37 research outputs found

    On the Utility of Representation Learning Algorithms for Myoelectric Interfacing

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    Electrical activity produced by muscles during voluntary movement is a reflection of the firing patterns of relevant motor neurons and, by extension, the latent motor intent driving the movement. Once transduced via electromyography (EMG) and converted into digital form, this activity can be processed to provide an estimate of the original motor intent and is as such a feasible basis for non-invasive efferent neural interfacing. EMG-based motor intent decoding has so far received the most attention in the field of upper-limb prosthetics, where alternative means of interfacing are scarce and the utility of better control apparent. Whereas myoelectric prostheses have been available since the 1960s, available EMG control interfaces still lag behind the mechanical capabilities of the artificial limbs they are intended to steer鈥攁 gap at least partially due to limitations in current methods for translating EMG into appropriate motion commands. As the relationship between EMG signals and concurrent effector kinematics is highly non-linear and apparently stochastic, finding ways to accurately extract and combine relevant information from across electrode sites is still an active area of inquiry.This dissertation comprises an introduction and eight papers that explore issues afflicting the status quo of myoelectric decoding and possible solutions, all related through their use of learning algorithms and deep Artificial Neural Network (ANN) models. Paper I presents a Convolutional Neural Network (CNN) for multi-label movement decoding of high-density surface EMG (HD-sEMG) signals. Inspired by the successful use of CNNs in Paper I and the work of others, Paper II presents a method for automatic design of CNN architectures for use in myocontrol. Paper III introduces an ANN architecture with an appertaining training framework from which simultaneous and proportional control emerges. Paper Iv introduce a dataset of HD-sEMG signals for use with learning algorithms. Paper v applies a Recurrent Neural Network (RNN) model to decode finger forces from intramuscular EMG. Paper vI introduces a Transformer model for myoelectric interfacing that do not need additional training data to function with previously unseen users. Paper vII compares the performance of a Long Short-Term Memory (LSTM) network to that of classical pattern recognition algorithms. Lastly, paper vIII describes a framework for synthesizing EMG from multi-articulate gestures intended to reduce training burden

    Evaluating EEG鈥揈MG Fusion-Based Classification as a Method for Improving Control of Wearable Robotic Devices for Upper-Limb Rehabilitation

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    Musculoskeletal disorders are the biggest cause of disability worldwide, and wearable mechatronic rehabilitation devices have been proposed for treatment. However, before widespread adoption, improvements in user control and system adaptability are required. User intention should be detected intuitively, and user-induced changes in system dynamics should be unobtrusively identified and corrected. Developments often focus on model-dependent nonlinear control theory, which is challenging to implement for wearable devices. One alternative is to incorporate bioelectrical signal-based machine learning into the system, allowing for simpler controller designs to be augmented by supplemental brain (electroencephalography/EEG) and muscle (electromyography/EMG) information. To extract user intention better, sensor fusion techniques have been proposed to combine EEG and EMG; however, further development is required to enhance the capabilities of EEG鈥揈MG fusion beyond basic motion classification. To this end, the goals of this thesis were to investigate expanded methods of EEG鈥揈MG fusion and to develop a novel control system based on the incorporation of EEG鈥揈MG fusion classifiers. A dataset of EEG and EMG signals were collected during dynamic elbow flexion鈥揺xtension motions and used to develop EEG鈥揈MG fusion models to classify task weight, as well as motion intention. A variety of fusion methods were investigated, such as a Weighted Average decision-level fusion (83.01 卤 6.04% accuracy) and Convolutional Neural Network-based input-level fusion (81.57 卤 7.11% accuracy), demonstrating that EEG鈥揈MG fusion can classify more indirect tasks. A novel control system, referred to as a Task Weight Selective Controller (TWSC), was implemented using a Gain Scheduling-based approach, dictated by external load estimations from an EEG鈥揈MG fusion classifier. To improve system stability, classifier prediction debouncing was also proposed to reduce misclassifications through filtering. Performance of the TWSC was evaluated using a developed upper-limb brace simulator. Due to simulator limitations, no significant difference in error was observed between the TWSC and PID control. However, results did demonstrate the feasibility of prediction debouncing, showing it provided smoother device motion. Continued development of the TWSC, and EEG鈥揈MG fusion techniques will ultimately result in wearable devices that are able to adapt to changing loads more effectively, serving to improve the user experience during operation

    The Effect of Postural Perturbations on Cardiovascular and Skeletal Muscle Function in Healthy Adults

