Surface EMG Recordings Research Articles

Automatic detection of motor unit innervation zones of the external anal sphincter by multichannel surface EMG

A method to detect automatically the location of innervation zones (IZs) from 16-channel surface EMG (sEMG) recordings from the external anal sphincter (EAS) muscle is presented in order to guide episiotomy during child delivery. The new algorithm (2DCorr) is applied to individual motor unit action potential (MUAP) templates and is based on bidimensional cross correlation between the interpolated image of each MUAP template and two images obtained by flipping upside-down (around a horizontal axis) and left–right (around a vertical axis) the original one. The method was tested on 640 simulated MUAP templates of the sphincter muscle and compared with previously developed algorithms (Radon Transform, RT; Template Match, TM). Experimental signals were detected from the EAS of 150 subjects using an intra-anal probe with 16 equally spaced circumferential electrodes. The results of the three algorithms were compared with the actual IZ location (simulated signal) and with IZ location provided by visual analysis (VA) (experimental signals). For simulated signals, the inter quartile error range (IQR) between the estimated and the actual locations of the IZ was 0.20, 0.23, 0.42, and 2.32 interelectrode distances (IED) for the VA, 2DCorr, RT and TM methods respectively.

Accuracy assessment of a surface electromyogram decomposition system in human first dorsal interosseus muscle

Objective. The aim of this study is to assess the accuracy of a surface electromyogram (sEMG) motor unit (MU) decomposition algorithm during low levels of muscle contraction. Approach. A two-source method was used to verify the accuracy of the sEMG decomposition system, by utilizing simultaneous intramuscular and surface EMG recordings from the human first dorsal interosseous muscle recorded during isometric trapezoidal force contractions. Spike trains from each recording type were decomposed independently utilizing two different algorithms, EMGlab and dEMG decomposition algorithms. The degree of agreement of the decomposed spike timings was assessed for three different segments of the EMG signals, corresponding to specified regions in the force task. A regression analysis was performed to examine whether certain properties of the sEMG and force signal can predict the decomposition accuracy. Main results. The average accuracy of successful decomposition among the 119 MUs that were common to both intramuscular and surface records was approximately 95%, and the accuracy was comparable between the different segments of the sEMG signals (i.e., force ramp-up versus steady state force versus combined). The regression function between the accuracy and properties of sEMG and force signals revealed that the signal-to-noise ratio of the action potential and stability in the action potential records were significant predictors of the surface decomposition accuracy. Significance. The outcomes of our study confirm the accuracy of the sEMG decomposition algorithm during low muscle contraction levels and provide confidence in the overall validity of the surface dEMG decomposition algorithm.

Simulation of surface EMG for the analysis of muscle activity during whole body vibratory stimulation

This study aims to reproduce the effect of motor-unit synchronization on surface EMG recordings during vibratory stimulation to highlight vibration evoked muscle activity. The authors intended to evaluate, through numerical simulations, the changes in surface EMG spectrum in muscles undergoing whole body vibration stimulation. In some specific bands, in fact, vibration induced motion artifacts are also typically present.In addition, authors meant to compare the simulated EMGs with respect to real recordings in order to discriminate the effect of synchronization of motor units discharges with vibration frequencies from motion artifacts.Computations were performed using a model derived from previous studies and modified to consider the effect of vibratory stimulus, the motor unit synchronization and the endplates-electrodes relative position on the EMG signal.Results revealed that, in particular conditions, synchronization of MUs’ discharge generates visible peaks at stimulation frequency and its harmonics. However, only a part of the total power of surface EMGs might be enclosed within artifacts related bands (±1Hz centered at the stimulation frequency and its superior harmonics) even in case of strong synchronization of motor units discharges with the vibratory stimulus.

Anterior Cruciate Ligament Reconstruction May Alter Muscle Activation Patterns of Knee Flexors

Reconstructing the ACL by using a graft from the hamstrings muscle group may impact the firing patterns of the ipsilateral knee flexors, as indicated by surface EMG recordings during open- and closed-chain exercises in athletes with a history of ACL reconstruction compared to healthy age- and gender-matched controls.

