Surface Electromyographic Recordings Research Articles

Magnetic Resonance-Compatible Arm-Crank Ergometry: A New Platform Linking Whole-Body Calorimetry to Upper-Extremity Biomechanics and Arm Muscle Metabolism.

IntroductionEvaluation of the effect of human upper-body training regimens may benefit from knowledge of local energy expenditure in arm muscles. To that end, we developed a novel arm-crank ergometry platform for use in a clinical magnetic resonance (MR) scanner with 31P spectroscopy capability to study arm muscle energetics. Complementary datasets on heart-rate, whole-body oxygen consumption, proximal arm-muscle electrical activity and power output, were obtained in a mock-up scanner. The utility of the platform was tested by a preliminary study over 4 weeks of skill practice on the efficiency of execution of a dynamic arm-cranking task in healthy subjects.ResultsThe new platform successfully recorded the first ever in vivo 31P MR spectra from the human biceps brachii (BB) muscle during dynamic exercise in five healthy subjects. Changes in BB energy- and pH balance varied considerably between individuals. Surface electromyography and mechanical force recordings revealed that individuals employed different arm muscle recruitment strategies, using either predominantly elbow flexor muscles (pull strategy; two subjects), elbow extensor muscles (push strategy; one subject) or a combination of both (two subjects). The magnitude of observed changes in BB energy- and pH balance during ACT execution correlated closely with each strategy. Skill practice improved muscle coordination but did not alter individual strategies. Mechanical efficiency on group level seemed to increase as a result of practice, but the outcomes generated by the new platform showed the additional caution necessary for the interpretation that total energy cost was actually reduced at the same workload.ConclusionThe presented platform integrates dynamic in vivo 31P MRS recordings from proximal arm muscles with whole-body calorimetry, surface electromyography and biomechanical measurements. This new methodology enables evaluation of cyclic motor performance and outcomes of upper-body training regimens in healthy novices. It may be equally useful for investigations of exercise physiology in lower-limb impaired athletes and wheelchair users as well as frail patients including patients with debilitating muscle disease and the elderly.

Effects of a six-week endurance weight training program on bioelectrical activity of muscles and functional tests in patients with type 2 diabetes mellitus

Background. Type 2 diabetes mellitus (T2DM) is a common metabolic disease associated with pathophysiological changes in the neuromuscular system. The present study aimed to investigate the effects of a 6-week endurance training program on muscle strength, electrophysiological parameters, and functional activities in T2DM patients. Methods. The study period was divided into 6 weeks without training and 6 weeks with training. Twelve T2DM patients participated in this study. During the training period, the same T2DM patients went through an endurance training program. The assessment process included measurement of muscle strength, surface electromyography (SEMG) recording, and functional tests. Twelve healthy individuals were evaluated to compare their data with the T2DM patients. Results. The results showed that the muscle strength and the amplitudes of the SEMG signals of T2DM patients were lower than those of the healthy subjects. The bioelectric activity of T2DM patients increased after six weeks of the endurance training program. The functional tests showed significant improvement after the endurance training program in T2DM patients, while no significant difference was observed between the T2DM and healthy subjects. Conclusions. The short-term endurance-training program for lower limb muscles increased muscle strength and SEMG amplitudes of the knee extensor and flexor muscles and improved functional tests in T2DM patients, which may be attributed to neural adaptation after the endurance-training program.

Muscle activity and acute stress in fibromyalgia

BackgroundFibromyalgia (FM) patients are likely to differ from healthy controls in muscle activity and in reactivity to experimental stress.MethodsWe compared psychophysiological reactivity to cognitive stress between 51 female FM patients aged 18 to 65 years and 31 age- and sex-matched healthy controls. They underwent a 20-minute protocol consisting of three phases of relaxation and two phases of cognitive stress. We recorded surface electromyography normalized to maximum voluntary muscle contraction (%EMG), the percentage of time with no muscle activity (EMG rest time), and subjective pain and stress intensities. We compared group reactivity using linear modelling and adjusted for psychological and life-style factors.ResultsThe FM patients had a significantly higher mean %EMG (2.2 % vs. 1.0 %, p < 0.001), pain intensity (3.6 vs. 0.2, p < 0.001), and perceived stress (3.5 vs. 1.4, p < 0.001) and lower mean EMG rest time (26.7 % vs. 47.2 %, p < 0.001). In the FM patients, compared with controls, the pain intensity increased more during the second stress phase (0.71, p = 0.028), and the %EMG decreased more during the final relaxation phase (-0.29, p = 0.036). Within the FM patients, higher BMI predicted higher %EMG but lower stress. Leisure time physical activity predicted lower %EMG and stress and higher EMG rest time. Higher perceived stress predicted lower EMG rest time, and higher trait anxiety predicted higher pain and stress overall.ConclusionsOur results suggest that repeated cognitive stress increases pain intensity in FM patients. FM patients also had higher resting muscle activity, but their muscle activity did not increase with pain. Management of stress and anxiety might help control FM flare-ups.Trial registrationRetrospectively registered on ClinicalTrials.gov (NCT03300635).

