Surface EMG Recordings Research Articles

T48. Hypersensitivity of the persistent inward current

Motor cortex controls movements but a sensitive mechanism called persistent inward current (PIC) at the spinal cord plays a major role in adjusting the strength. The PIC is subject to descending neuromodulatory systems but also peripheral sensory afferent activity. Hypersensitivity of PIC may cause spasms which are stimulation sensitive. We describe a 46-year old male patient who had frequent and severe but relatively short-lasting bouts of stimulus-sensitive spasms after a suspected myelitis 10 years earlier. Stiff person syndrome and channelopathy of the muscle membrane were closed out. The spasms were very therapy resistant and intrathecal baclofen therapy was planned. A six-channel surface EMG recording of the right upper extremity (muscles: opponens pollicis, abductor digiti minimi, flexor carpi radialis, extensor carpi radialis, biceps brachii, triceps brachii) and repeated serial electrical stimuli of the radial nerve (30 Hz, 10 mA, 50 stimuli) and the median nerve at wrist (30 Hz, 6 mA, 50 stimuli) and vibratory stimulation of muscles. H-reflex measurements of the median nerve and needle EMG recordings during spasms. The serial, but not single, electrical stimuli caused activation of all the recorded muscles with different delay times ranging from 250 to 2500 ms. We saw augmentation of the responses with shortening delay times with repeated serial stimuli. Vibratory stimulation of the abductor digiti minimi muscle also caused activation of all the muscles recorded but with little augmentation. Vibratory stimulus of the biceps brachii muscle caused a very strong contraction of all the muscles recorded. This stimulus could not be repeated because of the strong response. The post-stimulus contractions were confined to the right upper extremity. EMG recorded with needle during spasms resembled normal muscle activity. When measuring the median nerve H-reflex, getting an M-response increased the amplitude of H-reflex. With this patient we could reveal typical behavior of PIC hypersensitivity to peripheral stimuli. The delay times of stimulus-sensitive motor reactions of different muscles varied but they were relatively long indicating the involvement of a neuromodulatory system (G-proteins, intracellular cascades) instead of the ionotrophic activation. The responses were confined to one extremity. Serial stimuli of both A beta and A alpha sensory axons caused reactions. We saw augmentation of the responses and shortening of the delay times with repeated serial or vibratory stimuli. The motor contractions lasted for a few minutes at most and were mainly tonic. Measurements of H-reflex showed that even a small muscle afferent activation caused an increased PIC response. EMG during spasms resembled normal muscle activation. With these features hypersensitivity of PIC can be diagnosed and differentiated from other syndromes with sustained motor symptoms.

Motor Unit Discharge Characteristics And Walking Performance Of Individuals With Multiple Sclerosis.

PURPOSE: To examine the associations between strength, force steadiness, and motor unit discharge characteristics of lower leg muscle with assessments of walking performance and disability status in individuals with multiple sclerosis (MS). METHODS: Persons with MS (n=23, 9 men, 53 ± 7 yrs) attended 1 to 3 evaluation sessions that were performed before, immediately after, and 4 wks after a clinical trial of neuromuscular electrical stimulation. Outcomes included 3 questionnaires (Patient Determined Disease Steps [PDDS], Modified Fatigue Impact Scale [MFIS], and MS Walking Scale-12 [MSWS-12]), 25-ft walk test, 6-min walk test, and maximal torque and force steadiness (10 and 20% MVC) for lower leg muscles. High-density surface EMG recordings were obtained from the tibialis anterior (TA), soleus (Sol), and medial gastrocnemius (MG) during the steady contractions and decomposed into discharge times of motor unit action potentials. RESULTS: Greater levels of self-reported disability (PDDS, MFIS, MSWS-12) were associated with less distance walked in 6 min and longer times to walk 25 ft. Mean interspike intervals (ISI) were 110 ± 23 ms and 102 ± 22 ms (10% and 20% MVC force, respectively) for TA motor units (n= 1,634), 138 ± 36 ms and 135 ± 34 ms for MG motor units (n=696), and 150 ± 33 ms and 145 ± 34 ms for Sol motor units (n = 902). A multiple regression model explained 40% (P=0.001) of the variance in 6-min distance with two predictor variables: mean ISI of MG (partial r = -0.48) and MVC dorsiflexor torque of the more affected leg (partial r=0.37). Similarly, another multiple regression model explained 47% of the variance (P<0.001) in 25-ft time with three predictor variables: mean ISI of soleus (partial r=0.51), MVC dorsiflexor torque of the more affected leg (partial r = -0.43), and force steadiness of the plantar flexors (partial r = 0.39). CONCLUSION: Moderate amounts of the variance in two walking tests for persons with MS were explained by mean discharge times of action potentials by motor units in plantar flexor muscles during steady submaximal contractions, the strength of the dorsiflexor muscles in the more affected leg, and force steadiness during an isometric contraction. This research was supported by the Eunice Kennedy Shriver National Institute of Child Health & Human Development of the NIH (R03HD079508).