Hot ambient conditions shift the Force / EMG relationship

PurposeThis manuscript reports the data from two interventions on human subjects aiming to determine the effect of elevated core (HOT-core, study 1, 14 participants) and skin (HOT-skin, study 2, 11 participants) temperature on the force / EMG relationship.MethodsIn both studies, participant underwent an experimental trial and a control (CON) trial, in which maximal voluntary contractions (MVC) of the plantar flexors, surface EMG recordings of both the soleus and gastrocnemius medialis (GM), and electrical stimulation of the tibial nerve were performed to determine the percentage of voluntary activation (VA). During the HOT-core trial, rectal temperature was passively increased and then clamped at 39°C by adjusting the room temperature in the range of 46-50°C. During the HOT-skin trial, tests were performed in a temperate environment (~20°C) and skin temperature was locally affected by applying a cool or a hot pack during 1 min.ResultsHOT-core resulted in a decrease in MVC torque (−19%) and VA (−5%) (p < 0.05). HOT-skin did not induce any changes in MVC torque (−1%) or VA (+0%). However, the EMG activity (RMS) was decreased both in HOT-core (soleus −40%, GM −33%) and HOT-skin (soleus −10%, GM −13%), compared with CON (p < 0.05).ConclusionThe effect of skin temperature on EMG recordings may be attributed to both methodological and physiological factors. Hot ambient conditions shift the Torque / EMG relationship to the left, with the decrement in torque induced with passive hyperthermia lower than the decrement in EMG.

Effects of motor skill learning on reciprocal inhibition

Learning a skilled movement is associated with more efficient use of subcortical motor circuits which can coordinate features of the movements such as the timing and patterns of activation of different muscles. Learning a motor skill could strengthen spinal interneuron circuits that facilitate the movement. We hypothesized that learning a simple, alternating movement would produce changes in spinal circuits that mediate reciprocal inhibition between antagonist muscles. Sixteen healthy adult subjects were trained to perform a wrist flexion and extension task to control the movement of a cursor between targets appearing on a computer display. The goal of the task was to hit the targets. Subjects practiced for 15 minutes daily until reaching the acquisition criterion. Surface EMG recordings from wrist flexor and extensor muscles showed reduced co-contraction during acquisition of the task. Compared to the initial session, in the final session short-latency reciprocal inhibition was enhanced during the late-extension phase in the final session. This phase-dependent increase in short-latency reciprocal inhibition is likely to facilitate switching activation between wrist antagonistic muscles. Learning a motor skill can produce alterations in spinal reflex circuits that facilitate the desired movement.

Quality of Residual Neuromuscular Control and Functional Deficits in Patients with Spinal Cord Injury

Study Design: Prospective cohort study.Objective: This study examined the relationship between motor control and clinical function outcomes after spinal cord injury (SCI).Setting: University of Louisville, Louisville, KY, USA.Materials: Eleven persons with SCI and 5 non-injured subjects were included in this study.Methods: The ASIA Impairment Scale (AIS) was used to categorize injury level and severity. Multi-muscle, surface EMG (sEMG) recording, was carried out using a protocol of reflex and volitional motor tasks and was analyzed using a vector-based tool that calculates index values that relate a distribution of multi-muscle activation pattern of each SCI subject to the prototype obtained from non-injured subject group and presents overall magnitude as a separate value. Functional Independence Measure motor sub-scale, Spinal Cord Injury Independence Measure (SCIM-III), and Walking Index for Spinal Cord Injury (WISCI) scale scores were compared to neurophysiological parameters.Results: AIS category and injury level correlated significantly with the WISCI and SCIM mobility sub-scales. sEMG-derived parameters were significantly correlated with SCIM and WISCI scores but only for examinations carried out 48 or more days post-injury.Conclusion: These results supported the hypothesis that clinically relevant function after SCI is related to the degree to which functional organization within the central nervous system is disrupted. Further, due likely to the constraints placed on the expression of functional ability by early post-injury immobilization and hospitalization, neurophysiological assessment of motor function may provide better sensitivity and reliability than can be obtained using the clinical function scales examined here within the early period after injury.

