sEMG Recordings Research Articles

Assessment of Dry Epidermal Electrodes for Long-Term Electromyography Measurements.

Commercially available electrodes can only provide quality surface electromyography (sEMG) measurements for a limited duration due to user discomfort and signal degradation, but in many applications, collecting sEMG data for a full day or longer is desirable to enhance clinical care. Few studies for long-term sEMG have assessed signal quality of electrodes using clinically relevant tests. The goal of this research was to evaluate flexible, gold-based epidermal sensor system (ESS) electrodes for long-term sEMG recordings. We collected sEMG and impedance data from eight subjects from ESS and standard clinical electrodes on upper extremity muscles during maximum voluntary isometric contraction tests, dynamic range of motion tests, the Jebsen Taylor Hand Function Test, and the Box & Block Test. Four additional subjects were recruited to test the stability of ESS signals over four days. Signals from the ESS and traditional electrodes were strongly correlated across tasks. Measures of signal quality, such as signal-to-noise ratio and signal-to-motion ratio, were also similar for both electrodes. Over the four-day trial, no significant decrease in signal quality was observed in the ESS electrodes, suggesting that thin, flexible electrodes may provide a robust tool that does not inhibit movement or irritate the skin for long-term measurements of muscle activity in rehabilitation and other applications.

Simultaneous Force Regression and Movement Classification of Fingers via Surface EMG within a Unified Bayesian Framework.

This contribution presents a novel methodology for myolectric-based control using surface electromyographic (sEMG) signals recorded during finger movements. A multivariate Bayesian mixture of experts (MoE) model is introduced which provides a powerful method for modeling force regression at the fingertips, while also performing finger movement classification as a by-product of the modeling algorithm. Bayesian inference of the model allows uncertainties to be naturally incorporated into the model structure. This method is tested using data from the publicly released NinaPro database which consists of sEMG recordings for 6 degree-of-freedom force activations for 40 intact subjects. The results demonstrate that the MoE model achieves similar performance compared to the benchmark set by the authors of NinaPro for finger force regression. Additionally, inherent to the Bayesian framework is the inclusion of uncertainty in the model parameters, naturally providing confidence bounds on the force regression predictions. Furthermore, the integrated clustering step allows a detailed investigation into classification of the finger movements, without incurring any extra computational effort. Subsequently, a systematic approach to assessing the importance of the number of electrodes needed for accurate control is performed via sensitivity analysis techniques. A slight degradation in regression performance is observed for a reduced number of electrodes, while classification performance is unaffected.

Is the timed loaded standing test a valid measure of back muscle endurance in people with vertebral osteoporosis?

The TLS test is suggested as a measure of back muscle endurance for patients with vertebral osteoporosis. However, to date, no study has demonstrated that TLS does measure back extensor or erector spinae (ES) muscle endurance. We used surface electromyography (sEMG) to investigate the performance of the thoracic ES muscles during TLS. Thirty-six people with vertebral osteoporosis with a mean age of 71.6 (range 45-86) years participated. sEMG recordings were made of the ES at T3 and T12 bilaterally during quiet standing (QS) and TLS. The relative (%) change in sEMG amplitude between conditions was compared. Fatigue was evaluated by analysing the change in median frequency (MF) of the sEMG signal during TLS, and the correlation between maximal TLS time and rate of MF decline was examined. Activity in the ES increased significantly during TLS at all electrode locations. During TLS, the MF declined at a mean rate of -24.2% per minute (95% C.I. -26.5 to -21.9%). The MF slope and test time were strongly correlated (r2 = 0.71), and at test end, the final MF dropped to an average 89% (95% C.I. 85 to 93%) of initial MF. Twenty-eight participants (78%) reported fatigue was the main reason for stopping, and for eight (22%), it was pain. This study demonstrates that TLS challenges the ES muscles in the thoracic region and results in ES fatigue. Endurance time and the point at which the TLS test ends are strongly related to ES fatigue.