M-wave normalization of EMG signal to investigate heat stress and fatigue

ObjectivesWe examined the extent to which peripheral changes affect EMG signal adjustments during repeated sprinting in temperate and hot conditions. DesignRandomised, crossover study. MethodsTen males performed 10×6-s ‘all-out’ cycling sprints (recovery=30s) in either a temperate (24°C/30%rH) or a hot (35°C/40%rH) environment with concomitant surface EMG recordings of the vastus lateralis (VL) and rectus femoris (RF). In addition, peak-to-peak M-wave amplitudes were obtained for each muscle after each sprint (i.e., 15s into recovery). ResultsFor both the VL and RF muscles RMS decreased across sprint repetitions (P<0.01), while significantly lower values for the VL (P=0.012), but not the RF (P=0.096), occurred in hot vs. temperate conditions. M-wave-normalised RMS for VL muscle decreased across sprint repetitions (P=0.030), with no condition or interaction effects (both P>0.621). M-wave-normalised RMS for the RF muscle was lower in the heat (P<0.034), with no significant sprint or interaction effects (both P>0.240). ConclusionsControlling for changes in maximal M-wave amplitude of the quadriceps muscles after each bout of a repeated cycling exercise in hot and temperate conditions allows researchers to account for fatigue- and/or heat-induced neural and peripheral adjustments.

Regionalization of the stretch reflex in the human vastus medialis

Regionalization of the stretch reflex, i.e. the notion that the activation of 1a afferents from a muscle region influences only the activation of motor units in the same region, has been demonstrated previously in animals but not in humans. Mechanical stretches applied to regions of vastus medialis as close as 10mm apart resulted in recruitment of motor units localized topographically with respect to the location of the mechanical stretch. Stretch reflexes are regionalized in the human vastus medialis. The human spinal cord has the neuromuscular circuitry to preferentially activate motoneurones innervating muscle fibres located in different regions of the vastus medialis. The localization of motor unit territories provides an anatomical basis to suggest that the CNS may have more independence in motor unit recruitment and control strategies than what was previously thought. In this study, we investigated whether the human spinal cord has the neuromuscular circuitry to independently activate motor units located in different regions of the vastus medialis. Mechanical taps were applied to multiple locations in the vastus medialis (VM) in nine healthy individuals. Regional responses within the muscle were observed using a grid of 5×13 surface EMG electrodes. The EMG amplitude was quantified for each channel, and a cluster of channels showing the largest activation was identified. The spatial location of the EMG response was quantified as the position of the channels in the cluster. In a subset of three participants, intramuscular recordings were performed simultaneously with the surface EMG recordings. Mechanical taps resulted in localized, discrete responses for each participant. The spatial location of the elicited responses was dependent on the location of the tap (P<0.001). Recordings with intramuscular electrodes confirmed the regional activation of the VM for different tap locations. Selective stimulation of 1a afferents localized in a region of the VM results in reflex recruitment of motor units in the same region. These findings suggest that the human spinal cord has the neuromuscular circuitry to modulate spatially the motoneuronal output to vastus medialis regions, which is a neuroanatomical prerequisite for regional activation.

