Filtering the surface EMG signal: Movement artifact and baseline noise contamination

The surface electromyographic (sEMG) signal that originates in the muscle is inevitably contaminated by various noise signals or artifacts that originate at the skin-electrode interface, in the electronics that amplifies the signals, and in external sources. Modern technology is substantially immune to some of these noises, but not to the baseline noise and the movement artifact noise. These noise sources have frequency spectra that contaminate the low-frequency part of the sEMG frequency spectrum. There are many factors which must be taken into consideration when determining the appropriate filter specifications to remove these artifacts; they include the muscle tested and type of contraction, the sensor configuration, and specific noise source. The band-pass determination is always a compromise between (a) reducing noise and artifact contamination, and (b) preserving the desired information from the sEMG signal. This study was designed to investigate the effects of mechanical perturbations and noise that are typically encountered during sEMG recordings in clinical and related applications. The analysis established the relationship between the attenuation rates of the movement artifact and the sEMG signal as a function of the filter band pass. When this relationship is combined with other considerations related to the informational content of the signal, the signal distortion of filters, and the kinds of artifacts evaluated in this study, a Butterworth filter with a corner frequency of 20 Hz and a slope of 12 dB/oct is recommended for general use. The results of this study are relevant to biomechanical and clinical applications where the measurements of body dynamics and kinematics may include artifact sources.     

A new surface electromyography analysis method to determine spread of muscle fiber conduction velocities.

Muscle fiber conduction velocity (MFCV) estimation from surface signals is widely used to study muscle function, e.g., in neuromuscular disease and in fatigue studies. However, most analysis methods do not yield information about the velocity distribution of the various motor unit action potentials. We have developed a new method-the interpeak latency method (IPL)-to calculate both the mean MFCV and the spread of conduction velocities in vivo, from bipolar surface electromyogram (sEMG) during isometric contractions. sEMG was analyzed in the biceps brachii muscle in 15 young male volunteers. The motor unit action potential peaks are automatically detected with a computer program. Associated peaks are used to calculate a mean MFCV and the SD. The SD is taken as a measure of the MFCV spread. The main finding is that the IPL method can derive a measure of MFCV spread at different contraction levels. In conclusion, the IPL method provides accurate values for the MFCV and additionally gives information about the scatter of conduction velocities.     

Intramuscular fine-wire electromyography during cycling: Repeatability,normalisation and a comparison to surface electromyography

This study investigated (a) the feasibility and repeatability of intramuscular fine-wire electromyographic (fEMG) recordings from leg muscles during the repetitive, high-velocity cycling movement, (b) the influence of amplitude normalization technique on repeatability and statistical sensitivity, (c) the influence of test-retest interval duration on repeatability, and (d) differences between fEMG and surface EMG (sEMG) recordings of cycling. EMG activity of leg muscles was recorded using surface and fine-wire electrodes during one (n = 12, to investigate statistical sensitivity and compare sEMG and fEMG) or two sessions (T1 and T2, 5–20 days apart, n = 10, to investigate repeatability). fEMG recordings were feasible and there was high repeatability of fEMG recordings normalised to maximum measured EMG amplitude (MAX); mean coefficients of multiple correlation (CMC) ranged from .83 ± .13 to .88 ± .07. Data normalised to maximal (MVC) or submaximal contractions (sMVC) were less repeatable (p < .01). Statistical sensitivity was also greatest for data normalised to MAX (p < .01). Repeatability of fEMG increased with greater test-retest intervals (p < .01). The global pattern of muscle recruitment was consistent between sEMG and fEMG but sEMG recordings were characterized by additional myoelectric content. These findings support and guide the use of fEMG techniques to investigate leg muscle recruitment during cycling.     

Neural muscle activation detection: A deep learning approach using surface electromyography

The timing of muscles activation which is a key parameter in determining plenty of medical conditions can be greatly assessed by the surface EMG signal which inherently carries an immense amount of information. Many techniques for measuring muscle activity detection exist in the literature. However, due to the complex nature of the EMG signal as well as the interference from other muscles that is observed during the measurement of the EMG signal, the accuracy of these techniques is compromised. In this paper, we introduce the neural muscle activation detection (NMAD) framework that detects the muscle activation based on deep learning. The main motivation behind using deep learning is to allow the neural network to detect based on the appropriate signal features instead of depending on certain assumptions. Not only the presented approach significantly improves the accuracy of timing detection, but because of the training nature, it can adapt to operate under different levels of interference and signal-to-noise ratio.     

