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

Sensory electrical stimulation during cycling for the rehabilitation of muscle coordination

Gait (a person’s way of walking) is highly complex and involves the musculoskeletal and nervous systems to achieve coordinated movement. Gait is key in daily life, and its impairment greatly reduces the quality of life, personal freedom and self-esteem of afected people. Gait alterations arise from disruption of neuromuscular coordination mechanisms, either due to injury or degeneration (ictus, spinal cord injury...). The long term goal of the line of research that is started with the work presented in this Thesis is to build and validate a neurorehabilitation platform that uses biologically-inspired mechanisms in order to en- hance muscle coordination of walking in neurologically injured patients. As a frst step towards this ambitious goal, this Bachelor’s Thesis involved the design, development and technical validation of the neurorehabilitation platform that combines cycling with sensory electrical stimulation. Furthermore, a pilot study was conducted in order to assess the performance and usability of the neurorehabilitation platform. Prelim- inary results were encouraging, which gives the confdence toward the future applications of the platform. The present Bachelor’s Thesis has developed the necessary setups for performing a variety of experiments related with cycling and electrical stimulation. Future work should focus in further developing the experimental technique used for assessment of muscle coordina- tion, and using the developed neurorehabilitation platform for conducting broader studies with more subjects, both healthy and neurologically injured, with a variety of modali- ties and diverse stimulation patterns. Eventually, and based on the acquired knowledge about stimulation and neurorehabilitation, a commercial neurorehabilitation device could be created and distributed in order to enable low-cost walking rehabilitation for neurolog- ically injured patients.Ingeniería Biomédic

Effects of overground walking with a robotic exoskeleton on lower limb muscle synergies

Les exosquelettes robotisés de marche (ERM) représentent une intervention prometteuse dans le domaine de la réadaptation locomotrice. Sur le plan clinique, les ERM facilitent la mise en application de principes de neuroplasticité. Jusqu'à présent, la majorité des études analysant les effets de l’ERM a été menée avec des ERM fournissant une assistance robotique complète le long d’une trajectoire de mouvements prédéfinie des membres inférieurs (MI) de façon à reproduire la marche de façon quasi parfaite à très basse vitesse. La nouvelle génération d’ERM, maintenant disponible sur le marché, propose de nouveaux modes de contrôles qui permettent, entre autres, une liberté de mouvement accrue aux MIs (c.-à-d. trajectoire non imposée) et une possibilité d’offrir une assistance ou résistance aux mouvements de différentes intensités surtout pendant la phase d’oscillation du cycle de marche. Cependant, les effets de ces modes de contrôles sur la coordination musculaire des MI pendant la marche au sol avec l’ERM, caractérisé via l’extraction de synergies musculaires (SM), restent méconnus. Cette thèse mesure et compare les caractéristiques des SM (c.-à-d. nombre, profils d’activation, composition musculaire et contribution relative des muscles) pendant la la marche au sol sans ou avec un ERM paramétré avec six différents modes de contrôle chez des individus en bonne santé (articles #1 et #2) et d’autres ayant une lésion médullaire incomplète (LMI) (article #3). Les signaux électromyographiques (EMG) des différents muscles clés des MI, enregistrés lors de la marche, ont été utilisés afin d’extraire les SM avec un algorithme de factorisation matricielle non négative. La similarité des cosinus et les coefficients de corrélation ont caractérisé les similitudes entre les caractéristiques des SM. Les résultats montrent que: 1) les profils d'activation temporelle et le nombre de SM sont modifiés en fonction de la vitesse de marche avec, entre autres une augmentation de la vitesse de marche entrainant une fusion de SM, chez les individus en bonne santé marchant sans ERM ; 2) lorsque ces derniers marchent avec un ERM, les différents modes de contrôle testés ne dupliquent pas adéquatement les SM retrouvées lors de la marche sans ERM. En fait, uniquement le mode de contrôle libérant la contrainte de trajectoire de mouvements des MIs dans le plan sagittal lors de la phase d’oscillation reproduit les principales caractéristiques des SM retrouvées pendant la marche sans ERM ; 3) le nombre et la composition musculaire des SM sont modifiés pendant la marche sans ERM chez les personnes ayant une LMI. Cependant, parmi tous les modes de contrôle étudiés, seul le mode de contrôle libérant le contrôle de la trajectoire de mouvements des MI et assistant l’oscillation du MIs (c.-à-d. HASSIST) permets l’extraction de SM similaire à celles observées chez des individus en santé lors d'une marche sans ERM. Dans l’ensemble, cette thèse a mis en évidence le fait que différentes demandes biomécaniques liées à la marche (c.-à-d. vitesse de marche, modes de contrôle de l’ERM) modifient le nombre et les caractéristiques de SM chez les personnes en santé. Cette thèse a également confirmé que la coordination musculaire, mise en évidence via l’analyse de SM, est altérée chez les personnes ayant une LMI et a tendance à se normaliser lors de la marche avec l’ERM paramétré dans le mode de HASSIST. Les nouvelles preuves appuieront les professionnels de la réadaptation dans le processus de prise de décision concernant la sélection du mode de contrôle des MIs lors de l’entrainement locomoteur utilisant avec un ERM.Wearable robotic exoskeletons (WRE) represent a promising rehabilitation intervention for locomotor rehabilitation training that aligns with activity-based neuroplasticity principles in terms of optimal sensory input, massed repetition, and proper kinematics. Thus far, most studies that investigated the effects of WRE have used WRE that provide full robotic assistance and fixed trajectory guidance to the lower extremity (L/E) to generate close-to-normal walking kinematics, usually at very slow speeds. Based on clinicians’ feedback, current commercially-available WRE have additional control options to be able to integrate these devices into the recovery process of individuals who have maintained some ability to walk after an injury to the central nervous system. In this context, WRE now offer additional degrees of movements for the L/E to move freely and different strategies to assist or resist movement, particularly during the gait cycle’s swing phase. However, the extent that these additional WRE control options affect L/E neuromuscular control during walking, typically characterized using muscle synergies (MSs), remains unknown. This thesis measures and compares MSs characteristics (i.e., number, temporal activation profile, and muscles contributing to a specific synergy [weightings]) during typical overground walking, with and without a WRE, in six different control modes, in abled-bodied individuals (Articles #1 and #2) and individuals with incomplete spinal cord injury (iSCI; Article #3). Surface EMG of key L/E muscles were recorded while walking and used to extract MSs using a non-negative matrix factorization algorithm. Cosine similarity and correlation coefficients characterized, grouped, and indicated similarities between MS characteristics. Results demonstrated that: 1) the number of MSs and MS temporal activation profiles in able-bodied individuals walking without WRE are modified by walking speed and that, as speed increased, specific MSs were fused or merged compared to MSs at slow speeds; 2) In able-bodied individuals walking with WRE, few WRE control modes maintained the typical MSs characteristics that were found during overground walking without WRE. Moreover, freeing the L/E swing trajectory imposed by the WRE best reproduced those MSs characteristics during overground walking without the WRE; and 3) After an iSCI, alterations to the number and the composition of MSs were observed during walking without WRE. However, of all WRE control modes that were investigated, only HASSIST (i.e., freeing WRE control over L/E swing trajectory while assisting the user’s self-selected trajectory) reproduced the number and composition of MSs found in abled-bodied individuals during overground walking without WRE. Altogether, the results of this thesis demonstrated that different walking-related biomechanical demands (i.e., walking speed) and most of the WRE control modes can alter some MSs, and their characteristics, in able-bodied individuals. This research also confirmed that impaired muscle coordination, assessed via MSs, can adapt when walking with a WRE set with specific control options (e.g., HASSIST). These MS adaptations mimicked typical MS characteristics extracted during overground walking. The evidence generated by this thesis will support the decision-making process when selecting specific L/E control options during WRE walking, allowing rehabilitation professionals to refine WRE locomotor training protocols

