Central Cord Syndrome of Cervical Spinal Cord Injury: Widespread Changes in Muscle Recruitment Studied by Voluntary Contractions and Transcranial Magnetic Stimulation

Muscle recruitment after central cord syndrome (CCS), a cervical spinal cord injury leading to a weaker motor function in the upper limbs versus the lower limbs, was examined in 14 individuals by means of voluntary muscle contractions and transcranial magnetic stimulation (TMS). Previously obtained data from able-bodied (AB) and non-CCS spinal cord injured subjects were used for comparison. Surface EMG was recorded from as many as six pairs of affected muscles. Individual muscle EMG activity was scored from 0 to 5. Cortical stimulation was applied while subjects maintained a weak contraction in each muscle. When CCS subjects attempted to produce a maximal voluntary contraction of an isolated muscle, this frequently resulted in cocontraction of nonsynergists in the same limb or/and in other limbs. Although the EMG scores in both upper and lower extremity muscles improved within postinjury time, in general, the lower extremity muscles, particularly the distal ones, demonstrated better recovery than the upper extremity muscles. CCS and AB subjects showed a similar high probability of “well-defined” responses to TMS (amplitude >150 μV) in all studied muscles. In contrast, latencies to TMS-evoked motor responses were prolonged by significant amounts after CCS. The delays in muscle responses were not significantly different from those observed in subjects with more severe cervical injury. Despite improvement in EMG scores, repeated measurements of TMS-evoked muscle response latencies in the same CCS subjects did not reveal significant shortening in central conduction latency. This argues against remyelination as an important contributor to the recovery process.     

Anticipatory response-relevant muscle activity, CNV amplitude and simple reaction time

The present experiment was aimed at whether subjects, performing a forewarned simple reaction time (RT) task, do voluntarily tense agonist and antagonist muscles during the foreperiod; if so, would such muscle tension co-vary with CNV amplitude or RT? Although excessive eye movements caused 30% of the subjects to be removed from the analysis, it was still possible after the experiment to differentiate between subjects who gradually tensed their agonist during the foreperiod and subjects who did not. The former group showed higher CNV early and late wave amplitudes as compared with the latter group. A similar effect was found on the N1 amplitude of the potential evoked by the warning stimulus. The increased EMG in the agonist muscle at the end of the foreperiod was not concomitant with faster RTs. In addition, fast RTs were preceded by higher CNV late wave amplitudes at pre- and postcentral electrode positions. The observed relationships between CNV, EMG, and RT were discussed in terms of specific and general motor preparation.     

EMG of reinnervated motor units: a simulation study

Using computer simulation techniques, reinnervation of motor units (MUs) was studied by increasing the number of muscle fibers in the MU without changing the MU territory. The fiber density (FD) measured by single fiber EMG electrodes, the amplitude, area and number of turns of concentric needle (CN) EMG motor unit action potentials (MUAPs) and the amplitude of macro EMG MUAPs were most affected by partial reinnervation changes. The values of these features increased during simulated advanced reinnervation, as did the number of CNEMG MUAPs that had increased numbers of phases or turns and the mean CNEMG MUAP duration. The increase in macro EMG MUAP amplitude, FD and CNEMG MUAP area were proportional to the increase in the number of muscle fibers in the MU. When loss of muscle fibers due to so-called MU fractionation was simulated, values of all EMG features fell, but were still increased compared to normal. Two patterns of change in SFEMG and macro EMG values were identified that may distinguish between recordings made from reinnervated low force threshold MUs and those from higher force threshold MUs.     

Electromechanical changes during electrically induced and maximal voluntary contractions: Surface and intramuscular EMG responses during sustained maximal voluntary contraction

Changes in the electrical activity of the human gastrocnemius and soleus muscles during fatiguing maximal plantar flexions were studied with computer-aided EMG frequency power spectral analysis and intramuscular spike amplitude-frequency histogram analysis. In some experiments, brief supramaximal nerve stimulations of 80 Hz were given at 15-s intervals during sustained maximal voluntary contractions (MVCs). Multiple muscle biopsy samples were also obtained from the gastrocnemius muscle for fiber type determination. The surface EMG frequency spectral analysis showed a highly significant reduction in mean power frequency and root mean square EMG amplitude during sustained MVCs. The intramuscular spike amplitude-frequency histograms showed that the gastrocnemius muscle had a progressive reduction in the motor unit discharge frequency, particularly those with a relatively high amplitude, whereas the soleus muscle hardly showed a reduction in motor unit activity. Reduction in motor unit activity was also found to be more pronounced in gastrocnemius muscles with higher proportions of type II fibers. Brief maximal tetanic stimulations initially matching the MVC failed to increase the contraction force. Similarly, the evoked compound mass action potentials showed little change in the amplitude in subjects with different muscle fiber compositions. Results of this study suggest that during sustained MVCs, force fatigue could not be attributed to a failure of muscle membrane electrical propagation; a progressive reduction in motor unit activation does not result in a functional disadvantage, but may optimize excitation-contraction coupling by avoiding a muscle electrical conduction failure; and the extent of the reduction in motor unit activation seems to be muscle-fiber-type-dependent which may account for the reduction in amplitude and frequency of the surface EMG.     

