Estimation of EMG-Based force using a neural-network-based approach

© 2013 IEEE. The dynamics of human arms has a high impact on the humans' activities in daily life, especially when a human operates a tool such as interactions with a robot with the need for high dexterity. The dexterity of human arms depends largely on motor functionality of muscle. In this sense, the dynamics of human arms should be well analyzed. In this paper, in order to analyse the characteristic of human arms, a neural-network-based algorithm is proposed for exploring the potential model between electromyography (EMG) signal and human arm's force. Based on the analysis of force for humans, the mean absolute value of the electromyographic signal is selected as the input for the potential model. In this paper, in order to accurately estimate the potential model, three domains fuzzy wavelet neural network (TDFWNN) algorithm without prior knowledge of the biomechanical model is utilized. The performance of the proposed algorithm has been demonstrated by the experimental results in comparison with the conventional radial basis function neural network (RBFNN) method. By comparison, the proposed TDFWNN algorithm provides an effective solution to evaluate the influence of human factors based on biological signals

Force-Guided High-Precision Grasping Control of Fragile and Deformable Objects Using sEMG-Based Force Prediction

Regulating contact forces with high precision is crucial for grasping and manipulating fragile or deformable objects. We aim to utilize the dexterity of human hands to regulate the contact forces for robotic hands and exploit human sensory-motor synergies in a wearable and non-invasive way. We extracted force information from the electric activities of skeletal muscles during their voluntary contractions through surface electromyography (sEMG). We built a regression model based on a Neural Network to predict the gripping force from the preprocessed sEMG signals and achieved high accuracy (R2 = 0.982). Based on the force command predicted from human muscles, we developed a force-guided control framework, where force control was realized via an admittance controller that tracked the predicted gripping force reference to grasp delicate and deformable objects. We demonstrated the effectiveness of the proposed method on a set of representative fragile and deformable objects from daily life, all of which were successfully grasped without any damage or deformation.Comment: 8 pages, 11 figures, to be published on IEEE Robotics and Automation Letters. For the attached video, see https://youtu.be/0AotKaWFJD

A real-time and convex model for the estimation of muscle force from surface electromyographic signals in the upper and lower limbs

Surface electromyography (sEMG) is a signal consisting of different motor unit action potential trains and records from the surface of the muscles. One of the applications of sEMG is the estimation of muscle force. We proposed a new real-time convex and interpretable model for solving the sEMG-force estimation. We validated it on the upper limb during isometric voluntary flexions-extensions at 30%, 50%, and 70% Maximum Voluntary Contraction in five subjects, and lower limbs during standing tasks in thirty-three volunteers, without a history of neuromuscular disorders. Moreover, the performance of the proposed method was statistically compared with that of the state-of-the-art (13 methods, including linear-in-the-parameter models, Artificial Neural Networks and Supported Vector Machines, and non-linear models). The envelope of the sEMG signals was estimated, and the representative envelope of each muscle was used in our analysis. The convex form of an exponential EMG-force model was derived, and each muscle's coefficient was estimated using the Least Square method. The goodness-of-fit indices, the residual signal analysis (bias and Bland-Altman plot), and the running time analysis were provided. For the entire model, 30% of the data was used for estimation, while the remaining 20% and 50% were used for validation and testing, respectively. The average R-square (%) of the proposed method was 96.77 +/- 1.67 [94.38, 98.06] for the test sets of the upper limb and 91.08 +/- 6.84 [62.22, 96.62] for the lower-limb dataset (MEAN +/- SD [min, max]). The proposed method was not significantly different from the recorded force signal (p-value = 0.610); that was not the case for the other tested models. The proposed method significantly outperformed the other methods (adj. p-value < 0.05). The average running time of each 250 ms signal of the training and testing of the proposed method was 25.7 +/- 4.0 [22.3, 40.8] and 11.0 +/- 2.9 [4.7, 17.8] in microseconds for the entire dataset. The proposed convex model is thus a promising method for estimating the force from the joints of the upper and lower limbs, with applications in load sharing, robotics, rehabilitation, and prosthesis control for the upper and lower limbs

Modelling and EMG based Control of Upper Limb Exoskeletons for Hand Impairments

Functional losses associated with hand impairments have led to the growing development of hand exoskeletons. The main challenges are to develop the exoskeletons that work according to the user’s motion intention, which can be done by utilizing the electromyogram signals generated by forearm muscles contributed from the movement and/or grasping abilities of the hand. In this research, modelling and EMG based control of hand exoskeletons with the aim to assist stroke survivors in regaining their hand strength and functionality, and improve their quality of life is presented