Peak medial (but not lateral) hamstring activity is significantly lower during stance phase of running. An EMG investigation using a reduced gravity treadmill

The hamstrings are seen to work during late swing phase (presumably to decelerate the extending shank) then during stance phase (presumably stabilizing the knee and contributing to horizontal force production during propulsion) of running. A better understanding of this hamstring activation during running may contribute to injury prevention and performance enhancement (targeting the specific role via specific contraction mode). Twenty active adult males underwent surface EMG recordings of their medial and lateral hamstrings while running on a reduced gravity treadmill. Participants underwent 36 different conditions for combinations of 50%–100% altering bodyweight (10% increments) & 6–16km/h (2km/h increments, i.e.: 36 conditions) for a minimum of 6 strides of each leg (maximum 32). EMG was normalized to the peak value seen for each individual during any stride in any trial to describe relative activation levels during gait. Increasing running speed effected greater increases in EMG for all muscles than did altering bodyweight. Peak EMG for the lateral hamstrings during running trials was similar for both swing and stance phase whereas the medial hamstrings showed an approximate 20% reduction during stance compared to swing phase. It is suggested that the lateral hamstrings work equally hard during swing and stance phase however the medial hamstrings are loaded slightly less every stance phase. Likely this helps explain the higher incidence of lateral hamstring injury. Hamstring injury prevention and rehabilitation programs incorporating running should consider running speed as more potent stimulus for increasing hamstring muscle activation than impact loading.

Detection of Multiple Innervation Zones from Multi-Channel Surface EMG Recordings with Low Signal-to-Noise Ratio Using Graph-Cut Segmentation.

Knowledge of the location of muscle Innervation Zones (IZs) is important in many applications, e.g. for minimizing the quantity of injected botulinum toxin for the treatment of spasticity or for deciding on the type of episiotomy during child delivery. Surface EMG (sEMG) can be noninvasively recorded to assess physiological and morphological characteristics of contracting muscles. However, it is not often possible to record signals of high quality. Moreover, muscles could have multiple IZs, which should all be identified. We designed a fully-automatic algorithm based on the enhanced image Graph-Cut segmentation and morphological image processing methods to identify up to five IZs in 60-ms intervals of very-low to moderate quality sEMG signal detected with multi-channel electrodes (20 bipolar channels with Inter Electrode Distance (IED) of 5 mm). An anisotropic multilayered cylinder model was used to simulate 750 sEMG signals with signal-to-noise ratio ranging from -5 to 15 dB (using Gaussian noise) and in each 60-ms signal frame, 1 to 5 IZs were included. The micro- and macro- averaged performance indices were then reported for the proposed IZ detection algorithm. In the micro-averaging procedure, the number of True Positives, False Positives and False Negatives in each frame were summed up to generate cumulative measures. In the macro-averaging, on the other hand, precision and recall were calculated for each frame and their averages are used to determine F1-score. Overall, the micro (macro)-averaged sensitivity, precision and F1-score of the algorithm for IZ channel identification were 82.7% (87.5%), 92.9% (94.0%) and 87.5% (90.6%), respectively. For the correctly identified IZ locations, the average bias error was of 0.02±0.10 IED ratio. Also, the average absolute conduction velocity estimation error was 0.41±0.40 m/s for such frames. The sensitivity analysis including increasing IED and reducing interpolation coefficient for time samples was performed. Meanwhile, the effect of adding power-line interference and using other image interpolation methods on the deterioration of the performance of the proposed algorithm was investigated. The average running time of the proposed algorithm on each 60-ms sEMG frame was 25.5±8.9 (s) on an Intel dual-core 1.83 GHz CPU with 2 GB of RAM. The proposed algorithm correctly and precisely identified multiple IZs in each signal epoch in a wide range of signal quality and is thus a promising new offline tool for electrophysiological studies.

Human intersegmental reflexes from intercostal afferents to scalene muscles.

