Electromyography Data Processing Impacts Muscle Synergies during Gait for Unimpaired Children and Children with Cerebral Palsy

Muscle synergies calculated from electromyography (EMG) data identify weighted groups of muscles activated together during functional tasks. Research has shown that fewer synergies are required to describe EMG data of individuals with neurologic impairments. When considering potential clinical applications of synergies, understanding how EMG data processing impacts results and clinical interpretation is important. The aim of this study was to evaluate how EMG signal processing impacts synergy outputs during gait. We evaluated the impacts of two common processing steps for synergy analyses: low pass (LP) filtering and unit variance scaling. We evaluated EMG data collected during barefoot walking from five muscles of 113 children with cerebral palsy (CP) and 73 typically-developing (TD) children. We applied LP filters to the EMG data with cutoff frequencies ranging from 4 to 40 Hz (reflecting the range reported in prior synergy research). We also evaluated the impact of normalizing EMG amplitude by unit variance. We found that the total variance accounted for (tVAF) by a given number of synergies was sensitive to LP filter choice and decreased in both TD and CP groups with increasing LP cutoff frequency (e.g., 9.3 percentage points change for one synergy between 4 and 40 Hz). This change in tVAF can alter the number of synergies selected for further analyses. Normalizing tVAF to a z-score (e.g., dynamic motor control index during walking, walk-DMC) reduced sensitivity to LP cutoff. Unit variance scaling caused comparatively small changes in tVAF. Synergy weights and activations were impacted less than tVAF by LP filter choice and unit variance normalization. These results demonstrate that EMG signal processing methods impact outputs of synergy analysis and z-score based measures can assist in reporting and comparing results across studies and clinical centers

Superficial shoulder muscle synergy analysis in Facioscapulohumeral Dystrophy during humeral elevation tasks

Facioscapulohumeral Dystrophy (FSHD) is a progressive muscle-wasting disease which leads to a decline in upper extremity functionality. Although the scapulohumeral joint's stability and functionality are affected, evidence on the synergetic control of the shoulder muscles in FSHD individuals is still lacking. The aim of this study is to understand the neuromuscular changes in shoulder muscle control in people with FSHD. Upper arm kinematics and electromyograms (EMG) of eight upper extremity muscles were recorded during shoulder abduction-adduction and flexion-extension tasks in eleven participants with FSHD and eleven healthy participants. Normalized muscle activities were extracted from EMG signals. Non-negative matrix factorization was used to compute muscle synergies. Maximum muscle activities were compared using non-parametric analysis of variance. Similarities between synergies were also calculated using correlation. The Biceps Brachii was significantly more active in the FSHD group (25±2%) while Trapezius Ascendens and Serratus Anterior were less active (32±7% and 39±4% respectively). Muscle synergy weights were altered in FSHD individuals and showed greater diversity while controls mostly used one synergy for both tasks. The decreased activity by selected scapula rotator muscles and muscle synergy weight alterations show that neuromuscular control of the scapulohumeral joint is less consistent in people with FSHD compared to healthy participants. Assessments of muscle coordination strategies can be used to evaluate motor output variability and assist in management of the disease

A Review of EMG Techniques for Detection of Gait Disorders

Electromyography (EMG) is a commonly used technique to record myoelectric signals, i.e., motor neuron signals that originate from the central nervous system (CNS) and synergistically activate groups of muscles resulting in movement. EMG patterns underlying movement, recorded using surface or needle electrodes, can be used to detect movement and gait abnormalities. In this review article, we examine EMG signal processing techniques that have been applied for diagnosing gait disorders. These techniques span from traditional statistical tests to complex machine learning algorithms. We particularly emphasize those techniques are promising for clinical applications. This study is pertinent to both medical and engineering research communities and is potentially helpful in advancing diagnostics and designing rehabilitation devices

