians will recognize that different people with chronic pain have very different patterns of fear and avoidance behavior. However, an important remaining question for clinicians is "How can I identify and reconcile discrepancies in fear of movement and avoidance behavior observed in the same person, and adapt my management accordingly?" KEY RESULTS: We frame a clinical case of a patient with persistent low back pain to illustrate the key pieces of information that clinicians may consider in a person-centered evaluation (ie, patient interview, self-report measures, and behavioral assessment) when working with patients to manage fear of movement and avoidance behavior. CLINICAL APPLICATION: Understanding the discrepancies in a person's fear of movement and avoidance behavior is essential for musculoskeletal rehabilitation clinicians, as they work in partnership with patients to guide tailored approaches to changing behaviors. J Orthop Sports Phys Ther 2023;53(5):1-10. Epub: 9 March 2023. doi:10.2519/jospt.2023.11420.

Motor variability during a repetitive lifting task is impaired by wearing a passive back-support exoskeleton

PURPOSE

Evaluate whether wearing a passive back-support exoskeleton during repetitive lifting impairs motor variability of erector spinae muscle and spine movement and whether this association is influenced by lifting style.

SCOPE

Thirty-six healthy males performed ten lifts in four randomized conditions with exoskeleton (without, with) and lifting style (squat, stoop) as dependent variables. One lifting cycle contained four phases: bending/straighten without/with load. Erector spinae muscular activity, thoracic kyphosis and lumbar lordosis were measured with surface electromyography and gravimetric position sensors, respectively. Absolute and relative cycle-to-cycle variability were calculated. The effects of exoskeleton and exoskeleton × lifting style were assessed on outcomes during the complete lifting cycle and its four phases.

RESULTS

For the complete lifting cycle, muscular variability and thoracic kyphosis variability decreased whereas lumbar lordosis variability increased with exoskeleton. For lifting phases, effects of exoskeleton were mixed. Absolute and relative muscular variability showed a significant interaction effect for the phase straighten with load; variability decreased with exoskeleton during squat lifting.

CONCLUSION

Using the exoskeleton impaired several motor variability parameters during lifting, supporting previous findings that exoskeletons may limit freedom of movement. The impact of this result on longer-term development of muscular fatigue or musculoskeletal disorders cannot yet be estimated.

Reliability of high-density surface electromyography for assessing characteristics of the thoracic erector spinae during static and dynamic tasks

PURPOSE

To establish intra- and inter-session reliability of high-density surface electromyography (HDEMG)-derived parameters from the thoracic erector spinae (ES) during static and dynamic goal-directed voluntary movements of the trunk, and during functional reaching tasks.

METHODS

Twenty participants performed: 1) static trunk extension, 2) dynamic trunk forward and lateral flexion, and 3) multidirectional functional reaching tasks on two occasions separated by 7.5 ± 1.2 days. Muscle activity was recorded bilaterally from the thoracic ES. Root mean square (RMS), coordinates of the barycentre, mean frequency (MNF), and entropy were derived from the HDEMG signals. Reliability was determined with intraclass correlation coefficient (ICC), coefficient of variation, and standard error of measurement.

RESULTS

Good-to-excellent intra-session reliability was found for all parameters and tasks (ICC: 0.79-0.99), whereas inter-session reliability varied across tasks. Static tasks demonstrated higher reliability in most parameters compared to functional and dynamic tasks. Absolute RMS and MNF showed the highest overall reliability across tasks (ICC: 0.66-0.98), while reliability of the barycentre was influenced by the direction of the movements.

CONCLUSION

RMS and MNF derived from HDEMG show consistent inter-session reliability in goal-directed voluntary movements of the trunk and reaching tasks, whereas the measures of the barycentre and entropy demonstrate task-dependent reliability.

The effect of low back pain on neuromuscular control in cyclists

This study was designed to identify neuromuscular adaptations of low back pain (LBP) cyclists , and the impact of a cycling effort on spinal shrinkage. Forty-eight trained cyclists rode their road bike on a smart trainer for 1-hour. Surface electromyography (EMG) recorded muscle activity of the lumbar erector spinae (LES), 3D motion analysis system recorded kinematic of the trunk, and stadiometry measured spinal height. Statistical comparisons were made using repeated measure ANOVAs. The LBP group presented increase in pain levels throughout the effort (p < 0.001). A significant group difference was only observed for the thoracic angle (p = 0.03), which was less flexed for LBP. The one-hour cycling effort (time effect) significantly increased the trunk flexion (p < 0.001) and thoracic flexion (p < 0.001) for both groups. Significant lower LES activation (35% less) was observed at the end of the effort  as well as a decrease in spinal height (p = 0.01) for both groups. Neuromuscular adaptations to cycling effort is identified by a decrease in LES EMG amplitude and an increase flexion of the trunk. Adaptation to pain is seen by an increase in thoracic flexion. Despite these adaptations, LBP cyclists could not ride their bike pain-free.

Postural Variabilities Associated with the Most Comfortable Sitting Postures: A Preliminary Study

This study examined postural variabilities based on the self-perceived most comfortable postures of 12 participants (six men and six women) when sitting on three commonly used types of chairs (a stool, computer chair, and gaming chair). Participants’ global joint angles were recorded and analyzed. Of the chairs studied, the stool was not adjustable, but the computer and gaming chairs were moderately and highly adjustable, respectively. During the test, participants were encouraged to adjust the chairs until they perceived that the most comfortable posture had been reached. The results demonstrated that in a sitting position perceived to be comfortable, the participants’ postural variabilities with respect to global joint angle, calculated from five repetitions, were unexpectedly high for all three chair types, at approximately 9.4, 10.2, and 11.1° for head inclination, trunk angle, and knee angle, respectively. The average differences in range for each joint angle among the three chair types were relatively low, with all values within 3°. The result also showed that gender (p < 0.01) and chair type (p < 0.001) significantly affected trunk angle, whereas these variables did not affect head inclination or knee angle (p > 0.05). The preliminary results observed unexpectedly high variabilities in sitting posture when the participants sat at a posture that they perceived to be the most comfortable. The findings also indicated an inherent difference in comfortable sitting posture between genders; women tend to extend their trunk backward more than men. For permanent use with only an initial adjustment and memory-aided seat design, designers should minimize the loads that are borne by body parts over a prolonged period due to an unchanging sitting posture.