Abnormal loading of the major joints in knee osteoarthritis and the response to knee replacement

Knee osteoarthritis is common and patients frequently complain that they are ‘overloading’ the joints of the opposite leg when they walk. However, it is unknown whether moments or co-contractions are abnormal in the unaffected joints of patients with single joint knee osteoarthritis, or how they change following treatment of the affected knee. Twenty patients with single joint medial compartment knee osteoarthritis were compared to 20 asymptomatic control subjects. Gait analysis was performed for normal level gait and surface EMG recordings of the medial and lateral quadriceps and hamstrings were used to investigate co-contraction. Patients were followed up 12 months post-operatively and the analysis was repeated. Results are presented for the first 14 patients who have attended follow-up. Pre-operatively, adduction moment impulses were elevated at both knees and the contra-lateral hip compared to controls. Co-contraction of hamstrings and quadriceps was elevated bilaterally. Post-operatively, moment waveforms returned to near-normal levels at the affected knee and co-contraction fell in the majority of patients. However, abnormalities persisted in the contra-lateral limb with partial or no recovery of both moment waveforms and co-contraction in the majority. Patients with knee osteoarthritis do experience abnormal loads of their major weight bearing joints bilaterally, and abnormalities persist despite treatment of the affected limb. Further treatment may be required if we are to protect the other major joints following joint arthroplasty.

Multiplet discharges after electrical stimulation: New evidence for distal excitability changes in motor neuron disease

We hypothesized that action potentials evoked by distal stimulation might trigger ectopic activity (multiplet discharges, MDs). By studying MDs, we investigated the involvement of the axonal part of the peripheral motor neuron in amyotrophic lateral sclerosis (ALS) and progressive muscular atrophy (PMA). We performed stimulated high-density surface EMG recordings of the thenar muscles in 10 ALS/PMA patients, five recordings per patient over a three-month period. Furthermore, motor unit number estimates (MUNE) and ALSFRS-R scores were obtained in sessions 1 and 5. MDs were found in all patients, in 21% of the sampled motor units, and in response to 2.4% of the stimulations. The interspike interval range of the MD components was 2.9-6.5 ms, which is compatible only with a distal MD origin. The number of MDs, as percentage of the number of applied stimuli, was correlated with a decline in ALSFRS-R (r =0.80, p =0.006) and MUNE (r =0.72, p =0.02). In conclusion, MDs can be elicited with electrical stimulation in ALS and PMA patients. Analysis of MD characteristics provides further indications for pathophysiological excitability changes in the most distal part of the motor neuron. MDs are associated with clinical deterioration.

Dynamic equinus with hindfoot valgus in children with hemiplegia

In children with hemiplegia, it is important to distinguish between equinus with hindfoot varus (equinovarus) or valgus (equinovalgus). Premature onset of medial gastrocnemius (GM) EMG in individuals with equinus is well documented. Premature onset of Peroneus longus (PL) EMG has been described in neurologically impaired adults with equinovalgus, but not in children. Our aim was to record the onset of PL and GM activity on the hemiplegic side of children with equinovalgus deformity.Fifteen children GMFCS 1 (3.8yrs±2) with hemiplegia had a goniometric assessment of passive ankle range of motion and assessment of ankle function from video and surface EMG recording during gait. The clinical and video observations were used to determine the equinovalgus, as defined by Wren, at initial contact (IC). The premature onset of muscle activity was normalised as a swing (SW) percentage prior to IC of the following stance (ST). A paired T-test compared the onset of muscle activity between PL and GM.The ankle passive dorsiflexion was 13°±12° (hemiplegic side) versus 18°±10° (non-involved side) (p<0.05). For the non-involved limb, the onset of GM activity was at 14% of the gait cycle (midstance), the onset of PL activity was at 19% (p<0.05). For the hemiplegic limb with equinovalgus, there was a premature onset activity of PL (−24%) and GM(−8%) (p<0.001).On the non involved side, the onset of PL activity occurred, as in adults, after the onset of GM activity, during ST. On the hemiplegic side, there was no triceps surae contracture and the onset of PL activity occurred prior to the onset of GM activity, during terminal SW. This study confirmed the overactivity of PL in hemiplegic children with equinovalgus.

