Publications
788 results found
Dideriksen JL, Falla D, Bækgaard M, et al., 2009, Comparison between the degree of motor unit short-term synchronization and recurrence quantification analysis of the surface EMG in two human muscles., Clin Neurophysiol, Vol: 120, Pages: 2086-2092
OBJECTIVE: To verify if non-linear recurrence analysis of the surface EMG is a suitable tool for assessing motor unit short-term synchronization. METHODS: Surface and intramuscular EMG signals were recorded from the abductor digiti minimi and vastus medialis muscles of 12 and 10 healthy men, respectively, during isometric contractions. In the abductor digiti minimi, EMG signals were additionally recorded after a contraction sustained for 1min at 50% of the maximal force. In both muscles, percent of determinism (%DET) was estimated from the surface EMG and common input strength (CIS) index was computed from motor unit recordings. RESULTS: For both muscles, CIS did not correlate with %DET (abductor digiti minimi: R(2)=0.11, P=0.12; vastus medialis: R(2)=0.04, P=0.56). Although the values of CIS for the vastus medialis were lower than those of the abductor digiti minimi (P<0.001), the %DET values did not differ between the two muscles (71.6+/-5.5% vs 66.9+/-8.7%; P=0.12). CONCLUSION: The variable %DET extracted from the surface EMG is a poor indicator of the degree of motor unit short-term synchronization. SIGNIFICANCE: The study provides a systematic evaluation of a technique previously proposed for the estimation of a clinically relevant characteristic of motor unit behavior.
Vautrin D, Artusi X, Lucas M-F, et al., 2009, A novel criterion of wavelet packet best basis selection for signal classification with application to brain-computer interfaces., IEEE Trans Biomed Eng, Vol: 56, Pages: 2734-2738
This study proposes a method to select a wavelet basis for classification. It uses a strategy defined by Wickerhauser and Coifman and proposes a new additive criterion describing the contrast between classes. Its performance is compared with other approaches on simulated signals and on experimental EEG signals for brain-computer interface applications.
Carotti ESG, De Martin JC, Merletti R, et al., 2009, Compression of multidimensional biomedical signals with spatial and temporal codebook-excited linear prediction., IEEE Trans Biomed Eng, Vol: 56, Pages: 2604-2610
In this paper, we propose a model-based lossy coding technique for biomedical signals in multiple dimensions. The method is based on the codebook-excited linear prediction approach and models signals as filtered noise. The filter models short-term redundancy in time; the shape of the power spectrum of the signal and the residual noise, quantized using an algebraic codebook, is used for reconstruction of the waveforms. In addition to temporal redundancy, redundancy in the coding of the filter and residual noise across spatially related signals is also exploited, yielding better compression performance in terms of SNR for a given bit rate. The proposed coding technique was tested on sets of multichannel electromyography (EMG) and EEG signals as representative examples. For 2-D EMG recordings of 56 signals, the coding technique resulted in SNR greater than 3.4 +/- 1.3 dB with respect to independent coding of the signals in the grid when the compression ratio was 89%. For EEG recordings of 15 signals and the same compression ratio as for EMG, the average gain in SNR was 2.4 +/- 0.1 dB. In conclusion, a method for exploiting both the temporal and spatial redundancy, typical of multidimensional biomedical signals, has been proposed and proved to be superior to previous coding schemes.
Cabrera AF, Farina D, Dremstrup K, 2009, Smario: A toolbox for brain-computer interfacing analysis and design, Pages: 429-432
In this paper we introduce Smario, a MATLAB open source toolbox for the analysis of BCI signals and implementation of translation algorithms for BCI systems. The Smario functions have been created based on the design of EEGLAB [1], they are accessible through the graphic user interface but they can also be run and edited using MATLAB syntax. Smario reads BCI2000 files in DAT and MAT formats, and documentation is available to implement functions to read other formats. This toolbox incorporates two feature selection methods based on discriminative measures; r2 and SEPCOR. Using the graphical capabilities of EEGLAB [1], these feature selection modules provide 2-D and 3-D topographic maps of scalp data fields for selected features and graphs of the extracted features for selected channels. Smario's modularized design allows the user to create a translation algorithm using existing feature extraction, selection and classification modules. These modules are easily configurable and interchangeable, to provide the user with means to compare different translation algorithms. Furthermore, the implementation of new modules is possible and guidelines for this purpose have been included in the documentation. Available modules are Common Average Reference (CAR), MEM Filter, Autoregressive (AR) analysis, Fast Fourier Transform (FFT), Discrete Wavelet Transform (DWT), Bayesian Classifier, Linear Discriminant Analysis (LDA), Support Vector Machine (SVM), SEPCOR and r2. Smario is available for download at http://www.hst.aau.dk/bci/Smariov1/Smindex.html where documentation and sample files can also be found. ©2009 IEEE.