Motor unit reserve capacity in spinal muscular atrophy during fatiguing endurance performance

ObjectiveTo investigate the availability of any motor unit reserve capacity during fatiguing endurance testing in patients with spinal muscular atrophy (SMA). MethodsWe recorded surface electromyography (sEMG) of various muscles of upper- and lower extremities of 70 patients with SMA types 2–4 and 19 healthy controls performing endurance shuttle tests (ESTs) of arm and legs. We quantitatively evaluated the development of fatigability and motor unit recruitment using time courses of median frequencies and amplitudes of sEMG signals. Linear mixed effect statistical models were used to evaluate group differences in median frequency and normalized amplitude at onset and its time course. ResultsNormalized sEMG amplitudes at onset of upper body ESTs were significantly higher in patients compared to controls, yet submaximal when related to maximal voluntary contractions, and showed an inverse correlation to SMA phenotype. sEMG median frequencies decreased and amplitudes increased in various muscles during execution of ESTs in patients and controls. ConclusionsDecreasing median frequencies and increasing amplitudes reveal motor unit reserve capacity in individual SMA patients during ESTs at submaximal performance intensities. SignificancePreserving, if not expanding motor unit reserve capacity may present a potential therapeutic target in clinical care to reduce fatigability in individual patients with SMA.

Improving Botulinum Toxin Efficiency in Treating Post-Stroke Spasticity Using 3D Innervation Zone Imaging.

Spasticity is a common post-stroke syndrome that imposes significant adverse impacts on patients and caregivers. This study aims to improve the efficiency of botulinum toxin (BoNT) in managing spasticity, by utilizing a three-dimensional innervation zone imaging (3DIZI) technique based on high-density surface electromyography (HD-sEMG) recordings. Stroke subjects were randomly assigned to two groups: the control group ([Formula: see text]) which received standard ultrasound-guided injections, and the experimental group ([Formula: see text]) which received 3DIZI-guided injections. The amount of BoNT given was consistent for all subjects. The Modified Ashworth Scale (MAS), compound muscle action potential (CMAP) and muscle activation volume (MAV) from bilateral biceps brachii muscles were obtained at the baseline, 3 weeks, and 3 months after injection. Intra-group and inter-group comparisons of MAS, CMAP amplitude and MAV were performed. An overall improvement in MAS of spastic elbow flexors was observed during the 3-week visit ([Formula: see text]), yet no statistically significant difference found with intra-group or inter-group analysis. Compared to the baseline, a significant reduction of CMAP amplitude and MAV were observed in the spastic biceps muscles of both groups at 3-week post-injection, and returned to approximate baseline value at 12-week post injection. A significantly higher reduction was found in CMAP amplitude ([Formula: see text]% versus [Formula: see text]%, [Formula: see text]) and MAV ([Formula: see text]% versus [Formula: see text]%, [Formula: see text]) in the experimental group compared to the control group. The study has demonstrated preliminary evidence that precisely directing BoNT to the innervation zones (IZs) localized by 3DIZI leads to a significantly higher treatment efficiency improvement in spasticity management. Results have also shown the feasibility of developing a personalized BoNT injection technique for the optimization of clinical treatment for post-stroke spasticity using proposed 3DIZI technique.

The Effect of Fatigue on Wheelchair Users' Upper Limb Muscle Coordination Patterns in Time-Frequency and Principal Component Analysis.

