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Avaliação da fadiga muscular pela mecanomiografia durante a aplicação de um protocolo de EENM

BACKGROUND: Neuromuscular electrical stimulation (NMES) is a widely used technique for rehabilitation in physical therapy, however it causes muscle fatigue more rapidly than does voluntary contraction. In clinical practice, it becomes necessary to monitor muscle fatigue during NMES protocols to adjust the parameters of electrical current stimulation and, thus, increase stimulation time. OBJECTIVES: The aim of this study is to use mechanomyography (MMG) as a means of evaluating peripheral muscle fatigue during the execution of an NMES protocol. METHODS: An MMG signal acquisition system and an experimental protocol were developed. During in vivo tests, 10 participants performed maximal voluntary contractions (MVCs) for knee extension. A maximization phase was conducted with dynamic contractions generated by NMES at 10% of MVC (100 Hz, 400 µs) on the quadriceps muscle, and the main NMES protocol occurred at 30% of MVC (50 Hz, 400 µs). Simultaneously, MMGRMS (amplitude) and MMGMPF (frequency) signals of the rectus femoris and the knee extension torque were acquired. RESULTS: The tendency line of the MMGRMS was descendant, indicating that MMGRMS correlates with torque amplitude. However, MMGMPF did not show a significant correlation with torque for the present NMES protocol. CONCLUSIONS: MMG is a technique that can be simultaneously applied to NMES because there is no electrical interference and it can be used during functional movements in the NMES-generated muscle contraction. Article registered in the Australian New Zealand Clinical Trials Registry (ANZCTR) under the number ACTRN12609000866202.

Potencial de ação: do estímulo à adaptação neural

INTRODUCTION: The action potential (AP) arises due to a disturbance of the resting state of the cell membrane with consequent flow of ions across the membrane and ion concentration changes in intra and extra cellular space. OBJECTIVES: This article aims to summarize the scientific knowledge accumulated to date on the action potential and neural adaptation in the process of applying a constant stimulus. MATERIALS AND METHODS: This is a literature review on the bases Springer, ScienceDirect, PubMed, IEEE Xplore, Google Scholar, Capes Periodicals Portal as well as books on the topic. The selected preferred language was English with the keywords: action potential; adaptation, accommodation; rheobase; chronaxy; nerve impulse. We conducted a search of articles with a wide time window from 1931 to 2010 and books from 1791 to 2007. RESULTS: In the selected studies was extracted information about the following topics: action potential and its stages; nerve conduction; rheobase; chronaxie, accommodation, and adaptation. CONCLUSION: A stimulus that creates AP, if applied consistently, can reduce the frequency of depolarization as a function of time and, consequently, to adapt the cell. The time it takes the cell in the absence of stimuli, to recover its original frequency, is defined as a disadaptation.

A new approach to assess the spasticity in hamstrings muscles using mechanomyography antagonist muscular group

Several pathologies can cause muscle spasticity. Modified Ashworth scale (MAS) can rank spasticity, however its results depend on the physician subjective evaluation. This study aims to show a new approach to spasticity assessment by means of MMG analysis of hamstrings antagonist muscle group (quadriceps muscle). Four subjects participated in the study, divided into two groups regarding MAS (MAS0 and MAS1). MMG sensors were positioned over the muscle belly of rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) muscles. The range of movement was acquired with an electrogoniometer placed laterally to the knee. The system was based on a LabVIEW acquisition program and the MMG sensors were built with triaxial accelerometers. The subjects were submitted to stretching reflexes and the integral of the MMG (MMGINT) signal was calculated to analysis. The results showed that the MMGINT was greater to MAS1 than to MAS0 [muscle RF (p= 0.004), VL (p= 0.001) and VM (p= 0.007)]. The results showed that MMG was viable to detect a muscular tonus increase in antagonist muscular group (quadriceps femoris) of spinal cord injured volunteers.

Investigation of muscle behavior during different functional electrical stimulation profiles using Mechanomyography

Mechanomyography (MMG) is a technique for measuring muscle oscillations and fatigue. Functional electrical stimulation (FES) has been applied to control movements mainly in people with spinal cord injury (SCI). The goal of this study is the application of the MMG signal as a tool to investigate muscle response during FES. Ten healthy individuals (HI) and three SCI were submitted to four FES profiles in the rectus femoris (RF) and vastus lateralis (VL) muscles. Four FES profiles were applied in different days. The FES profile set to 1 kHz pulse frequency, 200 us active pulse duration and burst frequency of 50 Hz presented the lowest MMG root mean square and spectral median frequency values, suggesting less muscle modification. The MMG signal was different between HI and SCI but there was no difference between the RF and VL muscles.

Optimal FES parameters based on mechanomyographic efficiency index

Functional electrical stimulation (FES) can artificially elicit movements in spinal cord injured (SCI) subjects. FES control strategies involve monitoring muscle features and setting FES profiles so as to postpone the installation of muscle fatigue or nerve cell adaptation. Mechanomyography (MMG) sensors register the lateral oscillations of contracting muscles. This paper presents an MMG efficiency index (EI) that may indicate most efficient FES electrical parameters to control functional movements. Ten healthy and three SCI volunteers participated in the study. Four FES profiles with two FES sessions were applied with in-between 15min rest interval. MMG RMS and median frequency were inserted into the EI equation. EI increased along the test. FES profile set to 1kHz pulse frequency, 200εs active pulse duration and burst frequency of 50Hz was the most efficient.