What is the central question of this study? The aim was to determine whether specific reflex connections operate between intercostal afferents and the scalene muscles in humans, and whether these connections operate after a clinically complete cervical spinal cord injury. What is the main finding and its importance? This is the first description of a short-latency inhibitory reflex connection between intercostal afferents from intercostal spaces to the scalene muscles in able-bodied participants. We suggest that this reflex is mediated by large-diameter afferents. This intercostal-to-scalene inhibitory reflex is absent after cervical spinal cord injury and may provide a way to monitor the progress of the injury. Short-latency intersegmental reflexes have been described for various respiratory muscles in animals. In humans, however, only short-latency reflex responses to phrenic nerve stimulation have been described. Here, we examined the reflex connections between intercostal afferents and scalene muscles in humans. Surface EMG recordings were made from scalene muscles bilaterally, in seven able-bodied participants and seven participants with motor- and sensory-complete cervical spinal cord injury (median 32years postinjury, range 5months to 44years). We recorded the reflex responses produced by stimulation of the eighth or tenth left intercostal nerve. A short-latency (∼38ms) inhibitory reflex was evident in able-bodied participants, in ipsilateral and contralateral scalene muscles. This bilateral intersegmental inhibitory reflex occurred in 46% of recordings at low stimulus intensities (at threetimes motor threshold). It was more frequent (in 75-85% of recordings) at higher stimulus intensities (six and nine times motor threshold), but onset latency (38±9ms, mean±SD) and the size of inhibition (23±10%) did not change with stimulus intensity. The reflex was absent in all participants with spinal cord injury. As the intercostal-to-scalene reflex did not increase with larger stimulus intensities, it is likely to be mediated by large-diameter intercostal muscle afferents. This is the first demonstration of an intercostal-to-scalene reflex. As the reflex requires intact spinal connections, it may be a useful marker for recovery of thoracic or cervical spinal injury.

Evaluation of pharyngeal muscle activity through nasopharyngeal surface electromyography in a cohort of dysphagic patients with acute ischaemic stroke.

SUMMARYOro-pharyngeal dysphagia is frequently present during the acute phase of stroke. The aim of the present study was to evaluate whether the recording of surface EMG using a nasopharyngeal (NP) electrode could be applied to evaluation of pharyngeal muscle activity in acute stroke patients and if this neurophysiological measure is related with clinical assessment of swallowing. Patients were examined and clinical severity was assessed with the National Institute of Health Stroke Scale (NIHSS) score; dysphagia was evaluated through bedside screening test using the Gugging Swallowing Scale (GUSS). Extension of the ischaemic lesion was measured by quantitative score, based on CT scan [Alberta Stroke Programme Early CT Score (ASPECTS)]. We analysed 70 patients; 50 were classified as dysphagic (Dys+), and 20 as non-dysphagic (Dys–). Each participant underwent a surface NP EMG recording performed with a NP electrode, made of a Teflon isolated steel catheter, with a length of 16 cm and a tip diameter of 1.5 mm. The electrode was inserted through the nasal cavity, rotated and positioned approximately 3 mm anteroinferior to the salpingo-palatine fold. At least four consecutive swallowing-induced EMG bursts were recorded and analysed for each participant. Swallowing always induced a repetitive, polyphasic burst of activation of the EMG, lasting around 0.25 to 1 sec, with an amplitude of around 100-600mV. Two parameters of the EMG potentials recorded with the NP electrode were analyzed: duration and amplitude. The duration of the EMG burst was increased in Dys+ patients with a statistically significant difference compared to Dys- patients (p < 0.001). The amplitude was slightly reduced in the Dys+ group, but statistically significant differences were not observed (p = 0,775). Nevertheless, the burst amplitude showed a significant inverse correlation with NIHSS [r(48) = –0.31; p < 0.05] and ASPECTS scores [r(48) = –0.27; p < 0.05], meaning that the burst amplitude progressively reduced with an increase of clinical severity (NIHSS) and topographic extension of brain lesions in CT (ASPECTS). These results suggest that NP recordings can give a semi-quantitative measure of swallowing difficulties originating from pharyngeal dysfunction, in fact, electromyographic findings suggest reduced pharyngeal motility.