An assessment of shoulder muscle coordination patterns is important to gain insight into muscle fatigue during wheelchair propulsion. The objective of the present study was to quantify muscle coordination changes over time during fatiguing wheelchair propulsion, as the muscles go through distinct levels of fatigue, a) non-fatigued, b) transiting to fatigue and c) fatigued to exhaustion. We recorded surface electromyography (sEMG) signals of the anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), infraspinatus (IS), upper trapezius (UT), sternal head of the pectoralis major (PM), biceps brachii (BB), and triceps brachii (TB) during a wheelchair incremental exercise test. Nine wheelchair users with a diagnosis of spina bifida or T6-T12 spinal cord injury volunteered for the study. Oxygen uptake and SmartWheel kinetic parameters were also recorded during the test. EMG signals were processed by wavelet and principal component analysis (PCA), allowing for an assessment of how wheelchair users modify their muscle coordination patterns over time. Analyses of covariance (ANCOVA) were conducted to identify the main effect of fatigue levels on muscle coordination patterns by controlling for the effect of increased workload as covariate. A significant effect of fatigue levels on the PC1 and PC3 loading scores was found after controlling for the effect of increasing workloads (with both cases). In addition, PC3 reflects the most dominant fatigue effect on muscle coordination patterns which are not affected by increased ergometer workload. PC3 indicates muscle imbalance when muscles are fully fatigued and muscle co-contraction when muscles are beginning to fatigue. We conclude that fatigue-related changes in neuromuscular activity during wheelchair propulsion contribute to muscle imbalance and reflect a strategy of stiffening the shoulder joint.

Muscular and cortical activation during dynamic and static balance in the elderly: A scoping review.

Falls due to balance impairment are a major cause of injury and disability in the elderly. The study of neurophysiological correlates during static and dynamic balance tasks is an emerging area of research that could lead to novel rehabilitation strategies and reduce fall risk. This review aims to highlight key concepts and identify gaps in the current knowledge of balance control in the elderly that could be addressed by relying on surface electromyographic (EMG) and electroencephalographic (EEG) recordings. The neurophysiological hypotheses underlying balance studies in the elderly as well as the methodologies, findings, and limitations of prior work are herein addressed. The literature shows: 1) a wide heterogeneity in the experimental procedures, protocols, and analyses; 2) a paucity of studies involving the investigation of cortical activity; 3) aging-related alterations of cortical activation during balance tasks characterized by lower cortico-muscular coherence and increased allocation of attentional control to postural tasks in the elderly; and 4) EMG patterns characterized by delayed onset after perturbations, increased levels of activity, and greater levels of muscle co-activation in the elderly compared to younger adults. EMG and EEG recordings are valuable tools to monitor muscular and cortical activity during the performance of balance tasks. However, standardized protocols and analysis techniques should be agreed upon and shared by the scientific community to provide reliable and reproducible results. This will allow researchers to gain a comprehensive knowledge on the neurophysiological changes affecting static and dynamic balance in the elderly and will inform the design of rehabilitative and preventive interventions.

Utility of tremor electrophysiology studies

ObjectiveTo determine the utility of tremor electrophysiology testing in differentiating clinically indeterminate tremor due to organic, functional, and mixed tremor types. BackgroundPrior studies have shown that electrophysiological studies increase diagnostic sensitivity of tremor syndromes; however, few have examined mixed organic and functional tremors. MethodsPatients referred for tremor to the Mayo Clinic, Rochester movement disorders lab were consecutively selected and retrospectively reviewed. Surface electromyography (EMG) recordings of upper limb muscles were performed at rest, posture, with action and distractibility tasks. ResultsOf 116 patients, all were clinically described as having either a resting tremor, postural tremor, action tremor, postural and action tremor, mixed resting, postural, and action tremor, or nonspecific tremulousness. Based on electrophysiological features, patients were diagnosed with organic tremor (parkinsonian, essential, mixed, rubral, cerebellar, non-specific tremulousness), functional tremor, or mixed functional and organic tremors. The median disease duration at electrophysiological confirmation of diagnosis was shorter for functional tremor at 1.5 years (IQR 1–9.3), and organic tremor at 3 years (IQR 1–15), versus mixed organic and functional tremor at 11 years (IQR 2–15) (p = 0.0422). The electrophysiology study clarified the referral/clinical diagnosis in 87 patients (75%), 26 (29.5%) of whom had functional tremor, and 61 (70.1%) had organic tremor or mixed organic/functional tremor. Variability of tremor during electrophysiology testing was associated with a change in diagnosis (p = 0.0286). ConclusionOur findings show that electrophysiological assessment of tremor can be helpful in the clinical diagnosis of patients with both organic and functional tremor.