Hedayatpour N, Falla D, Arendt-Nielsen L, et al., 2009, Motor unit conduction velocity during sustained contraction after eccentric exercise., Med Sci Sports Exerc, Vol: 41, Pages: 1927-1933
BACKGROUND: Eccentric contractions induce muscle fiber damage that is associated with a decreased capacity to generate voluntary force and increased fiber membrane permeability. Changes in fiber membrane permeability results in cell depolarization that is expected to have an effect on the action potential propagation velocity of the muscle fibers. PURPOSE: The aim of the study was to investigate the action potential propagation velocity in individual motor units before and 24 and 48 h after eccentric exercise. METHODS: Multichannel surface and fine-wire intramuscular EMG signals were concurrently recorded from two locations of the right vastus medialis muscle of 10 healthy men during 60-s isometric contractions at 10% and 30% of the maximal force. RESULTS: The maximal force decreased by 26.1 ± 16.1% (P < 0.0001) at 24 h and remained reduced by 23.6 ± 14.5% (P < 0.0001) 48 h after exercise with respect to baseline. With respect to baseline, motor unit conduction velocity decreased (P < 0.05) by (average over 24 and 48 h after exercise) 7.7 ± 2.7% (10% maximal voluntary contraction (MVC), proximal), 7.2 ± 2.8% (10% MVC, distal), 8.6 ± 3.8% (30% MVC, proximal), and 6.2 ± 1.5% (30% MVC, distal). Moreover, motor unit conduction velocity decreased over time during the sustained contractions at faster rates when assessed 24 and 48 h after exercise with respect to baseline for both contraction forces and locations (P < 0.05). CONCLUSIONS: These results indicate that the electrophysiological membrane properties of muscle fibers are altered by exercise-induced muscle fiber damage.
Minetto MA, Holobar A, Botter A, et al., 2009, Discharge properties of motor units of the abductor hallucis muscle during cramp contractions., J Neurophysiol, Vol: 102, Pages: 1890-1901, ISSN: 0022-3077
We analyzed individual motor units during electrically elicited cramp contractions with the aim of characterizing the variability and degree of common oscillations in their discharges. Intramuscular and surface electromyographic (EMG) signals were detected from the abductor hallucis muscle of 11 healthy subjects (age 27.0+/-3.7 yr) during electrically elicited cramps. In all, 48 motor units were identified from the intramuscular EMG. These motor units were active for 23.6+/-16.2 s, during which their average discharge rate was 14.5+/-5.1 pulses/s (pps) and their minimum and maximum rates were, respectively, 6.0+/-0.8 and 25.0+/-8.0 pps (P<0.001). The coefficient of variation for the interspike interval (ISI) was 44.6+/-9.7% and doublet discharges constituted 4.1+/-4.7% of the total number of discharges. In 38 motor units, the SD of the ISI was positively correlated to the mean ISI (R2=0.37, P<0.05). The coherence spectrum between smoothed discharge rates of pairs of motor units showed one significant peak at 1.4+/-0.4 Hz for 29 of the 96 motor unit pairs and two significant peaks at 1.3+/-0.5 and 1.5+/-0.5 Hz for 8 motor unit pairs. The cross-correlation function between pairs of discharge rates showed a significant peak (0.52+/-0.11) in 26 motor unit pairs. In conclusion, motor units active during cramps showed a range of discharge rates similar to that observed during voluntary contractions but larger ISI variability, probably due to large synaptic noise. Moreover, the discharge rates of the active motor units showed common oscillations.
Gu Y, Dremstrup K, Farina D, 2009, Single-trial discrimination of type and speed of wrist movements from EEG recordings., Clin Neurophysiol, Vol: 120, Pages: 1596-1600
OBJECTIVE: The study explored the possibility of identifying movement type and speed from EEG recordings. METHODS: EEG signals were acquired from 9 healthy volunteers during imagination of four tasks of the right wrist that involved two speeds (fast and slow) and two types of movement (wrist extension and rotation), each repeated 60 times in random order. Average movement-related cortical potentials (MRCPs) were compared among the four tasks. Moreover, single-trial classification was performed using the rebound rate of MRCP and the power in the mu and beta bands as features. RESULTS: The rebound rate of the average MRCPs was greater for faster than for slower movements but did not depend on the type of movement. Accordingly, pairs of tasks executed at different speeds led to lower misclassification rate than pairs of tasks executed at the same speed. The average misclassification rate between task pairs was 21+/-2% for the best channel and task pair. CONCLUSION: The task parameter speed can be discriminated in single-trial EEG traces with greater accuracy than the type of movement when tasks are executed at the same joint. SIGNIFICANCE: The speed of movement execution may be included among the variables that characterize imagined tasks for brain-computer interface applications.