A randomized controlled trial on the effects induced by robot-assisted and usual-care rehabilitation on upper limb muscle synergies in post-stroke subjects

Muscle synergies are hypothesized to reflect connections among motoneurons in the spinal cord activated by central commands and sensory feedback. Robotic rehabilitation of upper limb in post-stroke subjects has shown promising results in terms of improvement of arm function and motor control achieved by reassembling muscle synergies into a set more similar to that of healthy people. However, in stroke survivors the potentially neurophysiological changes induced by robot-mediated learning versus usual care have not yet been investigated. We quantified upper limb motor deficits and the changes induced by rehabilitation in 32 post-stroke subjects through the movement analysis of two virtual untrained tasks of object placing and pronation. The sample analyzed in this study is part of a larger bi-center study and included all subjects who underwent kinematic analysis and were randomized into robot and usual care groups. Post-stroke subjects who followed robotic rehabilitation showed larger improvements in axial-to-proximal muscle synergies with respect to those who underwent usual care. This was associated to a significant improvement of the proximal kinematics. Both treatments had negative effects in muscle synergies controlling the distal district. This study supports the definition of new rehabilitative treatments for improving the neurophysiological recovery after stroke

Feasibility of Muscle Synergy Outcomes in Clinics, Robotics, and Sports: A Systematic Review

In the last years, several studies have been focused on understanding how the central nervous system controls muscles to perform a specific motor task. Although it still remains an open question, muscle synergies have come to be an appealing theory to explain the modular organization of the central nervous system. Even though the neural encoding of muscle synergies remains controversial, a large number of papers demonstrated that muscle synergies are robust across different tested conditions, which are within a day, between days, within a single subject and between subjects that have similar demographic characteristics. Thus, muscle synergy theory has been largely used in several research fields, such as clinics, robotics and sports. The present systematical review aims at providing an overview on the applications of muscle synergy theory in clinics, robotics and sports; in particular, the review is focused on the papers that provide tangible information for: (i) diagnosis or pathology assessment in clinics; (ii) robot-control design in robotics; and (iii) athletes’ performance assessment or training guidelines in sports

Do Muscle Synergies Improve Optimization Prediction of Muscle Activations During Gait?