Practical Recording of Surface Electromyography for Application to Robotic Equipment

Practical Recording of Surface Electromyography for Application to Robotic Equipment

Frequency of Sleep Bruxism Behaviors in Healthy Young Adults over a Four-Night Recording Span in the Home Environment

Objectives: This study aimed to assess frequency and multiple-night variability of sleep bruxism (SB) as well as sleep-time masticatory muscle activities (sMMA) in the home environment in healthy young adults using a portable device that provides electrocardiographic (ECG) and surface electromyographic (EMG) recordings from the masticatory muscles. Methods: The study was performed on 27 subjects (11 males, 16 females; mean age 28.3 ± 1.7 years) selected from a sample of healthy young students. Evaluation was carried out for four nights to record data on masticatory muscle activities using a compact portable device that previously showed an excellent agreement with polysomnography (PSG) for the detection of SB events. The number of SB episodes per sleep hour (bruxism index), and the number of tonic, phasic and mixed sMMA events per hour were assessed. A descriptive evaluation of the frequency of each condition was performed on all individuals, and gender comparison was investigated. Results: Mean sleep duration over the four recording nights was 7 ± 1.3 h. The average SB index was 3.6 ± 1.2. Most of the sMMA were tonic (49.9%) and phasic (44.1%). An ANOVA test showed the absence of significant differences between the four nights. No significant gender differences were detected for the SB index, phasic or tonic contractions; conversely, gender differences were detected for mixed sMMA events (p &lt; 0.05). Conclusion: This investigation supports the concept that sMMA events are quite frequent in healthy adults. Differences over the four-night recording span were not significant. These data could be compared to subjects with underlying conditions that may lead to an additive bruxism activity and possible clinical consequences.

Contribution of Trunk Muscles to Upright Sitting with Segmental Support in Children with Spinal Cord Injury.

To investigate and compare trunk control and muscle activation during uncompensated sitting in children with and without spinal cord injury (SCI). Static sitting trunk control in ten typically developing (TD) children (5 females, 5 males, mean (SD) age of 6 (2)y) and 26 children with SCI (9 females, 17 males, 5(2)y) was assessed and compared using the Segmental Assessment of Trunk Control (SATCo) test while recording surface electromyography (EMG) from trunk muscles. The SCI group scored significantly lower on the SATCo compared to the TD group. The SCI group produced significantly higher thoracic-paraspinal activation at the lower-ribs, and, below-ribs support levels, and rectus-abdominus activation at below-ribs, pelvis, and no-support levels than the TD group. The SCI group produced significantly higher lumbar-paraspinal activation at inferior-scapula and no-support levels. Children with SCI demonstrated impaired trunk control with the ability to activate trunk muscles above and below the injury level.

Recurrent aspiration pneumonia precipitated by obstructive sleep apnea

ObjectiveThe clearance of the pharynx by deglutition and the respiratory phase patterns associated with deglutition are important in protecting airways and lungs against aspiration. The deglutition and respiratory phase patterns during sleep in patients (without swallowing disorders while awake) with obstructive sleep apnea (OSA) precipitating recurrent intractable aspiration pneumonia were investigated. MethodsAfter videoendoscopic and videofluorographic examinations of swallowing showed subjects had no swallowing disorders while awake, two adults with recurrent intractable aspiration pneumonia precipitated by severe OSA were examined via time-matched digital recordings of polysomnography and surface electromyography of the muscles (thyrohyoid and suprahyoid muscles) related to swallowing and compared with the same patients before and under CPAP therapy. ResultsCPAP therapy cured recurrent intractable aspiration pneumonia. Swallows following and/or followed by inspiration (uncoordinated deglutition with respiration), which were frequently observed before CPAP therapy, were markedly reduced under CPAP therapy. On the other hand, swallows following and/or followed by expiration (coordinated deglutition with respiration) markedly increased under CPAP therapy. Deglutition was related to the sleep stage. The deeper the sleep stage, the lower the deglutition frequency. Before and under CPAP therapy, swallowing was infrequent and absent for long periods. However, respiratory phase patterns associated with sleep-related deglutition in patients with OSA under CPAP therapy markedly improved. ConclusionsIn patients (without swallowing disorders while awake) with OSA precipitating recurrent intractable aspiration pneumonia, the high rate of uncoordinated deglutition with respiration (swallows following and/or followed by inspiration) during sleep were markedly reduced and the rate of coordinated deglutition with respiration (swallows following and/or followed by expiration) was markedly increased under CPAP therapy.Sleep-related deglutition and respiratory phase patterns are likely to adversely influence aspiration pneumonia in patients with OSA. CPAP therapy improved not only apnea-hypopnea during sleep and sleep quality but also sleep-related deglutition, especially respiratory phase patterns associated with deglutition in patients with OSA. CPAP therapy may decrease the risk of aspiration and greatly improve aspiration-related diseases such as aspiration pneumonia.