Fractal analysis of surface electromyography signals: A novel power spectrum-based method

This paper presents a novel power spectrum-based method for fractal analysis of surface electromyography signals. This method, named the bi-phase power spectrum method, provides a bi-phase power-law which represents a multi-scale statistically self-affine signal. This form of statistical self-affinity provides an accurate approximation for stochastic signals originating from a strong non-linear combination of a number of similar distributions, such as surface electromyography signals which are formed by the summation of a number of single muscle fiber action potentials. This power-law is characterized by a set of spectral indicators, which are related to distributional and geometrical characteristics of the electromyography signal’s interference pattern. These novel spectral indicators are capable of sensing the effects of motor units’ recruitment and shape separately by exploiting the geometry of the interference pattern. The bi-phase power spectrum method is compared to geometrical techniques and the 1/f^α approach for fractal analysis of electromyography signals. The extracted indicators using the bi-phase power spectrum method are evaluated in the context of force and joint angle and the results of a human study are presented. Results demonstrate that the bi-phase power spectrum method provides reliable information, consisting of components capable of sensing force and joint angle effects separately, which could be used as complementary information for confounded conventional measures.     

Discrepancies in ploidy determination due to specimen sampling errors

Two techniques are described to enhance the detection of low frequency aneuploid cells in automated cell analysis. One method concerns a cell preparation technique; the other is focused on specific cell selection at the measurement level. The cell preparation method has been designed to select and process the tumour areas in paraffin blocks and can be used for image as well as for flow cytometry. The technique uses incident fluorescence microscopy for visual inspection of the surface of the fluorescently stained tissue block to select the specific tumour parts. Using image cytometry, it is shown that in tissue sections with very small tumour foci and many normal cells, aneuploidy could only be detected after enrichment of the cell sample with the specifically selected areas. The cell selection at the measurement level is directed towards detection of low frequency aneuploid cells on microscope slides using the specific capacities of LEYTAS (Leyden Television Analysis System). With this system, cells of interest can be selected by means of minimum size and intensity thresholds. In addition to measurement of the total cell population, all cells above a minimum DNA value can thus be specifically selected and measured. The advantage of both enrichment techniques is the possibility to detect and measure aneuploid cell lines in cases where normal, diploid cells dominate the paraffin tissue.     

Application of response surface methodology in enzymatic synthesis: A review

There are very chemical reactions with very slow rates which can be catalyzed by enzymes. These biocatalysts need to moderate conditions for their catalytic activity and are stable in low temperature (between 15–50°C), average pH (5–10) and aqueous media. One of important things in enzymatic synthesis which has been recently noticed is the yield of reactions. Nowadays wide application of response surface methodology (RSM) was observed in organic chemistry. In one-variable-at-a-time technique only one parameter is changed and other parameters are kept at a constant level. It does not study the interactive effects among the variables, and does not illustrate the complete effects of the parameters on the process. Increasing the yield of product without increase in casts is carried out by modeling and optimization of reaction variables through statistical techniques such as RSM. In this paper, we reviewed some articles that used the RSM for optimization in the enzymatic synthesis.     

A preliminary study of modification of gait in real-time using surface electromyography

Modification of abnormal gait was attempted in real-time using a surface electromyography-based protocol to teach recruitment of the anterior tibialis at the correct time in the gait cycle. Two children diagnosed with cerebral palsy were able to learn volitional control of the anterior tibialis as demonstrated by improved clearance of the toe on the swing phase of the gait and newly learned ability to recruit and relax the anterior tibialis. The children were able to walk with the new gait pattern and reproduce the old one at will. Implications for future research in this area are discussed.     

Heterogeneity of muscle activation in relation to force direction: A multi-channel surface electromyography study on the triceps surae muscle

Several skeletal muscles can be divided into sub-modules, called neuromuscular compartments (NMCs), which are thought to be controlled independently and to have distinct biomechanical functions. We looked for distinct muscle activation patterns in the triceps surae muscle (TS) using surface electromyography (EMG) during voluntary contraction. Nine subjects performed isometric and isotonic plantar flexions combined with forces along pre-defined directions. Besides the forces under the ball of the foot, multi-channel surface EMG was measured with electrodes homogeneously distributed over the entire TS. Using principal component analysis, common (global) components were omitted from the EMG signals, thereby estimating muscle activity sufficiently accurate to track fine fluctuations of force during an isotonic contraction (r = 0.80 ± 0.09). A subsequent cluster analysis showed a topographical organization of co-activated parts of the muscle that was different between subjects. Low and negative correlations between the EMG activity within clusters were found, indicating a substantial heterogeneity of TS activation. The correlations between cluster time series and forces at the foot in specific directions differed substantially between clusters, showing that the differentially activated parts of the TS had specific biomechanical functions.     

