Location of innervation zones of sternocleidomastoid and scalene muscles--a basis for clinical and research electromyography applications.

OBJECTIVES: Advances in surface electromyography (sEMG) techniques provide a clear indication that refinement of electrode location relative to innervation zones (IZ) is required in order to optimise the accuracy, relevance and repeatability of the sEMG signals. The aim of this study was to identify the IZ for the sternocleidomastoid and anterior scalene muscles to provide guidelines for electrode positioning for future clinical and research applications. METHODS: Eleven volunteer subjects participated in this study. Myoelectric signals were detected from the sternal and clavicular heads of the sternocleidomastoid and the anterior scalene muscles bilaterally using a linear array of 8 electrodes during isometric cervical flexion contractions. The signals were reviewed and the IZ(s) were identified, marked on the subjects' skin and measurements were obtained relative to selected anatomical landmarks. RESULTS: The position of the IZ lay consistently around the mid-point or in the superior portion of the muscles studied. CONCLUSIONS: Results suggest that electrodes should be positioned over the lower portion of the muscle and not the mid-point, which has been commonly used in previous studies. Recommendations for sensor placement on these muscles should assist investigators and clinicians to ensure improved validity in future sEMG applications.     

A method for positioning electrodes during surface EMG recordings in lower limb muscles

PURPOSE: The aim of this work is to provide information about the degree of inter-subject uniformity of location of innervation zone (IZ) in 13 superficial muscles of the lower limb. The availability of such information will allow researchers to standardize and optimize their electrode positioning procedure and to obtain accurate and repeatable estimates of surface electromyography (sEMG) signal amplitude, spectral variables and muscle fiber conduction velocity. METHODS: Surface EMG signals from gluteus maximus, gluteus medius, tensor faciae latae, biceps femoris, semitendinosus, vastus medialis obliquus, vastus lateralis, rectus femoris, tibialis anterior, peroneus longus, soleus, gastrocnemius medialis and lateralis muscles of ten healthy male subjects aged between 25 and 34 years (average = 29.2 years, S.D. = 2.5 years) were recorded to assess individual IZ location and signal quality. RESULTS: Tensor faciae latae, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius medialis and lateralis showed a high level of both signal quality and IZ location uniformity. In contrast, rectus femoris, gluteus medius and peroneus longus were found to show poor results for both indexes. Gluteus maximus, vastus medialis obliquus and tibialis anterior were found to show high signal quality but low IZ location uniformity. Finally, soleus muscle was found to show low signal quality but high IZ location uniformity. CONCLUSIONS: This study identifies optimal electrode sites for muscles in the lower extremity by providing a standard landmarking technique for the localization of the IZ of each muscle so that surface EMG electrodes can be properly positioned between the IZ and a tendon.     

Age‐associated changes in muscle activity during isometric contraction

Introduction: We investigated the effect of age on the complexity of muscle activity and the variance in the force of isometric contraction. Methods: Surface electromyography (sEMG) from biceps brachii muscle and force of contraction were recorded from 96 subjects (20–70 years of age) during isometric contractions. Results: There was a reduction in the complexity of sEMG associated with aging. The relationship of age and complexity was approximated using a bilinear fit, with the average knee point at 45 years. There was an age‐associated increase in the coefficient of variation (CoV) of the force of muscle contraction, and this increase was correlated with the decrease in complexity of sEMG (r² = 0.76). Conclusions: There was an age‐associated increase in CoV and also a reduction in the complexity of sEMG. The correlation between these 2 factors can be explained based on the age‐associated increase in motor unit density. Muscle Nerve 47: 545–549, 2013     

EMG processing to interpret a neural tension‐limiting mechanism with fatigue

Introduction: Surface electromyography (sEMG) amplitude increases with constant muscle tension during fatiguing sub‐maximum efforts. The purpose of this study was to determine if extreme highpass filtering and/or autoregressive whitening would result in a more consistent sEMG‐to‐moment ratio than a standard bandpass filter (20–500 Hz ) during repeated, dynamic maximal efforts of the quadriceps. Methods: We collected sEMG and knee extensor moment from 16 participants during the concentric and eccentric phases of repeated, maximal knee extensor efforts. Results: The alternative processing methods provided more consistent vastus medialis and lateralis sEMG‐to‐moment ratios. A neural tension‐limiting mechanism appeared to exist and was magnified during the eccentric phase, particularly with fatigue. Conclusions: There appears to be a difference in how the central nervous system controls concentric and eccentric efforts as the quadriceps fatigues, and this is more apparent with the alternative EMG processing methods we used. Muscle Nerve 50 : 384–392, 2014     