Difficulty Swallowing-The Degree of Dysphagia in the Polish Population Comparing Fiberoptic Endoscopic Evaluation of Swallowing with Surface Electromyography Preliminary Reports

Study background: Dysphagia is a problem with which patients increasingly seek medical care. Early involvement of specialists (gastroenterologist, ENT surgeons, nutritionists) aid in symptomatic treatment, and offer a good prognosis for the management of swallowing disorders. Symptoms generally arise periodically and on occasion may eradicate on their own. Although elderly patients are inherently predisposed to dysphagia, there is an increased prevalence in the younger population.Aim: The aim of the project is to develop comprehensive guidelines for dysphagia amongst the Polish population for various age groups. The research will determine the predisposition to dysphagia and the different etiologies that are attributed in the phases of the diseas non-neurological-GERD (gastroesophageal reflux disease), chronic laryngitis.Method: Analysis was conducted on a group of 92 patientes. We performed FEES (Fiberoptic Endoscopic Evaluation of Swallowing) with simultaneous superficial electromyography (sEMG) and registration of respiratory patterns in every patient.Results: During swallowing, biomechanical phenomena occurs-carrying out the plan of the study we can prove the strong correlation between the biomechanical phenomena in the process of swallowing and the corresponding changes in the sEMG recording, correlated with respiratory patterns.Conclusions: The preliminary results using the algorithm that studies the process of swallowing is a useful starting point for creating broad-based guidelines within the Polish population. The correlation of the results obtained from the sEMG in comparison with FEES examination is very promising.

SEMG Signal Acquisition Strategy towards Hand FES Control.

Due to damage of the nervous system, patients experience impediments in their daily life: severe fatigue, tremor or impaired hand dexterity, hemiparesis, or hemiplegia. Surface electromyography (sEMG) signal analysis is used to identify motion; however, standardization of electrode placement and classification of sEMG patterns are major challenges. This paper describes a technique used to acquire sEMG signals for five hand motion patterns from six able-bodied subjects using an array of recording and stimulation electrodes placed on the forearm and its effects over functional electrical stimulation (FES) and volitional sEMG combinations, in order to eventually control a sEMG-driven FES neuroprosthesis for upper limb rehabilitation. A two-part protocol was performed. First, personalized templates to place eight sEMG bipolar channels were designed; with these data, a universal template, called forearm electrode set (FELT), was built. Second, volitional and evoked movements were recorded during FES application. 95% classification accuracy was achieved using two sessions per movement. With the FELT, it was possible to perform FES and sEMG recordings simultaneously. Also, it was possible to extract the volitional and evoked sEMG from the raw signal, which is highly important for closed-loop FES control.

Classification of Upper limb phantom movements in transhumeral amputees using electromyographic and kinematic features

Recent studies have shown the ability of transhumeral amputees to generate surface electromyography (sEMG) patterns associated to distinct phantom limb movements of the hand, wrist and elbow. This ability could improve the control of myoelectric prostheses with multiple degrees of freedom (DoF). However, the main issue of these studies is that these ones record sEMG from sites that cannot always be integrated in a prosthesis socket. This study aims to evaluate the classification accuracy of eight main upper limb phantom movements and a no movement class in transhumeral amputees based on sEMG data recorded exclusively on the residual limb. A sub-objective of this study is to evaluate the impact of kinematic data on the classification accuracy. Five transhumeral amputees participated in this study. Classification accuracy obtained with an artificial neural network ranged between 60.9% and 93.0%. Accuracy decreased if the number of DoF considered in the classification increased, and/or if the phantom movements became more distal. Adding a kinematic feature produced an average increase of 4.8% in accuracy. This study may lead to the development of a new myoelectric control method for multi-DoF prostheses based on phantom movements of the amputee and kinematic data of the prosthesis.