The effect of thoracic spine high-velocity low-amplitude thrust manipulation on myoelectric activity of the lower trapezius and posterior deltoid muscles during treadmill walking

Objectives To investigate the effect of thoracic spine thrust manipulation on the EMG activity of posterior deltoid and lower trapezius during treadmill walking. Methods Volunteers ( n = 40; 19 males and 21 females) were randomly assigned to a ‘sham ultrasound’ control group ( n = 20) or a thoracic spine high-velocity thrust (HVLAT) manipulation group ( n = 20). Surface EMG recordings were collected from the right posterior deltoid and lower trapezius muscles whilst participants walked on a treadmill for 2 min, at 2.8 mph, both prior to and immediately post-intervention. EMG recordings were analysed by evaluating the difference of integral values for pre and post data using repeated measures ANOVA. Results Both control (sham ultrasound) and experimental groups (HVLAT) exhibited small non-significant reductions in post-intervention EMG activity of lower trapezius ( p = 0.201) and a significant reduction in posterior deltoid ( p = 0.003) during treadmill walking. No significant difference was found in the integrated EMG (IEMG) power between control and experimental group in either the ‘before’ or ‘after’ measurements for both target muscles. Conclusions Manipulation of the thoracic spine does not significantly alter the myoelectric activity of lower trapezius and posterior deltoid muscles during treadmill walking.

EMG of the hip adductor muscles in six clinical examination tests

ObjectivesTo assess activation of muscles of hip adduction using EMG and force analysis during standard clinical tests, and compare athletes with and without a prior history of groin pain. Study designControlled laboratory study. Participants21 male athletes from an elite junior soccer program. Main outcome measuresBilateral surface EMG recordings of the adductor magnus, adductor longus, gracilis and pectineus as well as a unilateral fine-wire EMG of the pectineus were made during isometric holds in six clinical examination tests. A load cell was used to measure force data. ResultsTest type was a significant factor in the EMG output for all four muscles (all muscles p < 0.01). EMG activation was highest in Hips 0 or Hips 45 for adductor magnus, adductor longus and gracilis. EMG activation for pectineus was highest in Hips 90. Injury history was a significant factor in the EMG output for the adductor longus (p < 0.05), pectineus (p < 0.01) and gracilis (p < 0.01) but not adductor magnus. For force data, clinical test type was a significant factor (p < 0.01) with Hips 0 being significantly stronger than Hips 45, Hips 90 and Side lay. BMI (body mass index) was a significant factor (p < 0.01) for producing a higher force. All other factors had no significant effect on the force outputs. ConclusionsHip adduction strength assessment is best measured at hips 0 (which produced most force) or 45° flexion (which generally gave the highest EMG output). Muscle EMG varied significantly with clinical test position. Athletes with previous groin injury had a significant fall in some EMG outputs.

상완이두근의 등장성 운동시 근피로인자로서 표면근전도의 저주파수대역 선정에 관한 연구

, 2011)Muscle fatigue is characterized as a progressive increase in discomfort arising from the active muscle at moderate load levels are maintained. The median frequency is the most commonly used as a parameter to describe muscle fatigue. However, the estimate of the median frequency is difficult to indicate muscle fatigue because of its high standard deviation and instability.This paper investigates the power changes of the appropriate low frequency band as a fatigue parameter in EMG during isotonic exercise. To select the appropriate band, linear regression lines are employed to calculate the slopes and the coefficient of determination. Three females and seven males volunteered to participate in surface EMG recordings placed on the biceps brachii and each recording experiment continued until their exhaustion. The results of experiment shows that the power changes of the selected low frequency band (15∼45 Hz) have linear slopes and high determinant coefficients. Therefore, this fatiguing parameter using the power changes of the low frequency band is valid to measure the state of muscular fatigue.