Muscle fiber velocity and electromyographic signs of fatigue in fibromyalgia

Introduction: Fibromyalgia (FM) is a disorder of widespread muscular pain. We investigated possible differences in surface electromyography (sEMG) in clinically unaffected muscle between patients with FM and controls. Methods: sEMG was performed on the biceps brachii muscle of 13 women with FM and 14 matched healthy controls during prolonged dynamic exercises, unloaded, and loaded up to 20% of maximum voluntary contraction. The sEMG parameters were: muscle fiber conduction velocity (CV); skewness of motor unit potential (peak) velocities; peak frequency (PF) (number of peaks per second); and average rectified voltage (ARV). Results: There was significantly higher CV in the FM group. Although the FM group performed the tests equally well, their electromyographic fatigue was significantly less expressed compared with controls (in CV, PF, and ARV). Conclusion: In the patients with FM, we clearly showed functional abnormalities of the muscle membrane, which led to high conduction velocity and resistance to fatigue in electromyography. Muscle Nerve 46: 738–745, 2012     

Power spectral changes of the superimposed M wave during isometric voluntary contractions of increasing strength

Introduction: We examined the power spectral changes of the compound muscle action potential (M wave) evoked during isometric contractions of increasing strength. Methods: Surface electromyography (sEMG) of the vastus lateralis and medialis was recorded from 20 volunteers who performed 4‐s step‐wise isometric contractions of different intensities. A maximal M wave was elicited by a single stimulus to the femoral nerve and superimposed on the voluntary contractions. The spectral characteristics (Fmean and Fmedian) of sEMG and M‐wave signals were calculated. Results: M‐wave spectral indicators increased systematically with contraction intensity up to 60% MVC and then leveled off at higher forces. Over the 10–60% MVC range, the increase in spectral indicators was 3 times higher for M waves (36%) than for sEMG (12%). Conclusions: The consistent increase in M‐wave spectral characteristics with force is due to the fact that the number of motor units recruited by the superimposed supramaximal stimulus is approximately stable. Muscle Nerve 51: 580–591, 2015     

High-yield decomposition of surface EMG signals

Objective

Automatic decomposition of surface electromyographic (sEMG) signals into their constituent motor unit action potential trains (MUAPTs).

Methods

A small five-pin sensor provides four channels of sEMG signals that are in turn processed by an enhanced artificial intelligence algorithm evolved from a previous proof-of-principle. We tested the technology on sEMG signals from five muscles contracting isometrically at force levels ranging up to 100% of their maximal level, including those that were covered with more than 1.5 cm of adipose tissue. Decomposition accuracy was measured by a new method wherein a signal is first decomposed and then reconstructed and the accuracy is measured by comparison. Results were confirmed by the more established two-source method.

Results

The number of MUAPTs decomposed varied among muscles and force levels and mostly ranged from 20 to 30, and occasionally up to 40. The accuracy of all the firings of the MUAPTs was on average 92.5%, at times reaching 97%.

Conclusions

Reported technology can reliably perform high-yield decomposition of sEMG signals for isometric contractions up to maximal force levels.

Significance

The small sensor size and the high yield and accuracy of the decomposition should render this technology useful for motor control studies and clinical investigations.     

Later stages of diabetic neuropathy affect the complexity of the neuromuscular system at the knee during low‐level isometric contractions

Introduction: This study evaluates the complexity of force and surface electromyography (sEMG) during knee extension and flexion at low‐level isometric contractions in individuals with different degrees of diabetic peripheral neuropathy (DPN). Methods: Ten control and 38 diabetic participants performed isometric contractions at 10%, 20%, and 30% of maximal voluntary contraction. Knee force and multichannel sEMG from vastus lateralis (VL) and biceps femoris were acquired. The SD of force and sample entropy (SaEn) of both force and sEMG were computed. Results: Participants with moderate DPN demonstrated high force‐SD and low force‐SaEn. Severely affected participants showed low SaEn in VL at all force levels. Discussion: DPN affects the complexity of the neuromuscular system at the knee for the extension task during low‐level isometric contractions, with participants in the later stages of the disease (moderate and severe) demonstrating most of the changes. Muscle Nerve 57 : 112–121, 2018     

Surface electromyography features in manual workers affected by carpal tunnel syndrome