Recording characteristics of the surface EMG electrodes

Routine motor nerve conduction studies are conducted using surface EMG electrodes. Most techniques of estimating the number of motor units (MUs) are based on surface EMG recordings. Therefore, it is important to assess the uptake area of these electrodes. We recorded surface EMG motor unit action potentials (SMUAPs) from the biceps muscle of normal subjects. The SMUAP amplitude fell from 42 μV for the superficially located MUs (i.e., within 10 mm of skin surface) to 11 μV for the deep MUs (i.e., more than 20 mm from the skin surface). We infer that the pickup radius of the surface electrode is less than 20 mm. The implications of the limited uptake area of the surface electrodes to the analysis of compound muscle action potentials, estimation of the number of MUs, and the surface EMG recordings are discussed. © 1994 John Wiley & Sons, Inc.     

Abnormal most-rapid isometric contractions in patients with Parkinson''s disease.

Fast isometric elbow flexor muscle contractions of specified amplitude in six normal subjects were compared with those of 11 patients with Parkinson's disease. Despite treatment, all patients exhibited deficits in this motor task. Three patients were able to produce rapid force pulses with normal contraction times, but the variability of their force responses was increased in comparison with the highly stereotyped responses produced by normal subjects. The other eight patients had prolonged contraction times and segmentation of the force profiles. The integrated area of the first agonist EMG burst and the rate of development of force (dF/dt) were less at any target level than what was needed to produce a fast response. The area of the EMG burst, however, did increase with target amplitude, and the relative increase of dF/dt, with target amplitude, was normal. It is concluded that the motor program subserving fast muscle contraction is preserved in Parkinson's disease, but its execution is characterised by improper scaling of motor output.     

Increased EMG of rat plantaris during locomotion following surgical removal of its synergists

A chronic EMG electrode implant system was used to determine recruitment patterns of rat plantaris, during treadmill locomotion, before and after surgical removal of its synergists, gastrocnemius and soleus. Bilateral synergist removal resulted in increased plantaris muscle weight and myofibrillar protein content of 59% and 44%, respectively, by 30 days following surgery. Evidence of increased plantaris EMG during treadmill walking (increases in amplitude and integral of EMG bursts to ca. 200% of pre-excision values) occurred at 15–30 days and decreased to non-significant levels at 35 days postsurgery. No corresponding alterations occurred in sham-operated controls. At 25 and 30 days, EMG of plantaris during locomotion was still submaximal, since burst amplitudes were 53% to 67% of those recorded during a dynamic grid-climbing task. The magnitude and time course of changes in EMG of overloaded plantaris during a standardized locomotor task, which reflect increased recruitment and rate of discharge of motor units, are consistent with the chronology of morphological and metabolic events previously described for this model.     

Mechanomyographic and electromyographic responses to eccentric muscle contractions

Little is known regarding the modulation of torque during eccentric muscle actions. Mechanomyographic (MMG) and electromyographic (EMG) signals have been used to examine motor control strategies. The purpose of this study was to examine the MMG and EMG amplitude and frequency in relation to torque during eccentric muscle contractions. Eight women performed eccentric leg extension muscle contractions at 10-100% of peak torque (PT). A piezoelectric crystal contact sensor and bipolar surface electrodes were placed on the vastus medialis to detect the MMG and EMG signals. Polynomial regression analyses indicated that EMG amplitude (r(2)=0.994) and MMG wavelet center frequency (CF) (r(2)=0.846) increased linearly to 100% eccentric PT, whereas there were no significant relationships for EMG wavelet CF or MMG amplitude and eccentric torque. These results suggested that eccentric torque is primarily modulated through changes in motor unit firing rate.     

Suppression of motor cortical excitability by magnetic stimulation of the cerebellum

EMG responses of the relaxed right thenar muscle evoked by magnetic stimulation over the sensorimotor cortex were suppressed by magnetic conditioning stimulation over the occiput. The optimal interstimulus interval for reduction of the EMG amplitude was 4–6 ms. The optimal conditioning position and induced current direction were 3–4 cm below the inion when the induced current in the center of the figure-8 coil flowed from right to left horizontally. It differed from that for activating the descending motor pathway. We consider this suppression to be due to the inhibition of motor cortex excitability caused by stimulation of the dentato-thalamo-cortical pathway at the dentate nuclei or superior cerebellar peduncle.     