A real-time and convex model for the estimation of muscle force from surface electromyographic signals in the upper and lower limbs

Surface electromyography (sEMG) is a signal consisting of different motor unit action potential trains and records from the surface of the muscles. One of the applications of sEMG is the estimation of muscle force. We proposed a new real-time convex and interpretable model for solving the sEMG—force estimation. We validated it on the upper limb during isometric voluntary flexions-extensions at 30%, 50%, and 70% Maximum Voluntary Contraction in five subjects, and lower limbs during standing tasks in thirty-three volunteers, without a history of neuromuscular disorders. Moreover, the performance of the proposed method was statistically compared with that of the state-of-the-art (13 methods, including linear-in-the-parameter models, Artificial Neural Networks and Supported Vector Machines, and non-linear models). The envelope of the sEMG signals was estimated, and the representative envelope of each muscle was used in our analysis. The convex form of an exponential EMG-force model was derived, and each muscle’s coefficient was estimated using the Least Square method. The goodness-of-fit indices, the residual signal analysis (bias and Bland-Altman plot), and the running time analysis were provided. For the entire model, 30% of the data was used for estimation, while the remaining 20% and 50% were used for validation and testing, respectively. The average R-square (%) of the proposed method was 96.77 ± 1.67 [94.38, 98.06] for the test sets of the upper limb and 91.08 ± 6.84 [62.22, 96.62] for the lower-limb dataset (MEAN ± SD [min, max]). The proposed method was not significantly different from the recorded force signal (p-value = 0.610); that was not the case for the other tested models. The proposed method significantly outperformed the other methods (adj. p-value &lt; 0.05). The average running time of each 250 ms signal of the training and testing of the proposed method was 25.7 ± 4.0 [22.3, 40.8] and 11.0 ± 2.9 [4.7, 17.8] in microseconds for the entire dataset. The proposed convex model is thus a promising method for estimating the force from the joints of the upper and lower limbs, with applications in load sharing, robotics, rehabilitation, and prosthesis control for the upper and lower limbs

Madala maksumusega elektromüograafide rakendatavus ergonoomikalises hindamises

A thesis for applying for the degree of Doctor of Philosophy in Engineering Sciences.Every year a considerable amount of gross domestic product in several countries is lost due to work-related musculoskeletal disorders (WMSDs). Thus, one of the goals of ergonomics is to prevent WMSDs. A body of knowledge required to prevent WMSDs has existed for decades; however, the exploitation of this knowledge is hindered by the shortcomings in the risk assessment methods. As a rule, objective methods should be preferred to subjective methods, though often access to objective methods is restricted by the cost of the apparatus. The potential to make one of such devices more accessible by reducing the costs was investigated in the thesis. The thesis focused on the electromyograph – a device to study and monitor the electrical activity produced by skeletal muscles. Nowadays one can assemble an electromyograph from low-cost semi-universal components; however, the functionality and usability of such a device is unknown. At first the technical characteristics of components that can be used to assemble an electromyograph were evaluated. Then the electromyographs were assembled and tested in the laboratory and in the field. The results showed that the low-cost electromyographs may be partially utilised in ergonomic risk assessment; however, the use of such equipment in comparison to commercial high-cost apparatus increases the demands on user knowledge, skills and time expenditure. On the other hand, the functionality of the do-it-yourself electromyograph may exceed the commercial device.Tööga seotud luu- ja lihaskonna ülekoormushaiguste tõttu kaotavad riigid igal aastal märkimisväärse osa sisemajanduse kogutoodangust. Seetõttu on üheks ergonoomika eesmärgiks luu- ja lihaskonna ülekoormushaiguste ennetamine. Teadmised töötaja ülekoormuse ennetamiseks on olemas juba aastakümneid. Paraku takistavad teadmiste tõhusat rakendamist puudused riskihindamise meetodites. Riskide hindamisel tuleb subjektiivsetele meetoditele eelistada objektiivseid meetodeid, kuid sageli piirab objektiivsete meetodite kasutamist mõõteseadmete maksumus. Doktoritöös uuriti ühe sellist liiki mõõteseadme, lihaste elektrilise aktiivsuse uurimiseks mõeldud seireseadme ehk elektrimüograafi kättesaadavuse ja rakendamise suurendamise võimalust seadme maksumuse vähendamisega. Nüüdisajal on võimalus elektromüograafe kokku panna madala maksumusega ja pool-universaalsetest komponentidest. Samas pole selge, milline on sellisel viisil valmistatud elektromüograafi funktsionaalsus ja kasutatavus. Doktoritöös hinnati esmalt elektromüograafi madala maksumusega komponentide tehnilisi omadusi ning seejärel katsetati koostatud elektromüograafe laboris ja töökeskkonnas. Doktoritöö andis kinnitust, et madala maksumusega elektromüograafe on võimalik riskihindamisel osaliselt rakendada, kuid selliste seadmete kasutamine eeldab riskihindajalt põhjalikumaid teadmisi ja oskusi ning suuremat ajakulu kui kallite kommertsseadmete kasutamine. Samas võib spetsialisti kokkupandud elektromüograafi funktsionaalsus kommertsseadmeid ületada.Publication of this thesis is supported by the Estonian University of Life Sciences. This research was supported by European Regional Development Fund’s Doctoral Studies and Internationalisation Programme DoR