Introduction: Alterations in surface electromyographic (sEMG) signals of the abductor pollicis brevis muscle were evaluated in 24 non‐manual workers and 40 manual workers (25 asymptomatic and 15 reporting CTS symptoms). Methods: The initial value (IV) and the normalized rate of change (NRC) of average rectified value (ARV), mean frequency of the power spectrum (MNF), and muscle fiber conduction velocity (MFCV) were calculated during contractions at 20% and 50% of maximal voluntary contraction (MVC). Neuromuscular efficiency (NME) and kurtosis of the sEMG amplitude distribution were estimated. Results: With respect to controls, manual workers showed higher NME, lower ARV IV, and reduced myoelectric manifestations of fatigue (lower MNF NRC for both contraction levels, and lower MFCV NRC at 50% MVC). Kurtosis at 20% MVC showed higher values in symptomatic manual workers than in the other two groups. Conclusions: Kurtosis seems to be a promising parameter for use in monitoring individuals who develop CTS. Muscle Nerve 45: 873–882, 2012     

Prediction of time-to-exhaustion in the first dorsal interosseous muscle from early changes in surface electromyography parameters

Introduction: In this study we evaluated the precision of the time‐to‐exhaustion (T_lim) prediction from the early changes in surface electromyography (sEMG) of the first dorsal interosseous muscle. Methods: Thirty subjects performed an index finger isometric abduction at 35% of maximal voluntary contraction (MVC) until exhaustion. Ten participants performed the same exercise at 50% MVC 1 week later. Changes in sEMG parameters across time were modeled using the area‐ratio and the linear regression slope. T_lim was plotted as a function of each of these indices of change, and the coefficient of determination (R²) was determined. Results: Null to moderate R² (0.22 and 0.56 at 35% and 50% MVC, respectively) values were calculated. The best T_lim estimation led to a high prediction error (21.6 ± 15.0% of T_lim for the 50% MVC task). Conclusions: Although the prediction of time‐to‐exhaustion is an appealing research topic, these results suggest that it cannot be done solely from sEMG. Muscle Nerve 45: 835–840, 2012     

Mechanomyographic responses are not influenced by the innervation zone for the vastus medialis

Introduction: The purposes of this study were to: (1) compare the power output–related patterns of absolute and normalized mechanomyographic (MMG) amplitude and mean power frequency (MPF) signals across the innervation zone (IZ) during incremental cycle ergometry; and (2) examine the influence of the IZ on the mean MMG amplitude and MPF values. Methods: Ten men performed incremental cycle ergometry tests to exhaustion. Surface MMG signals were recorded simultaneously from accelerometer arrangements placed on the vastus medialis over the IZ and proximal and distal to the IZ. Results: The results of polynomial regression indicate that the best‐fit model for each site was consistent for each subject for MMG amplitude, but not for MMG MPF. Two‐way analyses of variance (ANOVAs) revealed no site × power output interaction (P > 0.05) for absolute and normalized MMG amplitude and MPF values. Conclusion: Our findings demonstrate that the IZ does not influence the MMG signal during dynamic exercise. Muscle Nerve 44: 424–431, 2011     

NeuroGame Therapy to improve wrist control in children with cerebral palsy: A case series

Objective: This case series examines the feasibility, specificity, and preliminary effectiveness of NeuroGame Therapy (NGT) for improving wrist control in four children with cerebral palsy (CP). NGT uses surface electromyographic (sEMG) signals routed through motivating computer games to improve motor control.

Methods: Primary outcomes of NGT included feasibility (hours of play) and specificity (changes in sEMG activity during game play). Secondary outcomes included changes in co-contraction, range of motion, segmental alignment, and spontaneous upper extremity function following intervention.

Results: Participants completed a mean of 8.8 hours of NGT over 5–6 weeks. Participants demonstrated dramatic improvement of the sEMG activity during game play. Several participants also showed improvements in range of motion, co-contraction, and spontaneous upper extremity function following NGT.

Conclusion: This case series provides evidence for the feasibility, specificity, and effectiveness of NGT. Future studies will pair NGT with functional practice to improve transfer of learning to daily activities.     

