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 fiber's 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 areas304384401CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFINANCIADORA DE ESTUDOS E PROJETOS - FINEPsem informaçã

Neuromuscular fatigue detection by mechanomyography in people with complete spinal cord injury

Functional electrical stimulation (FES) is a method of activating paralyzed muscles. During FES application, fast muscle fatigue can occur (the inability of stimulated muscles to generate force). Therefore, it is beneficial to estimate the muscle fatigue for FES closed-loop control for walking to prevent unexpected muscle collapse and adapt the FES strategy in real time. Mechanomyography (MMG) is a noninvasive technique for registering myofiber vibrations, representing an ideal candidate for the provision of feedback. The hypothesis was that MMG signals could effectively detect muscle fatigue and, thus, provide feedback

Detecção de fadiga neuromuscular em pessoas com lesão medular completa utilizando transformada wavelet

Introduction: People with spinal cord injury (SCI) may have the paralyzed muscles activated through functional electrical stimulation (FES) on neural pathways present below the skin. These electrical stimulations are important to restore the neuromuscular trophism or during the movement control using neural prostheses. However, prolonged FES application causes fatigue, which decreases the contraction strength, mainly due the neuromuscular hypotrophy in this population. The acquisition of myofibers’ vibration is recognized by mechanomyography (MMG) system and does not suffer electrical interference from the FES system. Objective: To characterize the rectus femoris muscle vibration during electrically evoked neuromuscular fatigue protocol in complete spinal cord injury subjects. Methods: As sample, 24 limbs (right and left) from 15 male participants (age: 27±5 y.o.) and ranked as A and B according to American Spinal Injury Impairment Scale) were selected. An electrical stimulator operating as voltage source, specially developed for research, was configured as: pulse frequency set to 1 kHz (20% duty cycle) and burst (modulating) frequency set to 70 Hz (20% active period). The triaxial [X (transverse), Y (longitudinal) and Z (perpendicular)] MMG signal of rectus femoris muscle was processed with a third-order 5-50 Hz bandpass Butterworth filter. A load cell was used to register the force. The stimulator output voltage was increased (~3 V/s to avoid motoneuron adaptation/habituation) until the maximal electrically-evoked extension (MEEE) of the knee joint. After the load cell placement, the stimuli magnitude required to reach MEEE was applied and registered by the load cell as muscular F100% response. Stimuli intensity was increased during the control to keep the force in F100%. Four instants (I - IV) were selected from F100% up to the inability to keep the FES response force above 30% (F30%). The signal was processed in temporal (energy), spectral (median frequency) and wavelet (temporal-spectral with twelve band frequencies between 5 and 53 Hz) domains. All data were normalized by initial instant, creating arbitrary units (a.u.), and non-parametric tests were applied. Results: The median frequency did not show statistical significance. Regarding the MMG axes, the transverse axis showed most statistical differences. The MMG energy (temporal domain) indicates the decrease between the instants I (unfatigued) and II (pre-fatigue), as well as instants I and IV (fatigued). The wavelet domain focused on the transverse axis, especially on 13, 16, 20, 25 and 35 Hz frequency bands, for having shown significant reduction proven during neuromuscular fatigue. In focus on 25 Hz band frequency that showed a constant decrease between instants I (median value from data de 0.53 a.u.) with subsequent instants [II (0.30 a.u.), III (0.28 a.u.) and IV (0.24 a.u.). Conclusion: Neuromuscular fatigue is characterized by energy decrease in MMG X-axis (transverse) signal of vibration on the rectus femoris muscle for complete spinal cord injured subjects, in the temporal domain but mainly in the wavelet domain. The 25 Hz is the most important band frequency