A nonlinearities inverse distance weighting spatial interpolation approach applied to the surface electromyography signal

Spatial interpolation of a surface electromyography (sEMG) signal from a set of signals recorded from a multi-electrode array is a challenge in biomedical signal processing. Consequently, it could be useful to increase the electrodes' density in detecting the skeletal muscles' motor units under detection's vacancy. This paper used two types of spatial interpolation methods for estimation: Inverse distance weighted (IDW) and Kriging. Furthermore, a new technique is proposed using a modified nonlinearity formula based on IDW. A set of EMG signals recorded from the noninvasive multi-electrode grid from different types of subjects, sex, age, and type of muscles have been studied when muscles are under regular tension activity. A goodness of fit measure (R2) is used to evaluate the proposed technique. The interpolated signals are compared with the actual signals; the Goodness of fit measure's value is almost 99%, with a processing time of 100msec. The resulting technique is shown to be of high accuracy and matching of spatial interpolated signals to actual signals compared with IDW and Kriging techniques

Tutorial. Surface EMG detection, conditioning and pre-processing: Best practices

This tutorial is aimed primarily to non-engineers, using or planning to use surface electromyography (sEMG) as an assessment tool for muscle evaluation in the prevention, monitoring, assessment and rehabilitation fields. The main purpose is to explain basic concepts related to: (a) signal detection (electrodes, electrode–skin interface, noise, ECG and power line interference), (b) basic signal properties, such as amplitude and bandwidth, (c) parameters of the front-end amplifier (input impedance, noise, CMRR, bandwidth, etc.), (d) techniques for interference and artifact reduction, (e) signal filtering, (f) sampling and (g) A/D conversion, These concepts are addressed and discussed, with examples. The second purpose is to outline best practices and provide general guidelines for proper signal detection, conditioning and A/D conversion, aimed to clinical operators and biomedical engineers. Issues related to the sEMG origin and to electrode size, interelectrode distance and location, have been discussed in a previous tutorial. Issues related to signal processing for information extraction will be discussed in a subsequent tutorial

The human ECG - nonlinear deterministic versus stochastic aspects

We discuss aspects of randomness and of determinism in electrocardiographic signals. In particular, we take a critical look at attempts to apply methods of nonlinear time series analysis derived from the theory of deterministic dynamical systems. We will argue that deterministic chaos is not a likely explanation for the short time variablity of the inter-beat interval times, except for certain pathologies. Conversely, densely sampled full ECG recordings possess properties typical of deterministic signals. In the latter case, methods of deterministic nonlinear time series analysis can yield new insights.Comment: 6 pages, 9 PS figure

On the Effect of Walking Surface Stiffness on Inter-leg Coordination during Human Walking: a Unique Perspective to Robot-assisted Gait Rehabilitation

abstract: Millions of individuals suffer from gait impairments due to stroke or other neurological disorders. A primary goal of patients is to walk independently, but most patients only achieve a poor functional outcome five years after injury. Despite the growing interest in using robotic devices for rehabilitation of sensorimotor function, state-of-the-art robotic interventions in gait therapy have not resulted in improved outcomes when compared to traditional treadmill-based therapy. Because bipedal walking requires neural coupling and dynamic interactions between the legs, a fundamental understanding of the sensorimotor mechanisms of inter-leg coordination during walking is needed to inform robotic interventions in gait therapy. This dissertation presents a systematic exploration of sensorimotor mechanisms of inter-leg coordination by studying the effect of unilateral perturbations of the walking surface stiffness on contralateral muscle activation in healthy populations. An analysis of the contribution of several sensory modalities to the muscle activation of the opposite leg provides new insight into the sensorimotor control mechanisms utilized in human walking, including the role of supra-spinal neural circuits in inter-leg coordination. Based on these insights, a model is created which relates the unilateral deflection of the walking surface to the resulting neuromuscular activation in the opposite leg. Additionally, case studies with hemiplegic walkers indicate the existence of the observed mechanism in neurologically impaired walkers. The results of this dissertation suggest a novel approach to gait therapy for hemiplegic patients in which desired muscle activity is evoked in the impaired leg by only interacting with the healthy leg. One of the most significant advantages of this approach over current rehabilitation protocols is the safety of the patient since there is no direct manipulation of the impaired leg. Therefore, the methods and results presented in this dissertation represent a potential paradigm shift in robot-assisted gait therapy.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Measurement of central and peripheral fatigue during whole body exercise : a new method

