The influence of musculoskeletal pain disorders on muscle synergies-A systematic review

Muscle Strength Identification Based on Isokinetic Testing and Spine Musculoskeletal Modeling

Subject-specific spinal musculoskeletal modeling can help understand the spinal loading mechanism during human locomotion. However, existing literature lacks methods to identify the maximum isometric strength of individual spinal muscles. In this study, a muscle strength identification method combining isokinetic testing and musculoskeletal simulations was proposed, and the influence of muscle synergy and intra-abdominal pressure (IAP) on identified spinal muscle strength was further discussed. A multibody dynamic model of the spinal musculoskeletal system was established and controlled by a feedback controller. Muscle strength parameters were adjusted based on the measured isokinetic moments, and muscle synergy vectors and the IAP piston model were further introduced. The results of five healthy subjects showed that the proposed method successfully identified the subject-specific spinal flexor/extensor strength. Considering the synergistic activations of antagonist muscles improved the correlation between the simulated and measured spinal moments, and the introduction of IAP slightly increased the identified spinal extensor strength. The established method is beneficial for understanding spinal loading distributions for athletes and patients with sarcopenia.

Influence of musculoskeletal pain during gait on kinematics and selective motor control in individuals with spastic cerebral palsy: A pilot study

BACKGROUND

Individuals with cerebral-palsy commonly present with altered kinematics and selective-motor-control during gait, and may also experience musculoskeletal pain. This pilot study aims to investigate if the immediate experience of musculoskeletal pain during gait influences kinematics and selective-motor-control in individuals with spastic cerebral-palsy.

METHODS

Retrospective treadmill-based gait-analysis data for 145 individuals with spastic cerebral-palsy were screened. Participants were asked about experiencing lower-extremity musculoskeletal pain immediately during gait, with 26 individuals (18%) reporting this was the case (pain-group; mean 11.55 ± 3.15 years, Gross-Motor-Function-Classification-System levels I/II/III n = 5/13/8, Uni/bilateral involvement n = 11/15). Of the 77 individuals who did not report any pain, a no-pain group (n = 26) was individually matched. Kinematics were evaluated using the Gait-Profile-Score and spatiotemporal parameters (dimensionless-walking-speed, single-leg-support percentage and step-time). Selective-motor-control was assessed using the Walking-Dynamic-Motor-Control index.

FINDINGS

In the pain-group, 58% reported experiencing pain in their more-involved leg, 8% in the less-involved leg and 34% in both legs. Regarding the pain location, 38% of the pain-group reported experiencing pain in multiple locations. On a more specific level, 35%, 46% and 54% reported pain around the hip/thigh, knee/calf and ankle/ft, respectively. No significant differences were observed between the pain and no-pain groups for any of the outcome measures, in each leg or bilaterally.

INTERPRETATION

No significant differences in kinematics and selective-motor-control during gait were found between individuals with spastic cerebral-palsy, with and without musculoskeletal pain. This suggests that the individuals in this study may not present with obvious antalgic gait patterns, which may relate to the pre-existing altered kinematics and selective-motor-control.

Effect of movement-evoked and tonic experimental pain on muscle force production

INTRODUCTION

When performing an exercise or a functional test, pain that is evoked by movement or muscle contraction could be a stronger stimulus for changing how individuals move compared to tonic pain. We investigated whether the decrease in muscle force production is larger when experimentally-induced knee pain is directly associated to the torque produced (movement-evoked) compared to a constant painful stimulation (tonic).

METHODS

Twenty-one participants performed three isometric knee extension maximal voluntary contractions without pain (baseline), during pain, and after pain. Knee pain was induced using sinusoidal electrical stimuli at 10 Hz over the infrapatellar fat pad, applied continuously or modulated proportionally to the knee extension torque. Peak torque and contraction duration were averaged across repetitions and normalized to baseline.

RESULTS

During tonic pain, participants reported lower pain intensity during the contraction than at rest (p < 0.001), whereas pain intensity increased with contraction during movement-evoked pain (p < 0.001). Knee extension torque decreased during both pain conditions (p < 0.001), but a larger reduction was observed during movement-evoked compared to tonic pain (p < 0.001). Participants produced torque for longer during tonic compared to movement-evoked pain (p = 0.005).