Koutris M, Lobbezoo F, Naeije M, et al., 2009, Effects of intense chewing exercises on the masticatory sensory-motor system., J Dent Res, Vol: 88, Pages: 658-662
Nociceptive substances, injected into the masseter muscle, induce pain and facilitate the jaw-stretch reflex. It is hypothesized that intense chewing would provoke similar effects. Fourteen men performed 20 bouts of 5-minute chewing. After each bout, 20 min and 24 hrs after the exercise, muscle fatigue and pain scores and the normalized reflex amplitude from the left masseter muscle were recorded. Before, 20 min, and 24 hrs after the exercise, signs of temporomandibular disorders and pressure-pain thresholds of the masticatory muscles were also recorded. Fatigue and pain scores had increased during the exercise (P < 0.001), but the reflex amplitude did not (P = 0.123). Twenty minutes after the exercises, 12 participants showed signs of myofascial pain or arthralgia. Pressure-pain thresholds were decreased after 20 min (P = 0.009) and 24 hrs (P = 0.049). Intense chewing can induce fatigue, pain, and decreased pressure-pain thresholds in the masticatory muscles, without concomitant changes in the jaw-stretch reflex amplitude.
Tucker K, Falla D, Graven-Nielsen T, et al., 2009, Electromyographic mapping of the erector spinae muscle with varying load and during sustained contraction., J Electromyogr Kinesiol, Vol: 19, Pages: 373-379
The purpose of the study was to explore changes in the spatial distribution of erector spinae electromyography amplitude during static, sustained contractions and during contractions of increasing load. Surface electromyographic (EMG) signals were detected from nine healthy subjects using a grid of 13 x 5 electrodes placed unilaterally over the lumbar erector spinae musculature. Subjects stood in a 20 degrees forward flexed position and performed: (1) six 20-s long contractions with loads ranging from 2.5 kg to 12.5 kg (2.5 kg increments) and (2) a 6 min sustained contraction with 7.5 kg load. Root mean square (RMS) and mean power spectral frequency (MNF) were computed from the recorded EMG signals. EMG RMS increased (P<0.0001) and MNF remained constant during contractions of increased load. During the sustained contraction, MNF decreased (P<0.0001) and RMS did not change over time. The centroid (center of activity) of the RMS map shifted caudally (P<0.0001) with time during the sustained contraction but did not change with varying load. These results suggest a change in the distribution of erector spinae muscle activity with fatigue and a uniform distribution of muscle activation across loads.
Piancino MG, Farina D, Talpone F, et al., 2009, Muscular activation during reverse and non-reverse chewing cycles in unilateral posterior crossbite., Eur J Oral Sci, Vol: 117, Pages: 122-128
The aim of this study was to characterize the kinematics and masseter muscle activation in unilateral posterior crossbite. Eighty-two children (8.6 +/- 1.3 yr of age) with unilateral posterior crossbite and 12 children (8.9 +/- 0.6 yr of age) with normal occlusion were selected for the study. Electromyography (EMG) and kinematics were concurrently recorded during mastication of a soft bolus and a hard bolus. The percentage of reverse cycles in the group of patients was 59.0 +/- 33.1% (soft bolus) and 69.7 +/- 29.7% (hard bolus) when chewing on the crossbite side. When chewing on the non-affected side, the number of reverse cycles was 16.7 +/- 24.5% (soft bolus) and 16.7 +/- 22.3% (hard bolus). The reverse cycles on the crossbite side were narrower with respect to the cycles on the non-affected side. Although both types of cycles in patients resulted in lower EMG activity of the masseter of the crossbite side than of the contralateral masseter, the activity of the non-affected side was larger for reverse than for non-reverse cycles. It was concluded that when chewing on the crossbite side, the masseter activity is reduced on the mastication side (crossbite) and is unaltered (non-reverse cycles) or increased (reverse) on the non-affected side.