Sustained fatigue assessment during isometric exercises with time-domain near infrared spectroscopy and surface electromyography signals.

The effect of sustained fatigue during an upper limb isometric exercise is presented to investigate a group of healthy subjects with simultaneous time-domain (TD) NIRS and surface electromyography (sEMG) recordings on the deltoid lateralis muscle. The aim of the work was to understand which TD-NIRS parameters can be used as descriptors for sustained muscular fatigue, focusing on the slow phase of this process and using median frequency (MF) computed from sEMG as gold standard measure. It was found that oxygen saturation and deoxy-hemoglobin are slightly better descriptors of sustained fatigue, than oxy-hemoglobin, since they showed a higher correlation with MF, while total-hemoglobin correlation with MF was lower.

Muscles from the same muscle group do not necessarily share common drive: evidence from the human triceps surae.

It has been proposed that movements are produced through groups of muscles, or motor modules, activated by common neural commands. However, the neural origin of motor modules is still debated. Here, we used complementary approaches to determine: 1) whether three muscles of the same muscle group [soleus, gastrocnemius medialis (GM), and gastrocnemius lateralis (GL)] are activated by a common neural drive, and 2) whether the neural drive to GM and GL could be differentially modified by altering the mechanical requirements of the task. Eighteen human participants performed an isometric standing heel raise and submaximal isometric plantarflexions (10%, 30%, and 50% of maximal effort). High-density surface electromyography recordings were decomposed into motor unit action potentials and coherence analysis was applied on the motor unit spike trains. We identified strong common drive to each muscle but minimal common drive between the muscles. Further, large between-muscle differences were observed during the isometric plantarflexions, such as a delayed recruitment time of GL compared with GM and soleus motor units and opposite time-dependent changes in the estimates of neural drive to muscles during the torque plateau. Finally, the feet position adopted during the heel-raise task (neutral vs. internally rotated) affected only the GL neural drive with no change for GM. These results provide conclusive evidence that not all anatomically defined synergist muscles are controlled by strong common neural drive. Independent drive to some muscles from the same muscle group may allow for more flexible control to comply with secondary goals such as joint stabilization.NEW & NOTEWORTHY In this study, we demonstrated that the three muscles composing the human triceps surae share minimal common drive during isometric contractions. Our results suggest that reducing the number of effectively controlled degrees of freedom may not always be the strategy used by the central nervous system to control movements. Independent control of some, but not all, synergist muscles may allow for more flexible control to comply with secondary goals (e.g., joint stabilization).

Individual differences in the neural strategies to control the lateral and medial head of the quadriceps during a mechanically constrained task.

The interindividual variability in the neural drive sent from the spinal cord to muscles is largely unknown, even during highly constrained motor tasks. Here, we investigated individual differences in the strength of neural drive received by the vastus lateralis (VL) and vastus medialis (VM) during an isometric task. We also assessed the proportion of common neural drive within and between these muscles. Twenty-two participants performed a series of submaximal isometric knee extensions at 25% of their peak torque. High-density surface electromyography recordings were decomposed into motor unit action potentials. Coherence analyses were applied on the motor unit spike trains to assess the degree of neural drive that was shared between motor neurons. Six participants were retested ∼20 mo after the first session. The distribution of the strength of neural drive between VL and VM varied between participants and was correlated with the distribution of normalized interference electromyography (EMG) signals (r > 0.56). The level of within- and between-muscle coherence varied across individuals, with a significant positive correlation between these two outcomes (VL: r = 0.48; VM: r = 0.58). We also observed a large interindividual variability in the proportion of muscle-specific drive, that is, the drive unique to each muscle (VL range: 6%-83%, VM range: 6%-86%). All the outcome measures were robust across sessions, providing evidence that the individual differences did not depend solely on the variability of the measures. Together, these results demonstrate that the neural strategies to control the VL and VM muscles widely vary across individuals, even during a constrained task.NEW & NOTEWORTHY We observed that the distribution of the strength of neural drive between the vastus lateralis and vastus medialis during a single-joint isometric task varied across participants. Also, we observed that the proportion of neural drive that was shared within and between these muscles also varied across participants. These results provide evidence that the neural strategies to control the vastus lateralis and vastus medialis muscles widely vary across individuals, even during a mechanically constrained task.