CONCLUSION

Our results indicate that movement-evoked pain was a more potent stimulus to reduce knee extension torque than tonic pain. The longer contraction time observed during tonic pain may be a result of a lower perceived pain intensity during muscle contraction. Overall, our results suggest different motor adaptation to tonic and movement-evoked pain and support the notion that motor adaptation to pain is a purposeful strategy to limit pain. This mechanistic evidence suggests that individuals experiencing prevalently tonic or movement-evoked pain may exhibit different motor adaptations, which may be important for exercise prescription.

Is There a Difference in EEG Characteristics in Acute, Chronic, and Experimentally Induced Musculoskeletal Pain States? a Systematic Review

Electroencephalographic (EEG) alterations have been demonstrated in acute, chronic, and experimentally induced musculoskeletal (MSK) pain conditions. However, there is no cumulative evidence on the associated EEG characteristics differentiating acute, chronic, and experimentally induced musculoskeletal pain states, especially compared to healthy controls. The present systematic review was performed according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (PRISMA) to review and summarize available evidence for cortical brain activity and connectivity alterations in acute, chronic, and experimentally induced MSK pain states. Five electronic databases were systematically searched from their inception to 2022. A total of 3471 articles were screened, and 26 full articles (five studies on chronic pain and 21 studies on experimentally induced pain) were included for the final synthesis. Using the Downs and Black risk of assessment tool, 92% of the studies were assessed as low to moderate quality. The review identified a 'very low' level of evidence for the changes in EEG and subjective outcome measures for both chronic and experimentally induced MSK pain based on the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) criteria. Overall, the findings of this review indicate a trend toward decreased alpha and beta EEG power in evoked chronic clinical pain conditions and increased theta and alpha power in resting-state EEG recorded from chronic MSK pain conditions. EEG characteristics are unclear under experimentally induced pain conditions.

Muscle synergies analysis shows altered neural strategies in women with patellofemoral pain during walking

Several studies suggest that the central nervous system coordinates muscle activation by modulating neural commands directed to groups of muscles combined to form muscle synergies. Individuals with patellofemoral pain (PFP) move differently from asymptomatic individuals. Understanding the neural strategies involved in the execution of tasks such as walking can help comprehend how the movement is planned and better understand this clinical condition. The objective of this study was to compare muscle synergies between women with and without PFP during walking. Eleven women with PFP and thirteen asymptomatic women were assessed using three-dimensional kinematics and electromyography (EMG) while walking at self-selected speed. Kinematics of the trunk, pelvis and lower limbs were analyzed through the Movement Deviation Profile. Muscle synergies were extracted from the EMG signals of eight lower limb muscles collected throughout the whole gait cycle. Kinematic differences between the two groups (p<0.001, z-score = 3.06) were more evident during loading response, terminal stance, and pre-swing. PFP group presented a lower number of muscle synergies (p = 0.037), and greater variability accounted for (VAFtotal) when using 3 (p = 0.017), 4 (p = 0.004), and 5 (p = 0.012) synergies to reconstruct all EMG signals. The PFP group also presented higher VAFmuscle for rectus femoris (p = 0.048) and gastrocnemius medialis (p = 0.019) when considering 4 synergies. Our results suggest that women with PFP show lower motor complexity and deficit in muscle coordination to execute gait, indicating that gait in PFP is the result of different neural commands compared to asymptomatic women.

Test-retest reliability and construct validity of trunk extensor muscle force modulation accuracy