Holobar A, Farina D, Gazzoni M, et al., 2009, Estimating motor unit discharge patterns from high-density surface electromyogram., Clin Neurophysiol, Vol: 120, Pages: 551-562
OBJECTIVE: We systematically tested the capability of the Convolution Kernel Compensation (CKC) method to identify motor unit (MU) discharge patterns from the simulated and experimental surface electromyogram (sEMG) during low-force contractions. METHODS: sEMG was detected with a grid of 13 x 5 electrodes. In simulated signals with 20 dB signal-to-noise ratio, 11+/-3 out of 63 concurrently active MUs were identified with sensitivity >95% in the estimation of their discharge times. In experimental signals recorded at 0-10% of the maximal force, the discharge patterns of (range) 11-19 MUs (abductor pollicis; n=8 subjects), 9-17 MUs (biceps brachii; n=2), 7-11 MUs (upper trapezius; n=2), and 6-10 MUs (vastus lateralis; n=2) were identified. In the abductor digiti minimi muscle of one subject, the decomposition results from concurrently recorded sEMG and intramuscular EMG (iEMG) were compared; the two approaches agreed on 98+/-1% of MU discharges. CONCLUSION: It is possible to identify the discharge patterns of several MUs during low-force contractions from high-density sEMG. SIGNIFICANCE: sEMG can be used for the analysis of individual MUs when the application of needles is not desirable or in combination with iEMG to increase the number of sampled MUs.
Campanini I, Merlo A, Farina D, 2009, Motor unit discharge pattern and conduction velocity in patients with upper motor neuron syndrome., J Electromyogr Kinesiol, Vol: 19, Pages: 22-29, ISSN: 1050-6411
Motor unit properties were analyzed in patients with upper motor neuron syndrome (UMNS). Multi-channel surface electromyographic (EMG) signals were recorded for 300s from the biceps brachii muscle of seven male subacute patients (time from lesion, mean+/-SE, 4.9+/-1.0 months). In three patients, both arms were investigated, leading to 10 recorded muscles. Patients were analyzed in rest-like condition with motor units activated due to pathological muscle overactivity. For a total of 12 motor units, the complete discharge pattern was extracted from EMG decomposition. Interpulse interval variability was 7.8+/-0.9%. At minimum discharge rate (6.4+/-0.4 pulses per second, pps), conduction velocity was smaller than at maximum discharge rate (12.0+/-0.9pps) in all motor units (3.60+/-0.21m/s vs. 3.84+/-0.20m/s). Conduction velocity changed by 1.35+/-0.48% (different from zero, P<0.01) for each increase of 1pps in discharge rate. It was concluded that conduction velocity of low-threshold motor units in subacute patients with UMNS had similar values as reported in healthy subjects and was positively correlated to instantaneous discharge rate (velocity recovery function of muscle fibers).
Farina D, Falla D, 2009, Discharge rate of sternohyoid motor units activated with surface EMG feedback., J Neurophysiol, Vol: 101, Pages: 624-632, ISSN: 0022-3077
We analyzed individual motor units of the sternohyoid muscle with the aim of characterizing their minimum and maximum discharge rates and their variability in discharge during voluntary contractions. Surface EMG signals were recorded with an array of eight electrodes from the sternohyoid muscle of seven healthy men (age: 30.2+/-3.5 yr). The multichannel surface EMG signals were displayed as feedback for the subjects who identified and modulated the activity of one target motor unit in 30-s contractions during which the discharge rate was increased from minimum to maximum (ramp contraction), sustained at maximum level (sustained), or increased in brief bursts (burst). During the ramp contractions, the minimum average discharge rate over epochs of 1 s was 11.6+/-1.5 pulses per second (pps) and the maximum 57.0+/-5.7 pps (P<0.001). During the sustained contractions, the motor unit discharge rate decreased from 65.5+/-8.4 pps at the beginning to 52.9+/-7.6 pps at the end of the contraction (P<0.05). The coefficient of variation for the interspike interval during the sustained contractions was 40.2+/-9.8% and a large percentage of discharges had instantaneous rates>50 pps (52.2+/-12.5%) and>100 pps (8.0+/-1.2%), with peak values>150 pps. During the burst contractions, the instantaneous discharge rate reached average maximum values of 97.6+/-36.8 pps. The observed discharge rates and their variability are higher than those reported for limb muscles, which may be due to large synaptic input and noise received by these motor neurons.
Merletti R, Farina D, 2009, Analysis of intramuscular electromyogram signals., Philos Trans A Math Phys Eng Sci, Vol: 367, Pages: 357-368, ISSN: 1364-503X
Intramuscular electromyographic (EMG) signals are detected with needles or wires inserted into muscles. With respect to non-invasive techniques, intramuscular electromyography has high selectivity for individual motor unit action potentials and is thus used to measure motor unit activity. Decomposition of intramuscular signals into individual motor unit action potentials consists in detection and classification, usually followed by separation of superimposed action potentials. Although intramuscular EMG signal decomposition is the primary tool for physiological investigations of motor unit properties, it is rarely applied in clinical routine, because of the need for human interaction and the difficulty in interpreting the quantitative data provided by EMG signal decomposition to support clinical decisions. The current clinical use of intramuscular EMG signals relates to the diagnosis of myopathies, of diseases of the alpha-motor neuron and of the neuromuscular junction through the analysis of the interference signal or of the shape of some motor unit action potentials, usually without a full decomposition of the signal.