because its energy decreases with neuromuscular fatigue. These findings open the possibility of application in closed-loop systems during physical rehabilitation procedures using FES or in the control of neural prostheses.CNPqIntrodução: As pessoas com lesão medular (LM) podem ter seus músculos paralisados ativados por meio da estimulação elétrica funcional (FES) sobre vias neurais presentes próximas à pele. Estas estimulações elétricas são importantes para a recuperação do trofismo neuromuscular ou durante o controle de movimento por próteses neurais. No entanto, ao longo da aplicação da FES, a fadiga ocorre, diminuindo a eficiência da contração, principalmente devido à hipotrofia neuromuscular presente nessa população. A aquisição da vibração das fibras musculares como indicador de fadiga é registrada por meio da técnica de mecanomiografia (MMG), que não sofre interferências elétricas decorrentes da aplicação da FES. Objetivo: Caracterizar a vibração do músculo reto femoral durante protocolo de fadiga neuromuscular eletricamente evocada em pessoas com lesão medular completa. Método: 24 membros (direito e esquerdo) de 15 participantes (idade: 27±5 anos) do sexo masculino (A e B na American Spinal Injury Impairment Scale) foram selecionados. Um estimulador elétrico operando como fonte de tensão, desenvolvido especialmente para pesquisa, foi configurado com: freqüência de pulso em 1 kHz (20% de ciclo de trabalho) e trem de pulsos (modulação) em 70 Hz (20% período ativo). O sinal triaxial [X (transversal), Y (longitudinal) e Z (perpendicular)] da MMG foi processado com filtro Butterworth de terceira ordem e banda passante entre 5 e 50 Hz. Previamente ao protocolo, a tensão de saída do estimulador foi incrementada (~3 V/s evitando-se a adaptação/habituação dos motoneurônios) até alcançar a extensão máxima eletricamente estimulada (EMEE) da articulação do joelho. Uma célula de carga foi usada para registrar a resposta de força, onde após a sua colocação, a intensidade da FES necessária para alcançar a EMEE foi aplicada e registrada pela célula de carga como 100% da força (F100%). Durante o protocolo de fadiga neuromuscular, a intensidade do estímulo foi incrementada durante o controle para manter a força em F100%. Quatro instantes (I - IV) foram selecionados entre F100% e a incapacidade da FES manter a resposta de força acima de 30% (F30%). O sinal foi processado nos domínios temporal (energia), espectral (frequência mediana) e wavelet (temporal-espectral com doze bandas de frequência entre 5 e 53 Hz). Os dados extraídos foram normalizados pelo instante inicial (I) gerando unidades arbitrárias (u.a.), e testados com estatística não paramétrica. Resultados: A frequência mediana não apresentou significância estatística. Em relação aos eixos de deslocamento da MMG, o eixo transversal mostrou o maior número de resultados estatisticamente significantivos. A energia da vibração das fibras musculares (domínio temporal) indicou diminuição entre os instantes I (músculo fresco) e II (pré-fadiga), como também entre os instantes I e IV (fadigado) com redução significativa. O domínio wavelet teve como foco o eixo transversal, especialmente as bandas de frequência de 13, 16, 20, 25 e 35 Hz, por terem indicado redução significativa durante a fadiga neuromuscular; principalmente, a banda de 25 Hz, que indicou redução significativa entre o instante I (valor da mediana dos dados de 0,53 u.a.) e os demais instantes [II (0,30 u.a), III (0,28 u.a.) e IV (0,24 u.a.)]. Conclusão: A fadiga neuromuscular é caracterizada pela redução da energia do sinal no eixo de deslocamento transversal (X) da vibração do músculo reto femoral, em pessoas com lesão medular completa, tanto no domínio temporal quanto principalmente no domínio wavelet, sendo a banda de frequência de 25 Hz a mais relevante, porque sua energia diminui com a ocorrência da fadiga neuromuscular. Estes achados abrem a possibilidade de aplicação em sistemas de malha fechada durante procedimentos de reabilitação física utilizando FES ou no controle de próteses neurais

Use of wavelet analysis techniques with surface EMG and MMG to characterise motor unit recruitment patterns of shoulder muscles during wheelchair propulsion and voluntary contraction tasks