Low back pain is associated with changes in trunk muscle structure and function and motor control impairments. Voluntary force modulation (FM) of trunk muscles is a unique and under-investigated motor control characteristic. One of the reasons for this paucity of evidence is the lack of exploration and publication on the reliability and validity of trunk FM protocols. The purpose of this study was to determine the within- and between-day test-retest reliability and construct validity for trunk extensor muscle FM. Twenty-nine healthy participants were tested under three FM conditions with different modulation rates. Testing was performed on a custom-built apparatus designed for trunk isometric force testing. FM accuracy relative to a fluctuating target force (20-50%MVF) was quantified using the root mean square error of the participant's generated force relative to the target force. Reliability and precision of measurement were assessed using the Intraclass Correlation Coefficient (ICC), standard error of measurement (SEM), minimal detectable difference (MDD95), and Bland-Altman plots. In a subset of participants, we collected surface electromyography of trunk and hip muscles. We used non-negative matrix factorization (NNMF) to identify the underlying motor control strategies. Within- and between-day test-retest reliability was excellent for FM accuracy across the three conditions (ICC range: 0.865 to 0.979). SEM values ranged 0.9-1.8 Newtons(N) and MDD95 ranged from 2.4-4.9N. Conditions with faster rates of FM had higher ICCs. NNMF analysis revealed two muscle synergies that were consistent across participants and conditions. These synergies demonstrate that the muscles primarily involved in this FM task were indeed the trunk extensor muscles. This protocol can consistently measure FM accuracy within and between testing sessions. Trunk extensor FM, as measured by this protocol, is not specific to any trunk muscle group but is the result of modulation by all the trunk extensor muscles.

Neuromuscular adaptations to experimentally induced pain in the lumbar region: systematic review and meta-analysis

ABSTRACT

Experimental pain models are frequently used to understand the influence of pain on the control of human movement. In this systematic review, we assessed the effects of experimentally induced pain in the lumbar region of healthy individuals on trunk muscle activity and spine kinematics. Databases were searched from inception up to January 31, 2022. In total, 26 studies using either hypertonic saline injection (n = 19), heat thermal stimulation (n = 3), nociceptive electrical stimulation (n = 3), or capsaicin (n = 1) were included. The identified adaptations were task dependent, and their heterogeneity was partially explained by the experimental pain model adopted. Meta-analyses revealed an increase of erector spinae activity (standardized mean difference = 0.71, 95% confidence interval [CI] = 0.22-1.19) during full trunk flexion and delayed onset of transversus abdominis to postural perturbation tasks (mean difference = 25.2 ms, 95% CI = 4.09-46.30) in the presence of pain. Low quality of evidence supported an increase in the activity of the superficial lumbar muscles during locomotion and during voluntary trunk movements during painful conditions. By contrast, activity of erector spinae, deep multifidus, and transversus abdominis was reduced during postural perturbation tasks. Reduced range of motion of the lumbar spine in the presence of pain was supported by low quality of evidence. Given the agreement between our findings and the adaptations observed in clinical populations, the use of experimental pain models may help to better understand the mechanisms underlying motor adaptations to low back pain.

Data-driven network analysis identified subgroup-specific low back pain pathways: a cross-sectional GLA:D Back study

OBJECTIVES

To understand the physical, activity, pain, and psychological pathways contributing to low back pain (LBP) -related disability, and if these differ between subgroups.

METHODS

Data came from the baseline observations (n = 3849) of the "GLA:D Back" intervention program for long-lasting nonspecific LBP. 15 variables comprising demographic, pain, psychological, physical, activity, and disability characteristics were measured. Clustering was used for subgrouping, Bayesian networks (BN) were used for structural learning, and structural equation model (SEM) was used for statistical inference.

RESULTS

Two clinical subgroups were identified with those in subgroup 1 having worse symptoms than those in subgroup 2. Psychological factors were directly associated with disability in both subgroups. For subgroup 1, psychological factors were most strongly associated with disability (β = 0.363). Physical factors were directly associated with disability (β = -0.077), and indirectly via psychological factors. For subgroup 2, pain was most strongly associated with disability (β = 0.408). Psychological factors were common predictors of physical factors (β = 0.078), pain (β = 0.518), activity (β = -0.101), and disability (β = 0.382).

CONCLUSIONS

The importance of psychological factors in both subgroups suggests their importance for treatment. Differences in the interaction between physical, pain, and psychological factors and their contribution to disability in different subgroups may open the doors toward more optimal LBP treatments.