Falla D, Arendt-Nielsen L, Farina D, 2009, The pain-induced change in relative activation of upper trapezius muscle regions is independent of the site of noxious stimulation., Clin Neurophysiol, Vol: 120, Pages: 150-157
OBJECTIVE: To assess the effect of local excitation of nociceptors at different locations of the upper trapezius muscle on the spatial distribution of upper trapezius electromyographic (EMG) amplitude during sustained contraction. METHODS: Surface (EMG) signals were recorded from the upper trapezius muscle with a grid of 10x5 electrodes from nine healthy men during 90 degrees shoulder abduction sustained for 60s. In one experimental session, the subjects received separate injections of 0.4 ml of hypertonic saline (experimental muscle pain) into the cranial and caudal region of the upper trapezius. In a separate experimental session the same subjects received two injections of 0.2 ml each of hypertonic saline simultaneously in the cranial and caudal region. The EMG root mean square (RMS) values were computed for each electrode location to provide a topographical map of EMG amplitude. RESULTS: The RMS value averaged across all electrode locations decreased following injection of hypertonic saline (P<0.05) by a similar amount for the two experimental sessions. The pain-induced decrease was larger in the cranial than in the caudal region for both experimental sessions, as evidenced by a shift of the EMG amplitude distribution towards the caudal region of the muscle (P<0.0001). CONCLUSION: Muscle pain induces a consistent change in the spatial activation of the upper trapezius muscle which is independent of the site of noxious stimulation. SIGNIFICANCE: Pain-induced changes in the spatial distribution of muscle activity may induce overload of specific muscle regions in the long term.
Farina D, Holobar A, Gazzoni M, et al., 2009, Adjustments differ among low-threshold motor units during intermittent, isometric contractions., J Neurophysiol, Vol: 101, Pages: 350-359, ISSN: 0022-3077
We investigated the changes in muscle fiber conduction velocity, recruitment and derecruitment thresholds, and discharge rate of low-threshold motor units during a series of ramp contractions. The aim was to compare the adjustments in motor unit activity relative to the duration that each motor unit was active during the task. Multichannel surface electromyographic (EMG) signals were recorded from the abductor pollicis brevis muscle of eight healthy men during 12-s contractions (n = 25) in which the force increased and decreased linearly from 0 to 10% of the maximum. The maximal force exhibited a modest decline (8.5 +/- 9.3%; P < 0.05) at the end of the task. The discharge times of 73 motor units that were active for 16-98% of the time during the first five contractions were identified throughout the task by decomposition of the EMG signals. Action potential conduction velocity decreased during the task by a greater amount for motor units that were initially active for >70% of the time compared with that of less active motor units. Moreover, recruitment and derecruitment thresholds increased for these most active motor units, whereas the thresholds decreased for the less active motor units. Another 18 motor units were recruited at an average of 171 +/- 32 s after the beginning of the task. The recruitment and derecruitment thresholds of these units decreased during the task, but muscle fiber conduction velocity did not change. These results indicate that low-threshold motor units exhibit individual adjustments in muscle fiber conduction velocity and motor neuron activation that depended on the relative duration of activity during intermittent contractions.
Nielsen JLG, Holmgaard S, Jiang N, et al., 2009, Enhanced EMG signal processing for simultaneous and proportional myoelectric control., Annu Int Conf IEEE Eng Med Biol Soc, Vol: 2009, Pages: 4335-4338, ISSN: 2375-7477
A new signal processing scheme is presented for extracting neural control information from the multi-channel surface electromyographic signal (sEMG). The extracted information can be used to proportionally control a multi-degree of freedom (DOF) prosthesis. Four time-domain (TD) features were extracted from the multi-channel sEMG during a series of anisotonic, isometric wrist contractions, which involved simultaneous activations of the three DOF of the wrist. The forces produced at the three wrist DOFs during these contractions were also collected using a customized force sensor. The extracted features and the recorded force signals, as input/target pairs, were then used to train a multilayer perceptron (MLP) neural network. A five-fold cross-validation training/testing method was applied. The resulting performance is a significant improvement over a previously proposed sEMG processing method for the proportional, multi-DOF myoelectric control task.