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    Maintenance of standing balance is vital to daily living. Traditionally, perspectives on maintaining balance are achieved through the study of visual, vestibular and somatosensory inputs on motor outputs. While evidence suggests cardiovascular regulation also functions to assist postural control during orthostatic stress, how the cardiovascular system responds to postural perturbations is not well established. This dissertation includes four studies that investigated the effects of postural perturbations on the cardiovascular system and skeletal muscle responses in healthy adults. All of the studies involved exposing standing participants to surface-translation perturbations at different velocities, with known or unknown timing, and occurred while spontaneously breathing and breathing at six breaths per minute in young and older adults. Beat-to-beat heart rate and systolic blood pressure were measured continuously, while cardiac baroreflex sensitivity was calculated using the sequence method analysis. The results of Study One illustrated that heart rate and systolic blood pressure response were modulated following a perturbation and the initial cardiac response scaled with perturbation intensity. Additionally, cardiac baroreflex engagement was found to be involved in heart rate recovery. The sensitivity of the cardiac baroreflex was increased post-perturbation but was not intensity dependent. In Study Two, anticipatory cardiovascular responses to perturbations were not observed when the timing of the perturbation was controlled by the participant and perceived state anxiety was correlated with the initial heart rate response post-perturbation. In Studies Three and Four, when breathing at six breaths per minute, the latency of muscle burst onset decreased in young and older adults and muscle burst amplitude decreased in the lower limb musculature in young adults. Slow breathing decreased systolic blood pressure but had no effect on heart rate or cardiac baroreflex sensitivity post-perturbation in older adults. Together, the findings provide evidence that cardiovascular modulation occurs when standing balance is perturbed and support the notion that the cardiovascular, respiratory and motor control systems interact in a complex manner during postural perturbations

    Estimating hand-grip forces causing Cumulative Trauma Disorder

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    Wearable sensors have garnered considerable interest because of their potential for various applications. However, much less has been studied about the Stretchsense pressure sensor characteristics and its workability for industrial application to prevent potential risk situations such as accidents and injuries. The proposed study helps investigate Stretchsense pressure sensors\u27 applicability for measuring hand-handle interface forces under static and dynamic conditions. The BendLabs sensors - a multi-axis, soft, flexible sensing system was attached to the wrist to evaluate the wrist angle deviations. In addition, the StretchSense stretch sensors were attached to the elbow joint to help estimate the elbow flexion/extension. The research tests and evaluates the real-time pressure distribution across the hand while performing given tasks and investigates the relationship between the wrist and elbow position and grip strength. The research provides objective means to assess the magnitudes of high pressures that may cause pressure-induced discomfort and pain, thereby increasing the hand\u27s stress. The experiment\u27s most significant benefit lies in its applicability to the actual tool handles outside the laboratory settings

    EMG signal processing for the study of localized muscle fatigue鈥攑ilot study to explore the applicability of a novel method

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    This pilot study aimed to explore a method for characterization of the electromyogram frequency spectrum during a sustained exertion task, performed by the upper limb. Methods: Nine participants underwent an isometric localized muscle fatigue protocol on an isokinetic dynamometer until exhaustion, while monitored with surface electromyography (sEMG) of the shoulder鈥檚 external rotators. Firstly, three methods of signal energy analysis based on primer frequency contributors were compared to the energy of the entire spectrum. Secondly, the chosen method of analysis was used to characterize the signal energy at beginning (T1), in the middle (T2) and at the end (T3) of the fatigue protocol and compared to the torque output and the shift in the median frequencies during the trial. Results: There were statistically significant differences between T1 and T3 for signal energy (p < 0.007) and for central frequency of the interval (p = 0.003). Moreover, the isometric peak torque was also different between T1 and T3 (p < 0.001). Overall, there were no differences between the signal energy enclosed in the 40 primer frequency contributors and the analysis of the full spectrum energy; consequently, it was the method of choice. The reported fatigue and the decrease in the produced muscle torque was consistent with fatigue-induced alterations in the electromyogram frequency spectrum. In conclusion, the developed protocol has potential to be considered as an easy-to-use method for EMG-based analysis of isometric muscle exertion until fatigue. Thus, the novelty of the proposed method is to explore, in muscle fatigue, the use of only the main contributors in the frequency domain of the EMG spectrum, avoiding surplus information, that may not represent muscle functioning. However, further studies are needed to investigate the stability of the present findings in a more comprehensive sample.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support through national funds FCT/MCTES (PIDDAC) to CeDRI (UIDB/05757/2020 and UIDP/05757/2020) and SusTEC (LA/P/0007/2021).info:eu-repo/semantics/publishedVersio