Design of sEMG assembly to detect external anal sphincter activity: a proof of concept

Objective: Conditional trans-rectal stimulation of the pudendal nerve could provide a viable solution to treat hyperreflexive bladder in spinal cord injury. A set threshold of the amplitude estimate of the external anal sphincter surface electromyography (sEMG) may be used as the trigger signal. The efficacy of such a device should be tested in a large scale clinical trial. As such, a probe should remain in situ for several hours while patients attend to their daily routine; the recording electrodes should be designed to be large enough to maintain good contact while observing design constraints. The objective of this study was to arrive at a design for intra-anal sEMG recording electrodes for the subsequent clinical trials while deriving the possible recording and processing parameters. Approach: Having in mind existing solutions and based on theoretical and anatomical considerations, a set of four multi-electrode probes were designed and developed. These were tested in a healthy subject and the measured sEMG traces were recorded and appropriately processed. Main results: It was shown that while comparatively large electrodes record sEMG traces that are not sufficiently correlated with the external anal sphincter contractions, smaller electrodes may not maintain a stable electrode tissue contact. It was shown that 3 mm wide and 1 cm long electrodes with 5 mm inter-electrode spacing, in agreement with Nyquist sampling, placed 1 cm from the orifice may intra-anally record a sEMG trace sufficiently correlated with external anal sphincter activity. Significance: The outcome of this study can be used in any biofeedback, treatment or diagnostic application where the activity of the external anal sphincter sEMG should be detected for an extended period of time.

Proposal of surface electromyography signal acquisition protocols for masseter and temporalis muscles

Introduction The aim of this study was to propose a method of electrodes positioning on the superficial masseter and anterior temporalis muscles for surface electromyographic (sEMG) recordings in order to overcome some known methodological constraints. Methods Fifteen volunteers with normal occlusion participated in two experimental sessions within a 7 day-period. Surface electrodes were placed on two different locations that were based on palpable and individual anatomical references. Surface EMG signals (2000 Hz per channel; A/D: 16 bits; gain: 2000 X; band-pass filter: 20-500 Hz) were recorded under three conditions: mandibular rest position, 30% and 100% of maximum voluntary bite force. Three measurements of maximal bite force were taken by using a force transducer positioned over the lower right first molar region and the highest record was taken into account. The root mean square value was considered for analysis. Intraclass correlation coefficients (ICCs), paired t test, and the Bland-Altman method comprised the statistical analyses. The level of significance was set at 0.05. Results ICC records for right and left masseter and anterior temporalis muscles at T0 (first sEMG record) and T7 (second sEMG record) intervals were significantly different (p<0.05). The results showed satisfactory to excellent reproducibility of RMS values at rest, MVBF and 30% MVBF, as well as for MVBF in kgf. Conclusion The results showed reliable reproducibility for the sEMG signal recording in masseter and anterior temporalis muscles from the protocols presented and under the three conditions investigated.

Normalization of the trapezius sEMG signal – a reliability study on women with and without neck-shoulder pain

ObjectiveTo evaluate within- and between-days reliability of two normalization methods of surface electromyography (sEMG) recordings of the trapezius muscle. MethodsNineteen women were allocated into 2 groups (healthy and with neck-shoulder pain). The sEMG was recorded in two sessions with 7 days in between sessions. The four portions of the trapezius muscle (the clavicular and acromial fibers of the upper trapezius, the middle and the lower trapezius) were evaluated during maximal and submaximal isometric voluntary contractions. The within- and between-days reliability of both maximal and submaximal contractions were assessed through Intraclass Correlation Coefficient (ICC(2,1) was used for within-day analyses of both maximal and submaximal contractions, and for between-days analyses of maximal contractions while ICC(2,3) was used for between-days analyses of submaximal contractions), Coefficient of Variation, Standard Error of Measurement, and Bland–Altman analysis. ResultsIn general, submaximal contractions presented higher within-day reliability, with higher ICC values (e.g., middle trapezius – mean of 0.97), smaller Coefficient of Variation and Standard Error of Measurement ranges compared to maximal contractions (ICC values, e.g. for middle trapezius – mean of 0.94) in both groups. The same pattern was observed for between-days analyses, with submaximal contractions presenting higher ICC values (e.g., middle trapezius – mean of 0.84), smaller Coefficient of Variation and Standard Error of Measurement ranges than maximal contractions (ICC values, e.g. for middle trapezius – mean of 0.73) in both groups. ConclusionSubmaximal contractions are recommended for normalization procedures of trapezius sEMG, in both subjects with neck-shoulder pain and healthy individuals.