Background: This thesis sought to establish a new method for instantaneous measurement of central and peripheral fatigue during whole-body exercise up to maximal aerobic capacity in humans. Until now, measurement of central and peripheral fatigue has been limited to isolated muscle tasks or to time points after exercise where the physiological conditions that brought about the limiting symptoms for exercise have subsided. Thus, development of a method to overcome this would allow the first demonstration of the relative contributions of central and peripheral fatigue to limiting exercise that elicited maximal strain of the combined neuromuscular and cardiopulmonary systems. Objective: To develop and validate a method for quantifying peripheral muscle fatigue (MF, defined as the power produced for a given muscle stimulation), activation fatigue (AF, defined as the maximal evocable muscle activity), their sum, performance fatigue (PF, defined as the decline in maximal voluntary isokinetic power compared to the fresh, baseline, state) during cycling exercise at maximal aerobic capacity. In addition, this thesis aimed to determine the rate with which MF, AF and PF recovered to baseline after intolerance during whole-body exercise in humans. Methods: To quantify fatigue during whole-body exercise, a method was developed to allow a rapid switch from standard cycling (where the relationship between power and cadence is hyperbolic) to isokinetic cycling (where power is independent of cadence, and cadence is fixed) to be implemented. By asking the participant to give a maximal isokinetic effort at any point during exercise or recovery, allowed the velocity-specific decline in maximal isokinetic power (PISO) to be measured. The difference in PISO between baseline and exercise quantified PF. It was tested whether the baseline relationship between PISO and electromyographic power in 5 leg muscles (RMS EMG) was velocity dependent, linear and reproducible, such that the relative contributions to PF could be isolated from: 1) the decline in muscle activation (AF); and 2) the decline in PISO at a given activation (MF). Results: Healthy participants (n=13, 29 to 72 years old, ranging in aerobic capacity from 23.5 to 62.4 ml/min/kg) completed short (5 s) variable-effort isokinetic bouts at 50, 70, and 100 rpm to characterize the baseline relationship between RMS EMG and isokinetic power. Individual baseline EMG-PISO relationships were linear (r2 = 0.95 ± 0.04) and velocity dependent (analysis of covariance). Subsequently, repeated ramp incremental exercise tests were performed on a cycle ergometer and breath-by-breath gas exchange and ventilation was measured. Exercise was terminated with a maximal isokinetic effort (5 s) at 70 rpm. PISO at intolerance (two legs, 335 ± 88 W) was ~45% less than baseline (630 ± 156 W, p < 0.05). Following intolerance, PISO recovered within 3 minutes (p < 0.05). AF and MF (measured in one leg) were 97 ± 55 and 60 ± 50 W, respectively. Mean bias (± limits of agreement) for reproducibility were as follows: PISO at baseline 1 ± 30 W; PISO at 0-min recovery 3 ± 35 W; and EMG at PISO 3 ± 14%. Conclusions: The baseline EMG-PISO relationship was well modelled by a linear function, which was reproducible day-to-day. The variability of the individual EMG-PISO measurements between ~25% and 100% effort, around the linear model, was sufficiently tight that the baseline linear relationship allowed for a precise quantification of AF and MF at the limit of tolerance and in recovery from a maximal aerobic exercise task. It was also demonstrated that the EMG-PISO relationship was velocity dependent, as expected from the parabolic nature power-velocity curve. As such, this provides a valuable new method to identify the contributions of central and peripheral fatigue to limiting whole-body exercise in humans.Contexto: Esta tese procurou estabelecer um novo método de mensuração instantânea de fadiga central e periférica durante o exercício de corpo inteiro até a capacidade aeróbica máxima em seres humanos. Até agora, a mensuração da fadiga central e periférica tem sido limitada a tarefas musculares isoladas ou a momentos específicos após o exercício, nos quais as condições fisiológicas que levaram aos sintomas limitantes do exercício já estão abrandadas. Assim, desenvolver um método que supere estas limitações permitiria demonstrar pela primeira vez as contribuições relativas da fadiga central e periférica na limitação ao exercício, no qual haja estimulação máxima dos sistemas neuromuscular e cardiovascular. Objetivo: Desenvolver e validar um método para quantificar a fadiga muscular periférica (MF, definida como a potência produzida para uma determinada estimulação muscular), fadiga de ativação (AF, definida como a atividade muscular evocável máxima), sua soma, fadiga de desempenho (PF, definida como a perda de potência isocinética voluntária máxima em comparação com a basal) durante o exercício realizado no cicloergômetro em capacidade aeróbica máxima. Além disso, esta tese teve como objetivo determinar as taxas de recuperação nas quais MF, AF e PF retornaram à linha de base após a intolerância durante o exercício de corpo inteiro em seres humanos. Métodos: Para quantificar a fadiga durante o exercício de corpo inteiro, foi desenvolvido um método para permitir uma rápida transição do ciclismo padrão (em que a relação entre potência e cadência é hiperbólica) para o ciclismo isocinético (em que a potência é independente da cadência, e a cadência é fixa). Assim, ao pedir para o participante realizar um esforço isocinético máximo em qualquer ponto durante o exercício ou na fase de recuperação, permitiu-se quantificar o declínio velocidade-específica da potência isocinética máxima (PISO). A diferença na PISO entre a linha de base e o exercício quantifica a PF. Foi testado se a relação de base entre PISO e potência eletromiográfica em 5 músculos da perna (RMS EMG) era velocidade dependente, linear e reprodutível, de tal modo que as contribuições relativas para PF pudessem ser isoladas a partir de: 1) a diminuição da ativação muscular (AF) ; e 2) o declínio na PISO num dado grau de ativação (MF). Resultados: Participantes saudáveis (n=13, 29-72 anos, variando em capacidade aeróbica de 23,5 até 62,4 ml/min/kg) completaram tiros isocinéticos esforço-variável de curta duração (5 s) a 50, 70 e 100 rpm para caracterizar a relação basal entre EMG RMS e potência isocinética. As correlações entre EMG-Piso basais foram lineares (r2= 0,95 ± 0,04) e velocidade dependente (análise de covariância). Posteriormente, testes de exercício incrementais repetidos foram realizados em uma bicicleta ergométrica e as trocas gasosas e a ventilação foram mensuradas respiração a respiração. O exercício encerrava com um esforço isocinético máximo (5 s) a 70 rpm. Na intolerância, PISO (duas pernas, 335 ± 88 W) foi ~ de 45% menos do que na linha de base (630 ± 156 W, p <0,05). Após a intolerância, houve recuperação da PISO em 3 minutos (p <0,05). AF e MF (medido em uma perna) foram de 97 ± 55 e 60 ± 50 W, respectivamente. As médias de viés (± limites de concordância) para a reprodutibilidade foram as seguintes: PISO na linha de base 1 ± 30 W; PISO na recuperação 0-min 3 ± 35 W; e EMG em PISO 3 ± 14%. Conclusões: A relação basal EMG-PISO foi bem modelada por uma função linear, que foi reprodutível no dia-a-dia. A variabilidade das mensurações EMG-PISO individuais entre ~ 25% e 100% de esforço, em torno do modelo linear, foi suficientemente forte de modo que a relação linear basal permitiu uma quantificação precisa de AF e MF no limite de tolerância e na recuperação do exercício aeróbico máximo. Foi também demonstrado que a relação EMG-PISO foi velocidade dependente, como esperado a partir da curva parabólica de potência-velocidade. Assim, esta tese apresenta um novo método útil para identificar as contribuições da fadiga central e periférica na limitação do exercício de corpo inteiro em seres humanos