The high demand on the upper extremity during manual wheelchair use contributes to a high prevalence of shoulder pathology in people with spinal cord injury. The overall purpose of this thesis was to investigate shoulder muscle recruitment patterns and wheelchair kinetics in able-bodied participants over a range of daily activities and mobility tasks requiring manual wheelchair propulsion. With a complete understanding of the muscle recruitment patterns, physiotherapists and wheelchair users can improve rehabilitation protocols and wheelchair propulsion performance to prevent shoulder pathology and maintain comfort during locomotion. Motor unit recruitment patterns were examined first during isometric and isotonic contractions to determine if spectral properties from EMG and MMG could be related to the different motor units in biceps brachii by using wavelet techniques coupled with principle component analysis. The results indicated that motor unit recruitment patterns can be indicated by the spectral properties of the EMG and MMG signals. EMG activity of 7 shoulder muscles was recorded with surface electrodes on 15 able-bodied participants over a range of manual wheelchair propulsion activities. Wavelet and principle component analysis was used to simultaneously decompose the signals into time and frequency domain. There are three main conclusions that can be drawn: 1) Uphill and faster speed (1.6m/s) propulsion required higher activity levels in the shoulder muscles and greater resultant joint force than did slow speed propulsion on the ergometer (0.9m/s), thus potentially\ud resulting in shoulder pathology. 2) Prolonged wheelchair propulsion and greater muscle activity may result in fatigue and play a factor in the development of shoulder pain and pathology over time. 3) The instructed semicircular pattern has a positive effect on shoulder muscle recruitment patterns. Further investigations need to focus on a systematic integrated data collection and analysis of kinematic, kinetic, and electromyography (EMG) data from people with spinal cord injuries

Physiological and biomechanical responses during high intensity upper body exercise

Fatigue during sport and exercise substantially affects the intensity and duration of an activity that can be maintained. Upper body exercise (UBE) despite contributing to sport, exercise and health outcomes has received relatively little attention particularly for high intensity exercise. Consequently, the mechanisms of fatigue during UBE are not fully understood. Therefore, the aim s of this thesis were to investigate a range of high intensity UBE protocols with respect to performance and the development of fatigue. In the first study participants (n = 13) completed four 30-s Wingate anaerobic tests (WAnT) against four different resistive loadings (2%, 3%, 4% and 5% body mass) thus potentially manipulating force production and cadence. Corrected peak power output (PPO) was independent of load (P > 0.05) and uncorrected PPO increased with load (P 0.05). All participants reached their maximum cardiorespiratory responses (oxygen uptake & heart rate; beats-min'1) at fatigue. The data suggested that prior to Tlim changes in EMG activation and movement patterns were related to the exercise intensity. In general, all EMG activity increased with intensity and exercise duration, with the kinematic data indicating that trunk rotational velocity rather than trunk stabilisation occurred throughout all trials. Overall, untrained participants altered their body movement to maintain PO between 30 & 120 s, however between 120 s & Tlim, no further significant changes occurred. In the final study, participants (n = 12) completed a 6-week arm crank training programme. Preliminary performance tests included a WAnT, V 02peak and 100% PMP test to exhaustion. Each test was repeated following the training programme. Corrected and uncorrected PPO and fatigue index (FI) increased in the WAnT test post training (P < 0.01, P < 0.05, respectively). Muscles of the shoulder (anterior deltoid & infraspinatus) demonstrated reduced activation following training (P < 0.05) with trunk rotational velocity increasing at corrected PPO during the WAnT (P < 0.01). Therefore, increases in WAnT PO may be related to changes in technique rather than muscle activation. Following training there was a significant increase in PMP (P < 0.01) during the V 02peak test and a significant increase in Tlim (P < 0.01) for the repeated 100% PMP test. Following training there was a significant decrease in triceps brachii EMG activation (P < 0.05), changes in external oblique activation (P < 0.001) at 120 s and a significant increase in trunk rotational velocity at 30 s (P < 0.05). Although at Tim, the kinematic responses were the same. The results of this training study indicated that changes in performance were due to physiological adaptations and changes in technique. The three studies have demonstrated the importance of changes in EMG activity, trunk rotational velocity, and technique to arm crank PO rather than specific physiological changes alone which has implications for the use of arm cranking in testing, training and performance outcomes