Translation of surface electromyography to clinical and motor rehabilitation applications: The need for new clinical figures

Advanced sensors/electrodes and signal processing techniques provide powerful tools to analyze surface electromyographic signals (sEMG) and their features, to decompose sEMG into the constituent motor unit action potential trains, and to identify synergies, neural muscle drive, and EEG-sEMG coherence. However, despite thousands of articles, dozens of textbooks, tutorials, consensus papers, and European and International efforts, the translation of this knowledge into clinical activities and assessment procedures has been very slow, likely because of lack of clinical studies and competent operators in the field. Understanding and using sEMG-based hardware and software tools requires a level of knowledge of signal processing and interpretation concepts that is multidisciplinary and is not provided by most academic curricula in physiotherapy, movement sciences, neurophysiology, rehabilitation, sport, and occupational medicine. The chasm existing between the available knowledge and its clinical applications in this field is discussed as well as the need for new clinical figures. The need for updating the training of physiotherapists, neurophysiology technicians, and clinical technologists is discussed as well as the required competences of trainers and trainees. Indications and examples are suggested and provide a basis for addressing the problem. Two teaching examples are provided in the Supplementary Material.

Linking Pain and Motor Control: Conceptualization of Movement Deficits in Patients With Painful Conditions

When people experience or expect pain, they move differently. Pain-altered movement strategies, collectively described here as pain-related movement dysfunction (PRMD), may persist well after pain resolves and, ultimately, may result in altered kinematics and kinetics, future reinjury, and disability. Although PRMD may manifest as abnormal movements that are often evident in clinical assessment, the underlying mechanisms are complex, engaging sensory-perceptual, cognitive, psychological, and motor processes. Motor control theories provide a conceptual framework to determine, assess, and target processes that contribute to normal and abnormal movement and thus are important for physical therapy and rehabilitation practice. Contemporary understanding of motor control has evolved from reflex-based understanding to a more complex task-dependent interaction between cognitive and motor systems, each with distinct neuroanatomic substrates. Though experts have recognized the importance of motor control in the management of painful conditions, there is no comprehensive framework that explicates the processes engaged in the control of goal-directed actions, particularly in the presence of pain. This Perspective outlines sensory-perceptual, cognitive, psychological, and motor processes in the contemporary model of motor control, describing the neural substrates underlying each process and highlighting how pain and anticipation of pain influence motor control processes and consequently contribute to PRMD. Finally, potential lines of future inquiry-grounded in the contemporary model of motor control-are outlined to advance understanding and improve the assessment and treatment of PRMD.

IMPACT

This Perspective proposes that approaching PRMD from a contemporary motor control perspective will uncover key mechanisms, identify treatment targets, inform assessments, and innovate treatments across sensory-perceptual, cognitive, and motor domains, all of which have the potential to improve movement and functional outcomes in patients with painful conditions.

Modification of Hand Muscular Synergies in Stroke Patients after Robot-Aided Rehabilitation

The central nervous system (CNS) is able to control a very high number of degrees of freedom to perform complex movements of both upper and lower limbs. However, what strategies the CNS adopts to perform complex tasks are not completely clear and are still being studied. Recent studies confirm that stroke subjects with mild and moderate impairment show altered upper limb muscle patterns, but the muscular patterns of the hand have not completely investigated, although the hand represents a paramount tool for performing activities of daily living (ADLs) and stroke can significantly alter the mobilization of this part of the body. In this context, this study aims at investigating hand muscular synergies in chronic stroke patients and evaluating some possible benefits in the robot-aided rehabilitation treatment of the hand in these subjects. Seven chronic stroke patients with mild-to-moderate impairment (FM>30) were involved in this study. They received a 5-week robot-aided rehabilitation treatment with the Gloreha hand exoskeleton, and muscle synergies of both the healthy and injured hand were evaluated at the beginning and at the end of the treatment. The performed analysis showed a very high degree of similarity of the involved synergies between the healthy and the injured limb both before and after the rehabilitation treatment (mean similarity index values: H-BR: 0.88±0.03, H-AR: 0.94±0.03, BR-AR: 0.89±0.05). The increasing similarity is regarded as an effect of the robot-aided rehabilitation treatment and future activities will be performed to increase the population involved in the study.

In vivo effects of two shoulder girdle motor control exercises on acromiohumeral and coracohumeral distances in healthy men

INTRODUCTION

Altered motor control and proprioceptive deficits are associated with kinematics dysfunctions and may cause alterations in subacromial space (SAS) that could lead to shoulder pathologies. Dimensions of the subacromial space, as well as interventions aimed at its normal restitution, can be explored by ultrasound (US).