Functional adaptation of the masticatory system to implant-supported mandibular overdentures.

The purpose of this study was to investigate the adaptation behavior of the stomatognathic system after immediate loading (24 to 72h after surgery) of two implants supporting mandibular overdentures, assessed on insertion and three months later. The study hypothesis was that insertion of the overdentures would significantly change masticatory performance and muscle activity at both times. Thirty subjects (nine female, mean age 69.64±11.81years; 21 male, mean age 68.67±7.41years) who participated in a randomized clinical trial were included in the study. Each patient was examined three times: (i) at baseline, after already having worn new dentures for three months (T1); (ii) immediately after insertion of the overdentures on the implants (T2); and (iii) after an adaptation period of three months (T3). Examination comprised assessment of masticatory performance with artificial test food (Optocal), and simultaneous bilateral surface EMG recording of the masseter and anterior temporalis muscles. Particle-size distribution (representative value X50 ), maximum muscle contraction (MVC), and total muscle work (TMW; area under the curve) were compared by use of repeated-measures analysis of variance (ANOVA). At T3, all measured variables (i.e., masticatory performance and muscle activity) were significantly different from those at T1. At T2, no significant changes were observed. The study hypothesis had to be rejected for T2 but accepted for T3. Functional rehabilitation (in terms of masticatory performance and masticatory muscle activity) does not occur immediately after immediate loading of two implants with mandibular overdentures, but requires a significant time for functional improvement.

Multi-channel intramuscular and surface EMG decomposition by convolutive blind source separation

Objective. The study of motor unit behavior has been classically performed by selective recording systems of muscle electrical activity (EMG signals) and decomposition algorithms able to discriminate between individual motor unit action potentials from multi-unit signals. In this study, we provide a general framework for the decomposition of multi-channel intramuscular and surface EMG signals and we extensively validate this approach with experimental recordings. Approach. First, we describe the conditions under which the assumptions of the convolutive blind separation model are satisfied. Second, we propose an approach of convolutive sphering of the observations followed by an iterative extraction of the sources. This approach is then validated using intramuscular signals recorded by novel multi-channel thin-film electrodes on the Abductor Digiti Minimi of the hand and Tibilias Anterior muscles, as well as on high-density surface EMG signals recorded by electrode grids on the First Dorsal Interosseous muscle. The validation was based on the comparison with the gold standard of manual decomposition (for intramuscular recordings) and on the two-source method (for comparison of intramuscular and surface EMG recordings) for the three human muscles and contraction forces of up to 90% MVC. Main results. The average number of common sources identified for the validation was 14 ± 7 (averaged across all trials and subjects and all comparisons), with a rate of agreement in their discharge timings of 92.8 ± 3.2%. The average Decomposability Index, calculated on the automatic decomposed signals, was 16.0 ± 2.2 (7.3–44.1). For comparison, the same index calculated on the manual decomposed signals was 15.0 ± 3.0 (6.3–76.6). Significance. These results show that the method provides a solid framework for the decomposition of multi-channel invasive and non-invasive EMG signals that allows the study of the behavior of a large number of concurrently active motor units.

ID 382 – Electrophysiological evaluation of emotional expressions in the facial transplantation patients

It is stated that motor and sensory innervations of transplanted face of patients often completed in 6–9 months in the literature. However, we observed clinically a problem in facial mimics and the expression of emotions. So it is aimed that, those performed face transplant, the evaluation of differences of emotional mimics in face from normal subjects. Three male patients who underwent a complete face transplant were studied. Surface EMG recordings have been recorded from patients and 10 healthy individuals. The expressions of emotions have been recorded with surface electrodes during basic emotions. An angry facial expression activity has been observed predominantly in the bottom face. Fair facial expression; there is distribution differences. Happiness facial expression; significant activity and amplitude differences was detected in the bottom. Hate facial expression; different amplitude distributions have been observed predominantly in the bottom. Surprise facial expression; an activity has been observed in the upper face with different amplitude. Sad facial expression; two of the patients distinct activity has been detected in the bottom. The expression of emotions are different from healthy individuals in patients. Face transplant patients have difficulties to express of emotions. TUBITAK Project Number: 113E182.