Effect of the sEMG electrode (re)placement and feature set size on the hand movement recognition

Repositioning of recording electrode array across repeated electromyography measurements may result in a displacement error in hand movement classification systems.In order to examine if the classifier re-training could reach satisfactory results when electrode array is translated along or rotated around subject’s forearm for varying number of features, we recorded surface electromyography signals in 10 healthy volunteers for three types of grasp and 6 wrist movements. For feature extraction we applied principal component analysis and the feature set size varied from one to 8 principal components. We compared results of re-trained classifier with results from leave-one-out cross-validation classification procedure for three classifiers: LDA (Linear Discriminant Analysis), QDA (Quadratic Discriminant Analysis), and ANN (Artificial Neural Network).Our results showed that there was no significant difference in classification accuracy when the array electrode was repositioned indicating successful classification re-training and optimal feature set selection. The results also indicate expectedly that the number of principal components plays a key role for acceptable classification accuracy ∼90%. For the largest dataset (9 hand movements), LDA and QDA outperformed ANN, while for three grasping movements ANN showed promising results. Interestingly, we showed that interaction between electrode array position and the feature set size is not statistically significant.This study emphasizes the importance of testing the interaction of factors that influence classification accuracy and classifier selection altogether with their impact independently in order to establish guiding principles for design of hand movement recognition system.Data recorded for this study are stored on Zenodo repository (doi: https://doi.org/10.5281/zenodo.4039550).

Timing of the Sense of Volition in Patients With Schizophrenia.

Schizophrenic patients often do not have the sense that they direct their own movements or author their own thoughts (passivity phenomena). As willing must precede movement to be causal and thus generate the sense of agency, it is possible that the timing between the senses of willing and movement is shortened in schizophrenia. We tested the subjective perception of this time interval in patients with schizophrenia using a method based on Libet’s paradigm, in which subjects specify a time W – the time of willing a movement – and a time M – the time that movement occurred. Patients with schizophrenia and healthy volunteers made voluntary movements at times of their own choice while looking at a fast-rotating clock on a computer screen and reported when their movements were willed and made. We recorded surface electromyography to determine the time of actual movement, and electroencephalography to record brain potentials associated with movement. Results showed a significantly reduced interval between the reported M and W in patients with respect to the healthy volunteers (p < 0.05). Specifically, patients did not report a significant difference in the timing of W at 19 ms prior to movement onset and M at 7.4 ms prior to movement onset (p > 0.05), while the control group experienced a time W at 100 ms prior to movement onset and this differed significantly from their time M at 19 ms prior to movement onset (p < 0.01). These results suggest that patients with schizophrenia do have an altered timing of awareness of action – or an impaired judgment of the sequence of events – and that this might be etiologic in the development of the abnormal sense of agency.

A novel physiologic marker of bulbar motor involvement in amyotrophic lateral sclerosis: Jaw muscle synergy

ObjectiveTo identify a novel physiologic marker of bulbar motor involvement in amyotrophic lateral sclerosis (ALS) based on jaw muscle synergies. MethodsMuscle synergies were extracted from the surface electromyographic recordings of five jaw muscles during speech in 11 individuals at the prodromal or symptomatic stages of bulbar ALS and 10 neurologically-healthy controls, using non-negative matrix factorization. The disrupted muscle synergies in ALS were identified; their efficacy in differentiating individuals with ALS from healthy controls and relation to the previously-reported kinematic and functional speech deficits were determined. ResultsAn antagonist synergy (i.e., masseter × digastric) was significantly disrupted in ALS, which differentiated individuals with ALS from healthy controls with 82% sensitivity and 90% specificity. Such a disruption occurred prodromally and was associated with slowed jaw movement and reduced speaking rate across the range of severity. ConclusionsThe disruption of jaw antagonist synergy in ALS likely reflects the impact of impaired neural drive on the coordinative functioning of bulbar muscles, which may be used to assess bulbar motor involvement. SignificanceJaw antagonist synergy shows promise as a novel physiologic marker of bulbar motor involvement in ALS, which has the potential to serve as a quantitative measurement tool for bulbar assessment.