Neural control of gait in people with haemophilic arthropathy

La hemofilia es un trastorno hemorrágico causado por una deficiencia de los factores VIII o IX de la coagulación. Las personas con hemofilia grave pueden tener hemorragias espontáneas o hemorragias en respuesta a traumatismos menores; la mayoría de los eventos ocurren en las articulaciones y los músculos. La manifestación clínica más frecuente es la artropatía hemofílica, que resulta del sangrado intraarticular repetitivo y de la membrana sinovial inflamada, lo que puede resultar en dolor crónico y deterioro articular. El objetivo general de mi tesis fue investigar el control neural de la marcha en personas con artropatía hemofílica (PCAH). La hipótesis de mi tesis fue que control neural de la marcha se ve afectado en PCAH, y los cambios en el control neural de la marcha están asociados con el daño articular y la cronicidad de la restricción articular. Se seleccionó la marcha, ya que las rodillas y los tobillos son las articulaciones que más se afectan en adultos PCAH. El núcleo de mi tesis fue investigar el control neural mediante el estudio de patrones de actividad de electromiografía (EMG) de músculos individuales y/o sinergias musculares, así como su interacción con la cinemática articular y evaluaciones clínicas. En el capítulo 1, ofrezco una perspectiva general sobre el impacto de la hemofilia en el sistema musculoesquelético, las lagunas actuales en el conocimiento sobre el control neural de la marcha en la artropatía hemofílica y cómo evaluar el control neural de la marcha. En los Capítulos 2 y 4, a través de las evaluaciones de los patrones de activación muscular de músculos individuales, la coordinación entre pares de músculos antagonistas y el análisis de sinergia muscular, confirmamos la hipótesis de que el control neural de la marcha se ve afectado en PCAH. En los capítulos 3 y 5, confirmamos que el control neural alterado de la marcha en PCAH está asociado con la gravedad del daño articular y la cronicidad de la restricción articular. En el capítulo 6, discutimos los resultados de los capítulos centrados en las perspectivas clínicas y fisiológicas del control neural alterado de la marcha en PCAH. Además, discutimos cómo la evaluación del control neuronal a través del índice dynamic motor control index during walking (Walk-DMC) puede ser una alternativa para monitorear el deterioro motor en PCAH. Con base en nuestros resultados, también discutimos cómo mejorar los resultados de la fisioterapia y las intervenciones quirúrgicas que tienen como objetivo mejorar la locomoción en PCAH. Mi tesis contribuye a comprender las consecuencias de la artropatía hemofílica, en especial en la neuromecánica de la marcha. Los hallazgos de mi tesis indican que el control neural de la marcha se ve afectado en PCAH, y los cambios en el control neural de la marcha están asociados con el daño articular, el dolor y cronicidad de la restricción articular. Desde una perspectiva científica, los cambios en el control neural de la marcha en PCAH implican patrones de actividad alterados de los músculos del tren inferior y una reorganización modular de la marcha. Desde una perspectiva clínica, mi tesis brinda una nueva mirada sobre cómo monitorear la progresión de la enfermedad en PCAH utilizando el índice Walk-DMC, brindando nuevas perspectivas para mejorar las intervenciones terapéuticas que apuntan a recuperar la marcha en PCAH.Haemophilia is a bleeding disorder caused by a deficiency of coagulation factors VIII or factor IX. People with severe haemophilia may have spontaneous bleeding events or bleeding in response to minor trauma; most of the events occur in the joints and muscles. The most frequent clinical manifestation is haemophilic arthropathy, which results from repetitive intraarticular bleeding and inflamed synovial membrane, which may result in chronic pain and joint impairment. The overall aim of my thesis was to investigate the neural control of gait in people with haemophilic arthropathy (PWHA). I hypothesized that neural gait control is affected in PWHA, and the changes in neural control of gait are associated with joint damage and chronicity of the joint constraint. Gait was selected because the knees and ankles are the most prevalent affected joints in adults PWHA. The core of my thesis is investigating neural control by studying electromyography (EMG) activity patterns of single muscles and/or muscle synergies, as well as their interaction with joint kinematics and clinical outcomes. In chapter 1, I provide a general perspective about the impact of haemophilia on the musculoskeletal system, the current gaps in knowledge in the neural control of gait in haemophilic arthropathy, and how to assess the neural control of gait. In Chapters 2 and 4, through the assessments of muscle activation patterns of single muscles, coordination between antagonistic muscle pairs, and muscle synergy analysis, we confirmed the hypothesis that the neural control of gait is affected in PWHA. In chapters 3 and 5, we confirm that the altered neural control of gait in PWHA is associated with the severity of joint damage and chronicity of joint constraint. In chapter 6, we discussed the results of chapters focused on clinical and physiological perspectives of the altered neural control of gait in PWHA. In addition, we discuss how the evaluation of neural control through the Walk-DMC index can be an alternative to monitoring the motor impairment in PWHA. Based on our results, we also discussed on how to improve the outcomes of physical therapy and surgical interventions that aimed to improve the locomotion in PWHA. My thesis contributes to understanding the consequences of haemophilic arthropathy for the neuromechanics of gait. The findings of my thesis indicate that neural control of gait is affected in PWHA, and the changes in the neural control of gait are associated with joint damage, pain and chronicity of the joint constraint. From a scientific perspective, the changes in the neural control of gait in PWHA implicate altered activity patterns of single leg muscles and a modular reorganization of gait. From a clinical perspective, my thesis gives a new perspective on how to monitor disease progression in PWHA using the Walk-DMC index—providing new perspectives to improve the therapeutic interventions that aim to recover gait in PWHA

