An Attention-based Bidirectional LSTM Model for Continuous Cross-subject Estimation of Knee Joint Angle during Running from sEMG Signals

Running is an essential locomotion activity that plays a critical role in everyday life and exercise activities and may be impeded by joint disease and neurological impairments. Accurate and robust estimation of joint kinematics via surface electromyogram (sEMG) signals provides a human-machine interaction-based method that can be used to adequately control rehabilitation robots while performing complex movements such as running for motor function restoration in affected persons. To this end, this paper proposes a novel deep learning-based model (AM-BiLSTM) that integrates an attention mechanism (AM) and a bidirectional long short-term memory (BiLSTM) network. The proposed method was evaluated using knee joint kinematic and sEMG signals of fourteen subjects who performed running at 2 m/s speed. The proposed model’s generalizability was tested for within- and cross-subject scenarios and compared with standard LSTM and multi-layer perceptron (MLP) networks in terms of normalized root-mean-square error and correlation coefficient evaluation metrics. Based on the statistical tests, the proposed AM-BiLSTM model significantly outperformed the LSTM and MLP methods in both within- and cross-subject scenarios (p<0.05) and achieved state-of-the-art performance. © 20XX IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Sensor Technologies to Manage the Physiological Traits of Chronic Pain: A Review

Non-oncologic chronic pain is a common high-morbidity impairment worldwide and acknowledged as a condition with significant incidence on quality of life. Pain intensity is largely perceived as a subjective experience, what makes challenging its objective measurement. However, the physiological traces of pain make possible its correlation with vital signs, such as heart rate variability, skin conductance, electromyogram, etc., or health performance metrics derived from daily activity monitoring or facial expressions, which can be acquired with diverse sensor technologies and multisensory approaches. As the assessment and management of pain are essential issues for a wide range of clinical disorders and treatments, this paper reviews different sensor-based approaches applied to the objective evaluation of non-oncological chronic pain. The space of available technologies and resources aimed at pain assessment represent a diversified set of alternatives that can be exploited to address the multidimensional nature of pain.Ministerio de Economía y Competitividad (Instituto de Salud Carlos III) PI15/00306Junta de Andalucía PIN-0394-2017Unión Europea "FRAIL

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

Real-time human ambulation, activity, and physiological monitoring:taxonomy of issues, techniques, applications, challenges and limitations

Automated methods of real-time, unobtrusive, human ambulation, activity, and wellness monitoring and data analysis using various algorithmic techniques have been subjects of intense research. The general aim is to devise effective means of addressing the demands of assisted living, rehabilitation, and clinical observation and assessment through sensor-based monitoring. The research studies have resulted in a large amount of literature. This paper presents a holistic articulation of the research studies and offers comprehensive insights along four main axes: distribution of existing studies; monitoring device framework and sensor types; data collection, processing and analysis; and applications, limitations and challenges. The aim is to present a systematic and most complete study of literature in the area in order to identify research gaps and prioritize future research directions

Dynamics, Electromyography and Vibroarthrography as Non-Invasive Diagnostic Tools: Investigation of the Patellofemoral Joint

The knee joint plays an essential role in the human musculoskeletal system. It has evolved to withstand extreme loading conditions, while providing almost frictionless joint movement. However, its performance may be disrupted by disease, anatomical deformities, soft tissue imbalance or injury. Knee disorders are often puzzling, and accurate diagnosis may be challenging. Current evaluation approach is usually limited to a detailed interview with the patient, careful physical examination and radiographic imaging. The X-ray screening may reveal bone degeneration, but does not carry sufficient information of the soft tissue conditions. More advanced imaging tools such as MRI or CT are available, but expensive, time consuming and can be used only under static conditions. Moreover, due to limited resolution the radiographic techniques cannot reveal early stage arthritis. The arthroscopy is often the only reliable option, however due to its semi-invasive nature, it cannot be considered as a practical diagnostic tool. Therefore, the motivation for this work was to combine three scientific methods to provide a comprehensive, non-invasive evaluation tool bringing insight into the in vivo, dynamic conditions of the knee joint and articular cartilage degeneration. Electromyography and inverse dynamics were employed to independently determine the forces present in several muscles spanning the knee joint. Though both methods have certain limitations, the current work demonstrates how the use of these two methods concurrently enhances the biomechanical analysis of the knee joint conditions, especially the performance of the extensor mechanism. The kinetic analysis was performed for 12 TKA, 4 healthy individuals in advanced age and 4 young subjects. Several differences in the knee biomechanics were found between the three groups, identifying age-related and post-operative decrease in the extensor mechanism efficiency, explaining the increased effort of performing everyday activities experienced by the elderly and TKA subjects. The concept of using accelerometers to assess the cartilage degeneration has been proven based on a group of 23 subjects with non-symptomatic knees and 52 patients suffering from knee arthritis. Very high success (96.2%) of pattern classification obtained in this work clearly demonstrates that vibroarthrography is a promising, non-invasive and low-cost technique offering screening capabilities

