The electrical activity of skeletal muscle—the electromyogram (EMG)—is of value to many different application areas, including ergonomics, clinical biomechanics and prosthesis control. For many applications, the EMG is related to muscular tension, joint torque and/or applied forces. In these cases, a goal is for an EMG-torque model to emulate the natural relationship between the central nervous system (as evidenced in the surface EMG) and peripheral joints and muscles. This thesis work concentrated on experimental investigations of EMG-torque modeling. My contributions include: 1) continuing to evaluate the advantage of advanced EMG amplitude estimators, 2) studying system identification techniques (regularizing the least squares fit and increasing training data duration) to improve EMG-torque model performance, and 3) investigating the influence of joint angle on EMG-torque modeling. Results show that the advanced EMG amplitude estimator reduced the model error by 21%—71% compared to conventional estimators. Use of the regularized least squares fit with 52 seconds of training data reduced the model error by 20% compared to the least squares fit without regulation when using 26 seconds of training data. It is also demonstrated that the influence of joint angle can be modeled as a multiplicative factor in slowly force-varying and force-varying contractions at various, fixed angles. The performance of the models that account for the joint angle are not statistically different from a model that was trained at each angle separately and thus does not interpolate across angles. The EMG-torque models that account for joint angle and utilize advanced EMG amplitude estimation and system identification techniques achieved an error of 4.06±1.2% MVCF90 (i.e., error referenced to maximum voluntary contraction at 90° flexion), while models without using these advanced techniques and only accounting for a joint angle of 90° generated an error of 19.15±11.2% MVCF90. This thesis also summarizes other collaborative research contributions performed as part of this thesis. (1) EMG-force modeling at the finger tips was studied with the purpose of assessing the ability to determine two or more independent, continuous degrees of freedom of control from the muscles of the forearm [with WPI and Sherbrooke University]. (2) Investigation of EMG bandwidth requirements for whitening for real-time applications of EMG whitening techniques [with WPI colleagues]. (3) Investigation of the ability of surface EMG to estimate joint torque at future times [with WPI colleagues]. (4) Decomposition of needle EMG data was performed as part of a study to characterize motor unit behavior in patients with amyotrophic lateral sclerosis (ALS) [with Spaulding Rehabilitation Hospital, Boston, MA].

No description available.

High quality automated electromyogram (EMG) decomposition algorithms are necessary to insure the reliability of clinical and scientific information derived from them. In this work, we used experimental and simulated data to analyze the decomposition performance of three publicly available algorithms¡ªEMGLAB [McGill et al., 2005] (single-channel data only), Fuzzy Expert [Erim and Lin, 2008] and Montreal [Florestal et al., 2009]. Comparison data consisted of quadrifilar needle EMG from the tibialis anterior of 12 subjects (young and elderly) at three contraction levels (10, 20 and 50% MVC), single-channel clinical EMG from the biceps brachii of 10 subjects, and matched simulation data for both electrode types. Performance was assessed via agreement between pairs of algorithms for experimental data and accuracy with respect to the known decomposition for simulated data. For the quadrifilar data, median agreements between the Montreal and Fuzzy Expert algorithms at 10, 20 and 50% MVC were 95.7, 86.4 and 64.8%, respectively. For the single-channel data, median agreements between pairs of algorithms were 94.9% (Montreal vs. Fuzzy Expert) and 100% (EMGLAB vs. either Montreal or Fuzzy Expert). Accuracy on the simulated data exceeded this performance. Agreement/accuracy was strongly related to trial Complexity, as was motor unit signal to noise ratio, Dissimilarity and Decomposability Index. When agreement was high between algorithm pairs applied to the simulated data, so was the individual accuracy of each algorithm.

One of the most significant current discussions in forward fall research is the effect of walking speed on the likelihood of a fall after a trip. Considering the limited research studies perturbing individual participants at multiple walking speeds, the objective of this research study was to determine how walking speed influences tripping responses and recovery. A tripping device was built to apply large impulsive perturbations to the left ankle and induce stumbling reactions in humans walking on a motorized treadmill. The tripping device and experimental set-up were successful in eliciting large EMG responses following a perturbation at slow, medium, and fast walking speeds. However, during the final stages of piloting, electrical and mechanical issues lead to a breakdown of the tripping device. As a result, only a single set of participant data was collected and able to be fully processed. None the less, the qualitative kinematic and EMG results suggest an increased ability is required to activate muscles to take a recovery step and successfully decelerate the forward trunk motion and ultimately recover from a trip at faster speeds compared to slower walking speeds. / text