Evaluation of trunk muscle activities in response to three breastfeeding positions utilised by women

BACKGROUND

High prevalence of breastfeeding (BF)-related musculoskeletal disorders (MSDs) in nursing mothers have been reported in previous studies. Studies are scarce on the biomechanical effects of the commonly utilized BF positions.

OBJECTIVE

This study evaluated the electromyographic (EMG) activities of the trunk muscles in response to three BF positions commonly utilized by mothers globally.

METHODS

20 non-pregnant nulliparous females participated in this experimental study. EMG activities from erector spinae (ES) and external oblique (EO) muscles were recorded bilaterally in three BF conditions: cradle (C1); cross-cradle (C2); football (FB). Data were analyzed using descriptive statistics and inferential statistics of one-way analysis of variance with alpha level set at 0.05.

RESULTS

The activity levels of right EO and ES muscles significantly increased during the C2 hold, while the left EO and ES muscles revealed significantly higher EMG levels in the C1 trial. Asymmetrical activity between the right and the left parts of the EO muscle was significantly higher during the C2 hold.

CONCLUSION

These findings suggest that compared to C2 and C1 holds, FB hold may be more biomechanically efficient relative to its decreased muscular demands. The physical stresses associated with BF may be higher with the adoption of C2 and C1 holds, especially for prolonged periods.

Motor performance and back pain in children and adolescents: A systematic review

BACKGROUND AND OBJECTIVE

Motor performance during childhood and adolescence is recognized as a relevant determinant of present and future health, but its effects on back pain (BP) remain unclear. In this systematic review, we aimed to identify the association between motor performance and BP in children and adolescents.

DATABASES AND DATA TREATMENT

A literature search was performed in the MEDLINE, Scopus, Embase, SPORTDiscus and CINAHL databases. We included cross-sectional, cohort, case-control and controlled clinical trials (data from control groups). The inclusion criteria were as follows: (a) participants aged 6-19 years; (b) assessment motor performance components; (c) assessment of BP and (d) reported measures of association. The risk of bias was assessed by the Downs and Black instrument and the quality of evidence by the grading of recommendations, assessment, development and evaluation (GRADE).

RESULTS

A total of 2360 articles were identified, 25 of which were included in our systematic review. Of the 25 studies, 19 were evaluated as having a low risk of bias. GRADE indicated that 20 studies presented low or very low quality. Most of the studies evaluated flexibility (n = 16), muscle endurance (n = 18) and muscle strength (n = 9). Aerobic capacity, balance and speed were also examined in some studies (n < 5). Overall, motor performance (flexibility, muscle endurance, muscle strength, aerobic capacity, balance and speed) was not associated with BP. Most of the results were inconsistent because of the lack of studies, risk of bias and low quality of evidence. Only trunk extensor muscle endurance was associated with decreased BP with moderate quality of the supporting evidence. Prospective studies with a low risk of bias are warranted to further clarify this relationship in childhood and adolescence and findings may support more targeted and effective health promotion interventions.

SIGNIFICANCE

This systematic review shows that motor performance (flexibility, muscle endurance, muscle strength, aerobic capacity, balance and speed) was not associated with BP in children and adolescents. Most of the results were inconsistent because of the lack of studies, risk of bias and low quality of evidence. Only trunk extensor muscle endurance was associated with decreased BP with moderate quality of supporting evidence.

The influence of Kinesio Taping on muscle fatigue in individuals with low back pain: A randomised controlled trial

OBJECTIVE

To evaluate the effect of different taping techniques on back muscle fatigue in people with low back pain.

METHODS

Sixty women with chronic non-specific low back pain were randomly assigned to four groups of 15 participants each: control (CG), Kinesio Taping (KT) with tension (KTT), KT no tension (KTNT) and Micropore® (MP), which were applied over the erector spinae muscles. The median frequency (MF) fatigue slopes of the longissimus muscle and sustained contraction time during a trunk fatigue test (Ito test), and pain using the numerical pain rating scale (NPRS) were collected at three time points: pre-treatment, three and ten days after intervention at a university laboratory.

RESULTS

Significant differences were seen in the MF slopes between groups (p= 0.01, η2= 0.20), with the KTT showing a mean difference (MD = 0.31, p= 0.04) and KTNT (MD = 0.28, p= 0.04) compared with CG. Significant reductions in NPRS were seen between time points (p< 0.001, η2= 0.28), with a reduction between pre and 3 days (MD = 1.87, p< 0.001), and pre and 10 days (MD = 1.38, p< 0.001), with KTT and KTNT both showing clinically important changes.

CONCLUSION

KT, with or without tension, has a tendency to reduce back muscle fatigue and reduce pain in individuals with chronic non-specific low back pain.

Is movement variability altered in people with chronic non-specific low back pain: a protocol for a systematic review

INTRODUCTION

Motor variability is an important feature when performing repetitive movement, and in asymptomatic people functional tasks are typically performed with variable motor patterns. However, in the presence of chronic non-specific low back pain (LBP), people often present with different motor control strategies than those without pain. Movement variability has been assessed using a wide range of variables, including kinetic and kinematic components of motion. This has resulted in a wide range of findings reported in the literature and some contradicting results. Therefore, the aim of this systematic review is to investigate whether the amount and structure of motor variability are altered in people with chronic non-specific LBP, during both repetitive non-functional and functional tasks.