Computational Intelligence in Electromyography Analysis

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG may be used clinically for the diagnosis of neuromuscular problems and for assessing biomechanical and motor control deficits and other functional disorders. Furthermore, it can be used as a control signal for interfacing with orthotic and/or prosthetic devices or other rehabilitation assists. This book presents an updated overview of signal processing applications and recent developments in EMG from a number of diverse aspects and various applications in clinical and experimental research. It will provide readers with a detailed introduction to EMG signal processing techniques and applications, while presenting several new results and explanation of existing algorithms. This book is organized into 18 chapters, covering the current theoretical and practical approaches of EMG research

Automatic signal and image-based assessments of spinal cord injury and treatments.

Spinal cord injury (SCI) is one of the most common sources of motor disabilities in humans that often deeply impact the quality of life in individuals with severe and chronic SCI. In this dissertation, we have developed advanced engineering tools to address three distinct problems that researchers, clinicians and patients are facing in SCI research. Particularly, we have proposed a fully automated stochastic framework to quantify the effects of SCI on muscle size and adipose tissue distribution in skeletal muscles by volumetric segmentation of 3-D MRI scans in individuals with chronic SCI as well as non-disabled individuals. We also developed a novel framework for robust and automatic activation detection, feature extraction and visualization of the spinal cord epidural stimulation (scES) effects across a high number of scES parameters to build individualized-maps of muscle recruitment patterns of scES. Finally, in the last part of this dissertation, we introduced an EMG time-frequency analysis framework that implements EMG spectral analysis and machine learning tools to characterize EMG patterns resulting in independent or assisted standing enabled by scES, and identify the stimulation parameters that promote muscle activation patterns more effective for standing. The neurotechnological advancements proposed in this dissertation have greatly benefited SCI research by accelerating the efforts to quantify the effects of SCI on muscle size and functionality, expanding the knowledge regarding the neurophysiological mechanisms involved in re-enabling motor function with epidural stimulation and the selection of stimulation parameters and helping the patients with complete paralysis to achieve faster motor recovery

Effect of age and gender on sEMG signals and force steadiness

Challenges encountered during daily activities are easily overcome by young adults but may be potential risk for falls and injuries among the elderly due to age-associated sensorimotor deficits. To mitigate these risks, early detection of neuromuscular changes is essential and it is important for these to be cost-efficient, non-invasive, high throughput and non-hazardous. Electromyogram (EMG) is a non-invasive recording of the muscle activity that uses inexpensive equipment and hence may be considered for this purpose. However, it is a gross non-specific signal and thus there is need for careful investigation to identify its suitability for studying age-associated changes to the muscles. This research has investigated non-invasive, superficially recorded EMG signals to identify the differences between young healthy adults (20-35 years) and older (60-80 years) subjects of both genders while they were performing isometric ankle plantar flexion and dorsiflexion. The study also studied age and gender differences in the maximal voluntary force, its steadiness, the time to reach steadiness and modulus of the force output prior to steadiness as measured at the foot plate during dorsi- and plantar-flexion. This study has experimentally demonstrated the significant increase in co-activation index around the ankle joint, decrease in the agonistic activity and increase in antagonistic activity in the major lower leg muscles due to ageing. Female participants were noted to have a higher co-activation index in comparison to the males of corresponding age group. From the analysis, it was observed that ageing causes an overall decline in muscle signal complexity affecting the whole muscle strength in both genders. Furthermore, it was also established that within the triceps surae muscle group, Soleus and the gastrocnemii showed varied effects of aging. Another key finding is the significant age and gender difference in the maximal force and its steadiness around the ankle joint during dorsiflexion. However, these differences are less significant during plantarflexion. Results of this study revealed that with age, there was an increase in the total modulus of the force used by the participant to stabilize the foot at a desired level of contraction, difference being more significant during dorsiflexion. This study highlights the age associated neuromuscular adaptations in plantarflexor and dorsiflexor muscles. This is reflected in the altered activity of agonistic and antagonistic muscles during isometric contractions, the reduction in the overall muscle signal complexity, and decreased strength and steadiness of the force exerted by the calf muscles. It has established gender differences in the reduction of the co-activation index and decreased force strength during ankle flexion movements