Nonlinear and factorization methods for the non-invasive investigation of the central nervous system

This thesis focuses on the functional study of the Central Nervous System (CNS) with non-invasive techniques. Two different aspects are investigated: nonlinear aspects of the cerebrovascular system, and the muscle synergies model for motor control strategies. The main objective is to propose novel protocols, post-processing procedures or indices to enhance the analysis of cerebrovascular system and human motion analysis with noninvasive devices or wearable sensors in clinics and rehabilitation. We investigated cerebrovascular system with Near-infrared Spectroscopy (NIRS), a technique measuring blood oxygenation at the level of microcirculation, whose modification reflects cerebrovascular response to neuronal activation. NIRS signal was analyzed with nonlinear methods, because some physiological systems, such as neurovascular coupling, are characterized by nonlinearity. We adopted Empirical Mode Decomposition (EMD) to decompose signal into a finite number of simple functions, called Intrinsic Mode Functions (IMF). For each IMF, we computed entropy-based features to characterize signal complexity and variability. Nonlinear features of the cerebrovascular response were employed to characterize two treatments. Firstly, we administered a psychotherapy called eye movement desensitization and reprocessing (EMDR) to two groups of patients. The first group performed therapy with eye movements, the second without. NIRS analysis with EMD and entropy-based features revealed a different cerebrovascular pattern between the two groups, that may indicate the efficacy of the psychotherapy when administered with eye movements. Secondly, we administered ozone autohemotherapy to two groups of subjects: a control group of healthy subjects and a group of patients suffering by multiple sclerosis (MS). We monitored the microcirculation with NIRS from oxygen-ozone injection up 1.5 hours after therapy, and 24 hours after therapy. We observed that, after 1.5 hours after the ozonetherapy, oxygenation levels improved in both groups, that may indicate that ozonetherapy reduced oxidative stress level in MS patients. Furthermore, we observed that, after ozonetherapy, autoregulation improved in both groups, and that the beneficial effects of ozonetherapy persisted up to 24 hours after the treatment in MS patients. Due to the complexity of musculoskeletal system, CNS adopts strategies to efficiently control the execution of motor tasks. A model of motor control are muscle synergies, defined as functional groups of muscles recruited by a unique central command. Human locomotion was the object of investigation, due to its importance for daily life and the cyclicity of the movement. Firstly, by exploiting features provided from statistical gait analysis, we investigated consistency of muscle synergies. We demonstrated that synergies are highly repeatable within-subjects, reinforcing the hypothesis of modular control in motor performance. Secondly, in locomotion, we distinguish principal from secondary activations of electromyography. Principal activations are necessary for the generation of the movement. Secondary activations generate supplement movements, for instance slight balance correction. We investigated the difference in the motor control strategies underlying muscle synergies of principal (PS) and secondary (SS) activations. We found that PS are constituted by a few modules with many muscles each, whereas SS are described by more modules than PS with one or two muscles each. Furthermore, amplitude of activation signals of PS is higher than SS. Finally, muscle synergies were adopted to investigate the efficacy of rehabilitation of stiffed-leg walking in lower back pain (LBP). We recruited a group of patients suffering from non-specific LBP stiffening the leg at initial contact. Muscle synergies during gait were extracted before and after rehabilitation. Our results showed that muscles recruitment and consistency of synergies improved after the treatment, showing that the rehabilitation may affect motor control strategies