METHODS AND ANALYSIS

This protocol for a systematic review is informed by Cochrane guidelines and reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols. MEDLINE, EMBASE, CINAHL, ZETOC, Web of Science, PubMed and Scopus will be searched from their inception to December 2020 along with a comprehensive search of grey literature and key journals. Two independent reviewers will conduct the search, extract the data, assess risk of bias (using the Downs and Black Scale) for the included studies and assess overall quality of evidence based on Grading of Recommendations, Assessment, Development and Evaluation guidelines. Meta-analysis will be conducted if deemed appropriate. Alternatively, a narrative synthesis will be conducted and evidence summarised as an increase, decrease or no change in the motor variability of people with LBP compared with healthy controls.

ETHICS AND DISSEMINATION

This study raises no ethical issues. Results will be submitted for publication in a peer review journal and presented at conferences.

PROSPERO REGISTRATION NUMBER

CRD42020211580.

Understanding regional activation of thoraco-lumbar muscles in chronic low back pain and its relationship to clinically relevant domains

BACKGROUND

Altered regional activation of the lumbar extensors has been previously observed in individuals with low back pain (LBP) performing high-effort and fatiguing tasks. It is currently unknown whether similar alterations can be observed during low-effort functional tasks. Similarly, previous studies did not investigate whether side differences in regional activation are present in individuals with LBP. Finally, there is limited evidence of whether the extent of the alteration of regional activation is associated with clinical factors. Therefore, the aim of this study was to investigate whether individuals with LBP exhibit asymmetric regional activation of the thoraco-lumbar extensor muscles during functional tasks, and if the extent of neuromuscular control alteration is associated with clinical and psychosocial outcome domains.

METHODS

21 participants with and 21 without LBP performed five functional tasks (gait, sit-to-stand, forward trunk flexion, shoulder flexion and anterior pelvic tilt). The spatial distribution of activation of the thoraco-lumbar extensor muscles was assessed bilaterally using high-density electromyography. For each side, the distribution of electromyographic (EMG) amplitude was characterized in terms of intensity, location and size. Indices of asymmetry were calculated from these features and comparisons between groups and tasks were performed using ANOVA. The features that significantly differed between groups were correlated with self-reported measures of pain intensity and other outcome domains.

RESULTS

Indices of asymmetry did not differ between participants with and without LBP (p > 0.11). The cranio-caudal location of the activation differed between tasks (p < 0.05), but not between groups (p = 0.64). Participants with LBP showed reduced EMG amplitude during anterior pelvic tilt and loading response phase during gait (both p < 0.05). Pearson correlation revealed that greater pain intensity was associated with lower EMG amplitude for both tasks (R<-0.5, p < 0.05).

CONCLUSIONS

Despite clear differences between tasks, individuals with and without LBP exhibited similar distributions of EMG amplitude during low-effort functional activities, both within and between sides. However, individuals with LBP demonstrated lower activation of the thoraco-lumbar muscles during gait and anterior pelvic tilt, especially those reporting higher pain intensity. These results have implications in the development or refinement of assessment and intervention strategies focusing on motor control in patients with chronic LBP.

Reliability of Sonography Measures of the Lumbar Multifidus and Transversus Abdominis during Static and Dynamic Activities in Subjects with Non-Specific Chronic Low Back Pain

PURPOSE

The purpose of this study was to investigate the test-retest reliability of ultrasound (US) thickness measurements and the muscle contraction ratio (CR) of lumbar multifidus (LM) and transversus abdominis (TA) muscles in participants with and without nonspecific chronic low back pain (NCLBP).

METHODS

A total of 62 participants (37 with NCLBP, 25 without NCLBP) with participated in the study. The within-day and between-day reliability of US thickness measurements and CR in a lying (supine for TA and prone for LM) and sitting positions for both muscles (sitting on a gym ball with both feet on the ground or lifting one foot off the floor) were assessed. Reliability analysis was performed with intraclass correlations (ICCs) for these two static and dynamic positions.

RESULTS

Test-retest reliability was calculated to be good to high for the static position (ICC = 0.72-0.95) and the dynamic position (ICC = 0.74-0.94) sonographic measurements in both group of TA measurement. Test-retest reliability of LM measurements was good to high for the static position (ICC = 0.82-0.95) and the dynamic position (ICC = 0.85-0.97) sonographic measurements in both groups.

CONCLUSIONS

US imaging is a highly reliable method for the assessment of TA and LM thickness muscles in the dynamic position in participants with and without NCLBP. The CR measures may be adequately reliable in assessing the function of the TA and LM muscles in participants with NCLBP and healthy ones.

A systematic review of movement and muscular activity biomarkers to discriminate non-specific chronic low back pain patients from an asymptomatic population

The identification of relevant and valid biomarkers to distinguish patients with non-specific chronic low back pain (NSCLBP) from an asymptomatic population in terms of musculoskeletal factors could contribute to patient follow-up and to evaluate therapeutic strategies. Several parameters related to movement and/or muscular activity impairments have been proposed in the literature in that respect. In this article, we propose a systematic and comprehensive review of these parameters (i.e. potential biomarkers) and related measurement properties. This systematic review (PROSPERO registration number: CRD42020144877) was conducted in Medline, Embase, and Web of Knowledge databases until July 2019. In the included studies, all movements or muscular activity parameters having demonstrated at least a moderate level of construct validity were defined as biomarkers, and their measurement properties were assessed. In total, 92 studies were included. This allowed to identify 121 movement and 150 muscular activity biomarkers. An extensive measurement properties assessment was found in 31 movement and 14 muscular activity biomarkers. On the whole, these biomarkers support the primary biomechanical concepts proposed for low back pain. However, a consensus concerning a robust and standardised biomechanical approach to assess low back pain is needed.