Advances and perspectives of mechanomyography

INTRODUCTION: The evaluation of muscular tissue condition can be accomplished with mechanomyography (MMG), a technique that registers intramuscular mechanical waves produced during a fibers contraction and stretching that are sensed or interfaced on the skin surface. OBJECTIVE: Considering the scope of MMG measurements and recent advances involving the technique, the goal of this paper is to discuss mechanomyography updates and discuss its applications and potential future applications. METHODS: Forty-three MMG studies were published between the years of 1987 and 2013. RESULTS: MMG sensors are developed with different technologies such as condenser microphones, accelerometers, laser-based instruments, etc. Experimental protocols that are described in scientific publications typically investigated the condition of the vastus lateralis muscle and used sensors built with accelerometers, third and fourth order Butterworth filters, 5-100Hz frequency bandpass, signal analysis using Root Mean Square (RMS) (temporal), Median Frequency (MDF) and Mean Power Frequency (MPF) (spectral) features, with epochs of 1 s. CONCLUSION: Mechanomyographic responses obtained in isometric contractions differ from those observed during dynamic contractions in both passive and functional electrical stimulation evoked movements. In the near future, MMG features applied to biofeedback closed-loop systems will help people with disabilities, such as spinal cord injury or limb amputation because they may improve both neural and myoelectric prosthetic control. Muscular tissue assessment is a new application area enabled by MMG; it can be useful in evaluating the muscular tonus in anesthetic blockade or in pathologies such as myotonic dystrophy, chronic obstructive pulmonary disease, and disorders including dysphagia, myalgia and spastic hypertonia. New research becomes necessary to improve the efficiency of MMG systems and increase their application in rehabilitation, clinical and other health areas.

Correlation between mechanomyography features and passive movements in healthy and paraplegic subjects

Mechanomyography (MMG) measures both muscular contraction and stretching activities and can be used as feedback in the control of neuroprostheses with Functional Electrical Stimulation (FES). In this study we evaluated the correlation between MMG features and passive knee angular movement of rectus femoris and vastus lateralis muscles acquired from healthy volunteers (HV) and spinal cord injured volunteers (SCIV). Twelve HV and thirteen SCIV were submitted to passive and FES elicited knee extensions and in each extension, eleven windows of analysis with 0.5s length were inspected. Temporal (RMS and INT) and frequency (MF and μ3) features were extracted. Spearman correlation coefficients (p) were computed in order to check correlations between the features obtained from both MMG sensors. The correlation between MMGMF and MMG temporal analysis (RMS and INT) to HV was classified as positive, moderate (p from 0.635 to 0.681) and high (p from 0.859 to 0.870), and weak (positive e negative) to SCIV. These results differ from those obtained in voluntary contraction or artificially evoked by functional electrical stimulation and may be relevant in applications with closed loop control systems.

Mechanomyographic response during FES in healthy and paraplegic subjects

Mechanomyography (MMG) registers lateral oscillations of contracting muscles. Functional electrical stimulation (FES) improves the rehabilitation of paraplegic subjects and can be used in neuroprosthesis control. During FES application, muscular contraction responses may vary, possibly due to fatigue or adaptation of nerve cells face to electrical stimuli. This study measured the differences in MMG RMS and median frequency (MF) features between healthy (HV) and spinal cord injury (SCI) volunteers. Ten HV and three SCI participated in the research. FES waveform consisted of a monophasic square wave, 1kHz pulse frequency, 100us active pulse period and 3ms active burst period with burst frequency of 70Hz. For each stimulation series, three analysis windows were inspected. RMS and MF variations were inversely related. The obtained results may help to create new strategies of muscular closed-loop control.

Influence of Skinfold Thickness in Mechanomyography Features

The assessment and physiological register of muscular tissue can be done through mechanomyography (MMG). The oscillation of muscular displacement is acquired on the skin surface, insomuch that the skinfold thickness can influence in MMG response. The aim of this study is verify the influence of different skinfold thickness on MMG features responses. Triaxial MMG was used over the rectus femoris muscle belly of ten volunteers during maximal voluntary contraction. MMG spectral and temporal analyses were made and specific features (root mean square (RMS), Integral (Int), mean frequency (MF), zero-crossing (ZC), and μ3) were correlated with skinfold thickness. Moderate and high negative correlation occurred to MMG mean frequency in axes X (ρ = - 0.57) and Y (ρ = -0.75), respectively. As the fat tissue behaves like a low-pass filter, i.e. the thicker his skinfold the shorter its bandwidth; therefore, the skinfold thicknesses result in lower frequency responses. So, hereafter these results may be applied to calibrate MMG responses as biofeedback systems in, for instance, neuroprostheses.

Diffractive limited acoustic field of an apodized ultrasound transducer

The diffraction in the acoustic field of an ultrasound transducer can be modeled as the result of the interference of edge and plane waves generated from the periphery and the center of the piezoelectric element, respectively. Our objective in developing ultrasound transducers with apodized piezoelectric ceramic discs was to generate acoustical fields with reduced edge waves interference. Transducers were built with apodized ceramic discs (polarized more intensively in the central region than in the edges) and their mapped acoustic fields showed a distinct pattern when compared to those of conventional transducers. A polynomial equation describing the nonlinear poling field intensity, was used with the Rayleigh equation to simulate the nonuniform vibration amplitude distribution generated by the apodized transducers. Simulated acoustic fields were compared to experimental field mappings. The results of simulations and experimental tests showed reduction in the lateral spreading of acoustic fields produced by apodized transducers, compared to those produced by conventional transducers. The reduced presence of the lateral lobes in the apodized acoustic field is due to the minimized vibration of the disc periphery. The numerical and experimental results were in good agreement and showed that it was possible to reduce acoustic field diffraction through nonlinear polarization of the piezoelectric element.