Gu Y, Farina D, Murguialday AR, et al., 2009, Offline Identification of Imagined Speed of Wrist Movements in Paralyzed ALS Patients from Single-Trial EEG., Front Neurosci, Vol: 3
The study investigated the possibility of identifying the speed of an imagined movement from EEG recordings in amyotrophic lateral sclerosis (ALS) patients. EEG signals were acquired from four ALS patients during imagination of wrist extensions at two speeds (fast and slow), each repeated up to 100 times in random order. The movement-related cortical potentials (MRCPs) and averaged sensorimotor rhythm associated with the two tasks were obtained from the EEG recordings. Moreover, offline single-trial EEG classification was performed with discrete wavelet transform for feature extraction and support vector machine for classification. The speed of the task was encoded in the time delay of peak negativity in the MRCPs, which was shorter for faster than for slower movements. The average single-trial misclassification rate between speeds was 30.4 +/- 3.5% when the best scalp location and time interval were selected for each individual. The scalp location and time interval leading to the lowest misclassification rate varied among patients. The results indicate that the imagination of movements at different speeds is a viable strategy for controlling a brain-computer interface system by ALS patients.
Sałówka J, Nowakowski M, Wałega P, et al., 2008, Influence of extent of rectal resection on superficial electromyography of the external anal sphincter in patients with rectal cancer, Proktologia, Vol: 9, Pages: 237-253, ISSN: 1640-5382
A frequent sequel of sphincter-sparing resective procedures is anorectal dysfunction, usually taking the form of low anterior resection syndrome (LARS). One of key aetiologic factors thereof may be alterations of anal sphincter innervation. Aim of paper To assess the influence of extent of rectal resection on external anal sphincter innervation, based on superficial electromyographic study Material and method: Twenty-three patients undergoing anterior resection (AR) (6 patients) or low anterior resection (LAR) (17 patients). Analysed parameters included: superficial electromyographic study (sEMG) with determination of mean amplitude (śrRMS) and mean frequency (srMNF) of signal during relaxation and during maximal volitional contraction of external anal sphincter and manometrie study, recording mean resting pressure (MRP) and maximal supporting pressure (MSP) were obtained prior to and 1 month after surgery. Results: Mean distance from anal verge to anastomosis was 8.3 cm and 4.2 cm in the AR and LAR groups, respectively. In the LAR group, a significant reduction of śrRMS value (both at relaxation and at contraction), MRP and an increase of śrMNF (at relaxation) were noticed (p<0.05). A correlation between parameters of sEMG during relaxation phase with MRP values was observed. Conclusions: Extent of resection of rectum and mesorectum, dependant on location and local extent of tumour have an influence on somatic innervation of the external anal sphincter and its function. Our results indicate a correlation between extent of rectal resection on sEMG features. © Proktologia 2008.
Ge D, Carpentiert EL, Farina D, et al., 2008, Unsupervised bayesian EMG decomposition algorithm using tabu search
We introduce here the statistical model of the electromyographic (EMG) signal decomposition problem and then propose an algorithm with a Bayesian approach followed by its simulation data test results. We consider the classical problem of the multi-source impulse discharge separation from intramuscular EMG signals in the case where the impulse responses (motor unit action potentials, MUAPs) are supposed to be known to a certain degree. The main contribution ofthis work is the proposal ofa fully unsupervisedEMG decomposition algorithm that exploits both the signal model likelihood and the regularity of the motor unit discharge patterns in a Bayesian framework. The latter, though well-proven properties in the past, is essentially used as auxiliary information in an interactive procedure [1] involving human interventions. Another contribution consists ofusing the Tabu metaheuristics to solve the NP-hard problem over the complete search space of overlapped MUAP, unlike the existing methods that either performed on the restrained search spaces [2, 3] due to complexity or based on recursive algorithms [4, 1] with certain trial strategy and residual threshold estimations.
Leclerc F, Ravier P, Farina D, et al., 2008, Time-varying delay estimation with application to electromyography, ISSN: 2219-5491
Pathological or physiological state of the muscle can be assessed from the velocity of propagation of surface action potentials (conduction velocity - CV). The estimation of CV from surface electromyography (sEMG) implies an estimation of time delay between signals detected by two or more sensors along the muscle length. In this paper we investigate the possible use of a parameter estimation approach to follow changes of CV over time. The recursive least square algorithm was used. The error on estimation of CV was quantified in the case of Gaussian white noise (GWN) and band-limited signals. On this second type of signal, a decimation and a whitening filter were used to increase the robustness of the algorithm in case of additive noise. The results indicate that the frequency bandwidth substantially affects performance. The best performance was reached with GWN. For band-limited signals, the decimation processing followed by whitening substantially increased the quality of the estimation. copyright by EURASIP.