Spatial distribution of lumbar erector spinae muscle activity in individuals with and without chronic low back pain during a dynamic isokinetic fatiguing task

BACKGROUND

Individuals with chronic low back pain (CLBP) commonly present with increased trunk muscle fatigability; typically assessed as reduced time to task failure during non-functional isometric contractions. Less is known about the specific neuromuscular responses of individuals with CLBP during dynamic fatiguing tasks. We investigate the regional alteration in muscle activation and peak torque exertion during a dynamic isokinetic fatiguing task in individuals with and without CLBP.

METHODS

Electromyography (EMG) was acquired from the lumbar erector spinae unilaterally of 11 asymptomatic controls and 12 individuals with CLBP, using high-density EMG (13 × 5 grid of electrodes). Seated in an isokinetic dynamometer, participants performed continuous cyclic trunk flexion-extension at 60^o/s until volitional exhaustion.

FINDINGS

Similar levels of muscle activation and number of repetitions were observed for both groups (p > 0.05). However, the CLBP group exerted lower levels of peak torque for both flexion and extension moments (p < 0.05). The centre of lumbar erector spinae activity was shifted cranially in the CLBP group throughout the task (p < 0.05), while the control participants showed a more homogenous distribution of muscle activity.

INTERPRETATION

People with CLBP displayed altered and potentially less efficient activation of their lumbar erector spinae during a dynamic fatiguing task. Future studies should consider using high-density EMG biofeedback to optimise the spatial activation of the paraspinal musculature in people with low back pain (LBP).

Reliability of ultrasound measurement of the lateral abdominal and lumbar multifidus muscles in individuals with chronic low back pain: A cross-sectional test-retest study

OBJECTIVES

Ultrasound (US) imaging has been suggested to evaluate the morphology and function of trunk muscles; however, little is known about the reliability of the US measures in patients with chronic low back pain (CLBP). This study aimed to evaluate intrarater reliability of US imaging of the lateral abdominal and lumbar multifidus muscles in individuals with nonspecific CLBP.

METHODS

In this cross-sectional study, intrarater within-day and between-day reliability of US measurements of the transversus abdominis, internal oblique, external oblique and lumbar multifidus (at the L3-L4, L4-L5, and L5-S1 levels) muscles were obtained on both sides. The resting and contracted thickness and contraction ratio of each muscle were measured in 21 individuals with nonspecific CLBP.

RESULTS

All US measurements of the lateral abdominal and lumbar multifidus muscles demonstrated good to excellent within-day (Intraclass correlation coefficients (ICCs: 0.80-0.98) and between-day (ICCs: 0.80-0.97) reliability. The standard error of the measurement (SEMs) and minimal detectable change (MDCs) of the lateral abdominal muscles on both sides ranged 0.5-1.6 mm and 0.4-4.4 mm, respectively. The SEMs and MDCs of the LM muscles on both sides ranged 1.1-2.7 mm and 2.86-7.49 mm, respectively.

CONCLUSION

The findings indicate that US imaging has good to high intrarater within- and between-day reliability for assessing absolute thickness and contraction ratio of the trunk muscles on both right and left sides in patients with nonspecific CLBP. The vertical alignment of the US transducer is a reliable method for assessing the lateral abdominal muscles.

Effects of Prolonged Sitting with Slumped Posture on Trunk Muscular Fatigue in Adolescents with and without Chronic Lower Back Pain

Background and Objectives: This study investigated the effects of prolonged sitting on trunk muscular fatigue and discomfort in participants with and without chronic lower back pain (LBP). Material and Methods: This study included 15 patients with LBP and 15 healthy controls. All participants were instructed to sit on a height-adjustable chair with their knee and hip joints bent at 90° for 30 min, in slumped sitting postures. Surface electromyography was used to assess the median frequency of the internal obliques (IO)/transversus abdominis (TrA) and multifidus (MF) muscles. Perceived discomfort was measured using a Borg category ratio-scale. Median frequency of the trunk muscles and perceived discomfort after 30 min of sitting were compared with baseline. Result: There were no significant differences within the group and between both groups in the median frequency of bilateral IO and MF muscles. The LBP group showed significantly greater perceived discomfort after prolonged sitting, as compared to the control group. Conclusions: Prolonged sitting with slumped posture could increase the risk of experiencing lower back discomfort.

Combined abnormal muscle activity and pain-related factors affect disability in patients with chronic low back pain: An association rule analysis

Objectives

In patients with chronic low back pain (CLBP), reduced lumbar flexion-relaxation and reduced variability of muscle activity distribution are reported as abnormal muscle activity. It is not known how abnormal muscle activity and pain-related factors are related to CLBP-based disability. Here, we performed an association rule analysis to investigated how CLBP disability, muscle activity, and pain-related factors in CLBP patients are related.

Methods

Surface electromyographic signals were recorded from over the bilateral lumbar erector spinae muscle with four-channel electrodes from 24 CLBP patients while they performed a trunk flexion re-extension task. We calculated the average value of muscle activities of all channels and then calculated the flexion relaxation ratio (FRR) and the spatial variability of muscle activities. We also assessed the pain-related factors and CLBP disability by a questionnaire method. A clustering association rules analysis was performed to determine the relationships among pain-related factors, the FRR, and the variability of muscle activity distribution.

Results

The association rules of severe CLBP disability were divisible into five classes, including ‘low FRR-related rules.’ The rules of the mild CLBP disability were divisible into four classes, including ‘high FRR-related rules’ and ‘high muscle variability-related rules.’ When we combined pain-related factors with the FRR and muscle variability, the relationship between abnormal FRR/muscle variability and CLBP disability became stronger.

Discussion

Our findings thus highlight the importance of focusing on not only the patients’ pain-related factors but also the abnormal motor control associated with CLBP, which causes CLBP disability.