Acute Warm-up Effects in Submaximal Athletes: An EMG Study of Skilled Violinists.

Warm-up is commonly recommended for injury prevention and performance enhancement across all activities, yet this recommendation is not supported by evidence for repetitive submaximal activities such as instrumental music performance. The objective of this study is to quantify the effects of cardiovascular, core muscle, and musical warm-ups on muscle activity levels, musical performance, and subjective experience in skilled violinists. Fifty-five undergraduate, postgraduate, or professional violinists performed five randomly ordered 45-s musical excerpts of varying physical demands both before and after a randomly assigned 15-min, moderate-intensity cardiovascular, core muscle, musical (technical violin exercises), or inactive control warm-up protocol. Surface EMG data were obtained for 16 muscles of the trunk, shoulders, and right arm during each musical performance. Sound recording and perceived exertion (RPE) data were also obtained. Sound recordings were randomly ordered and rated for performance quality by blinded adjudicators. Questionnaire data regarding participant pain sites and fitness levels were used to stratify participants according to pain and fitness levels. Data were analyzed using two- and three-factor ANCOVA (surface EMG and sound recording) and Wilcoxon matched pairs tests (RPE). None of the three warm-up protocols had significant effects on muscle activity levels (P ≥ 0.10). Performance quality did not significantly increase (P ≥ 0.21). RPE significantly decreased (P < 0.05) after warm-up for each of the three experimental warm-ups; control condition RPE did not significantly decrease (P > 0.23). Acute physiological and musical benefits from cardiovascular, core muscle, and musical warm-ups in skilled violinists are limited to decreases in RPE. This investigation provides data from the performing arts in support of sports medical evidence suggesting that warm-up only effectively enhances maximal strength and power performance.

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).

Impaired regulation post-stroke of motor unit firing behavior during volitional relaxation of knee extensor torque assessed using high density surface EMG decomposition.

The purpose of this study was to use high density surface EMG recordings to quantify stroke-related abnormalities in motor unit firing behavior during repeated sub-maximal knee extensor contractions. A high density surface EMG system (sEMG) was used to record and extract single motor unit firing behavior in the vastus lateralis muscle of 6 individuals with chronic stroke and 8 controls during repeated sub-maximal isometric knee extension contractions. Paretic motor unit firing rates were increased with subsequent contractions (6.19±0.35 pps vs 7.89±0.66 pps, P <; 0.05) during task phases of torque decline as compared to controls (6.95±0.40 pps vs 6.68±0.41 pps). In addition, corresponding rates of torque decline were decreased for the paretic leg as compared to the non-paretic leg. These results suggest that regulation of declining forces may be impaired post stroke due to prolonged firing of paretic motor units.

Disturbed muscular adaptation and changed motor strategies in recurrent low back pain patients during stair walking after experimental back-muscle fatigue