DETERMINING SELECTIVE VOLUNTARY MOTOR CONTROL OF THE LOWER EXTREMITY IN CHILDREN WITH CEREBRAL PALSY

For physiotherapists working in neuro-paediatric gait-rehabilitation, improving motor control of the lower extremity is a major focus. Nevertheless, our understanding of selective voluntary motor control (SVMC) is in its infancy. This PhD project aimed to contribute to close this gap by investigating the nature of SVMC of the lower extremity in children with cerebral palsy (CP) and providing a psychometric robust yet sensitive measurement instrument for quantifying SVMC. The first study investigated the influence of SVMC and other lower extremity and trunk motor impairments on gait capacity using multiple regression-analyses. Although SVMC was not kept within the final model, these study results revealed the importance of SVMC in relation to muscle strength, trunk control and gait capacity. The aim of the second study was to establish validity and reliability of the German version of the ‘Selective Control Assessment of the Lower Extremity’ (SCALE). Although the psychometric properties of the German SCALE were good, information about its responsiveness is lacking. Accordingly, a systematic review was carried out to identify a SVMC measurement instrument with the highest level of evidence for its psychometric properties and best clinical utility. As the findings showed the absence of appropriate, responsive SVMC measures, the aim of the last study was to modify the existing SCALE to make it more sensitive. Due to the positive findings in relation to the psychometric properties of the SCALE, its procedure was combined with a surface electromyography Similarity Index (SI). The first validity and reliability results of the SCALE-SI are promising and serve as benchmarks when applying the SCALE-SI in future clinical and scientific practice. However, to use the SCALE-SI as an outcome measure for detecting therapy-induced changes of SVMC in children with CP, its responsiveness needs to be evaluated in future studies. Key Words: cerebral palsy, selective voluntary motor control, psychometric properties, lower extremity, gait rehabilitatio

DETERMINING SELECTIVE VOLUNTARY MOTOR CONTROL OF THE LOWER EXTREMITY IN CHILDREN WITH CEREBRAL PALSY

For physiotherapists working in neuro-paediatric gait-rehabilitation, improving motor control of the lower extremity is a major focus. Nevertheless, our understanding of selective voluntary motor control (SVMC) is in its infancy. This PhD project aimed to contribute to close this gap by investigating the nature of SVMC of the lower extremity in children with cerebral palsy (CP) and providing a psychometric robust yet sensitive measurement instrument for quantifying SVMC. The first study investigated the influence of SVMC and other lower extremity and trunk motor impairments on gait capacity using multiple regression-analyses. Although SVMC was not kept within the final model, these study results revealed the importance of SVMC in relation to muscle strength, trunk control and gait capacity. The aim of the second study was to establish validity and reliability of the German version of the ‘Selective Control Assessment of the Lower Extremity’ (SCALE). Although the psychometric properties of the German SCALE were good, information about its responsiveness is lacking. Accordingly, a systematic review was carried out to identify a SVMC measurement instrument with the highest level of evidence for its psychometric properties and best clinical utility. As the findings showed the absence of appropriate, responsive SVMC measures, the aim of the last study was to modify the existing SCALE to make it more sensitive. Due to the positive findings in relation to the psychometric properties of the SCALE, its procedure was combined with a surface electromyography Similarity Index (SI). The first validity and reliability results of the SCALE-SI are promising and serve as benchmarks when applying the SCALE-SI in future clinical and scientific practice. However, to use the SCALE-SI as an outcome measure for detecting therapy-induced changes of SVMC in children with CP, its responsiveness needs to be evaluated in future studies. Key Words: cerebral palsy, selective voluntary motor control, psychometric properties, lower extremity, gait rehabilitatio