Spatial Distribution and Asymmetry of Surface Electromyography on Lumbar Muscles of Soldiers with Chronic Low Back Pain

This study investigated spatial distribution and asymmetry of surface electromyography on lumbar muscles during a sustained contraction in soldiers with and without chronic low back pain. Twenty healthy soldiers and twenty chronic low back pain (CLBP) soldiers had performed the Sorensen test with a duration of 60 seconds. The corresponding muscle fatigue, spatial distribution, and the asymmetry of muscle activity over bilateral paraspinal lumbar regions were measured by the high-density surface electromyography (HDsEMG). The paired and independent samples t-tests were performed to compare the degree of muscle fatigue and asymmetry. The repeated-measures analyses of variance (ANOVA) were used to compare spatial distribution between groups and muscle fatigue. The baseline characteristics of soldiers between groups were comparable. CLBP soldiers had significantly less muscle fatigue on both sides of erector spinae compared to healthy ones. The spatial distribution was significantly associated with the group factor but independent of muscle fatigue. In addition, the asymmetry of erector spinae activity in the CLBP soldiers was significantly higher than the healthy one. In conclusion, uneven spatial distribution and asymmetry of lumbar muscle activity play significant roles in CLBP patients. The HDsEMG could be used as an objective method in distinguishing the function of the erector spinae between healthy individuals and CLBP patients during 1 min sustained contraction.

Cortical dynamics of movement-evoked pain in chronic low back pain

KEY POINTS

Cortical activity underlying movement-evoked pain is not well understood, despite being a key symptom of chronic musculoskeletal pain. We combined high-density electroencephalography with a full-body reaching protocol in a virtual reality environment to assess cortical activity during movement-evoked pain in chronic low back pain. Movement-evoked pain in individuals with chronic low back pain was associated with longer reaction times, delayed peak velocity and greater movement variability. Movement-evoked pain was associated with attenuated disinhibition in prefrontal motor areas, as evidenced by an attenuated reduction in beta power in the premotor cortex and supplementary motor area.

ABSTRACT

Although experimental pain alters neural activity in the cortex, evidence of changes in neural activity in individuals with chronic low back pain (cLBP) remains scarce and results are inconsistent. One of the challenges in studying cLBP is that the clinical pain fluctuates over time and often changes during movement. The goal of the present study was to address this challenge by recording high-density electroencephalography (HD-EEG) data during a full-body reaching task to understand neural activity during movement-evoked pain. HD-EEG data were analysed using independent component analyses, source localization and measure projection analyses to compare neural oscillations between individuals with cLBP who experienced movement-evoked pain and pain-free controls. We report two novel findings. First, movement-evoked pain in individuals with cLBP was associated with longer reaction times, delayed peak velocity and greater movement variability. Second, movement-evoked pain was associated with an attenuated reduction in beta power in the premotor cortex and supplementary motor area. Our observations move the field forward by revealing attenuated disinhibition in prefrontal motor areas during movement-evoked pain in cLBP.

The Effects of Cross-Legged Sitting on the Trunk and Pelvic Angles and Gluteal Pressure in People with and without Low Back Pain

The purpose of this study was to investigate the effects of cross-legged sitting on the trunk flexion angle, pelvic obliquity, and gluteal pressure of subjects with and without low back pain (LBP). The study subjects were 30 LBP patients and 30 healthy individuals. They were instructed to sit on a chair, the height of which was adjustable, so that their knee and hip joints were bent at 90°. All subjects were asked to perform two sitting postures: erect sitting and cross-legged sitting. Trunk flexion angle and pelvic obliquity were measured using a three-dimensional motion-capture system, and gluteal pressure was measured using a force plate. Compared to erect sitting, cross-legged sitting showed a significantly lower trunk flexion angle and greater pelvic obliquity in both groups. Compared to healthy subjects, the patients with LBP had lower trunk flexion angles and greater gluteal pressure asymmetry during cross-legged sitting. The pelvic obliquity was greater in the cross-legged sitting posture than in the erect sitting posture, but there was no difference between the groups. We found that the trunk became more slouched in the cross-legged sitting posture than in the erect sitting posture, and this tendency was more pronounced in patients with LBP.

Dynamics of Changes in Isometric Strength and Muscle Imbalance in the Treatment of Women with Low back Pain

The aim of the study was to evaluate the dynamics of isometric changes in strength and muscular lumbar-pelvic imbalances in the treatment of women with low back pain. Forty-one women, nineteen in the study group (A) and twenty-two in the control group (B), participated in the study. Magnetic resonance imaging (MRI) was performed to assess the degree of degenerative changes in the lumbar spine. The diagnosis of isometric muscle strength and their imbalances was performed with the Tergumed 700 device. After six weeks of therapy in the study group (A), there was a significant improvement in the strength of all the examined muscle groups. However, in the control group (B), significant improvement occurred only in the strength of the lumbar flexor muscles and the flexor muscles on the left side. Furthermore, there was a significant intensification of the imbalance of left flexor muscle strength compared to right flexor strength in group B. Significant differences in favour of the study group (A) concerned the strength of the rotator muscles to the left, the strength of the extensor muscles of the lumbar spine, the strength of the flexors of the lumbar spine to the right, and the balance of the strength of the lumbar spine flexors to the left compared to the strength of the flexor muscles to the right. Therapy with the Tergumed 700 system leads to an increase in the muscle strength of the lumbar and pelvic complex, compensating for its imbalance, bringing beneficial effects in the treatment of low back pain.