斜方肌肌电图运动单位动作电位成人正常参考值的建立

目的 探讨不同血清抗体重症肌无力(MG)的临床特征.方法 用荧光免疫沉淀法(FIPA)和荧光免疫细胞染色法(CBA)检测119例MG患者血清乙酰胆碱受体抗体(AChR-Ab)和肌肉特异性受体酪氨酸激酶抗体(MuSK-Ab)水平.比较AChR-Ab阳性、MuSK-Ab阳性、血清抗体阴性MG的临床特征.结果 纳入119例患者中,90例AChR-Ab阳性(75.6%),29例阴性:其中5例MuSK-Ab阳性(17.2%),24例血清抗体阴性(82.8%).AChR-Ab阳性、MuSK-Ab阳性和血清抗体阴性MG 3组比较,男女比例和平均发病年龄差异均无统计学意义.3例MuSK-Ab阳性的患者主要表现为延髓肌受累;79.2%(19/24)的血清抗体阴性MG患者表现为美国MG协会(MGFA)Ⅰ型;2例MuSK-Ab阳性的患者MGFA≥Ⅲ型;MuSK-Ab滴度水平与患者病情严重程度相关(r=0.941,P=0.014);MuSK-Ab阳性的患者均未发现有胸腺的异常.结论 MuSK-Ab仅出现在AChR-Ab阴性患者的血清中.MuSK-Ab阳性的患者主要表现为延髓肌受累,病情较重且不伴有胸腺的病变.MuSK-Ab阳性的MG可能是不同于血清AChR-Ab阳性的MG的又一亚型.     

神经肌电图对特发性面瘫治疗及预后评估的研究

目的探讨神经肌电图(神经电图electroneurography,ENG和肌电图electromyography,EMG)在特发性面瘫治疗及预后评估中的价值。方法采用丹麦生产的keypointⅣ肌电图仪对96例确诊为特发性面瘫的患者进行患侧与健侧ENG、EMG检测,分别记录患侧面神经颞支、颧支、颊支的运动传导潜伏期、波幅以及所支配的额肌、眼轮匝肌、口轮匝肌的肌电图情况,并与自身健侧作对比。结果特发性面瘫患者患侧面神经运动传导潜伏期延长、M波波幅降低,与自身健侧相比,差异有统计学意义(P<0.05)。波幅下降<70%、NCV(神经传导速度)减慢<20%、EMG大致正常的轻度患者,3个月内面肌完全恢复,治愈率100%;波幅下降70%～90%、NCV减慢20%～50%、EMG呈部分神经源性损害的中度患者,3个月内大部分可完全恢复,治愈率87.8%;波幅下降>90%、NCV减慢>50%、EMG呈部分或完全神经源性损害的中重度患者,3个月内面肌完全恢复者为50%;诱发电位消失、NCV引不出、EMG呈完全神经源性损害的重度患者,3个月内面肌完全恢复者为25%。结论 ENG和EMG检测对特发性面瘫的神经损伤、面肌恢复等预后评估有重要价值,能对临床治疗提供客观依据。     

Decoding the neural drive to muscles from the surface electromyogram

This brief review discusses the methods used to estimate the neural drive to muscles from the surface electromyogram (EMG). Surface EMG has been classically used to infer the neural activation of muscle by associating its amplitude with the number of action potentials discharged by a population of motor neurons. Although this approach is valuable in some applications, the amplitude of the surface EMG is only a crude indicator of the neural drive to muscle. More advanced methods are now available to estimate the neural drive to muscle from the surface EMG. These approaches identify the discharge times of a few motor units by decomposing the EMG signal to determine the relative changes in neural activation. This approach is reliable in several conditions and muscles for isometric contractions of moderate force, but is limited to the few superficial units that can be identified in the recordings.     

Acoustic myography: A noninvasive monitor of motor unit fatigue

Acoustic myography is the recording of sounds produced by contracting muscle. These sounds become louder with increasing force of contraction. We have compared muscle sounds with surface EMG to monitor the dissociation of electrical from mechanical events (presumably, the loss of excitation–contraction coupling) which occur with motor unit fatigue. Acoustic signals were amplified using a standard phonocardiograph, recorded on FM magnetic tape, and digitally analyzed. Muscles were examined at rest, with intermittent contractions, and with sustained contractions. We found that with fatigue, the acoustic amplitude decayed, but the surface EMG amplitude did not. With decreased effort, however, the acoustic and the surface EMG amplitudes declined simultaneously. By simultaneously recording acoustic signals and needle EMG, individual motor units were resolved acoustically in two muscles with decreased numbers of motor units and increased motor unit size. Fasciculations also produced acoustic signals, although no acoustic signal has yet been found that correlates with fibrillations. Analysis of acoustic signals from muscle provides a noninvasive method for monitoring motor unit fatigue in vivo. It may also be useful in distinguishing muscle fatigue from decreased volition.     

