Improvement of spatial resolution in surface-EMG: a theoretical and experimental comparison of different spatial filters
01 Jul 1997-IEEE Transactions on Biomedical Engineering (IEEE Trans Biomed Eng)-Vol. 44, Iss: 7, pp 567-574
TL;DR: The simulations show that an isotropic spatial filtering procedure reduces the spatial extension of the filter response and improves the spatial resolution of the electromyography-recording arrangement in comparison to anisotropic spatial filters up to 30%, which increases the spatial selectivity of the arrangement.
Abstract: In the present study, different isotropic and anisotropic filters have been compared by means of theoretical field simulations and experiments in volunteers. A tripole model for an excited motor unit (MU) was used as the basis for simulating the spatial extension of the filter response for each of the investigated filters. The spatial extension is an indicative of the spatial resolution. For the experimental validation, the total number of single motor units was not directly investigated, but the signal-to-noise ratio (SNR) has been determined. Therefore, the potential distribution generated on the skin surface during maximum voluntary contraction has been simultaneous spatially filtered with each of the investigated filters. The simulations show that an isotropic spatial filtering procedure reduces the spatial extension of the filter response and improves the spatial resolution of the electromyography (EMG)-recording arrangement in comparison to anisotropic spatial filters up to 30%. In other words, the spatial selectivity of the arrangement is increased. This improvement in the filter performance is more pronounced for MU's located close to the skin surface than for MU's more distantly located. Additionally, this theoretical improvement in selectivity depends on the direction of the excitation spread relative to the filter alignment. However, the investigations also show that isotropic filters offer an advantage, compared to anisotropic filters, only when the investigated MU is located extremely close to the filter input. The results of the simulations can be confirmed by the experimental investigations. An improvement of 11% in the SNR, relative to anisotropic spatial filters, can be established when using an isotropic spatial filter. This experimental improvement in selectivity is less than the theoretical improvement because the experimentally investigated MU's have less portion in the anisotropic range of the filters than the simulated one at best.
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TL;DR: The review describes the limitations of techniques used to infer the level of muscle activation, the type of motor unit recruited, the upper limit ofMotor unit recruitment, the average discharge rate, and the degree of synchronization between motor units.
Abstract: 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.
1,376 citations
Cites background from "Improvement of spatial resolution i..."
...A recent experimental study (29) and simulation analyses (17, 28, 51) suggest several conclusions about crosstalk: 1) signals detected far from the source are mainly due to the extinction of the action potentials at the ends of the fibers; 2) because of differences in the sources of the propagating and nonpropagating signals, the cross-correlation coefficient is generally not indicative of the amount of crosstalk; 3) the frequency content of an EMG signal does not identify the presence of crosstalk; 4) temporal high-pass filtering of surface EMG can fail to reduce crosstalk signals; and 5) the use of spatial filtering as a method to decrease crosstalk remains to be validated because the theoretical analyses of spatial filters have been limited to propagating signals (18, 69, 70)....
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TL;DR: The problems associated with surface EMG in muscle force estimation are discussed and the solutions that novel methodological developments provide to this problem are discussed.
332 citations
TL;DR: The influence of thickness of the subcutaneous tissue layers, fiber inclination, fiber depth, electrode size and shape, spatial filter transfer function, interelectrode distance, length of the fibers on surface, single-fiber action-potential amplitude, frequency content, and estimated conduction velocity are investigated in this paper.
Abstract: Many previous studies were focused on the influence of anatomical, physical, and detection-system parameters on recorded surface EMG signals Most of them were conducted by simulations Previous EMG models have been limited by simplifications which did not allow simulation of several aspects of the EMG generation and detection systems We recently proposed a model for fast and accurate simulation of the surface EMG It characterizes the volume conductor as a non-homogeneous and anisotropic medium, and allows simulation of EMG signals generated by finite-length fibers without approximation of the current-density source The influence of thickness of the subcutaneous tissue layers, fiber inclination, fiber depth, electrode size and shape, spatial filter transfer function, interelectrode distance, length of the fibers on surface, single-fiber action-potential amplitude, frequency content, and estimated conduction velocity are investigated in this paper Implications of the results on electrode positioning procedures, spatial filter design, and EMG signal interpretation are discussed
331 citations
Cites background from "Improvement of spatial resolution i..."