Identifying Gait Deficits in Stroke Patients Using Inertial Sensors

Falls remain a significant problem for stroke patients. Tripping, the main cause of falls, occurs when there is insufficient clearance between the foot and ground. Based on an individual’s gait deficits, different joint angles and coordination patterns are necessary to achieve adequate foot clearance during walking. However, gait deficits are typically only quantified in a research or clinical setting, and it would be helpful to use wearable devices – such as accelerometers – to quantify gait disorders in real-world situations. Therefore, the objective of this project was to understand gait characteristics that influence the risk of tripping, and to detect these characteristics using accelerometers. Thirty-five participants with a range of walking abilities performed normal walking and attempted to avoid tripping on an unexpected object while gait characteristics were quantified using motion capture techniques and accelerometers. Multiple regression was used to identify the relationship between joint coordination and foot clearance, and multiple analysis of variance was used to determine characteristics of gait that differ between demographic groups, as well as those that enable obstacle avoidance. Machine learning techniques were employed to detect joint angles and the risk of tripping from patterns in accelerometer signals. Measures of foot clearance that represent toe height throughout swing instead of at a single time point are more sensitive to changes in joint coordination, with hip-knee coordination during midswing having the greatest effect. Participants with a history of falls or stroke perform worse than older non-fallers and young adults on many factors related to falls risk, however, there are no differences in the ability to avoid an unexpected obstacle between these groups. Individuals with an inability to avoid an obstacle have lower scores on functional evaluations, exhibit limited sagittal plane joint range of motion during swing, and adopt a conservative walking strategy. Machine learning processes can be used to predict knee range of motion and classify individuals at risk for tripping based on an ankle-worn accelerometer. This work is significant because a portable device that detects gait characteristics relevant to the risk of tripping without expensive motion capture technology may reduce the risk of falls for stroke patients

Pathology detection mechanisms through continuous acquisition of biological signals