In vivo investigation of muscle behaviour during voluntary and electrically induced muscle contraction using B-Mode ultrasound imaging

Musculoskeletal Ultrasound Imaging (USI) is a growing field in literature. It has been proven to be a useful tool for investigating the properties of the muscle. There is growing interest in ultrasound imaging techniques for the description of skeletal muscle function, and different algorithms have been developed for this purpose. The majority of studies limit their focus on a particular area of the muscle, such as the aponeuroses, or on architectural parameters such as fiber length and pennation angle. The investigation of the entire muscle visualised on the ultrasound image may help elucidate the muscle function under normal conditions or when external factors compromise or alter the muscle function. Functional electrical stimulation (FES) is a technique based on the use of electrical current to activate skeletal muscles and facilitate their contraction. It is commonly used for strength training or in rehabilitation to accelerate or enhance the recovery of skeletal muscle's function. The ability of this technique to improve muscle performance in both healthy and diseased muscles has been demonstrated in research and in clinical practice. However the artificial nature of the muscle activation during FES leads to some important differences from the voluntary muscle contraction. Ultrasound Imaging (USI) is a potential tool that could provide objective measurements of the muscle's response during electrical stimulation, thus helping to describe and understand these differences. The aim of this study is to develop techniques based on USI that helps to elucidate the muscle function during electrical stimulation and allow comparison with voluntary contractions. Ultrasound videos were collected from healthy participants during experimental procedures involving voluntary and electrically induced muscle contractions. The videos were analysed using software algorithms for the tracking of features in US images. The resulting parameters were used as the basis for characterisation methods to describe the muscle contraction, both globally and locally. The effectiveness of the USI analysis techniques was tested and methods for extraction of physiological information from the video analysis were implemented. The regional distribution of muscle displacement during the tasks was analysed. Larger displacements were observed at deeper portions of the muscle in both the voluntary and the electrically induced contractions. Differential displacements across muscle depths were observed to differ during voluntary and FES contractions. The electric currents applied induce a uniform muscle contraction across different depths, most likely influenced by the way the electric field recruits muscle fibers. Muscle displacement was correlated to the force exerted by the muscle. Areas close to the deep aponeurosis have higher correlation with torque exerted and a second order polynomial can be used to define the relationship between displacement and torque. The relationship between the whole muscle displacement at different depths and the torque exerted was described using a polynomial surface fitting. Mechanical strain was used to map the muscle activation. Middle areas of the muscle undergo higher positive vertical strain (i.e. the muscle thickens) while deeper portions of the muscle are the most affected by shortening horizontal strain (i.e. the muscle shortens) in both voluntary and FES contractions. The muscle contractility was analysed through strain rate. A time-frequency analysis of the strain rate was performed. More frequency components and higher bandwidths were observed in FES induced contractions when compared to the voluntary. The frequency components might reflect the motor unit activation, suggesting that during FES all the motor units, firing at different rates, are recruited. In this project, USI was used as a tool to characterise the muscle behaviour locally. Regional muscle displacement and strain distribution have been used to elucidate the muscle function and quantify how different muscle areas are mechanically involved in the contraction. Strain rate was correlated with the muscle contractility and hypotheses regarding the correlation with motor units firing rate have been proposed. In conclusion a number of techniques were developed with the purpose to investigate the muscle function in normal conditions and when external factors, such as electrical stimulation, alter the natural muscle behaviour

Investigation and Quantification of FES Exercise – Isometric Electromechanics and Perceptions of Its Usage as an Exercise Modality for Various Populations