Background: The majority of low back pain (LBP) patients experience no symptoms after 4 weeks but up to 70–80% will relapse within one year and up to 40% develops recurrent LBPand reduced functional capacity.Recurrent LBP thereby is a major cause of dysfunction, decreased quality of life and economical expenditures. The evidence on causality is generally low, but motor control is a potential factor linked with LBP. The trunk-muscle activity is affected by pain but the majority of the evidence is based on investigation of non-functional motor tasks. The transfer of results to functional and complex motor tasks is challenged, since the motor output is a result of the interaction between central and peripheral dynamic mechanisms. Experimental fatigue of the backmuscles in healthy and LBP patients affects the control of the trunk and the muscle activity is earlier affected in patients during exercising towards fatigue. Disturbed control of the muscular control can influence the development of LBP but the underlying mechanisms and consequences on motor control during motor tasks requiring motor planning and higher stability and dynamic force development remains unknown. Purpose: To explore the trunk muscle activity and motor task timing in healthy and recurrent LBP patients during stair ascend and descend before and after lumbarmuscle fatiguing. Methods: 45 participants (25 LBP) performed 10 concurrent ascend and descend steps before and after fatiguing the back extensors by repetitive dynamic exercises to exhaustion. 3 ascending and 3 descending gait phases were detected. The duration of the phases and changes in i-EMG activity from surface EMG-recordings of 3 back-, 3 abdominaland 2 gluteus-muscles before and after fatigue were calculated and compared by ANOVA statistics. Results: The duration of the step tasks were shorter in LBP patients before (P< 0.01) and after (P< 0.01) fatiguing the back extensors. Fatigue furthermore resulted in increased duration during phases with preparation of single-leg weightbearing (P< 0.001) and decreased during the weight bearing phases (P< 0.001). Back extensor fatigue resulted in increased back and abdominal muscle activity in healthy (P< 0.01) and unchanged muscle activity in LBP patients in most phases, but during the descend phase with single-legged weight bearing the activity remained unchanged in healthy and decreased in LBP patients (P< 0.001). Conclusion(s): Back extensor muscle fatigue resulted in increased trunk muscle activity in healthy and unchanged trunk muscle activity in LBP patients during stair stepping and the patients could be at higher risk of inappropriate load of potential painful structures. In phases with high stability demands the patients utilized movement strategies that in short-term might reduce the stability demands, but the long-term structural consequence is unknown. Furthermore it remains unknown if these strategies will affect recurrent LBP patients during other functional motor tasks and more research is needed to explore these questions. Implications: Affected control of the spine in high stability demands is important in evaluation of recurrent LBP patients. More research is needed to explore the basic mechanisms and the potential role of motor control during functional motor tasks in LBP development.

Influence of Lateral Dominance of Sight on the Quality of the Natural Locomotion Performance at the Senior Preschool Age

The article shows age-specific peculiarities of the formation of the asymmetry of visual perception and justifies the mechanisms of participation of the visual sensory system in the implementation of natural motor actions that contribute to the development of concepts of motor systems management, the development of the strategy of the typological approach to training and development of preschool children who demonstrate different types of lateral dominance. Experimental results were obtained using certified hardware. Recording of the surface EMG was performed using the “Neuro-Mvp” multipurpose computer system. Motor tasks under the control of binocular vision in the age of 5-6 years are implemented with the key role of the dominant eye. The narrowing of the visual field by means of closing the dominant eye during performance of a single manual action reduces the bioelectric activity of muscles due to the decrease in the maximum amplitude of the EMG signal, which indicates the reduction in the rate of muscles contraction. At the binocular method of sight, EMG of all studied muscle groups is characterized by the uniform bioelectric activity. When one is holding the “Flamingo” pose with closed eyes, disruption of the stability of the parameters of bioelectric activity takes place, which is manifested as appearing sharp bursts of the bioelectric activity in the EMG patterns. The sight space narrowing at closing the dominant eye leads to disruption of the bioelectric stability of postural muscles of the back and thigh. The sight space narrowing at closing the subdominant eye during holding the “Flamingo” pose leads to disruption of the bioelectric stability of postural muscles of the thigh.

A real-time, practical sensor fault-tolerant module for robust EMG pattern recognition.