Piancino MG, Bracco P, Vallelonga T, et al., 2008, Effect of bolus hardness on the chewing pattern and activation of masticatory muscles in subjects with normal dental occlusion., J Electromyogr Kinesiol, Vol: 18, Pages: 931-937, ISSN: 1050-6411
The aim of the study was to evaluate the effect of bolus hardness on the kinematic of mastication and jaw-elevator muscle activity in subjects with normal dental occlusion and function. The mandibular motion and the surface EMG envelope of the masseter and temporalis anterior muscles were assessed in twelve subjects during mastication of a soft and hard bolus of the same size. When chewing the hard bolus, the chewing pattern in the frontal plane was significantly higher and wider, with smaller closure angle and higher peak velocity than when chewing the soft bolus. EMG peak amplitude of both the masseter and anterior temporalis muscles was higher for the side of the bolus but the contralateral side increased its activity significantly more than the ipsilateral side when the hardness of the bolus increased (for the masseter, mean+/-SD: 130.4+/-108.1% increase for the contralateral side and 29.6+/-26.9% for the ipsilateral side). Moreover, the peak EMG activity for both muscles occurred more distant from the closure point with hard bolus. The increased activity of the contralateral side may help maintaining the mandibular equilibrium, with indirect participation to the power stroke generated by the chewing-side masseter. The results provide kinematic and EMG adaptations to bolus hardness in healthy subjects and can be used as normative data in the development of methods for early diagnosis of impaired chewing function.
Merletti R, Holobar A, Farina D, 2008, Analysis of motor units with high-density surface electromyography., J Electromyogr Kinesiol, Vol: 18, Pages: 879-890, ISSN: 1050-6411
Although the behaviour of individual motor units is classically studied with intramuscular EMG, recently developed techniques allow its analysis also from EMG recorded in multiple locations over the skin surface (high-density surface EMG). The analysis of motor units from the surface EMG is useful when the insertion of needles is not desirable or not possible. Moreover, surface EMG allows the measure of motor unit properties which are difficult to assess with invasive technology (e.g., muscle fiber conduction velocity or location of innervation zones) and may increase the number of detectable motor units with respect to selective intramuscular recordings. Although some limitations remain, both the discharge pattern and muscle fiber properties of individual motor units can currently be analyzed non-invasively. This review presents the conditions and methodologies which allow the investigation of motor units with surface EMG.
Falla D, Farina D, Kanstrup Dahl M, et al., 2008, Pain-induced changes in cervical muscle activation do not affect muscle fatigability during sustained isometric contraction., J Electromyogr Kinesiol, Vol: 18, Pages: 938-946, ISSN: 1050-6411
This study investigated whether pain-induced changes in cervical muscle activation affect myoelectric manifestations of cervical muscle fatigue. Surface EMG signals were detected from the sternocleidomastoid and splenius capitis muscles bilaterally from 14 healthy subjects during 20-s cervical flexion contractions at 25% of the maximal force. Measurements were performed before and after the injection of 0.5 ml of hypertonic (painful) or isotonic (control) saline into either the sternocleidomastoid or splenius capitis in two experimental sessions. EMG average rectified value and mean power spectral frequency were estimated throughout the sustained contraction. Sternocleidomastoid or splenius capitis muscle pain resulted in lower sternocleidomastoid EMG average rectified value on the side of pain (P < 0.01). However, changes over time of sternocleidomastoid EMG average rectified value and mean frequency (myoelectric manifestations of fatigue) during sustained flexion were not changed during muscle pain. These results demonstrate that pain-induced modifications of cervical muscle activity do not change myoelectric manifestations of fatigue. This finding has implications for interpreting the mechanisms underlying greater cervical muscle fatigue in people with neck pain disorders.
Roatta S, Arendt-Nielsen L, Farina D, 2008, Sympathetic-induced changes in discharge rate and spike-triggered average twitch torque of low-threshold motor units in humans., J Physiol, Vol: 586, Pages: 5561-5574
Animal and in vitro studies have shown that the sympathetic nervous system modulates the contractility of skeletal muscle fibres, which may require adjustments in the motor drive to the muscle in voluntary contractions. In this study, these mechanisms were investigated in the tibialis anterior muscle of humans during sympathetic activation induced by the cold pressor test (CPT; left hand immersed in water at 4 degrees C). In the first experiment, 11 healthy men performed 20 s isometric contractions at 10% of the maximal torque, before, during and after the CPT. In the second experiment, 12 healthy men activated a target motor unit at the minimum stable discharge rate for 5 min in the same conditions as in experiment 1. Intramuscular electromyographic (EMG) signals and torque were recorded and used to assess the motor unit discharge characteristics (experiment 1) and spike-triggered average twitch torque (experiment 2). CPT increased the diastolic blood pressure and heart rate by (mean +/- S.D.) 18 +/- 9 mmHg and 4.7 +/- 6.5 beats min(-1) (P < 0.01), respectively. In experiment 1, motor unit discharge rate increased from 10.4 +/- 1.0 pulses s(-1) before to 11.1 +/- 1.4 pulses s(-1) (P < 0.05) during the CPT. In experiment 2, the twitch half-relaxation time decreased by 15.8 +/- 9.3% (P < 0.05) during the CPT with respect to baseline. These results provide the first evidence of an adrenergic modulation of contractility of muscle fibres in individual motor units in humans, under physiological sympathetic activation.