    XXII International Conference on Mechanics in Medicine and Biology - Abstracts Book

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    This book contain the abstracts presented the XXII ICMMB, held in Bologna in September 2022. The abstracts are divided following the sessions scheduled during the conference

    Acute effects of suspension training and other perturbative sources on lower limb strength tasks

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    Actualment, els dispositius de suspensi贸 s贸n un dels materials m茅s utilitzats per produir pertorbaci贸 i enfortir de forma global la majoria de grups musculars. Encara que, manquen evid猫ncies dels seus efectes sobre l鈥檈xtremitat inferior. Aix铆, l鈥檕bjectiu principal d鈥檃questa tesi doctoral va ser quantificar la producci贸 de for莽a, l鈥檃ctivitat muscular i la magnitud de la pertorbaci贸 a l鈥檈squat b煤lgar i altres exercicis de l鈥檈xtremitat inferior en condicions d鈥檌nestabilitat. Es van analitzar 18 estudis per dur a terme una revisi贸 sistem脿tica (estudi 1) i 75 participants f铆sicament actius van ser reclutats per realitzar els diferents estudis transversals sobre els efectes dels dispositius de suspensi贸, les superf铆cies inestables i les vibracions mec脿niques (plataforma vibrat貌ria i vibraci贸 superposada) en exercicis de l鈥檈xtremitat inferior (estudis 2-6). Es va confirmar que l鈥檃ctivaci贸 a la part inferior del cos nom茅s va ser investigada en el concentrat d鈥檌squiosurals en suspensi贸 (estudi 1). La posici贸 i el ritme d鈥檈xecuci贸 (70 bpm) van ser determinants per la producci贸 de for莽a exercida sobre el tirant de suspensi贸 a l鈥檈squat b煤lgar (estudi 2). El dispositiu de suspensi贸 a l鈥檈squat b煤lgar va augmentar les forces verticals contra el terra (estudi 3). Sobre el dispositiu la producci贸 de for莽a va ser major quan el nivell d鈥檌nestabilitat era baix (estudi 3 i 4), per貌 a nivell muscular el dispositiu va ser igual de demandant que l鈥檈xercici tradicional (estudi 3). Un augment de la pertorbaci贸, va incrementar l鈥檃ctivaci贸 muscular (estudis 3, 4, 5) i la magnitud de la inestabilitat per l鈥檈squat b煤lgar i el mig squat amb barra (estudis 4 i 5). Aix铆, la vibraci贸 superposada en un dispositiu de suspensi贸 esdev茅 un repte per incrementar el nivell de pertorbaci贸 i millorar la for莽a, la resist猫ncia muscular i l鈥檈stabilitzaci贸 (estudi 6). A m茅s, els sensors de for莽a s贸n una eina adequada i usable per valorar les forces exercides sobre els dispositius de suspensi贸, i l鈥櫭簊 de l鈥檃cceler貌metre permet determinar la magnitud de la pertorbaci贸 que ofereixen els diferents materials desestabilitzadors mesurant l鈥檃cceleraci贸 del centre de masses corporal.Actualmente, los dispositivos de suspensi贸n son uno de los materiales m谩s utilizados para producir perturbaci贸n y fortalecer globalmente la mayor铆a de los m煤sculos. Aunque, faltan evidencias de sus efectos sobre la extremidad inferior. As铆, el objetivo principal de esta tesis doctoral fue cuantificar la producci贸n de fuerza, la actividad muscular y la magnitud de la perturbaci贸n en la sentadilla b煤lgara y otros ejercicios de la extremidad inferior en condiciones de inestabilidad. Se analizaron 18 estudios para llevar a cabo una revisi贸n sistem谩tica (estudio 1) y 75 participantes f铆sicamente activos fueron reclutados para realizar los diferentes estudios transversales sobre los efectos de los dispositivos de suspensi贸n, las superficies inestables y las vibraciones mec谩nicas (plataforma vibratoria y vibraci贸n superpuesta) en ejercicios de la extremidad inferior (estudios 2-6). Se confirm贸 que la activaci贸n en la parte inferior del cuerpo s贸lo fue investigada en el concentrado de isquiosurales en suspensi贸n (estudio 1). La posici贸n y el ritmo de ejecuci贸n (70 bpm) fueron determinantes para la producci贸n de fuerza ejercida sobre el tirante de suspensi贸n en la sentadilla b煤lgara (estudio 2). El dispositivo de suspensi贸n en la sentadilla b煤lgara aument贸 las fuerzas verticales contra el suelo (estudio 3). Sobre el dispositivo la producci贸n de fuerza fue mayor cuando el nivel de inestabilidad era bajo (estudio 3 y 4), pero a nivel muscular el dispositivo fue igual de demandante que el ejercicio tradicional (estudio 3). Un aumento de la perturbaci贸n increment贸 la activaci贸n muscular (estudios 3, 4, 5) y la magnitud de la inestabilidad en la sentadilla b煤lgara y la media sentadilla con barra (estudios 4 y 5). As铆, la vibraci贸n superpuesta en un dispositivo de suspensi贸n se convierte en un reto para incrementar el nivel de perturbaci贸n y mejorar la fuerza, la resistencia muscular y la estabilizaci贸n (estudio 6). Adem谩s, los sensores de fuerza son una herramienta adecuada y usable para valorar las fuerzas ejercidas sobre los dispositivos de suspensi贸n, y el uso del aceler贸metro permite determinar la magnitud de la perturbaci贸n que ofrecen los diferentes materiales desestabilizadores midiendo la aceleraci贸n del centro de masas corporal.Nowadays, suspension devices are one of the most widely used pieces of equipment to produce perturbation and strengthen most muscle groups globally. However, there is a lack of evidence of their effects on the lower limb. Thus, the main objective of this doctoral thesis was to quantify force production, muscle activity and the magnitude of perturbation in the Bulgarian squat and other lower extremity exercises under unstable conditions. Eighteen studies were analysed for a systematic review (study 1) and 75 physically active participants were recruited to perform the different cross-sectional studies on the effects of suspension devices, unstable surfaces, and mechanical vibrations (vibration platform and superimposed vibration) on lower limb exercises (studies 2-6). It was confirmed that lower body activation had only been previously investigated in the suspended hamstring curl (study 1). Position and pace (70 bpm) were determinants for the force exerted on the suspension strap in the Bulgarian squat (study 2). The suspension device in the Bulgarian squat increased the vertical ground reaction forces (study 3). The force production was higher on the device when the level of instability was low (study 3 and 4), but for muscle activity the device was just as demanding as a traditional exercise (study 3). Increased perturbation enhanced muscle activation (studies 3, 4, 5) and the magnitude of instability in the Bulgarian squat and barbell half-squat (studies 4 and 5). Thus, superimposed vibration on a suspension device becomes a challenge to increase the level of perturbation and improve strength, muscular endurance, and stabilisation (study 6). In addition, load cells are a suitable and practical tool to assess the forces exerted on suspension devices, and the use of an accelerometer makes it possible to determine the magnitude of the perturbation offered by different equipment providing instability by measuring the acceleration of the body's centre of mass