Grasp force estimation from the transient EMG using high-density surface recordings.

Objective: Understanding the neurophysiological signals underlying voluntary motor control and decoding them for prosthesis control are among the major challenges in applied neuroscience and bioengineering. Usually, information from the electrical activity of residual forearm muscles (i.e. the electromyogram, EMG) is used to control different functions of a prosthesis. Noteworthy, forearm EMG patterns at the onset of a contraction (transient phase) have shown to contain predictive information about upcoming grasps. However, decoding this information for the estimation of grasp force was so far overlooked. Approach: High Density-EMG signals (192 channels) were recorded from twelve participants performing a pick-and-lift task. The final grasp force was estimated offline using linear regressors, with four subsets of channels and ten features obtained using three channels-features selection methods. Two different evaluation metrics (absolute error and R2), complemented with statistical analysis, were used to select the optimal configuration of the parameters. Different windows of data starting at the grasp force (GF) onset were compared to determine the time at which the grasp force can be ascertained from the EMG signals. Main results: The prediction accuracy improved by increasing the window length from the moment of the onset and kept improving until the steady state at which a plateau of performances was reached. With our methodology, estimations of the grasp force through 16 EMG channels reached an absolute error of 2.52% the maximum voluntary force using only transient information and 1.99% with the first 500ms of data following the onset. Significance: The final GF estimation from transient EMG was comparable to the one obtained using steady state data, confirming our hypothesis that the transient phase contains information about the final grasp force. This result paves the way to fast online myoelectric controllers capable of decoding grasp strength from the very early portion of the EMG signal