The design of current electromyography (EMG) systems focuses on specific applications. One design focuses on the use of bipolar electrodes to monitor a single muscle group. Several of these electrodes can then be used to monitor different muscles on the body simultaneously. Another design places many electrodes in an array on a limb or over a single muscle. One cannot be used for the other. Additionally the design of an EMG system must account for several sources of noise that can be orders of magnitude larger than the EMG signal itself. The goal of this work was to design an active EMG electrode that could be used as bipolar electrodes or in an electrode array. Two electrodes were designed and tested. One design only worked in bipolar and the other did not possess the desired noise immunity. Explanations to the behavior of the electrodes are presented along with possible modifications the the electrodes to achieve the desired performance. / Master of Science / Electromyography or EMG is the measurement of the electrical activity produced by muscles when moving or lifting. These measurements are taken by metal electrodes placed on the surface of the skin. To properly measure the electrical activity precise measurement circuits have to be used and steps have to be taken to reduce any interference. EMG systems are typically setup in one of two layouts. The first layout is a few electrodes are used to monitor a muscle but many different muscles can be monitored simultaneously. The second is to place many electrodes that are close to each other to monitor a single muscle. In either layout there are many types of interference that can effect the data and must be accounted for in the systems design. In this work two electrodes were designed. The goal was to produce an electrode that would function in either layout. After testing both of the electrodes it was determined that both of the electrodes work but not as well as desired. Several future steps and design modifications are presented.

Running is achieved by cyclic execution of movements that ultimately allows a person to move. Each cycle is divided into two phases. The first phase is where power is absorbed as the body\'s center of mass is lowered and decelerated. The second being where power is generated and the center of mass is propelled upwards and forwards. Power absorption is primarily done by quadriceps muscles while plantar flexors generate most of the power during push-off phase. Variations in speed and slope are met by adjustments in the same direction of force produced by lower limb muscles and, due to changes in energy expenditure, of heart rate. In this context, analysis of variability offer a non-invasive way to measure how well-adjusted muscles are to cope with variations in demand. Thus, our aim was to investigate the relationship between the variability of contractions of muscles from the quadriceps and plantar flexors with changes in speed and slope and in heart rate. Secondarily, we sought to verify if the patterns observed in a restricted group of subjects could also be noted in a wider population. To answer these questions, we used electromyography to collect data of intervals between successive contractions of vasti and gastrocnemius muscles of seventeen runners across several target runs. These runs were chosen with several different speeds and slopes. Runners were divided into two experimental groups: Experiment 1 contained no restrictions regarding age and fitness level while Experiment 2 did control for these variables. Linear regressions and gradients showed that even though variability estimators correlated negatively to speed and/or slope, they could be better explained by changes in heart rate. Thus our main conclusion was that variability between contractions is inversely proportional to muscle activation, in relation to its maximum capacity. As a consequence, different combinations of speed and slope could result in the same variability despite differences in metabolic profile, as long as the power output remains constant. Due to methodological issues, we could not reach a decisive conclusion regarding the comparison between the more restricted and more heterogeneous groups of volunteers, although results suggest that the runners respond to changes of speed and slope in a similar way regardless of differences in age and fitness level / Durante a corrida, uma série de movimentos é realizada de forma cíclica que, em última análise, fazem com que o corpo se desloque. Cada ciclo é dividido em uma fase em que ocorre absorção de trabalho conforme o centro de massa é rebaixado e desacelerado e uma fase em que ocorre produção de trabalho, conforme o centro de massa é impulsionado para cima e para frente. Os músculos do quadríceps e flexores plantares são os principais responsáveis pela absorção e geração de trabalho, respectivamente. Variações na velocidade da corrida e na inclinação do terreno requerem ajustes da força muscular e, como consequência, da freqüência cardíaca. Neste contexto, análises de variabilidade oferecem uma maneira de medir a adequação do sistema muscular às variações na demanda. Assim, buscamos investigar a relação entre a variabilidade das contrações de músculos do quadríceps e flexores plantares com alterações na velocidade, inclinação e potência; bem como verificar se os padrões observados em um grupo restrito de indivíduos se aplicavam a uma amostra mais variada. Para isso, coletamos dados de intervalos entre contrações do vasto e gastrocnêmio de dezessete voluntários durante corridas realizadas em diferentes combinações de velocidade e inclinação da esteira. Os sujeitos foram divididos em dois grupos experimentais: no Experimento 1, não houve restrições quanto à idade e condicionamento, enquanto que no Experimento 2 essas variáveis foram controladas. Regressões lineares e gradientes mostraram que, embora os estimadores de variabilidade correlacionem negativamente com velocidade e inclinação, eles são melhor explicados por mudanças no consumo energético (i.e.,frequência cardíaca). Assim, concluímos que a variabilidade é inversamente proporcional à força muscular, em relação à sua capacidade máxima. Como conseqüência, diferentes combinações de velocidade e inclinação podem resultar na mesma variabilidade, apesar das diferenças no perfil metabólico. Devido a complicações metodológicas, não pudemos chegar a uma conclusão definitiva em relação a comparação entre voluntários dos Experimentos 1 e 2, embora os resultados sugiram que corredores respondam a mudanças de velocidade e inclinação de maneira semelhante, independentemente de diferenças de idade e nível de condicionamento