von Tscharner V, Nigg BM, 2008, Point: spectral properties of the surface EMG can characterize/do not provide information about motor unit recruitment strategies and muscle fiber type., J Appl Physiol (1985), Vol: 105, Pages: 1671-1673, ISSN: 8750-7587
Farina D, 2008, Last word on point:counterpoint: spectral properties of the surface EMG can characterize/do not provide information about motor unit recruitment and muscle fiber type., J Appl Physiol (1985), Vol: 105, ISSN: 8750-7587
Falla D, Farina D, 2008, Non-uniform adaptation of motor unit discharge rates during sustained static contraction of the upper trapezius muscle., Exp Brain Res, Vol: 191, Pages: 363-370
The aim of the study was to investigate the adaptations of motor unit discharge rate and additional motor unit recruitment in different regions of the upper trapezius muscle during sustained contraction. Intramuscular EMG signals were recorded from three locations (cranial, middle, and caudal) within the upper trapezius of eleven healthy men during 60-s static shoulder abduction at 25% of the maximal force. Surface EMG signals were recorded concurrently with a 10 x 5 electrode grid. Fifty-one (cranial location), 39 (middle), and 19 (caudal) motor units were identified from the intramuscular EMG signals. Motor unit discharge rates at the beginning of the contraction were greater in the caudal than in the other two locations (cranial: 16.5 +/- 3.4 pps; n = 28, middle: 16.2 +/- 3.4 pps; n = 32, caudal: 19.6 +/- 3.1 pps; n = 13; P < 0.05). Because the decrease in discharge rate over time was larger for the caudal location, at the end of the contraction the discharge rates were comparable at all locations (cranial: 15.7 +/- 3.3 pps; n = 28, middle: 14.9 +/- 2.3 pps; n = 32, caudal: 15.8 +/- 3.6 pps; n = 13). Additional motor unit recruitment was observed in all locations but more frequently in the caudal region (19 motor units recruited after the beginning of the contraction vs. only 4 in each of the other two locations). The mean position of the distribution of surface EMG amplitude over the grid moved by 1.4 +/- 0.7 mm (P < 0.001) in the cranial direction at the end with respect to the beginning of the contraction. The results showed that the neural drive received by the upper trapezius depends on the muscle region, which may indicate non-uniform descending drive to the motor neuron pool.
Farina D, 2008, Counterpoint: spectral properties of the surface EMG do not provide information about motor unit recruitment and muscle fiber type., J Appl Physiol (1985), Vol: 105, Pages: 1673-1674, ISSN: 8750-7587
do Nascimento OF, Farina D, 2008, Movement-related cortical potentials allow discrimination of rate of torque development in imaginary isometric plantar flexion., IEEE Trans Biomed Eng, Vol: 55, Pages: 2675-2678
The aim of this study was to discriminate on a single-trial basis the cortical activity associated to two rates of torque development (RTDs) in imaginary isometric plantar flexions. Electroencephalographic (EEG), electrooculographic (EOG), and electromyographic (EMG) signals were recorded while ten healthy subjects imagined right-sided isometric ankle plantar-flexion tasks at moderate [from 0% to 60% of the maximal voluntary contraction (MVC) in 4 s] and ballistic (from 0% to 60% MVC as fast as possible) RTDs. The EEG signals were classified using feature extraction based on the marginal distribution of a discrete wavelet transform with optimization of the mother wavelet. The classifier was based on support vector machines (SVMs). Minimum misclassification rate for the best case was 8.3%. Average minimum misclassification rate over the ten subjects was (17.4 +/- 8.4)%. The two RTDs could be best differentiated from channel C4 on average. In conclusion, different RTDs could be differentiated in imaginary isometric plantar-flexion by only using cortical potentials recorded with surface EEG. This result constitutes the first step for the development of a new type of brain-computer interfaces that rely on kinetic parameters of a single limb rather than movements of opposite limbs.
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