Mención Internacional en el título de doctorPattern identification is a widely known technology, which is used on a daily basis for both identification and authentication. Examples include biometric identification (fingerprint or facial), number plate recognition or voice recognition. However, when we move into the world of medical diagnostics this changes substantially. This field applies many of the recent innovations and technologies, but it is more difficult to see cases of pattern recognition applied to diagnostics. In addition, the cases where they do occur are always supervised by a specialist and performed in controlled environments. This behaviour is expected, as in this field, a false negative (failure to identify pathology when it does exists) can be critical and lead to serious consequences for the patient. This can be mitigated by configuring the algorithm to be safe against false negatives, however, this will raise the false positive rate, which may increase the workload of the specialist in the best case scenario or even result in a treatment being given to a patient who does not need it. This means that, in many cases, validation of the algorithm’s decision by a specialist is necessary, however, there may be cases where this validation is not so essential, or where this first identification can be treated as a guideline to help the specialist. With this objective in mind, this thesis focuses on the development of an algorithm for the identification of lower body pathologies. This identification is carried out by means of the way people walk (gait). People’s gait differs from one person to another, even making biometric identification possible through its use. however, when the people has a pathology, both physical or psychological, the gait is affected. This alteration generates a common pattern depending on the type of pathology. However, this thesis focuses exclusively on the identification of physical pathologies. Another important aspect in this thesis is that the different algorithms are created with the idea of portability in mind, avoiding the obligation of the user to carry out the walks with excessive restrictions (both in terms of clothing and location). First, different algorithms are developed using different configurations of smartphones for database acquisition. In particular, configurations using 1, 2 and 4 phones are used. The phones are placed on the legs using special holders so that they cannot move freely. Once all the walks have been captured, the first step is to filter the signals to remove possible noise. The signals are then processed to extract the different gait cycles (corresponding to two steps) that make up the walks. Once the feature extraction process is finished, part of the features are used to train different machine learning algorithms, which are then used to classify the remaining features. However, the evidence obtained through the experiments with the different configurations and algorithms indicates that it is not feasible to perform pathology identification using smartphones. This can be mainly attributed to three factors: the quality of the signals captured by the phones, the unstable sampling frequency and the lack of synchrony between the phones. Secondly, due to the poor results obtained using smartphones, the capture device is changed to a professional motion acquisition system. In addition, two types of algorithm are proposed, one based on neural networks and the other based on the algorithms used previously. Firstly, the acquisition of a new database is proposed. To facilitate the capture of the data, a procedure is established, which is proposed to be in an environment of freedom for the user. Once all the data are available, the preprocessing to be carried out is similar to that applied previously. The signals are filtered to remove noise and the different gait cycles that make up the walks are extracted. However, as we have information from several sensors and several locations for the capture device, instead of using a common cut-off frequency, we empirically set a cut-off frequency for each signal and position. Since we already have the data ready, a recurrent neural network is created based on the literature, so we can have a first approximation to the problem. Given the feasibility of the neural network, different experiments are carried out with the aim of improving the performance of the neural network. Finally, the other algorithm picks up the legacy of what was seen in the first part of the thesis. As before, this algorithm is based on the parameterisation of the gait cycles for its subsequent use and employs algorithms based on machine learning. Unlike the use of time signals, by parameterising the cycles, spurious data can be generated. To eliminate this data, the dataset undergoes a preparation phase (cleaning and scaling). Once a prepared dataset has been obtained, it is split in two, one part is used to train the algorithms, which are used to classify the remaining samples. The results of these experiments validate the feasibility of this algorithm for pathology detection. Next, different experiments are carried out with the aim of reducing the amount of information needed to identify a pathology, without compromising accuracy. As a result of these experiments, it can be concluded that it is feasible to detect pathologies using only 2 sensors placed on a leg.La identificación de patrones es una tecnología ampliamente conocida, la cual se emplea diariamente tanto para identificación como para autenticación. Algunos ejemplos de ello pueden ser la identificación biométrica (dactilar o facial), el reconocimiento de matrículas o el reconocimiento de voz. Sin embargo, cuando nos movemos al mundo del diagnóstico médico esto cambia sustancialmente. Este