Nous avons généré des souris déficientes pour les gènes codant pour les échangeurs Na/Ca de type I (NCX1) et de type III (NCX3) afin d'étudier, in vivo, le rôle de ces deux protéines. L‘analyse phénotypique des souris adultes totalement déficientes pour le gène Ncx1 (Ncx1-/-) n'a pu être menée étant donné que ces souris décèdent au cours du développement embryonnaire. Les souris déficientes pour le gène Ncx3 (Ncx3-/-) sont viables et fertiles. Nous avons analysé l'effet de l'inactivation du gène Ncx3 dans le muscle squelettique et plus particulièrement au niveau de la jonction neuromusculaire. L'analyse histologique des muscles squelettiques de souris Ncx3-/- a révélé des altérations des fibres musculaires caractérisées par la présence de foyers de fibres nécrotiques et d'infiltrats de cellules mononuclées. L'analyse électromyographique classique a montré un électromyogramme anormal du muscle gastrocnémien de souris Ncx3-/-, révélant une affection neuromusculaire pré- et post-synaptique caractérisée par (i) la petitesse de l'amplitude de la réponse M au repos, (ii) le décrément après stimulation répétitive à basse fréquence, (iii) l'incrément après stimulation répétitive à haute fréquence et (iv) la facilitation post-exercice. L'électromyographie à fibre unique a révélé une MCD élevée et des blocages anormaux de la transmission neuromusculaire, reflétant une atteinte post-synaptique de la jonction neuromusculaire chez les souris Ncx3-/-. L'ensemble de ces anomalies électromyographiques sont les caractéristiques du syndrome myasthénique de Lambert-Eaton. Finalement, pour déterminer les conséquences de l'inactivation du gène Ncx3 sur l'activité physique des souris Ncx3-/-, nous avons réalisé des tests comportementaux sur ces souris. Ces tests ont permis de détecter un épuisement et une faiblesse musculaire accrus à l'effort chez ces souris. En conclusion, nos observations montrent que les souris Ncx3-/- présentent des anomalies électromyographiques similaires à celles du syndrome myasthénique de Lambert-Eaton. Ces résultats suggèrent que l'échangeur NCX3 est peut-être impliqué dans la pathogenèse de certaines formes de cette maladie. Des études supplémentaires afin de confirmer notre hypothèse devront donc être réalisées. / We produced and analyzed mice deficient for Na/Ca exchanger 3 (NCX3), a protein which mediates cellular Ca2+ efflux (forward mode) or Ca2+ influx (reverse mode) and thus controls intracellular Ca2+ concentration. NCX3-deficient mice (Ncx3-/-) present a skeletal muscle fiber necrosis and a defective neuromuscular transmission, reflecting the absence of NCX3 in the sarcolemma of the muscle fibers and at the neuromuscular junction. The defective neuromuscular transmission is characterized by the presence of electromyographic abnormalities including low compound muscle action potential amplitude, a decremental response at low frequency nerve stimulation, an incremental response and a prominent post-exercise facilitation at high frequency nerve stimulation as well as neuromuscular blocks. The analysis of quantal transmitter release in Ncx3-/- neuromuscular junctions revealed an important facilitation superimposed on the depression of synaptic responses and an elevated delayed release during high frequency nerve stimulation. It is suggested that Ca2+ entering nerve terminals is cleared relatively slowly in the absence of NCX3, thereby enhancing residual Ca2+ and evoked and delayed quantal transmitter release during repetitive nerve stimulation. Our findings indicate that NCX3 plays an important role in vivo in the control of Ca2+ concentrations in the skeletal muscle fibers and at the neuromuscular junction.