...1b), defined by the following filter masks (Disselhorst-Klug et al. 1997): MSD ¼ 1 1 !...
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...The effect of detection system parameters (e.g., spatial filter used, shape and size of the recording electrodes, and interelectrode distance) has been investigated theoretically (Disselhorst-Klug et al. 1997; Farina and Correspondence to: R. Merletti (e-mail: merletti@polito.it, Tel....
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...…Helal and Bouissou 1992; Lindstrom and Magnusson 1977; Rau et al. 1997; Rau and DisselhorstKlug 1997; Reucher et al. 1987b) and experimentally (Disselhorst-Klug et al. 1997; Farina and Cescon 2001; Farina et al. 2002a; Helal and Bouissou 1992; Lynn et al. 1978; Reucher et al. 1987a; Roeleveld…...
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TL;DR: The aim of this review is to present the state of the art of the technology of detection and conditioning systems for surface electromyography (sEMG) in terms of electrode classification, impedance, noise, transfer function, and the spatial filtering effect of surface electrode configurations on the recorded sEMG signal.
321 citations
Cites methods from "Improvement of spatial resolution i..."
...This and other two-dimensional spatial filter configurations have been applied to extract single MU information from surface recordings (Disselhorst-Klug et al., 1997, 1999; Ostlund et al., 2004)....
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TL;DR: It is concluded that multichannel sEMG adds unique, and sometimes indispensable, spatial information to the authors' knowledge of the motor unit.
Abstract: The generation of the surface electromyogram (sEMG) is described with regard to the properties of the single muscle fiber action potential as source, the physical aspects of volume conduction and recording configuration, and the properties and firing pattern of motor units (MUs). The spatial aspect of the motor unit action potential (MUP) is emphasized in relation to the results of high-density, multichannel sEMG measurements. The endplate zone, depth, size, and position of MUs can be estimated. The use of muscle fiber conduction velocity measurements in channelopathies and the changes in pathological fatigue are described. Using the unique patterns of spatial spread of MUPs over the skin (MU fingerprint), MU classification and the determination of firing moments is done noninvasively. Clinical applications of high-density sEMG measurements are reviewed. Emerging possibilities provided by MUP size and fingerprint measurements in neuromuscular disease and motor control are discussed. We conclude that multichannel sEMG adds unique, and sometimes indispensable, spatial information to our knowledge of the motor unit.
288 citations
References
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Book•
01 Jan 1978
TL;DR: The first logical deduction of muscle-generated electricity was first documented by Italian Francesco Redi in 1666 as discussed by the authors, who suspected that thenshock of the electric ray fish was muscular in origin and wrote, lIt appeared to me as if the painful action was located innthese two sickle-shaped bodies, or muscles, more than any other part of the body.