People With Low Back Pain Display a Different Distribution of Erector Spinae Activity During a Singular Mono-Planar Lifting Task

This study aimed to investigate the variation in muscle activity and movement in the lumbar and lumbothoracic region during a singular mono-planar lifting task, and how this is altered in individuals experiencing low back pain (LBP). Muscle activity from the lumbar and lumbothoracic erector spinae of 14 control and 11 LBP participants was recorded using four 13 × 5 high-density surface electromyography (HDEMG) grids. Root mean squared HDEMG signals were used to create spatial maps of the distribution of muscle activity. Three-dimensional kinematic data were recorded focusing on the relationship between lumbar and thoracic movements. In the task, participants lifted a 5 kg box from knee height to sternal height, and then returned the box to the starting position. The center of muscle activity for LBP participants was found to be systematically more cranial throughout the task compared to the control participants (P < 0.05). Participants with LBP also had lower signal entropy (P < 0.05) and lower absolute root mean squared values (P < 0.05). However, there were no differences between groups in kinematic variables, with no difference in contributions between lumbar and thoracic motion segments (P > 0.05). These results indicate that participants with LBP utilize an altered motor control strategy to complete a singular lifting task which is not reflected in their movement strategy. While no differences were identified between groups in the motion between lumbar and thoracic motion segments, participants with LBP utilized a less homogenous, less diffuse and more cranially focussed contraction of their erector spinae to complete the lifting movement. These results may have relevance for the persistence of LBP symptoms and the development of new treatments focussing on muscle retraining in LBP.

Low Back Pain: The Potential Contribution of Supraspinal Motor Control and Proprioception

Motor control, which relies on constant communication between motor and sensory systems, is crucial for spine posture, stability and movement. Adaptions of motor control occur in low back pain (LBP) while different motor adaption strategies exist across individuals, probably to reduce LBP and risk of injury. However, in some individuals with LBP, adapted motor control strategies might have long-term consequences, such as increased spinal loading that has been linked with degeneration of intervertebral discs and other tissues, potentially maintaining recurrent or chronic LBP. Factors contributing to motor control adaptations in LBP have been extensively studied on the motor output side, but less attention has been paid to changes in sensory input, specifically proprioception. Furthermore, motor cortex reorganization has been linked with chronic and recurrent LBP, but underlying factors are poorly understood. Here, we review current research on behavioral and neural effects of motor control adaptions in LBP. We conclude that back pain-induced disrupted or reduced proprioceptive signaling likely plays a pivotal role in driving long-term changes in the top-down control of the motor system via motor and sensory cortical reorganization. In the outlook of this review, we explore whether motor control adaptations are also important for other (musculoskeletal) pain conditions.

Short-term effect of delayed-onset muscle soreness on trunk proprioception during force reproduction tasks in a healthy adult population: a crossover study

PURPOSE

The aim of this study was to evaluate the effects of lumbar muscle delayed-onset muscle soreness (DOMS) on the ability of the trunk muscles to reproduce different levels of force.

METHODS

Twenty healthy adults (10 males and 10 females) were recruited for this study. Force reproduction in trunk extension and flexion was assessed at 50 and 75% of participants' maximal isometric voluntary contraction in flexion and extension before and after a lumbar muscle DOMS protocol. Trunk proprioception was evaluated and compared between these conditions using different variables such as constant errors (CE), absolute errors (AE), variable errors (VE) and time to peak force (TPF). For each variable, repeated measure ANOVAs were conducted.

RESULTS

AE were higher when participants had to reach the target post-DOMS protocol in extension compared to flexion and in the presence of higher demand of force (p = 0.02). For VE, results showed that participants were more variable in extension than in flexion when the required force was higher (p = 0.04). CE variable was higher when participants had to reach the force target in extension compared to flexion under the effect of DOMS (p = 0.02). Results also showed that participants took less time to reach the force target post-DOMS protocol in extension (0.62 ± 0.20 s) and in flexion (0.53 ± 0.19 s) than pre-DOMS protocol in extension (0.55 ± 0.15) and in flexion (0.50 ± 0.20) (p < 0.001).

CONCLUSION

Lumbar muscle DOMS affects trunk proprioception during force reproduction tasks especially in trunk extension and at higher force.

Are there differences in lifting technique between those with and without low back pain? A systematic review

Background and aims

To systemically review the literature to compare freestyle lifting technique, by muscle activity and kinematics, between people with and without low back pain (LBP).

Methods

Five databases were searched along with manual searches of retrieved articles by a single reviewer. Studies were included if they compared a freestyle lifting activity between participants with and without LBP. Data were extracted by two reviewers, and studies were appraised using the CASP tool for case-control studies.

Results

Nine studies were eligible. Heterogeneity did not allow for meta-analysis. Most studies (n = 8 studies) reported that people with LBP lift differently to pain-free controls. Specifically, people with LBP lift more slowly (n = 6 studies), use their legs more than their back especially when initiating lifting (n = 3 studies), and jerk less during lifting (n = 1 studies). Furthermore, the four larger studies involving people with more severe LBP also showed that people with LBP lift with less spinal range of motion and greater trunk muscle activity for a longer period.

Conclusions

People with LBP move slower, stiffer, and with a deeper knee bend than pain-free people during freestyle lifting tasks. Interestingly, such a lifting style mirrors how people, with and without LBP, are often told how to lift during manual handling training. The cross-sectional nature of the comparisons does not allow for causation to be determined.

Implications

The changes described may show embodiment of cautious movement, and the drive to protect the back. There may be value in exploring whether adopting a lifting style closer to that of pain-free people could help reduce LBP.

Individuals With Recurrent Low Back Pain Exhibit Significant Changes in Paraspinal Muscle Strength After Intramuscular Fine Wire Electrode Insertion

OBJECTIVE

To examine how insertion and presence of intramuscular fine-wire electromyography electrodes (IFWEs) in lumbar multifidus affect paraspinal muscle strength, endurance, and activation in persons with and without recurrent lower back pain (RLBP) during activities that require high levels of muscle contraction.

DESIGN

Case-control with randomization of conditions.

SETTING

Clinical research laboratory.

PARTICIPANTS

Forty participants age 18 to 40 years were recruited (18 female; mean age = 25.5 years); 20 with a history of RLBP were compared to a matching control group of 20 without RLBP.

INTERVENTIONS

Each participant was tested under three conditions over three sessions. On Session 1, the baseline condition, we assessed muscle performance without IFWE insertion. On Sessions 2 and 3, participants were randomly alternated between two experimental conditions: (1) wire-in, in which the IFWE was inserted and remained within the muscle during testing; and (2) wire-out, in which the IFWE was inserted and immediately removed.