    Rehabilitation Engineering

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    Population ageing has major consequences and implications in all areas of our daily life as well as other important aspects, such as economic growth, savings, investment and consumption, labour markets, pensions, property and care from one generation to another. Additionally, health and related care, family composition and life-style, housing and migration are also affected. Given the rapid increase in the aging of the population and the further increase that is expected in the coming years, an important problem that has to be faced is the corresponding increase in chronic illness, disabilities, and loss of functional independence endemic to the elderly (WHO 2008). For this reason, novel methods of rehabilitation and care management are urgently needed. This book covers many rehabilitation support systems and robots developed for upper limbs, lower limbs as well as visually impaired condition. Other than upper limbs, the lower limb research works are also discussed like motorized foot rest for electric powered wheelchair and standing assistance device

    Biomechanical Spectrum of Human Sport Performance

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    Writing or managing a scientific book, as it is known today, depends on a series of major activities, such as regrouping researchers, reviewing chapters, informing and exchanging with contributors, and at the very least, motivating them to achieve the objective of publication. The idea of this book arose from many years of work in biomechanics, health disease, and rehabilitation. Through exchanges with authors from several countries, we learned much from each other, and we decided with the publisher to transfer this knowledge to readers interested in the current understanding of the impact of biomechanics in the analysis of movement and its optimization. The main objective is to provide some interesting articles that show the scope of biomechanical analysis and technologies in human behavior tasks. Engineers, researchers, and students from biomedical engineering and health sciences, as well as industrial professionals, can benefit from this compendium of knowledge about biomechanics applied to the human body
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