629 research outputs found
Robust outlier detection in high-density surface electromyographic signals
No full textConf Proc IEEE Eng Med Biol Soc. 2010;2010:4850-3. PubMed PMID: 2109664
Automatic localisation of innervation zones: a simulation study of the external anal sphincter
No full textTraumas of the innervation zone (IZ) of the external anal sphincter (EAS), e.g. during delivery, can promote the development of faecal incontinence. Recently developed probes allow high-resolution detection
of EMG signals from the EAS. The analysis of pelvic floor muscles by surface EMG (in particular, the estimation of the location of the IZ) has potential applications in the diagnosis and investigation of the mechanisms of incontinence.
An automatic method (based on matched filter approach) for the estimation of the IZ distribution of
EAS from surface EMG is discussed and tested using an analytical model of generation of EMG signals
from sphincter muscles. Simulations are performed varying length of the fibres, thickness of the mucosa,
position of the motor units, and force level. Different distributions of IZs are simulated.
The performance of the proposed method in the estimation of the IZ distribution is affected by surface
MUAP amplitude (as the estimation made by visual inspection), by mucosa thickness (performance
decreases when fibre length is higher) and by different MU distributions. However, in general the method
is able to identify the position of two IZ locations and can measure asymmetry of the IZ distribution. This
strengthens the potential applications of high density surface EMG in the prevention and investigation of
incontinence
Investigation of motor unit recruitment during stimulated contractions of tibialis anterior muscle
No full textThe extraction of neural strategies from the surface EMG: an update
No full textA surface EMG signal represents the linear transformation of motor neuron discharge times by the compound action potentials of the innervated muscle fibers and is often used as a source of information about neural activation of muscle. However, retrieving the embedded neural code from a surface EMG signal is extremely challenging. Most studies use indirect approaches in which selected features of the signal are interpreted as indicating certain characteristics of the neural code. These indirect associations are constrained by limitations that have been detailed previously (Farina D, Merletti R, Enoka RM. J Appl Physiol 96: 1486 -1495, 2004) and are generally difficult to overcome. In an update on these issues, the current review extends the discussion to EMG-based coherence methods for assessing neural connectivity. We focus first on EMG amplitude cancellation, which intrinsically limits the association between EMG amplitude and the intensity of the neural activation and then discuss the limitations of coherence methods (EEG-EMG, EMG-EMG) as a way to assess the strength of the transmission of synaptic inputs into trains of motor unit action potentials. The debated influence of rectification on EMG spectral analysis and coherence measures is also discussed. Alternatively, there have been a number of attempts to identify the neural information directly by decomposing surface EMG signals into the discharge times of motor unit action potentials. The application of this approach is extremely powerful, but validation remains a central issu
The extraction of neural strategies from surface EMG
No full textFarina, Dario, Roberto Merletti, and Roger M. Enoka. The extraction of neural strategies from the surface EMG. J Appl Physiol 96: 1486-1495, 2004; 10.1152/japplphysiol.01070.2003.—This brief review examines some of the methods used to infer central control strategies from surface electromyogram (EMG) recordings. Among the many uses of the surface EMG in studying the neural control of movement, the review critically evaluates only some of the applications. The focus is on the relations between global features of the surface EMG and the underlying physiological processes. Because direct measurements of motor unit activation are not available and many factors can influence the signal, these relations are frequently misinterpreted. These errors are compounded by the counterintuitive effects that some system parameters can have on the EMG signal. The phenomenon of crosstalk is used as an example of these problems. The review describes the limitations of techniques used to infer the level of muscle activation, the type of motor unit recruited, the upper limit of motor unit recruitment, the average discharge rate, and the degree of synchronization between motor units. Although the global surface EMG is a useful measure of muscle activation and assessment, there are limits to the information that can be extracted from this signal
EMG of Electrically Stimulated Muscles
No full textThis chapter addresses stimulation techniques, the issue of the stimulation electrode positioning, motor unit (MU) activation order, and spinal involvement in electrically elicited contractions. Two stimulation techniques are commonly used: bipolar, and monopolar stimulation. The differences between these two methods concern the geometry and relative position of the stimulation electrodes. Surface electromyography (sEMG) signals can be detected during selective electrical stimulation of a nerve branch or of a motor point of a muscle. The resultant sEMG signal is a compound motor action potential (CMAP), also termed as M-wave. Since the M-wave represents the sum of the potentials of the concurrently activated MUs, its change is generally assumed to reflect changes either in the number or in the sarcolemmal properties of activated MUs. Neuromuscular electrical stimulation (NMES) combined with sEMG isolates the contributions of peripheral fatigue because it gives the experimenter control of MU firing frequency and recruitment
A Finite Element Model for Describing the Effect of Muscle Shortening on Surface EMG
No full textUdgivelsesdato: AP
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