Abstract: IntroductionElectromyography is the study of muscle function through the inquirynof the electrical signal the muscles emanate.Inherent movement is the prime sign of animal life. For this and manynother reasons, man has shown a perpetual curiosity about the organs ofnlocomotion in his own body and in those of other creatures. Indeed,nsome of the earliest scientific experiments known to us concerned musclenand its functions.With the reawakening of science during the Renaissance, interest innmuscles was inevitable. Leonardo da Vinci, for example, devoted muchnof his thought to the analysis of muscles and their functions. So, too, didnthe acknowledged lfatherr of modern anatomy, Andreas Vesalius, whoseninfluence through his monumental work, the Fabrica, extends down tonthis day. In one sense, however, the heritage of Vesalius was unfortunatenbecause it stressed the appearance and the geography of dead musclesnrather than their dynamics (Fig. 1.1).During subsequent years, a series of scientists gave life back to thenmuscles. The first logical deduction of muscle-generated electricity wasndocumented by Italian Francesco Redi in 1666. He suspected that thenshock of the electric ray fish was muscular in origin and wrote, lItnappeared to me as if the painful action of the electric ray was located innthese two sickle-shaped bodies, or muscles, more than any other partrn(Biederman, 1898). The relationship between electricity and musclencontraction was first observed by Luiggi Galvani in 1791. In his epochmakingnexperiments, he depolarized the muscles of a frogrs legs byntouching them with metal rods (see Fig. 1.2). His concept of lanimalnelectricityr was enthusiastically received throughout Europe. Galvanirsnoriginal book, De Viribus Electricitatis, has been translated into Englishnby Green (1953). This discovery is generally acknowledged as representingnthe birth of neurophysiology, thereby making Galvani the father ofnthis field which continues to expand rapidly.Many rushed to confirm Galvanirs results and praise his discovery.nAmong them was Alessandro Volta, who initially embraced the discoverynand in retrospect wrote lit contains one of the most beautiful andnsurprising discoveries and the germ of many othersr (Volta, 1816). But,nwithin two years, in 1793, Volta questioned Galvanirs findings by provingnthat dissimilar metals in contact with an electrolyte (such as those presentnin body tissues) would generate an electric current. In the following yearnGalvani reaffirmed his concept when he found that a muscle contractionncould be elicited by placing the free end of a nerve across a musclenwithout the intervention of metals. n n
1,775 citations
Book•
01 Jan 1979TL;DR: A systematic introduction to the concepts and techniques of computer image processing and recognition is presented in this paper, where the authors give an overview of such topics as image formation and perception; computer representation of images; image enhancement and restoration; reconstruction from projections; digital television, encoding, and data compression; scene understanding; scene matching and recognition; and processing techniques for linear systems.
Abstract: A systematic introduction to the concepts and techniques of computer image processing and recognition is presented. Consideration is given to such topics as image formation and perception; computer representation of images; image enhancement and restoration; reconstruction from projections; digital television, encoding, and data compression; scene understanding; scene matching and recognition; and processing techniques for linear systems.
617 citations
TL;DR: It is concluded that a surface myoelectric signal detected on the skin above a leg muscle and having a peak-to-peak amplitude of up to 16.6% of a signal detected above a neighboring muscle may be due to cross-talk rather than to activation of the muscle below the electrode.
328 citations
"Improvement of spatial resolution i..." refers background in this paper
...The single differentiating filter enhances the signals of MU’s located close to the skin surface [4]–[6], [12]....
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...I. INTRODUCTION I N human movement and locomotion the voluntary andactive contraction of a skeletal muscle is initiated by the electrophysiological excitation of a large number of motor units (MU’s) [1]....
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182 citations
Additional excerpts
...Asterisk indicates corresponding author....
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TL;DR: Even in high levels of muscle contraction, single motor unit impulses that are suitably shaped by filtering can be repeatedly recognized in the surface EMG signal.
Abstract: Complementary to its conventional applications, surface EMG is also suited to gain more detailed information on the functional state of a muscle, when measurement configurations with smaller pickup areas are used. A new category of suitable measurement configurations is obtained by application of the spatial filtering principle to electromyography. In a spatial filter unit, the signals of several recording electrodes are combined to form one output signal channel. The filter characteristic is determined by the weighting factors used and by the geometrical arrangement of the electrodes. Extended multielectrode arrays and multichannel recording make possible the detection of correlated excitations at different sites of the muscle. Even in high levels of muscle contraction, single motor unit impulses that are suitably shaped by filtering can be repeatedly recognized in the surface EMG signal. In clinical studies, pathologically shaped impulses have been identified indicating multiple innervation zones. The initiation and the propagation of excitation within single motor units can be detected with improved accuracy even from very small muscles.
162 citations