BackgroundUnreliability of surface EMG recordings over time is a challenge for applying the EMG pattern recognition (PR)-controlled prostheses in clinical practice. Our previous study proposed a sensor fault-tolerant module (SFTM) by utilizing redundant information in multiple EMG signals. The SFTM consists of multiple sensor fault detectors and a self-recovery mechanism that can identify anomaly in EMG signals and remove the recordings of the disturbed signals from the input of the pattern classifier to recover the PR performance. While the proposed SFTM has shown great promise, the previous design is impractical. A practical SFTM has to be fast enough, lightweight, automatic, and robust under different conditions with or without disturbances.MethodsThis paper presented a real-time, practical SFTM towards robust EMG PR. A novel fast LDA retraining algorithm and a fully automatic sensor fault detector based on outlier detection were developed, which allowed the SFTM to promptly detect disturbances and recover the PR performance immediately. These components of SFTM were then integrated with the EMG PR module and tested on five able-bodied subjects and a transradial amputee in real-time for classifying multiple hand and wrist motions under different conditions with different disturbance types and levels.ResultsThe proposed fast LDA retraining algorithm significantly shortened the retraining time from nearly 1 s to less than 4 ms when tested on the embedded system prototype, which demonstrated the feasibility of a nearly “zero-delay” SFTM that is imperceptible to the users. The results of the real-time tests suggested that the SFTM was able to handle different types of disturbances investigated in this study and significantly improve the classification performance when one or multiple EMG signals were disturbed. In addition, the SFTM could also maintain the system’s classification performance when there was no disturbance.ConclusionsThis paper presented a real-time, lightweight, and automatic SFTM, which paved the way for reliable and robust EMG PR for prosthesis control.

Premovement Changes in Corticospinal Excitability of the Biceps Brachii are Not Different Between Arm Cycling and an Intensity-Matched Tonic Contraction.

The purpose of this study was to determine if supraspinal and/or spinal motoneuron excitability of the biceps brachii were differentially modulated before: 1) arm cycling and 2) an intensity-matched tonic contraction. Surface EMG recordings of motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs) were used to assess supraspinal and spinal motoneuron excitability, respectively. MEP amplitudes were larger and onset latencies shorter, before arm cycling and tonic contraction when compared with rest with no intent to move, but with no difference between motor outputs. CMEP amplitudes and onset latencies remained unchanged before cycling and tonic contraction compared with rest. Premovement enhancement of corticospinal excitability was due to an increase in supraspinal excitability that was not task-dependent. This suggests that a common neural drive is used to initiate both motor outputs with task-dependent changes in neural excitability only being evident once the motor outputs have begun.

Increased supernormality in patients with multiplet discharges: Evidence for a common pathophysiological mechanism behind multiplets and fasciculations

ObjectiveTo determine whether there is a relation between electrically evoked multiplet discharges (MDs) and motor axonal excitability properties. We hypothesized that electrically evoked MDs share their underlying pathophysiological mechanism with fasciculations. MethodsHigh-density surface EMG and motor nerve excitability recordings of the thenar muscles were performed in 22 patients with motor neuron disease (MND) in their differential diagnosis and who were referred for EMG examination. ResultsSupernormality (hyperexcitable phase following the refractory period) was significantly increased in patients with MDs (n=10) compared to patients without MDs (n=12) (25.5% vs 17.0%; p=0.02). Depolarizing threshold electrotonus differed significantly between both groups as well (TEdpeak, 76.6% vs 66.6%, p<0.01; TEd90-100ms, 51.7% vs 44.3%, p<0.01) ConclusionsOur findings imply that the same pathophysiological excitability changes are involved in generating MDs and fasciculations. Yet, MDs may be quantified more easily, and may be more specific for abnormal distal excitability than fasciculations, because fasciculations may originate along the motor axon as well as in the neuron cell body. SignificanceMDs are potentially useful as objective measure of increased distal axonal excitability at individual motor unit level and might complement clinical studies in MND.

Internal muscle activity imaging from multi-channel surface EMG recordings: a validation study.

The developed muscle activity imaging approach (MAI) was validated with surface EMG and intramuscular EMG signals simultaneously acquired from the biceps of a healthy male subject. 128 unipolar channels were employed for surface EMG measurement and one bipolar channel was employed for simultaneous intramuscular EMG measurement for the validation purpose. Ultrasound scans were also specifically performed to localize the location of the wire electrode inserted into the biceps. The surface EMG measurements, after noise filtering and signal decomposition, were used to reconstruct the internal muscle activities for the biceps by using the MAI approach. The locations of the reconstructed muscle activities were compared against the location of the wire electrode in the biceps identified from ultrasound images. Results demonstrate the feasibility and validity of the MAI approach in imaging internal muscle activities from multi-channel surface EMG recordings.