MAIN OUTCOME MEASUREMENTS

Lumbar spinal extensor peak strength, endurance, and normalized electromyography (EMG) amplitude during the endurance test.

RESULTS

Individuals with RLBP showed a significant decrease in peak strength during conditions that involved IFWE insertion and tend to experience more pain during muscle testing. Both groups exhibited similar levels of performance and muscle activation during the endurance test.

CONCLUSION

Our findings indicate that individuals with RLBP exhibited reduced lumbar extensor strength in response to IFWE insertion to the deep paraspinal muscles. This behavior is different from those without RLBP. Researchers should carefully consider the use of IFWE in individuals with RLBP during high exertion activities.

High-Density Electromyography Provides New Insights into the Flexion Relaxation Phenomenon in Individuals with Low Back Pain

Recent research using high-density electromyography (HDEMG) has provided a more precise understanding of the behaviour of the paraspinal muscles in people with low back pain (LBP); but so far, HDEMG has not been used to investigate the flexion relaxation phenomenon (FRP). To evaluate this, HDEMG signals were detected with grids of electrodes (13 × 5) placed bilaterally over the lumbar paraspinal muscles in individuals with and without LBP as they performed repetitions of full trunk flexion. The root mean square of the HDEMG signals was computed to generate the average normalized amplitude; and the spatial FRP onset was determined and expressed as percentage of trunk flexion. Smoothing spline analysis of variance models and the contrast cycle difference approach using the Bayesian interpretation were used to determine statistical inference. All pain-free controls and 64.3% of the individuals with LBP exhibited the FRP. Individuals with LBP and the FRP exhibited a delay of its onset compared to pain-free controls (significant mean difference of 13.3% of trunk flexion).  They also showed reduced normalized amplitude compared to those without the FRP, but still greater than pain-free controls (significant mean difference of 27.4% and 11.6% respectively). This study provides novel insights into changes in lumbar muscle behavior in individuals with LBP.

The effect of chronic, non-specific low back pain on superficial lumbar muscle activity: a protocol for a systematic review and meta-analysis

INTRODUCTION

Chronic, non-specific low back pain is a major global cause of disability. One factor which might potentially contribute to ongoing pain is maladaptive variation in the level of activity in the lumbar musculature. Several studies have investigated this activity using surface electromyography, in varied muscles and during a number of functional activities. Due to differences in the applied methodology, the results have been difficult to compare, and previous reviews have been limited in scope. In this protocol, we aim to perform a comprehensive review of the effect of chronic low back pain on lumbar muscle activity.

METHODS AND ANALYSIS

This protocol was informed by the Preferred Reporting Items for Systematic Review and Meta-analysis Protocols (PRISMA-P) and results will be reported in line with the PRISMA. Searches will be conducted on the Web of Science, PubMed, MEDLINE, EMBASE, ZETOC and CINAHL databases, along with a comprehensive review of grey literature and key journals. One reviewer will conduct the searches, but two independent reviewers will screen potential studies and assess the risk of bias within studies which meet the inclusion criteria. The Newcastle-Ottawa risk of bias tool, and the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) guidelines will be used to assess the quality of the data. Meta-analysis will be conducted where appropriate on groups of studies with homogenous methodology. Where studies are too heterogeneous to allow for meta-analysis, meta-synthesis will instead be completed, comparing results in terms of net increases or decreases of activity.

ETHICS AND DISSEMINATION

This review aims to identify common adaptations of muscle activity in people with low back pain and it is expected that the results will influence future research directions and future rehabilitation approaches. The results will be submitted for publication in a peer-reviewed journal and presented at conferences.

PROSPERO REGISTRATION NUMBER

CRD42019125156.

Altered neural oscillations within and between sensorimotor cortex and parietal cortex in chronic jaw pain

Pain perception is associated with priming of the motor system and the orienting of attention in healthy adults. These processes correspond with decreases in alpha and beta power in the sensorimotor and parietal cortices. The goal of the present study was to determine whether these findings extend to individuals with chronic pain. Individuals with chronic jaw pain and pain-free controls anticipated and experienced a low pain or a moderate pain-eliciting heat stimulus. Although stimuli were calibrated for each subject, stimulus temperature was not different between groups. High-density EEG data were collected during the anticipation and heat stimulation periods and were analyzed using independent component analyses, EEG source localization, and measure projection analyses. Direct directed transfer function was also estimated to identify frequency specific effective connectivity between regions. Between group differences were most evident during the heat stimulation period. We report three novel findings. First, the chronic jaw pain group had a relative increase in alpha and beta power and a relative decrease in theta and gamma power in sensorimotor cortex. Second, the chronic jaw pain group had a relative increase in power in the alpha and beta bands in parietal cortex. Third, the chronic jaw pain group had less connectivity strength in the beta and gamma bands between sensorimotor cortex and parietal cortex. Our findings show that the effect of chronic pain attenuates rather than magnifies neural responses to heat stimuli. We interpret these findings in the context of system-level changes in intrinsic sensorimotor and attentional circuits in chronic pain.

Lack of Exercise-Induced Hypoalgesia to Repetitive Back Movement in People with Chronic Low Back Pain

PURPOSE

To investigate whether people with chronic low back pain (LBP) show dysfunctional exercise-induced hypoalgesia (EIH) in response to repeated contractions of their back muscles during a lifting task.

METHODS

In this cross-sectional observational study conducted on asymptomatic participants (n = 18) and participants with chronic LBP (n = 21), quantitative sensory testing (QST) was applied extensively over the lumbar region and a remote area before and after a repeated task that involved lifting a 5-kg box for ~7 minutes. QST included pressure pain thresholds (PPTs), thermal detection, pain thresholds, and measures of temporal summation. Topographical maps of the percentage change in PPT detected at 16 locations over the lumbar region were generated to explore regional differences and compared between groups.