fNIRS complexity analysis for the assessment of motor imagery and mental arithmetic tasks

Conventional methods for analyzing functional near-infrared spectroscopy (fNIRS) signals primarily focus on characterizing linear dynamics of the underlying metabolic processes. Nevertheless, linear analysis may underrepresent the true physiological processes that fully characterizes the complex and nonlinear metabolic activity sustaining brain function. Although there have been recent attempts to characterize nonlinearities in fNIRS signals in various experimental protocols, to our knowledge there has yet to be a study that evaluates the utility of complex characterizations of fNIRS in comparison to standard methods, such as the mean value of hemoglobin. Thus, the aim of this study was to investigate the entropy of hemoglobin concentration time series obtained from fNIRS signals and perform a comparitive analysis with standard mean hemoglobin analysis of functional activation. Publicly available data from 29 subjects performing motor imagery and mental arithmetics tasks were exploited for the purpose of this study. The experimental results show that entropy analysis on fNIRS signals may potentially uncover meaningful activation areas that enrich and complement the set identified through a traditional linear analysis

A Methodology Towards Comprehensive Evaluation of Shape Memory Alloy Actuators for Prosthetic Finger Design

Presently, DC motors are the actuator of choice within intelligent upper limb prostheses. However, the weight and dimensions associated with suitable DC motors are not always compatible with the geometric restrictions of a prosthetic hand; reducing available degrees of freedom and ultimately rendering the prosthesis uncomfortable for the end-user. As a result, the search is on-going to find a more appropriate actuation solution that is lightweight, noiseless, strong and cheap. Shape memory alloy (SMA) actuators offer the potential to meet these requirements. To date, no viable upper limb prosthesis using SMA actuators has been developed. The primary reasons lie in low force generation as a result of unsuitable actuator designs, and significant difficulties in control owing to the highly nonlinear response of SMAs when subjected to joule heating. This work presents a novel and comprehensive methodology to facilitate evaluation of SMA bundle actuators for prosthetic finger design. SMA bundle actuators feature multiple SMA wires in parallel. This allows for increased force generation without compromising on dynamic performance. The SMA bundle actuator is tasked with reproducing the typical forces and contractions associated with the human finger in a prosthetic finger design, whilst maintaining a high degree of energy efficiency. A novel approach to SMA control is employed, whereby an adaptive controller is developed and tuned using the underlying thermo-mechanical principles of operation of SMA wires. A mathematical simulation of the kinematics and dynamics of motion provides a platform for designing, optimizing and evaluating suitable SMA bundle actuators offline. This significantly reduces the time and cost involved in implementing an appropriate actuation solution. Experimental results show iii that the performance of SMA bundle actuators is favourable for prosthesis applications. Phalangeal tip forces are shown to improve significantly through bundling of SMA wire actuators, while dynamic performance is maintained owing to the design and implementation of the selected control strategy. The work is intended to serve as a roadmap for fellow researchers seeking to design, implement and control SMA bundle actuators in a prosthesis design. Furthermore, the methodology can also be adopted to serve as a guide in the evaluation of other non-conventional actuation technologies in alternative applications