Infrared thermography reveals effect of working posture on skin temperature in office workers

Introduction. Musculoskeletal symptoms related to using traditional computer workstations are common. Quantitative methods for measuring muscle stress and strain are needed to improve ergonomics of workstations. We hypothesize that infrared thermography (IRT) is suited for this purpose. Methods. This hypothesis was evaluated by estimating muscle activity in upright and traditional working postures with IRT and surface electromyography (sEMG). IRT and sEMG measurements were conducted in 14 female participants with both working postures. First, measurements with the traditional posture were performed. Later, participants had 1 month to adjust to the upright working posture before repeating the measurements. IRT images were acquired before and after a full working day, with sEMG recordings being conducted throughout the measurement days. Participants evaluated their neck pain severity using neck disability index (NDI) questionnaires before the first and after the second measurement day. Results. Spatial variation in upper back temperature was higher (p = 0.008) when working in traditional posture and the upright working posture reduced (p < 0.05) upper back muscle activity. The NDI was significantly lower (p = 0.003) after working in the upright posture. Conclusion. IRT was found suitable for evaluating muscle activity and upright working posture to reduce the NDI and muscle activity in the upper back.

Assessment of elbow spasticity with surface electromyography and mechanomyography based on support vector machine.

The Modified Ashworth Scale (MAS) is the gold standard in clinical for grading spasticity. However, its results greatly depend on the physician evaluations and are subjective. In this study, we investigated the feasibility of using support vector machine (SVM) to objectively assess elbow spasticity based on both surface electromyography (sEMG) and mechanomyography (MMG). sEMG signals and tri-axial accelerometer mechanomyography (ACC-MMG) signals were recorded simultaneously on patients' biceps and triceps when they extended or bended elbow passively. 39 post-stroke patients participated in the study, and were divided into four groups regarding MAS level (MAS=0, 1, 1+ or 2). The three types of features, root mean square (RMS), mean power frequency (MPF), and median frequency (MF), were calculated from sEMG and MMG signal recordings. Spearman correlation analysis was used to investigate the relationship between the features and spasticity grades. The results showed that the correlation between MAS and each of the five features (MMG-RMS of the biceps, MMG-RMS of the triceps, the EMG-RMS of the biceps, EMG-RMS of the triceps, EMG-MPF of the triceps) was significant (p<;0.05). The four spasticity grades were identified with SVM, and the classification accuracy of SVM with sEMG, MMG, sEMG-MMG were 70.9%, 83.3%, 91.7%, respectively. Our results suggest that using the SVM-based method with sEMG and MMG to assess elbow spasticity would be suitable for clinical management of spasticity.

Inter-Gender sEMG Evaluation of Central and Peripheral Fatigue in Biceps Brachii of Young Healthy Subjects.

PurposeThe purpose of the present study was to evaluate inter-arm and inter-gender differences in fractal dimension (FD) and conduction velocity (CV) obtained from multichannel surface electromyographic (sEMG) recordings during sustained fatiguing contractions of the biceps brachii.MethodsA total of 20 recreationally active males (24±6 years) and 18 recreationally active females (22±9 years) performed two isometric contractions at 120 degrees elbow joint angle: (1) at 20% maximal voluntary contraction (MVC) for 90 s, and (2) at 60% MVC until exhaustion the time to perform the task has been measured. Signals from sEMG were detected from the biceps brachii using bidimensional arrays of 64 electrodes and initial values and rate of change of CV and FD of the sEMG signal were calculated.ResultsNo difference between left and right sides and no statistically significant interaction effect of sides with gender were found for all parameters measured. A significant inter-gender difference was found for MVC (p<0.0001). Initial values of CV were higher in females than in males at both force levels (20% MCV: p<0.0001; 60% MCV: p<0.05) whereas a lower initial estimate of FD was observed in females compared to males (20% MCV: p<0.05; 60% MCV: p<0.0001). No difference in CV and FD slopes was found at 20% MVC between genders. At 60% MVC significantly lower CV and FD slopes (CV and FD: p<0.05) and a more protracted time to exhaustion were found in females than in males (p<0.0001). When considering time to exhaustion at both levels of contraction no difference in percentage change (Δ%) of CV and FD slopes was found between genders (p>0.05). During the sustained 60% MVC no statistical correlation was found between MVC and CV or FD initial estimates nor between MVC and CV or FD slopes both in males and females whereas. A significant positive correlation between CV and FD slopes was found in both genders (males: r = 0,61; females: r = 0,55).ConclusionsFatigue determines changes in FD and CV values in biceps brachii during sustained contractions at 60% MVC. In particular males show greater increase in the rate of change of CV and FD than females whereas no difference in percentage change of these sEMG descriptors of fatigue was found. A significant correlation between FD and CV slopes found in both genders highlights that central and peripheral myoelectric components of fatigue may interact during submaximal isometric contractions.