Comparing Muscle Activity and Spine Shape in Various Sitting Styles

Lower back pain is experienced by approximately 70% of the world's population, contributing to the worldwide burden of disease. Americans experience lower back pain at an estimated economic cost of $560–$635 billion. One contributing factor for back pain is posture, and more particularly, lack of awareness of dysfunctional posture. For example, many people sit in a slouched or forward-bent position, exacerbated by poor ergonomics while sitting or extended use of handheld digital devices while standing, such as looking down at a smartphone for long periods of time. This report describes a stacksitting technique that is one of the components of the Gokhale Method® for healthy, relaxed sitting and increased awareness of posture. The stacksitting process is illustrated with a case study, where the shape of the spine and the muscle activity are analyzed in parallel during three sitting styles: slouching, arched, and stacksitting. The spine curvature was characterized by the Gokhale SpineTracker™ wearable, which consists of five sensor units attached along the subjects' spines that are used to plot the spinal curve on a digital device such as a smartphone, tablet, or computer. Surface electromyographic (SEMG) recordings were made from the right upper trapezius, left upper trapezius, right midback, and left midback with a second device (Myoscan Pro sensors recorded with Biograph Procomp Infinity) while participants were seated in three postures: a slouched (forward-bent) position, an upright arched position, and an upright stacksitting position as trained by a Gokhale Method teacher. The case observations showed no significant difference in trapezius SEMG activity during each of the three positions. There was a slight increase in SEMG activity of the midback during stacksitting (1.1 μV) as compared with when slouched (0.64 μV), and a significant increase in SEMG activity when sitting arched (4.9 μV). As expected, the spinal activity tracking device showed significant straightening of the lower spine during the stacksitting position as compared with the slouched and arched positions. The observations suggest that the stacksitting position can be taught to others in a way that allows the vertebrae to be parallel to each other with very low levels of corresponding muscle activity. In contrast, sitting in an arched or slouched position could increase asymmetrical pressure on the disks, contributing to vertebral wedging, which could also contribute to spinal disk bulging and eventual back injury. The observations suggest that proper coaching may foster a stacksitting position of the spine, which could foster a healthier posture than slouched or arched spinal positions.

Dry Epidermal Electrodes Can Provide Long-Term High Fidelity Electromyography for Limited Dynamic Lower Limb Movements.

Due to the limitations of standard wet Silver/Silver Chloride (Ag/AgCl) hydrogel electrodes and the growing demand for long-term high fidelity surface electromyography (EMG) recording, dry epidermal electrodes are of great interest. Evaluating the usability and signal fidelity of dry epidermal electrodes could help determine the extent of potential applications using EMG electrodes. We collected EMG signals over eight days from the right rectus femoris of seven subjects using single-use dry epidermal electrodes and traditional Ag/AgCl electrodes while covered and uncovered during dynamic movements (leg extension, sit-to-stand, and treadmill walking at 0.75 m/s and 1.30 m/s). We quantified signal fidelity using signal-to-noise ratio (SNR); signal-to-motion ratio (SMR); and a metric we previously developed, the Signal Quality Index, which considers that better EMG signal quality requires both good signal-to-noise ratio and good signal-to-motion ratio. Wear patterns over the eight days degraded EMG signal quality. Uncovered epidermal electrodes that remained intact and maintained good adhesion to the skin had signal-to-noise ratios, signal-to-motion ratios, and Signal Quality Index values that were above the acceptable thresholds for limited dynamic lower limb movements (leg extension and sit-to-stand). This indicated that dry epidermal electrodes could provide good signal quality across all subjects for five days for these movements. For walking, the signal-to-noise ratios of the uncovered epidermal electrodes were still above the acceptable threshold, but signal-to-motion ratios and the Signal Quality Index values were far below the acceptable thresholds. The signal quality of the epidermal electrodes that showed no visible wear was stable over five days. As expected, covering the epidermal electrodes improved signal quality, but only for limited dynamic lower limb movements. Overall, single-use dry epidermal electrodes were able to maintain high signal quality for long-term EMG recording during limited dynamic lower limb movements, but further improvement is needed to reduce motion artifacts for whole body dynamic movements such as walking.