OBJECTIVE

To describe the effect of two shoulder girdle motor control exercises with cognitive training strategies on SAS dimensions, measured with US.

METHODS

Cognitive movement control strategies, with visual and haptic feedback were applied on 21 healthy participants. SAS dimensions were measured through in vivo variations of acromiohumeral (AHD) and coracohumeral distances (CHD) using US.

RESULTS

Our results show that as exercise repetitions are performed, an increasing trend in both measures can be observed, being wider for AHD (i.e. humeral head descent exercise) than CHD (i.e. scapular retraction exercise).

CONCLUSION

Specific cognitive and motor control exercises improve congruence joint and centering of the humeral head.

Machine learning approaches applied in spinal pain research

The purpose of this narrative review is to provide a critical reflection of how analytical machine learning approaches could provide the platform to harness variability of patient presentation to enhance clinical prediction. The review includes a summary of current knowledge on the physiological adaptations present in people with spinal pain. We discuss how contemporary evidence highlights the importance of not relying on single features when characterizing patients given the variability of physiological adaptations present in people with spinal pain. The advantages and disadvantages of current analytical strategies in contemporary basic science and epidemiological research are reviewed and we consider how analytical machine learning approaches could provide the platform to harness the variability of patient presentations to enhance clinical prediction of pain persistence or recurrence. We propose that machine learning techniques can be leveraged to translate a potentially heterogeneous set of variables into clinically useful information with the potential to enhance patient management.

Flexible Recruitments of Fundamental Muscle Synergies in the Trunk and Lower Limbs for Highly Variable Movements and Postures

The extent to which muscle synergies represent the neural control of human behavior remains unknown. Here, we tested whether certain sets of muscle synergies that are fundamentally necessary across behaviors exist. We measured the electromyographic activities of 26 muscles, including bilateral trunk and lower limb muscles, during 24 locomotion, dynamic and static stability tasks, and we extracted the muscle synergies using non-negative matrix factorization. Our results show that 13 muscle synergies that may have unique functional roles accounted for almost all 24 tasks by combinations of single and/or merging of synergies. Therefore, our results may support the notion of the low dimensionality in motor outputs, in which the central nervous system flexibly recruits fundamental muscle synergies to execute diverse human behaviors. Further studies are required to validate the neural representation of the fundamental components of muscle synergies.

Interpretable machine learning models for classifying low back pain status using functional physiological variables

PURPOSE

To evaluate the predictive performance of statistical models which distinguishes different low back pain (LBP) sub-types and healthy controls, using as input predictors the time-varying signals of electromyographic and kinematic variables, collected during low-load lifting.

METHODS

Motion capture with electromyography (EMG) assessment was performed on 49 participants [healthy control (con) = 16, remission LBP (rmLBP) = 16, current LBP (LBP) = 17], whilst performing a low-load lifting task, to extract a total of 40 predictors (kinematic and electromyographic variables). Three statistical models were developed using functional data boosting (FDboost), for binary classification of LBP statuses (model 1: con vs. LBP; model 2: con vs. rmLBP; model 3: rmLBP vs. LBP). After removing collinear predictors (i.e. a correlation of > 0.7 with other predictors) and inclusion of the covariate sex, 31 predictors were included for fitting model 1, 31 predictors for model 2, and 32 predictors for model 3.

RESULTS

Seven EMG predictors were selected in model 1 (area under the receiver operator curve [AUC] of 90.4%), nine predictors in model 2 (AUC of 91.2%), and seven predictors in model 3 (AUC of 96.7%). The most influential predictor was the biceps femoris muscle (peak [Formula: see text]  = 0.047) in model 1, the deltoid muscle (peak [Formula: see text] =  0.052) in model 2, and the iliocostalis muscle (peak [Formula: see text] =  0.16) in model 3.

CONCLUSION

The ability to transform time-varying physiological differences into clinical differences could be used in future prospective prognostic research to identify the dominant movement impairments that drive the increased risk. These slides can be retrieved under Electronic Supplementary Material.