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

Actualment, els dispositius de suspensió són un dels materials més utilitzats per produir pertorbació i enfortir de forma global la majoria de grups musculars. Encara que, manquen evidències dels seus efectes sobre l’extremitat inferior. Així, l’objectiu principal d’aquesta tesi doctoral va ser quantificar la producció de força, l’activitat muscular i la magnitud de la pertorbació a l’esquat búlgar i altres exercicis de l’extremitat inferior en condicions d’inestabilitat. Es van analitzar 18 estudis per dur a terme una revisió sistemàtica (estudi 1) i 75 participants físicament actius van ser reclutats per realitzar els diferents estudis transversals sobre els efectes dels dispositius de suspensió, les superfícies inestables i les vibracions mecàniques (plataforma vibratòria i vibració superposada) en exercicis de l’extremitat inferior (estudis 2-6). Es va confirmar que l’activació a la part inferior del cos només va ser investigada en el concentrat d’isquiosurals en suspensió (estudi 1). La posició i el ritme d’execució (70 bpm) van ser determinants per la producció de força exercida sobre el tirant de suspensió a l’esquat búlgar (estudi 2). El dispositiu de suspensió a l’esquat búlgar va augmentar les forces verticals contra el terra (estudi 3). Sobre el dispositiu la producció de força va ser major quan el nivell d’inestabilitat era baix (estudi 3 i 4), però a nivell muscular el dispositiu va ser igual de demandant que l’exercici tradicional (estudi 3). Un augment de la pertorbació, va incrementar l’activació muscular (estudis 3, 4, 5) i la magnitud de la inestabilitat per l’esquat búlgar i el mig squat amb barra (estudis 4 i 5). Així, la vibració superposada en un dispositiu de suspensió esdevé un repte per incrementar el nivell de pertorbació i millorar la força, la resistència muscular i l’estabilització (estudi 6). A més, els sensors de força són una eina adequada i usable per valorar les forces exercides sobre els dispositius de suspensió, i l’ús de l’acceleròmetre permet determinar la magnitud de la pertorbació que ofereixen els diferents materials desestabilitzadors mesurant l’acceleració del centre de masses corporal.Actualmente, los dispositivos de suspensión son uno de los materiales más utilizados para producir perturbación y fortalecer globalmente la mayoría de los músculos. Aunque, faltan evidencias de sus efectos sobre la extremidad inferior. Así, el objetivo principal de esta tesis doctoral fue cuantificar la producción de fuerza, la actividad muscular y la magnitud de la perturbación en la sentadilla búlgara y otros ejercicios de la extremidad inferior en condiciones de inestabilidad. Se analizaron 18 estudios para llevar a cabo una revisión sistemática (estudio 1) y 75 participantes físicamente activos fueron reclutados para realizar los diferentes estudios transversales sobre los efectos de los dispositivos de suspensión, las superficies inestables y las vibraciones mecánicas (plataforma vibratoria y vibración superpuesta) en ejercicios de la extremidad inferior (estudios 2-6). Se confirmó que la activación en la parte inferior del cuerpo sólo fue investigada en el concentrado de isquiosurales en suspensión (estudio 1). La posición y el ritmo de ejecución (70 bpm) fueron determinantes para la producción de fuerza ejercida sobre el tirante de suspensión en la sentadilla búlgara (estudio 2). El dispositivo de suspensión en la sentadilla búlgara aumentó las fuerzas verticales contra el suelo (estudio 3). Sobre el dispositivo la producción 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 perturbación incrementó la activación muscular (estudios 3, 4, 5) y la magnitud de la inestabilidad en la sentadilla búlgara y la media sentadilla con barra (estudios 4 y 5). Así, la vibración superpuesta en un dispositivo de suspensión se convierte en un reto para incrementar el nivel de perturbación y mejorar la fuerza, la resistencia muscular y la estabilización (estudio 6). Además, los sensores de fuerza son una herramienta adecuada y usable para valorar las fuerzas ejercidas sobre los dispositivos de suspensión, y el uso del acelerómetro permite determinar la magnitud de la perturbación que ofrecen los diferentes materiales desestabilizadores midiendo la aceleración 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

The relationship between perception of effort and physiological responses to an acute fatiguing task of the elbow flexors. Evaluation of a new rating scale of perception of effort

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.While fatigue is a common daily phenomenon, the exact relationship between perception of effort and fatigue is still unknown. Existing tools for assessing perception of effort are effectively limited to whole body exercise, while current methods for assessing voluntary activation are painful and not feasible for clinical application. The main aims of this thesis were to evaluate existing methodologies for their appropriateness in assessing perception of effort and voluntary activation following isolated muscle function testing, and to examine the relationship between subjective perception of effort and objective changes in the healthy motor control system. The implementation of reliable and valid assessment tools in clinical practice may enable clarification of the pathogenesis of many neurological conditions that have chronic fatigue as a key feature. Four studies of within-subjects repeated measures design have been conducted. Sixtynine healthy volunteers were recruited among staff and students of Brunel University. Magnetic stimulation was tested as a valid alternative to electrical stimulation in the conventional single-pulse Twitch Interpolation Technique. The 0–10 Numeric Rating Scale (NRS) was also tested for its reliability and validity in assessing the perception of effort during isometric exercise of elbow flexors. The changes of perception of effort following a submaximal elbow flexion fatiguing task, as well as following transcranial direct current stimulation (tDCS) over the motor cortex were also tested. The main findings showed significant differences between peripheral and magnetic stimulation in conventional single-pulse Twitch Interpolation Technique. The 0–10 NRS demonstrated linear properties and reported excellent test-retest reliability and good concurrent criterion validity in recording perception of effort under repeated isometric contractions of elbow flexors. Ten minutes of a submaximal intermittent isometric fatiguing exercise produced a significant elevation in rating of perceived effort, which was associated with central and peripheral neurophysiological changes of the motor control system. In contrast, perception of effort did not change significantly following 10 minutes of tDCS. The major findings of this thesis suggest the 0–10 NRS is a valid and reliable scale for rating perception of effort in healthy individuals. Further testing of the scale on patients is needed to establish its validity in clinical settings. Additionally, the findings indicate a substantial role of perception of effort in the voluntary motor control system. However, further research towards revealing the underlying mechanisms of perceived effort regulation in both health and disease is required