The influence of electrode shift over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus isometric torque relationships for the vastus medialis muscle

The purpose of the present study was to: (a) examine the influence of the innervation zone (IZ) for the vastus medialis on EMG signals from bipolar electrode arrangements that have their center point directly over the IZ, 10mm distal to the IZ, 10mm proximal to the IZ, and 20mm distal to the IZ, and (b) investigate the effects of normalization on EMG amplitude and center frequency values over the IZ. Ten men (mean+/-S.D. age=23.6+/-3.0 years) performed submaximal to maximal isometric muscle actions of the dominant leg extensors, and four separate bipolar surface EMG signals were detected simultaneously from the vastus medialis. One bipolar electrode arrangement had its center point located directly over the IZ, while the other electrode arrangements had their center points 10mm proximal, 10mm distal, and 20mm distal to the IZ. The results showed that there were no consistent patterns among the four electrode arrangements for the absolute and normalized EMG amplitude and mean power frequency (MPF) versus isometric torque relationships. Generally speaking, the IZ had the greatest effect on the EMG signal when the center point of the bipolar electrode arrangement was directly over it or 10mm proximal to it. In addition, normalization reduced the influence of the IZ on the absolute EMG amplitude and MPF values. Thus, these findings supported the practice of normalization, and indicated that it is a useful technique for reducing the influence of electrode location on EMG amplitude and MPF data. Future studies should examine the potential for movement of the IZ during isometric muscle actions.     

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.     

Muscle conduction velocity,surface electromyography variables,and echo intensity during concentric and eccentric fatigue

Introduction: Concentric (CON) and eccentric (ECC) contractions may involve different mechanisms related to changes in sarcolemma status and the consequent alteration of action potential transmission along muscle fibers. Methods: Muscle conduction velocity (CV), surface electromyography signal (sEMG), muscle quality, and blood lactate concentrations were analyzed during CON and ECC actions. Results: Compared with ECC, the CON protocol resulted in greater muscle force losses, blood lactate concentrations, and changes in sEMG parameters. Similar reductions in CV were detected in both protocols. Higher echo intensity values were observed 2 days after ECC due to greater muscle damage. Conclusions: The effects of the muscle damage produced by ECC exercise on the transmission of action potentials along muscle fibers (measured as the CV) may be comparable with the effects of hydrogen accumulation produced by CON exercise (related to greater lactate concentrations), which causes greater force loss and change in other sEMG variables during CON than during ECC actions. Muscle Nerve 49 :389–397, 2014     

The epileptogenic zone in pharmaco‐resistant temporal lobe epilepsy with amygdala enlargement

Aims. Temporal lobe epilepsy with amygdala enlargement (TLE‐AE) has been considered a subtype of TLE. We evaluated the epileptogenic zone in patients with TLE‐AE, who underwent intracranial video‐EEG (ivEEG) and/or intraoperative electrocorticography (ioECoG) as well as epilepsy surgery. Methods. Eleven patients with TLE‐AE were enrolled and investigated based on seizure profile, volumetric MRI, the Wechsler Memory Scale‐Revised (WMS‐R), the location of seizure onset zone (SOZ) and irritative zone (IZ) based on ivEEG (n=8), the location of interictal epileptiform discharges (IEDs) based on ioECoG (11), surgical procedure, and seizure outcome. Results. The mean age at seizure onset was 34.9 years (range: 23–57). The mean duration of seizures was 5.0 years (range: 1–10). The number of AEDs was 2.3 (range: 1–5). The mean seizure frequency was nine per month (range: 1–30/month). All patients presented with focal impaired awareness seizures with (n=9) and without (2) secondary generalized convulsions. Volumetric MRI analysis showed unilateral enlarged amygdala with statistical significance (p<0.01). None of the patients' hippocampi had any abnormality based on MRI. Pre‐operative mean verbal, visual, and delayed recall scores based on the WMS‐R were over 100. The SOZ and IZ were identified in both the amygdala and hippocampus in seven patients and in only the amygdala in one patient based on ivEEG. IEDs were identified in the hippocampus in six patients and in both the amygdala and hippocampus in four patients based on ioECoG. All 11 patients underwent anterior temporal lobectomy, including amygdala resection, with multiple hippocampal transections (dominant hemisphere: seven patients) and resection (non‐dominant hemisphere: three patients). Nine (81.8%) of 11 patients achieved seizure freedom with a mean follow‐up of 26 months (range: 12–47). Post‐operative WMS‐R results did not show any significant deterioration, with a mean follow‐up of 15 months (range: 12–24). The resected amygdala showed no histopathological abnormality. Conclusion. The epileptogenic zone of TLE‐AE involves both the amygdala and hippocampus. ivEEG may be needed to explore the SOZ in normal hippocampus in addition to enlarged amygdala. Amygdala resection and multiple hippocampal transections may control the epileptogenic limbic system and save memory function in patients with TLE‐AE.     

Non-invasive monitoring of functionally distinct muscle activations during swallowing.