Intarsia-sensorized band and textrodes for real-time myoelectric pattern recognition.

Surface Electromyography (sEMG) has applications in prosthetics, diagnostics and neuromuscular rehabilitation. Self-adhesive Ag/AgCl are the electrodes preferentially used to capture sEMG in short-term studies, however their long-term application is limited. In this study we designed and evaluated a fully integrated smart textile band with electrical connecting tracks knitted with intarsia techniques and knitted textile electrodes. Real-time myoelectric pattern recognition for motor volition and signal-to-noise ratio (SNR) were used to compare its sensing performance versus the conventional Ag-AgCl electrodes. After a comprehending measurement and performance comparison of the sEMG recordings, no significant differences were found between the textile and the Ag-AgCl electrodes in SNR and prediction accuracy obtained from pattern recognition classifiers.

Denoising of HD-sEMG signals using canonical correlation analysis.

High-density surface electromyography (HD-sEMG) is a recent technique that overcomes the limitations of monopolar and bipolar sEMG recordings and enables the collection of physiological and topographical informations concerning muscle activation. However, HD-sEMG channels are usually contaminated by noise in an heterogeneous manner. The sources of noise are mainly power line interference (PLI), white Gaussian noise (WGN) and motion artifacts (MA). The spectral components of these disruptive signals overlap with the sEMG spectrum which makes classical filtering techniques non effective, especially during low contraction level recordings. In this study, we propose to denoise HD-sEMG recordings at 20% of the maximum voluntary contraction by using a second-order blind source separation technique, named canonical component analysis (CCA). For this purpose, a specific and automatic canonical component selection, using noise ratio thresholding, and a channel selection procedure for the selective version (sCCA) are proposed. Results obtained from the application of the proposed methods (CCA and sCCA) on realistic simulated data demonstrated the ability of the proposed approach to retrieve the original HD-sEMG signals, by suppressing the PLI and WGN components, with high accuracy (for five different simulated noise dispersions using the same anatomy). Afterward, the proposed algorithms are employed to denoise experimental HD-sEMG signals from five healthy subjects during biceps brachii contractions following an isometric protocol. Obtained results showed that PLI and WGN components could be successfully removed, which enhances considerably the SNR of the channels with low SNR and thereby increases the mean SNR value among the grid. Moreover, the MA component is often isolated on specific estimated sources but requires additional signal processing for a total removal. In addition, comparative study with independent component analysis, CCA-wavelet and CCA-empirical mode decomposition (EMD) proved a higher efficiency of the presented method over existing denoising techniques and demonstrated pointless a second filtering stage for denoising HD-sEMG recordings at this contraction level.

Long-term decoding of movement force and direction with a wireless myoelectric implant

Objective. The ease of use and number of degrees of freedom of current myoelectric hand prostheses is limited by the information content and reliability of the surface electromyography (sEMG) signals used to control them. For example, cross-talk limits the capacity to pick up signals from small or deep muscles, such as the forearm muscles for distal arm amputations, or sites of targeted muscle reinnervation (TMR) for proximal amputations. Here we test if signals recorded from the fully implanted, induction-powered wireless Myoplant system allow long-term decoding of continuous as well as discrete movement parameters with better reliability than equivalent sEMG recordings. The Myoplant system uses a centralized implant to transmit broadband EMG activity from four distributed bipolar epimysial electrodes. Approach. Two Rhesus macaques received implants in their backs, while electrodes were placed in their upper arm. One of the monkeys was trained to do a cursor task via a haptic robot, allowing us to control the forces exerted by the animal during arm movements. The second animal was trained to perform a center-out reaching task on a touchscreen. We compared the implanted system with concurrent sEMG recordings by evaluating our ability to decode time-varying force in one animal and discrete reach directions in the other from multiple features extracted from the raw EMG signals. Main results. In both cases, data from the implant allowed a decoder trained with data from a single day to maintain an accurate decoding performance during the following months, which was not the case for concurrent surface EMG recordings conducted simultaneously over the same muscles. Significance. These results show that a fully implantable, centralized wireless EMG system is particularly suited for long-term stable decoding of dynamic movements in demanding applications such as advanced forelimb prosthetics in a wide range of configurations (distal amputations, TMR).