[Abstract]: Determination of muscle forces during motion can help to understand motor control, assess pathological movement, diagnose neuromuscular disorders, or estimate joint loads. Difficulty of in vivo measurement made computational analysis become a common alternative in which, as several muscles serve each degree of freedom, the muscle redundancy problem must be solved. Unlike static optimization (SO), synergy optimization (SynO) couples muscle activations across all time frames, thereby altering estimated muscle co-contraction. This study explores whether the use of a muscle synergy structure within an SO framework improves prediction of muscle activations during walking. A motion/force/electromyography (EMG) gait analysis was performed on five healthy subjects. A musculoskeletal model of the right leg actuated by 43 Hill-type muscles was scaled to each subject and used to calculate joint moments, muscle–tendon kinematics, and moment arms. Muscle activations were then estimated using SynO with two to six synergies and traditional SO, and these estimates were compared with EMG measurements. Synergy optimization neither improved SO prediction of experimental activation patterns nor provided SO exact matching of joint moments. Finally, synergy analysis was performed on SO estimated activations, being found that the reconstructed activations produced poor matching of experimental activations and joint moments. As conclusion, it can be said that, although SynO did not improve prediction of muscle activations during gait, its reduced dimensional control space could be beneficial for applications such as functional electrical stimulation or motion control and prediction.Ministerio de Ciencia, Innovación y Universidades; PGC2018-095145-B-I0

Developing protocols for analysis of cellular adaptations to peripheral injury in proprioceptive circuits

Proprioception, the sense of position and movement of parts of the body is crucial for proper motor control, and its disruption is associated with various pathologies, particularly joint or muscle injury. While there have been studies into the functional changes of proprioception after injury, the underlying cellular and molecular mechanisms underlying this phenomenon are mostly unknown. Pain hypersensitivity following tissue or nerve damage is a possible analog to proprioceptive disruption. Inflammatory and damage-induced pain have been linked to activation of specific signaling pathways as well as the upregulation of various proteins. We set out to elucidate any parallel between injury-associated pain and proprioceptive disruption at the level of the spinal cord and dorsal root ganglia (DRGs). First, we analyzed global gene expression in dorsal root ganglia (DRGs) in a rat model of anterior cruciate ligament (ACL) injury, a condition commonly associated with altered proprioception. Subsequently, we sought to develop a protocol for targeting specific cells in the muscle proprioceptive circuitry, including DRG neurons and gamma motoneurons (γ-MNs) by combining DiI retrograde axonal tracing with single-cell RNA isolation. Preliminary results suggest an upregulation of matrix metalloproteinase 9 (MMP-9) and neurotrophin-4 (NTF-4) in DRG innervating lesioned knees in rats, suggesting neuropathic pain development, but no significant changes were found in any genes specific to proprioceptive afferents. DiI traced to the correct DRG and spinal cord regions, and a dissociated cell produced an adequate quantity of cDNA. The muscle tracing protocol provides a useful tool for further investigating proprioceptive alterations, the potential to modify the protocol for knee injections may further our understanding of complications in recovery from ACL injuries

Temporal and spatial muscle synergy features and its neural origins during sit-to-stand and stand-to-sit tasks

Sit-to-stand (STS) and stand-to-sit (StandTS) play a vital role in our daily lives. These two transitional motions are considered crucial for independent living. Many people with neurological disorders that lack neuromuscular control lose the ability to perform the transition tasks normally. Several muscles act together to achieve these motions and the inability to perform these daily life tasks, therefore, present the need to understand why they are important and what is the role of muscle synergy in the performance of such tasks. Reduced number of synergies have been found in populations with neurological disorders and the differences in the number of muscle synergies reflect descending neural pathway disruptions and present a correlation with motor deficits. Therefore, this review aims to understand the importance of these two transitional motions and muscle synergy extensively to help develop targeted interventions for healthy and clinical populations.Kinesiology and Health Educatio

Effects of robotic guidance on the coordination of locomotion

Functional integration of motor activity patterns enables the production of coordinated movements, such as walking. The activation of muscles by weightened summation of activation signals has been demonstrated to represent the spatiotemporal components that determine motor behavior during walking. Exoskeleton robotic devices are now often used in the rehabilitation practice to assist physical therapy of individuals with neurological disorders. These devices are used to promote motor recovery by providing guidance force to the patients. The guidance should in principle lead to a muscle coordination similar to physiological human walking. However, the influence of robotic devices on locomotor patterns needs still to be characterized. The aim of this study was to analyze the effect of force guidance and gait speed on the modular organization of walking in a group of eight healthy subjects.This project is funded by the European Commission, project "BETTER" (contract number 247935) and Spanish Consolider-Ingenio Programme, project "HYPER" (contract number CSD2009-00067) and Universita Degli Studi di Roma "Foro Italico", research project "Dynamic sensorimotor interaction during locomotion: influences of perturbations and/or body unloading"