A new approach for detecting and analyzing cutaneous reflexes during locomotion

During human walking, due to their small amplitude, individual cutaneous reflex responses are difficult to detect in surface EMG recordings. In this study, we present a new algorithm to automatically detect individual cutaneous reflex responses and to extract their corresponding onset latency, amplitude, duration, and sign. To discriminate reflex responses from the intrinsic variability of the background EMG, each stimulated cycle is compared with 10 adjacent nonstimulated cycles, looking for consistent differences. In the first 200 ms after stimulation, reflex responses are detected when ≥ 9/10 of these differences are either positive or negative. This approach does not require amplitude thresholds or fixed time windows for reflex detection. To reduce false detections, a postprocessing step selects 50 nonstimulated cycles randomly, processes them through the algorithm as stimulated cycles, and establishes a minimal reflex duration criterion that it then used to validate the detected responses. Validated responses from an entire test session are then reported on a colormap (reflex activity map) from which specific responses can be identified and quantified. The new method was validated in ten participants, three cutaneous nerves, and two protocols (phase modulation and recruitment curves). Compared with the classical method, the new algorithm showed better performance in terms of detection accuracy, specificity, and reliability. Although tested here to evaluate cutaneous reflexes during human walking, the simplicity of this method is such that it could easily be used with other reflexes, signals, and preparations.

Motor unit number index (MUNIX): A novel neurophysiological technique to follow disease progression in amyotrophic lateral sclerosis

Motor unit number estimation techniques in amyotrophic lateral sclerosis (ALS) patients are technically challenging and time-consuming. The Motor Unit Number Index (MUNIX) is a novel technique based on surface-EMG recordings and requires only 3-5 minutes per muscle. The objective was to explore the feasibility of longitudinal MUNIX measurements in ALS patients. In seven patients enrolled in a clinical trial, eight muscles were studied every 2 months for up to 15 months in addition to the revised ALS-functional rating scale, slow vital capacity, and compound muscle action potentials. The method was well tolerated and easy to perform. Initial MUNIX measures were significantly reduced compared to controls (487 +/- 194 vs. 1459 +/- 113; P < 0.001). Relative drop from baseline paralleled the clinical course and was greater than the drop of other markers of disease progression. MUNIX measurements in multiple muscles are suitable for serial neurophysiologic investigations in ALS. Further longitudinal data are needed for reliability validation.

Long-lasting involuntary motor activity after spinal cord injury

Study DesignProspective cohort studyObjectiveThis study was designed to neurophysiologically characterize spinal motor activity during recovery from spinal cord injury (SCI).SettingUniversity of Louisville, Louisville, Kentucky, USA.MaterialTwenty five consecutive acute SCI admissions were recruited for this study.MethodsThe American Spinal Injury Association Impairment Scale (AIS) was used to categorize injury level and severity at onset. Surface EMG recording, was carried out initially between the day of admission and 17 days post onset (6.0 ± 4.3, mean ± SD days). Follow-up recordings were performed for up to 9 months after injury. Initial AIS distribution was: 7 AIS-A; 3 AIS-B; 2 AIS-C; 13 AIS-D.ResultsTwelve subjects (48%) showed long-duration involuntary motor unit activation during relaxation. This activity was seen on initial examination in nine and on follow-up by three months post-injury in three others. It was seen in muscles innervated from the injury zone in 11 and caudal to the lesion in 9 subjects. This activity was independent of the presence or absence of tendon reflexes and the ability to volitionally suppress plantar stimulation elicited reflex withdrawal.ConclusionsThe form of involuntary activity described here is the likely result of the altered balance of excitation and inhibition reaching spinal motor neurons due to the loss of inhibitory interneurons or their reduced activation by damaged supraspinal drive and the synaptic reorganization that follows SCI. As such, this activity may be useful for monitoring the effects of neuroprotective and restorative intervention strategies in persons with SCI.