Activity of the masticatory muscles and occlusal contacts in young adults with and without orthodontic treatment.

BackgroundSymmetry evaluation of the craniofacial complex generally involves models of mandibular movement and masticatory muscle activity, especially during the development of the craniofacial complex.The aim of this screening study was to detect differences in the asymmetry and activity indices and in the occlusal contact distribution in groups with and without orthodontic treatment, and between the sexes in the healthy population.Material and MethodThis screening study involved the participation of 149 Caucasian (F = 101, M = 48) 18-year-old volunteers, of whom 77 had received orthodontic treatment (Group I) and 72 had not (Group II). All participants underwent sEMG recording with an eight-channel electromyograph (Bio EMG III). A T-Scan III device was used to analyze the occlusal contact points.We measured the voltage of the right and left temporalis anterior (RTA, LTA) and of the right and left masseter muscles (RMM, LMM). On the basis of the Naeije study, we calculated the Asymmetry and Activity indices (AsI, AcI).ResultsNo significant differences were found in the asymmetry or activity indices, or in the occlusal contact distribution of young adult subjects with or without orthodontic treatment.There were two findings in the females. First (p = 0.04), a higher voltage (131.12 μV) was recorded in the right temporalis anterior muscle in female group, compared to 119.65 μV in the male group. Secondly (p = 0.002), the activity index showed a predominance of the temporalis anterior (AcI = 10.52). In the males, the activity index showed a predominance of the masseter muscles (AcI =−1.22).ConclusionsThe null hypothesis was supported, as we found that no significant differences were observed in occlusal contact, asymmetry, or activity indices between healthy young adults with or without orthodontic treatment. However, there do exist significant differences in the activity index between genders.

Assessing altered motor unit recruitment patterns in paretic muscles of stroke survivors using surface electromyography

Objective. The advancement of surface electromyogram (sEMG) recording and signal processing techniques has allowed us to characterize the recruitment properties of a substantial population of motor units (MUs) non-invasively. Here we seek to determine whether MU recruitment properties are modified in paretic muscles of hemispheric stroke survivors. Approach. Using an advanced EMG sensor array, we recorded sEMG during isometric contractions of the first dorsal interosseous muscle over a range of contraction levels, from 20% to 60% of maximum, in both paretic and contralateral muscles of stroke survivors. Using MU decomposition techniques, MU action potential amplitudes and recruitment thresholds were derived for simultaneously activated MUs in each isometric contraction. Main results. Our results show a significant disruption of recruitment organization in paretic muscles, in that the size principle describing recruitment rank order was materially distorted. MUs were recruited over a very narrow force range with increasing force output, generating a strong clustering effect, when referenced to recruitment force magnitude. Such disturbances in MU properties also correlated well with the impairment of voluntary force generation. Significance. Our findings provide direct evidence regarding MU recruitment modifications in paretic muscles of stroke survivors, and suggest that these modifications may contribute to weakness for voluntary contractions.

Transradial Amputee Gesture Classification Using an Optimal Number of sEMG Sensors: An Approach Using ICA Clustering.