Assessment of movement coordination strategies to inform health of movement and guide retraining interventions

INTRODUCTION

Exploring characteristics of human movement has long been the focus of clinicians and researchers. Changes in movement coordination strategies have been identified in the presence of pain highlighting the need for assessment in clinical practice. A major development in the understanding of movement related disorders is recognition of individual differences in presentation and consequently the need to tailor interventions based on assessment.

PURPOSE

The purpose of this masterclass is to build a rationale for the clinical assessment of movement coordination strategies, exploring loss of movement choices, coordination variability, and to present a clinical framework for individualised management, including the use of cognitive movement control tests and retraining interventions. An approach for the qualitative rating of movement coordination strategies is presented. A compromised movement system may be one characterised by a lack of ability to access motor abundance and display choice in the use of movement coordination strategies. The identification of lost movement choices revealed during the assessment of movement coordination strategies is proposed as a marker of movement health.

IMPLICATIONS FOR PRACTICE

The health of the movement system may be informed by the ability to display choice in movement coordination strategies. There is evidence that restoring these choices has clinical utility and an influence on pain and improved function. This approach seeks to provide individuals with more flexible problem solving, enabled through a movement system that is robust to each unique challenge of function. This assessment framework sits within a bigger clinical reasoning picture for sustained quality of life.

Myofascial trigger points alter the modular control during the execution of a reaching task: a pilot study

Myofascial trigger points (TP) constitute a conundrum in research and clinical practice as their etiopathogenesis is debated. Several studies investigating one or few muscles have shown that both active and latent TP causes an increased muscle activity, however the influence of TP on modular motor control during a reaching task is still unclear. Electromyographic signals, recorded from the muscles of the shoulder girdle and upper arm during a reaching task, were decomposed with Non-Negative Matrix Factorization algorithm. The extracted matrices of motor modules and activation signals were used to label the muscles condition as dominant or non-dominant. The presence of latent and active TP was detected in each muscle with manual examination. Despite a similar muscle activity was observed, we found that muscles with active TP had increased weighting coefficients when labeled in the dominant condition. No influences were found when muscles were in the non-dominant condition. These findings suggest that TP altered the motor control without co-contraction patterns. As a preliminary evidence, the present results suggest that the increased weighting coefficients in presence of TPs are associated with an alteration of the modular motor control without affecting the dimensionality of motor modules for each individual and reciprocal inhibition.

Retraining in a Female Elite Rower with Persistent Symptoms Post-Arthroscopy for Femoroacetabular Impingement Syndrome: A Proof-of-Concept Case Report

Athletes with femoroacetabular impingement syndrome (FAIS) managed arthroscopically do not always return to sport. Inability to control back/pelvis, hip and lower limb movements may contribute to the onset and recurrence of symptoms. Our hypothesis is that results from a battery of cognitive movement control tests can inform a cognitive movement control (neuromuscular) retraining programme for improving the clinical presentation and quality of life in an athlete with FAIS. This case report presents a female elite rower with persistent left-sided anterior hip pain, four years post-arthroscopic surgery for FAIS, whose symptoms failed to respond to conventional physical therapy. Hip and groin outcome score (HAGOS), passive and active hip flexion range of motion (ROM) workload (time training on water), hip and pelvic kinematics (3-D motion analysis) and electromyography during a seated hip flexion movement control test, and a movement control test battery to identify movement control impairments (The Foundation Matrix), were assessed pre-intervention (week 0) and immediately post-intervention (week 16). Impaired movement control was targeted in a tailored 16-week cognitive movement control retraining exercise program. All measures improved: HAGOS (all 6 sub-scales); symptoms (61/100 pre-training to 96/100 post-training); physical activities participation (13/100 to 75/100); and active hip flexion ROM increased (78 to 116 and 98 to 118 degrees, respectively); workload increased from 4 to 18 h/week; and movement control impairment reduced (25/50 to 9/50). Pelvic motion on kinematic analysis were altered, and delayed activation onset of tensor fascia latae and rectus femoris muscles reduced. This proof-of-concept case report supports the hypothesis that cognitive movement control tests can inform a targeted cognitive movement control retraining program to improve symptoms, function and quality of life, in an elite rower with persistent hip pain. This training offers an alternative approach to conventional physical therapy, which has failed to restore function in FAIS, and the present study illustrates how specific cognitive movement control assessment can direct individual training programmes.