RESULTS

Mean (standard deviation) PPTs measured from 16 sites over the lower back changed significantly in asymptomatic participants (+29.78 kPa [41.4]) following task completion, indicative of EIH, whereas no significant change was observed for the low back pain (LBP) group (-14.87 kPa [61.2]). No changes were detected at the remote site for either group. No changes were revealed for the thermal tests. Temporal summation data revealed decreasing pain sensitivity as the test progressed, but the test response did not change after the exercise for either group.

CONCLUSION(S)

Unlike asymptomatic individuals, participants with LBP lacked EIH over the lumbar erector spinae muscles following repeated lifting. Although these results should be considered in relation to the study limitations, particularly the absence of a control group, the findings support impaired EIH in patients with LBP.

Deformations of abdominal muscles under experimentally induced low back pain

PURPOSE

Low back pain (LBP) is associated with altered motor control and muscle activity; however, it remains unknown whether these changes predispose humans to injury and pain or are the consequence of ongoing nociceptive processes. In this experimental study, we aimed to use a novel ultrasound imaging technique for the measurement of lateral abdominal wall muscle activity: the tissue deformation index (TDI).

METHODS

Forty-two healthy subjects (22.30 ± 1.49 years of age) were exposed to postural perturbation induced by rapid arm movement. Activity of three muscles, the transversus abdominis (TrA) and the internal and external oblique (EO), was recorded by ultrasound imaging (M-mode) with and without induction of LBP. Pain was induced by electrical stimulation applied bilaterally to the lumbar spine.

RESULTS

No significant differences in the TDI between right and left sides of the body (p > 0.05) were found. Generally, muscles deformed slower with pain compared to non-painful conditions; however, only EO muscle displayed a statistically significant reduction in deformation velocity (p ≤ 0.00001). TDI for EO decreased from 0.065% per ms ( ± 0.038, 95% CI 0.057-0.074) to 0.053% per ms ( ± 0.035, 95% CI 0.046-0.061). Furthermore, characteristic inter-muscular TDI gradients were observed, directed from inner towards outer muscular layers, with TrA showing the lowest TDI and EO the highest.

CONCLUSION

Experimentally induced LBP suppresses deformation of the superficial abdominal muscles and increases the variability of local/deep muscles. Further research is required to confirm these observations. These slides can be retrieved under Electronic Supplementary Material.

Rate of force development and maximal force: reliability and difference between non-climbers, skilled and international climbers

The goal of this study was to assess (i) test-retest reliability between sessions and within sessions, and (ii) the difference among three skill levels (international n = 12, skilled n = 10 and non-climbers n = 9) for finger flexor maximal force (Fmax) and rate of force development (RFD) at different time scales. Each climber performed a maximal finger flexion on a dynamometer in two different conditions: half crimp and slope crimp. The inter-session revealed no difference with low to high correlation from 0.56 to 0.94. Intra-session reliability reveals intraclass correlation ranging from 0.40 to 0.98 for all groups. The coefficients of variation ranged from 7.77% to 28.34% for RFD and 2.90% to 9.99% for Fmax. Maximal force, expressed as an absolute or normalised value, reveals a significant difference between all samples (22.11% difference between international and 38.58% between skilled and non-climbers). Finally, the difference in RFD_200ms and RFD_95% among the three groups suggests that the practice of intensive climbing causes many changes in neural and structural factors. Last, RFD_200ms and RFD_95% are highly reliable and can be used to discriminate samples, suggesting that these variables could be used in monitoring training.

Reduced muscle activity variability in lumbar extensor muscles during sustained sitting in individuals with chronic low back pain

The purpose of this study was to investigate muscle activity variability within and between the right and left side of lumbar muscles in patients with chronic low back pain (cLBP) compared to healthy controls (HCs) during sustained quiet sitting. Surface electromyographic (EMG) signals were collected bilaterally from the lumbar muscles with 2 high density surface EMG grids of 9x14 electrodes. Root mean square values (RMS) over 1-sec epochs of all bipolar EMG leadings were obtained. Between-sides alternating activation was computed, as well as temporal- and spatial variability within the electrode grids through the coefficient of variation and correlations between RMS distributions. The subjective influence of sitting was evaluated by the rating of perceived exertion and the amount of LBP on a numeric pain rating scale. Compared to HCs, the patients with cLBP had lower temporal (p = 0.03) and similar spatial muscle activity variability during sitting, despite a more variable sitting position. This did not result in increased muscle fatigue indicated by EMG, but the patients with cLBP reported higher levels of RPE during- and more LBP after the sitting and as a consequence ended the sitting earlier than HCs (p < 0.01). Present findings lend support to the presence of less tolerance for low-level static muscle load in patients with cLBP.

Variation in the spatial distribution of erector spinae activity during a lumbar endurance task in people with low back pain

This study aimed to investigate the spatial distribution and redistribution of lumbar erector spinae (ES) activity during a lumbar extension endurance task in pain-free participants and how this is modified in people with low back pain (LBP). High density surface electromyography (HDEMG) was recorded using 13 × 5 electrode grids placed over the lumbar ES in 13 LBP and 13 control participants while completing an Ito test to task failure. The root mean square of the HDEMG signals was computed, a topographical map of the EMG amplitude generated and the centre of the activity (centroid) determined throughout the task. The centroid of the EMG amplitude map was systematically more cranial (F = 6.09, P = 0.022) for the LBP participants compared with the control subjects. Regression analysis showed that the extent of redistribution of ES activity was associated with longer endurance. These results show that LBP participants utilised a different motor strategy to perform the endurance task, characterised by greater activation of more cranial regions of the ES and less redistribution of ES activity throughout the task. This study provides new insight into the functional activation of the lumbar ES and how it is modified when people have pain.