Innervation zones of the upper and lower limb muscles estimated by using multichannel surface EMG.

The distribution of innervation zones was investigated in 3 subjects for 17 muscles and 8 muscle groups in the upper and lower limb, by detecting bi-directional propagation of motor unit action potentials (MUAPs) with the multichannel surface electrode array. Clarification of the distribution of innervation zones depended on the ease in detecting the propagation of MUAPs and the actual scattering of innervation zones, which were closely related with muscle morphology with respect to the arrangements of muscle fibers. In muscles having fibers running parallel to each other, such as the biceps brachii, intrinsic hand muscles, vastus lateralis and medialis, tensor fasciae latae, peronei, soleus, tibialis anterior, and hypothenar muscles in the foot, it was relatively easy to detect the propagating MUAPs, and the innervation zones were distributed in a relatively narrow band around muscle belly. On the other hand, in muscles with a complicated structure including pinnation of muscle fibers, in-series muscle fibers and aponeurotic tissues, such as the deltoid, flexors and extensors in the forearm, rectus femoris, sartorius, hamstrings and gastrocnemius, it was more difficult to detect the propagating MUAPs and to identify the innervation zones, which were widely scattered or distributed in complex configurations. The distribution of the innervation zones clarified in the present study can be used to find the optimal location of electrodes in surface EMG recordings and of stimulus electrodes in the functional and therapeutic electrical stimulations. It may also be useful in motor point biopsy for diagnosis of neuromuscular diseases as well as in the botulinum toxin injection for the treatment of spasticity.

An automated ECG-artifact removal method for trunk muscle surface EMG recordings

This study aimed at developing a method for automated electrocardiography (ECG) artifact detection and removal from trunk electromyography signals. Independent Component Analysis (ICA) method was applied to the simulated data set of ECG-corrupted surface electromyography (SEMG) signals. Independent Components (ICs) correspond to ECG artifact were then identified by an automated detection algorithm and subsequently removed. The detection performance of the algorithm was compared to that by visual inspection, while the artifact elimination performance was compared with Butterworth high pass filter at 30 Hz cutoff (BW HPF 30). The automated ECG-artifact detection algorithm successfully recognized the ECG source components in all data sets with a sensitivity of 100% and specificity of 99%. Better performance indicated by a significantly higher correlation coefficient ( p < 0.001) with the original EMG recordings was found in the SEMG data cleaned by the ICA-based method, than that by BW HPF 30. The automated ECG-artifact removal method for trunk SEMG recordings proposed in this study was demonstrated to produce a very good detection rate and preserved essential EMG components while keeping its distortion to minimum. The automatic nature of our method has solved the problem of visual inspection by standard ICA methods and brings great clinical benefits.

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

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

Objective measurement of muscle rigidity in parkinsonian patients treated with subthalamic stimulation

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been shown to be an effective treatment for Parkinson's disease (PD). The intraoperative positioning of DBS electrodes and postoperative adjustment of the stimulation parameters, however, require continuous, precise evaluation. Moreover, ambulatory measurements of the symptoms would also help to evaluate changes in the progression of PD in these patients. To this aim, we objectified rigidity measurements via surface EMG recordings of the Mm. biceps (bic) and triceps brachii (tric) in patients treated with chronic stimulation of the STN. We show that cessation and initiation of DBS have effects on the EMG profile during standardized extension and flexion movements in the elbow joint. These data correlate significantly with clinical ratings. Thus, EMG recordings of the Mm. bic and tric during this standardized extension-flexion movement can be used to objectively measure rigidity and to monitor its course over time. In view of its low technical requirements, this technique lends itself to use during DBS implantation surgery and in the clinical environment.