Surface electromyography (sEMG)-based pattern recognition studies have been widely used to improve the classification accuracy of upper limb gestures. Information extracted from multiple sensors of the sEMG recording sites can be used as inputs to control powered upper limb prostheses. However, usage of multiple EMG sensors on the prosthetic hand is not practical and makes it difficult for amputees due to electrode shift/movement, and often amputees feel discomfort in wearing sEMG sensor array. Instead, using fewer numbers of sensors would greatly improve the controllability of prosthetic devices and it would add dexterity and flexibility in their operation. In this paper, we propose a novel myoelectric control technique for identification of various gestures using the minimum number of sensors based on independent component analysis (ICA) and Icasso clustering. The proposed method is a model-based approach where a combination of source separation and Icasso clustering was utilized to improve the classification performance of independent finger movements for transradial amputee subjects. Two sEMG sensor combinations were investigated based on the muscle morphology and Icasso clustering and compared to Sequential Forward Selection (SFS) and greedy search algorithm. The performance of the proposed method has been validated with five transradial amputees, which reports a higher classification accuracy ( > 95%). The outcome of this study encourages possible extension of the proposed approach to real time prosthetic applications.

Impact of proprioception during the oral phase on initiating the swallowing reflex.

We hypothesized that proprioceptive signals during the oral phase play a pivotal role in the initiation of pharyngeal phase during volitional swallowing. Therefore, we tested if swallowing could be modified by changing the amount of proprioceptive feedback from a number of different receptors while holding a food bolus in the mouth and clenching. Basic research. Surface electromyography (sEMG) recordings of the masticatory muscles were obtained during volitional swallowing movements from seven healthy adults with no clinical history of swallowing difficulties. The swallowing procedure involved holding 5 ml of jelly on the tongue before swallowing it completely, according to visual cues on a computer display. Initiation of the swallowing reflex was detected by an anterior shift of the thyroid cartilage using a laser displacement sensor and by submental sEMG signals. To vary the proprioceptive input, the participants were instructed to occlude their teeth at various intensities (weak, intermediate, and strong) while holding the 5-ml jelly bolus on the tongue. Rectified and integrated sEMG (iEMG) signals obtained from the submental area showed two upward deflections. Contractile forces of the masseter muscles showed significant negative values for Pearson correlation coefficient against time intervals from the onset of the second submental iEMG deflection to the onset of the anterior shift of the thyroid cartilage in six of the seven participants (average -0.534, standard deviation 0.176). Contractile forces of the masseter muscles during occlusion tended to correlate negatively with electromechanical delays on suprahyoid muscle contraction. NA Laryngoscope, 126:1595-1599, 2016.

Spatial variability in cortex-muscle coherence investigated with magnetoencephalography and high-density surface electromyography.

Cortex-muscle coherence (CMC) reflects coupling between magnetoencephalography (MEG) and surface electromyography (sEMG), being strongest during isometric contraction but absent, for unknown reasons, in some individuals. We used a novel nonmagnetic high-density sEMG (HD-sEMG) electrode grid (36 mm × 12 mm; 60 electrodes separated by 3 mm) to study effects of sEMG recording site, electrode derivation, and rectification on the strength of CMC. Monopolar sEMG from right thenar and 306-channel whole-scalp MEG were recorded from 14 subjects during 4-min isometric thumb abduction. CMC was computed for 60 monopolar, 55 bipolar, and 32 Laplacian HD-sEMG derivations, and two derivations were computed to mimic "macroscopic" monopolar and bipolar sEMG (electrode diameter 9 mm; interelectrode distance 21 mm). With unrectified sEMG, 12 subjects showed statistically significant CMC in 91-95% of the HD-sEMG channels, with maximum coherence at ∼25 Hz. CMC was about a fifth stronger for monopolar than bipolar and Laplacian derivations. Monopolar derivations resulted in most uniform CMC distributions across the thenar and in tightest cortical source clusters in the left rolandic hand area. CMC was 19-27% stronger for HD-sEMG than for "macroscopic" monopolar or bipolar derivations. EMG rectification reduced the CMC peak by a quarter, resulted in a more uniformly distributed CMC across the thenar, and provided more tightly clustered cortical sources than unrectifed sEMGs. Moreover, it revealed CMC at ∼12 Hz. We conclude that HD-sEMG, especially with monopolar derivation, can facilitate detection of CMC and that individual muscle anatomy cannot explain the high interindividual CMC variability.