OBJECTIVES: Dysphagia is an important consequence of many diseases. As some of the muscles of deglutition tend to be deep to the surface, needle electrodes are typically used, but this limits the number of muscles that can be simultaneously recorded. Since control of swallowing involves central pattern generators (CPGs) which distribute commands to several muscles, monitoring several muscles simultaneously is desirable. Here we describe a novel method, based on computing the independent components (ICs) of the simultaneous sEMG recordings (Muscle Nerve Suppl 9 (2000) 9) to detect the underlying functional muscle activations during swallowing using only surface EMG (sEMG) electrodes. METHODS: Seven normal subjects repeatedly swallowed liquids of varying consistency while sEMG was recorded from 15 electrodes from the face and throat. Active areas of EMG were excised from the recordings and the ICs of the sEMG were calculated. RESULTS: The ICs demonstrated less swallow-to-swallow variability than the raw sEMG. The ICs, each consisting of a unique temporal waveform and a spatial distribution, provided a means to segregate the complex sequence of muscle activation into rigorously defined separate functional units. The temporal profiles of the ICs and their spatial distribution were consistent with prior needle EMG studies of the cricopharyngeal, superior pharyngeal constrictor, submental and possibly arytenoid muscles. Other components appeared to correspond to EKG artifact contaminating the EMG recordings, laryngeal excursion, tongue movement and activation of the buccal and/or masseter musculature At least two of the components were affected by the consistency of the liquids swallowed. Re-testing one subject a week later demonstrated good intertrial reliability. CONCLUSIONS: We propose that the ICs of the sEMG provide a non-invasive means to assess the complex muscle sequence activation of deglutition.     

Gender‐specific neuromuscular adaptations to unloading in isolated rat soleus muscles

Introduction: The potential of gender to affect unloading‐induced neuromuscular adaptations was investigated. Methods: Twenty male and 20 female rats were assigned to control (CTL), or unloaded (UL) conditions. After 2 weeks of unloading, soleus muscles were removed, and neuromuscular function was assessed during a train of alternating indirect (neural) and direct (muscle) stimuli. Results: In rested muscle, strength showed significant (P ≤ 0.05) main effects for gender (male > female) and treatment (CTL > UL). By the end of the testing protocol, when muscles showed fatigue, gender‐related and treatment‐related differences in strength had disappeared. Neuromuscular transmission efficiency and strength suffered a greater decline during the testing protocol in males than females. Unloaded male muscles displayed greater contractile velocity than female muscles both when rested and fatigued. Conclusions: Gender affected unloading‐induced neuromuscular adaptations. The greater strength of rested male muscles was due to greater muscle mass and neuromuscular transmission efficiency. Muscle Nerve 54 : 300–307, 2016     

Fatigue and recovery from dynamic contractions in men and women differ for arm and leg muscles

Introduction: Whether there is a gender difference in fatigue and recovery from maximal velocity fatiguing contractions and across muscles is not understood. Methods: Sixteen men and 19 women performed 90 isotonic contractions at maximal voluntary shortening velocity (maximal velocity concentric contractions, MVCC) with the elbow flexor and knee extensor muscles (separate days) at a load equivalent to 20% maximal voluntary isometric contraction (MVIC). Results: Power (from MVCCs) decreased similarly for men and women for both muscles (P > 0.05). Men and women had similar declines in MVIC of elbow flexors, but men had greater reductions in knee extensor MVIC force and MVIC electromyogram activity than women (P < 0.05). The decline in MVIC and power was greater, and force recovery was slower for the elbow flexors compared with knee extensors. Conclusions: The gender difference in muscle fatigue often observed during isometric tasks was diminished during fast dynamic contractions for upper and lower limb muscles. Muscle Nerve 48 : 436–439, 2013     

Ultrasound combined with electrodiagnosis improves lesion localization and outcome in posterior interosseous neuropathy

Introduction: Posterior interosseous nerve (PIN) syndrome is a rare compression neuropathy. Electrodiagnostic studies (EDx) combined with neuromuscular ultrasound (US) enable precise lesion localization and may improve patient outcome. Methods: In 4 patients with finger extension weakness, US was used to accurately localize concentric electromyographic (EMG) needle placement in PIN muscles and to visualize the lesion site. Results: EMG with US guidance showed decreased recruitment with abnormal configuration in PIN muscles. Active denervation was not always observed. US scanning demonstrated larger PIN diameter in the affected arm. All patients had surgical intervention to confirm EDx and US findings and had improved outcome on follow‐up. Conclusion: These cases demonstrate the benefits of augmenting EDx with US by guiding accurate electrode localization and providing diagnostic information about lesion location. Muscle Nerve 52 : 1117–1121, 2015