Systematic errors in data evaluation due to ethanol stripping and water vaporization

Systematic errors due to the neglect of water and/or ethanol partition between liquid and gaseous phases are discussed for bioreactors equipped with or without a condenser. Both water vapor and ethanol vapor are present in the off-gas leaving the condenser. Presence of residual water vapor largely influences the gas measurements by dilution. As a consequence, the oxygen consumption rate can be overestimated by a factor of 3 if calculations are not corrected for water vapor content or if no additional device is implemented after the condenser to completely dry the off-gases. The mass balance and partition equations predict that the condenser has only a small effect on reduction of the ethanol vapor content of the off-gas. The reason is the high ethanol concentration of the condensate droplets on the condenser wall in contact with the off-gases. Model predictions as well as experimental results show that ethanol evaporation represents a large fraction of the ethanol production rate and influences greatly the elemental recoveries. For a reactor working at 30 degrees C without condensation of the vapors and for a volumetric aeration rate of 0.63vvm, stripping of ethanol resulted in a gaseous dilution rate of 0.016 h-1 for ethanol. The dilution rate by stripping was reduced to 0.014 h-1 when a condenser at 12 degrees C was implemented. The fraction of ethanol that is stripped is mainly dependent on the ratio D/vvm (liquid to gaseous flow rates), and the effect is only slightly influenced by low condenser temperature. The evaporation of ethanol may account for more than 20% of the ethanol formation rate. Therefore, the condenser does not succeed to reflux all ethanol to the reactor broth. In terms of a unit operation, ethanol vapor can be efficiently reduced by absorption instead of condensation. To demonstrate the feasibility, a simple modification of the reactor was tested for continuous cultures: the feed port was changed from the top-plate to the top of the condenser, which was used as an absorption column. Ethanol stripping was reduced by a factor of 4 as compared to the condensation setup (at 12 degrees C): it accounted for 2% of the ethanol production rate as compared to 8.2% at D = 0.19 h-1 and 0.63vvm.     

IMPACT 2002+: A new life cycle impact assessment methodology

The new IMPACT 2002+ life cycle impact assessment methodology proposes a feasible implementation of a combined midpoint/damage approach, linking all types of life cycle inventory results (elementary flows and other interventions) via 14 midpoint categories to four damage categories. For IMPACT 2002+, new concepts and methods have been developed, especially for the comparative assessment of human toxicity and ecotoxicity. Human Damage Factors are calculated for carcinogens and non-carcinogens, employing intake fractions, best estimates of dose-response slope factors, as well as severities. The transfer of contaminants into the human food is no more based on consumption surveys, but accounts for agricultural and livestock production levels. Indoor and outdoor air emissions can be compared and the intermittent character of rainfall is considered. Both human toxicity and ecotoxicity effect factors are based on mean responses rather than on conservative assumptions. Other midpoint categories are adapted from existing characterizing methods (Eco-indicator 99 and CML 2002). All midpoint scores are expressed in units of a reference substance and related to the four damage categories human health, ecosystem quality, climate change, and resources. Normalization can be performed either at midpoint or at damage level. The IMPACT 2002+ method presently provides characterization factors for almost 1500 different LCI-results, which can be downloaded at http://www.epfl.ch/impact     

Increase in surface area due to atomic scale roughness

A simple calculation indicates that the surface area of a macromolecule can be expected to be larger than that for a smooth object by a factor of , because of the atomic scale roughness of the surface.     

Use of preparative CsCl gradients to estimate DNA buoyant densities: potential errors due to fractionation artifacts

The equilibrium banding behavior of high molecular weight DNA has been examined after centrifugation in CsCl gradients on angle rotors in the Spinco preparative ultracentrifuge. DNAs of base composition ranging from 30% GC to 71% GC, from a variety of species, band in close agreement to a calculated curve relating density and radial distance in angle preparative gradients, but only if the DNA is sheared prior to centrifugation. Unsheared DNA, after bottom tube puneture and drop collection by conventional methods, displays a characteristic unsymmetrical profile and the fraction with the largest concentration of DNA appears in a much lower fraction number than expected. This artifact leads to misealculation of buoyant densities from preparative gradients and interferes with fractionation of DNA, as for instance in separating satellite bands. Collection of the gradient from the top reverses the direction of the profile asymmetry and shearing eliminates it entirely.     

Human odor detectability: new methodology used to determine threshold and variation

Current ambiguity concerning the related issues of optimal means for measurement of odor sensitivity and the functional properties of the olfactory system hinders progress in basic and applied research on the human sense of smell. To address these needs, we selected n-amyl acetate (nAA) as a test odorant and developed a methodology in which participants (Ps) receive multiple presentations each session of several concentrations. Yes-no responses as to whether odor was detected are analyzed using binomial statistics, with the probability that a given proportion of yes responses (or greater) would occur by chance alone being treated as the inverse of detectability. Over the course of multiple sessions, this information is also used to maximize the collection of data in the peri-threshold region. Surprisingly, data collected over as many as 14 sessions were fit well by a single logistic regression model relating probability and concentration. Threshold concentrations, defined as those corresponding to a probability of 0.05, varied from 7.11 to 167.53 p.p.b. (v/v) for 11 Ps. Our approach and findings, if shown to be representative of other combinations of Ps and odorants, could accelerate the pace of research in human olfaction by providing a comprehensive operational definition of the limit of the olfactory system to detect odorant molecules.