This dissertation of various aspects of electromyogram (EMG: muscle electrical activity) signal processing is comprised of two projects in which I was the lead investigator and two team projects in which I participated. The first investigator-led project was a study of reconstructing continuous EMG discharge rates from neural impulses. Related methods for calculating neural firing rates in other contexts were adapted and applied to the intramuscular motor unit action potential train firing rate. Statistical results based on simulation and clinical data suggest that performances of spline-based methods are superior to conventional filter-based methods in the absence of decomposition error, but they unacceptably degrade in the presence of even the smallest decomposition errors present in real EMG data, which is typically around 3-5%. Optimal parameters for each method are found, and with normal decomposition error rates, ranks of these methods with their optimal parameters are given. Overall, Hanning filtering and Berger methods exhibit consistent and significant advantages over other methods. In the second investigator-led project, the technique of signal whitening was applied prior to motion classification of upper limb surface EMG signals previously collected from the forearm muscles of intact and amputee subjects. The motions classified consisted of 11 hand and wrist actions pertaining to prosthesis control. Theoretical models and experimental data showed that whitening increased EMG signal bandwidth by 65-75% and the coefficients of variation of temporal features computed from the EMG were reduced. As a result, a consistent classification accuracy improvement of 3-5% was observed for all subjects at small analysis durations (< 100 ms). In the first team-based project, advanced modeling methods of the constant posture EMG-torque relationship about the elbow were studied: whitened and multi-channel EMG signals, training set duration, regularized model parameter estimation and nonlinear models. Combined, these methods reduced error to less than a quarter of standard techniques. In the second team-based project, a study related biceps-triceps surface EMG to elbow torque at seven joint angles during constant-posture contractions. Models accounting for co-contraction estimated that individual flexion muscle torques were much higher than models that did not account for co-contraction.

The electromyogram has numerous applications in engineering and science. One specific application is to model a system for the torque generated by the elbow joint. This application has been long studied and applied in controller designs for artificial prosthetics limbs. Previous research had shown that nonlinear and multiple channel whitened EMG signal models gave the best EMG to torque estimates compared to linear un-whitened models. This thesis describes the methodologies for predicting the torque into the future up to 1 second. Four specific types of finite impulse response models (linear and nonlinear, single channel un-whitened and multi-channel whitened) are compared based on the EMG-based predicted torque and the actual torque. The errors were measured as the difference between actual and predicted torque. It was observed that the error was mostly constant at the minimum error value between 0 and 80 ms for all four models, with the lowest error being 5.48 % maximum voluntary contraction (MVC) flexion. Further comparison was performed between different lower order models and a Butterworth second order model for predicting torque ahead in time. Such models are common in the literature. This thesis separately investigates the effect of band limiting the whitened EMG signal and using the advanced EMG processors for estimating the torque. Whitened EMG data were passed through a low pass filter with selectable cutoff frequency from 2048 Hz down to 20 Hz to limit the whitened band width. It was observed that the error was not significantly different for bandwidths down to approximately 400-600 Hz, grew gradually as the band width further decreased to 200 Hz, beyond which the error increased sharply. It can be inferred that for this particular study consisting of lower contraction levels, there is no significant power usable for whitening in the EMG signal at higher frequencies, providing an opportunity for lower sampling rate, effective noise suppression, better signal to noise ratio and implementation of low cost electrodes. This research work lead to two conference paper publications at the 2013 IEEE 39th Annual Northeast Bioengineering Conference. Two journal papers are in the writing and preparation stage which will be submitted after their completion.

<p><p>The intention of this thesis project report is to control a servo motor by using Electromyography(EMG) signals in the purpose of learning about bioamplifers and how ATMEL AVR Series microcontrollers work.</p><p>EMG is the a test that is used to record the electrical activity of muscles. In order to fulfill our intention an EMG amplifier, an ADC converter and a servo motor controller is build to be used with the simple mechenical gripper where the control of the gripper is directly related with the amplitude of the EMG signals taken from the hand muscles. In the development and USART serial communication part is also added enabling to see the ADC results in computer.</p></p>