campo aplica muchas de las innovaciones y tecnologías recientes, pero es más difícil ver casos de reconocimiento de patrones aplicados al diagnóstico. Además, los casos donde se dan siempre están supervisados por un especialista y se realizan en ambientes controlados. Este comportamiento es algo esperado, ya que, en este campo, un falso negativo (no identificar la patología cuando esta existe) puede ser crítico y provocar consecuencias graves para el paciente. Esto se puede intentar paliar, configurando el algoritmo para que sea seguro frente a los falsos negativos, no obstante, esto aumentará la tasa de falsos positivos, lo cual puede aumentar el trabajo del especialista en el mejor de los casos o incluso puede provocar que se suministre un tratamiento a un paciente que no lo necesita. Esto hace que, en muchos casos sea necesaria la validación de la decisión del algoritmo por un especialista, sin embargo, pueden darse casos donde esta validación no sea tan esencial, o que se pueda tratar a esta primera identificación como una orientación de cara a ayudar al especialista. Con este objetivo en mente, esta tesis se centra en el desarrollo de un algoritmo para la identificación de patologías del tren inferior. Esta identificación se lleva a cabo mediante la forma de caminar de la gente (gait, en inglés). La forma de caminar de la gente difiere entre unas personas y otras, haciendo posible incluso la identificación biométrica mediante su uso. Sin embargo, esta también se ve afectada cuando se presenta una patología, tanto física como psíquica, que afecta a las personas. Esta alteración, genera un patrón común dependiendo del tipo de patología. No obstante, esta tesis se centra exclusivamente la identificación de patologías físicas. Otro aspecto importante en esta tesis es que los diferentes algoritmos se crean con la idea de la portabilidad en mente, evitando la obligación del usuario de realizar los paseos con excesivas restricciones (tanto de vestimenta como de localización). En primer lugar, se desarrollan diferentes algoritmos empleando diferentes configuraciones de teléfonos inteligentes para la adquisición de la base de datos. En concreto se usan configuraciones empleando 1, 2 y 4 teléfonos. Los teléfonos se colocan en las piernas empleando sujeciones especiales, de tal modo que no se puedan mover libremente. Una vez que se han capturado todos los paseos, el primer paso es filtrar las señales para eliminar el posible ruido que contengan. Seguidamente las señales se procesan para extraer los diferentes ciclos de la marcha (que corresponden a dos pasos) que componen los paseos. Una vez terminado el proceso de extracción de características, parte de estas se emplean para entrenar diferentes algoritmos de machine learning, los cuales luego son empleados para clasificar las restantes características. Sin embargo, las evidencias obtenidas a través de la realización de los experimentos con las diferentes configuración y algoritmos indican que no es viable realizar una identificación de patologías empleando teléfonos inteligentes. Principalmente esto se puede achacar a tres factores: la calidad de las señales capturadas por los teléfonos, la frecuencia de muestreo inestable y la falta de sincronía entre los teléfonos. Por otro lado, a raíz de los pobres resultados obtenidos empleado teléfonos inteligentes se cambia el dispositivo de captura a un sistema profesional de adquisición de movimiento. Además, se plantea crear dos tipos de algoritmo, uno basado en redes neuronales y otro basado en los algoritmos empleados anteriormente. Primeramente, se plantea la adquisición de una nueva base de datos. Para ellos se establece un procedimiento para facilitar la captura de los datos, los cuales se plantea han de ser en un entorno de libertad para el usuario. Una vez que se tienen todos los datos, el preprocesado que se realizar es similar al aplicado anteriormente. Las señales se filtran para eliminar el ruido y se extraen los diferentes ciclos de la marcha que componen los paseos. Sin embargo, como para el dispositivo de captura tenemos información de varios sensores y varias localizaciones, el lugar de emplear una frecuencia de corte común, empíricamente se establece una frecuencia de corte para cada señal y posición. Dado que ya tenemos los datos listos, se crea una red neuronal recurrente basada en la literatura, de este modo podemos tener una primera aproximación al problema. Vista la viabilidad de la red neuronal, se realizan diferentes experimentos con el objetivo de mejorar el rendimiento de esta. Finalmente, el otro algoritmo recoge el legado de lo visto en la primera parte de la tesis. Al igual que antes, este algoritmo se basa en la parametrización de los ciclos de la marcha, para su posterior utilización y emplea algoritmos basado en machine learning. A diferencia del uso de señales temporales, al parametrizar los ciclos, se pueden generar datos espurios. Para eliminar estos datos, el conjunto de datos se somete a una fase de preparación (limpieza y escalado). Una vez que se ha obtenido un conjunto de datos preparado, este se divide en dos, una parte se usa para entrenar los algoritmos, los cuales se emplean para clasificar las muestras restantes. Los resultados de estos experimentos validan la viabilidad de este algoritmo para la detección de patologías. A continuación, se realizan diferentes experimentos con el objetivo de reducir la cantidad de información necesaria para identificar una patología, sin perjudicar a la precisión. Resultado de estos experimentos, se puede concluir que es viable detectar patologías empleando únicamente 2 sensores colocados en una pierna.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidente: María del Carmen Sánchez Ávila.- Secretario: Mariano López García.- Vocal: Richard Matthew Gues