Functional Electrical Stimulation (FES) is the triggering of muscle contraction by use of an electrical current. It can be used to give paralyzed individuals several health benefits, through allowing artificial movement and exercise. Although many FES devices exist, many aspects require innovation to increase usability and home translation. In addition, the effect of changing electrical parameters on limb biomechanics is not entirely understood; in particular with regards to stimulation duty cycle. This thesis has two distinct components. In the first (public health component), interview studies were conducted to understand several issues related to FES technology enhancement, implementation and home translation. In the second (computational biomechanics component), novel signal processing algorithms were designed that can be used to measure mechanical responses of muscles subjected to electrical stimulation. These experiments were performed by changing duty cycle and measuring its effect on quadriceps-generated knee torque. The studies of this thesis have presented several ideas, toolkits and results which have the potential to guide future FES biomechanics studies and the translatability of systems into regular usage for patients. The public health studies have provided conceptual frameworks upon which FES may be used in the home by patients. In addition, they have elucidated a range of issues that need to be addressed should FES technology reach its true potential as a therapy. The computational biomechanics studies have put forward novel data analysis techniques which may be used for understanding how muscle responds to electrical stimulation, as measured via torque. Furthermore, the effect of changing the electrical stimulation duty cycle on torque was successfully described, adding to an understanding of how electrical stimulation parameter modulation can influence joint biomechanics

Physiological and biomechanical responses during high intensity upper body exercise

Fatigue during sport and exercise substantially affects the intensity and duration of an activity that can be maintained. Upper body exercise (UBE) despite contributing to sport, exercise and health outcomes has received relatively little attention particularly for high intensity exercise. Consequently, the mechanisms of fatigue during UBE are not fully understood. Therefore, the aim s of this thesis were to investigate a range of high intensity UBE protocols with respect to performance and the development of fatigue. In the first study participants (n = 13) completed four 30-s Wingate anaerobic tests (WAnT) against four different resistive loadings (2%, 3%, 4% and 5% body mass) thus potentially manipulating force production and cadence. Corrected peak power output (PPO) was independent of load (P > 0.05) and uncorrected PPO increased with load (P 0.05). All participants reached their maximum cardiorespiratory responses (oxygen uptake & heart rate; beats-min'1) at fatigue. The data suggested that prior to Tlim changes in EMG activation and movement patterns were related to the exercise intensity. In general, all EMG activity increased with intensity and exercise duration, with the kinematic data indicating that trunk rotational velocity rather than trunk stabilisation occurred throughout all trials. Overall, untrained participants altered their body movement to maintain PO between 30 & 120 s, however between 120 s & Tlim, no further significant changes occurred. In the final study, participants (n = 12) completed a 6-week arm crank training programme. Preliminary performance tests included a WAnT, V 02peak and 100% PMP test to exhaustion. Each test was repeated following the training programme. Corrected and uncorrected PPO and fatigue index (FI) increased in the WAnT test post training (P < 0.01, P < 0.05, respectively). Muscles of the shoulder (anterior deltoid & infraspinatus) demonstrated reduced activation following training (P < 0.05) with trunk rotational velocity increasing at corrected PPO during the WAnT (P < 0.01). Therefore, increases in WAnT PO may be related to changes in technique rather than muscle activation. Following training there was a significant increase in PMP (P < 0.01) during the V 02peak test and a significant increase in Tlim (P < 0.01) for the repeated 100% PMP test. Following training there was a significant decrease in triceps brachii EMG activation (P < 0.05), changes in external oblique activation (P < 0.001) at 120 s and a significant increase in trunk rotational velocity at 30 s (P < 0.05). Although at Tim, the kinematic responses were the same. The results of this training study indicated that changes in performance were due to physiological adaptations and changes in technique. The three studies have demonstrated the importance of changes in EMG activity, trunk rotational velocity, and technique to arm crank PO rather than specific physiological changes alone which has implications for the use of arm cranking in testing, training and performance outcomes