Cerebral correlates of muscle tone fluctuations in restless legs syndrome: a pilot study with combined functional magnetic resonance imaging and anterior tibial muscle electromyography

BACKGROUND: The pathology of restless legs syndrome (RLS) is still not understood. To investigate the pathomechanism of the disorder further we recorded a surface electromyogram (EMG) of the anterior tibial muscle during functional magnetic resonance imaging (fMRI) in patients with idiopathic RLS. METHODS: Seven subjects with moderate to severe RLS were investigated in the present pilot study. Patients were lying supine in the scanner for over 50 min and were instructed not to move voluntarily. Sensory leg discomfort (SLD) was evaluated on a 10-point Likert scale. For brain image analysis, an algorithm for the calculation of tonic EMG values was developed. RESULTS: We found a negative correlation of tonic EMG and SLD (p <0.01). This finding provides evidence for the clinical experience that RLS-related subjective leg discomfort increases during muscle relaxation at rest. In the fMRI analysis, the tonic EMG was associated with activation in motor and somatosensory pathways and also in some regions that are not primarily related to motor or somatosensory functions. CONCLUSIONS: By using a newly developed algorithm for the investigation of muscle tone-related changes in cerebral activity, we identified structures that are potentially involved in RLS pathology. Our method, with some modification, may also be suitable for the investigation of phasic muscle activity that occurs during periodic leg movements.     

Respiratory electrophysiological studies in Guillain-Barré syndrome.

Respiratory failure is a common and potentially life threatening complication in patients with Guillain-Barré syndrome. The incidence of phrenic nerve involvement and the predictive value of phrenic nerve conduction and diaphragmatic needle EMG were studied in 40 patients with Guillain-Barré syndrome within the first three days of admission to hospital. The negative peak onset latency of the diaphragmatic compound muscle action potential (CMAP), and its amplitude, duration, and area were abnormal in 83%. The need for ventilation was correlated with diaphragmatic CMAP amplitude (P = 0.005), and area (P = 0.001), but not with latency or duration. Abnormalities in diaphragmatic needle EMG were found in 45%, mainly a decreased number of motor unit potentials. The abnormalities correlated with the need for ventilation (P = 0.013). Of the 40% who required ventilation, all had either abnormal phrenic conduction, abnormal diaphragmatic needle EMG, or both. Eighty one per cent of the ventilated patients had abnormal forced vital capacity on the day of the electrophysiological examination. The results indicate that phrenic nerve conduction studies and diaphragmatic EMG are useful in detecting respiratory involvement in patients with Guillain-Barré syndrome and in identifying those at risk of respiratory failure.     

Movement-related cortical potentials associated with progressive muscle fatigue in a grasping task.

OBJECTIVE: The present research was aimed to further address the general empirical question regarding the behavioral and neurophysiological indices and mechanisms that contribute to and/or compensate for muscle fatigue. In particular, we examined isometric force production, EMG, and EEG correlates of progressive muscle fatigue while subjects performed a grasping task. METHODS: Six neurologically healthy subjects were instructed to produce and maintain 70% of maximum voluntary contraction (MVC) for a total of 5 s in a sequence of 120 trials using a specially designed grip dynamometer. Three components of movement-related potentials (Bereitschaftspotential, BP, Motor potential, MP, and Movement-monitoring potential, MMP) were extracted from continuous EEG records and analyzed with reference to behavioral indicators of muscle fatigue. RESULTS: Experimental manipulations induced muscle fatigue that was demonstrated by decreases in both MVC values and mean force levels produced concomitant to increases in EMG root mean square (RMS) amplitude with respect to baseline levels, and EMG slope. EEG data revealed a significant increase in MP amplitude at precentral (Cz and FCz) and contralateral (C3) electrode sites, and increases in BP amplitude at precentral (Cz and FCz) electrode sites. CONCLUSIONS: The increases in EMG amplitude, EMG slope, and MP amplitudes suggest a possible link between the control signal originating in the motor cortex and activity level of the alpha-motoneuron pool as a function of progressive muscle fatigue. Overall, the data demonstrate that progressive muscle fatigue induced a systematic increase in the electrocortical activation over the supplementary motor and contralateral sensorimotor areas as reflected in the amplitude of movement-related EEG potentials.     

Quantitative EMG and motor unit recruitment threshold using a concentric needle with quadrifilar electrode

According to Henneman's size principle, small motor units are recruited before large ones. We used the electromyographic (EMG) signal decomposition technique to determine the quantitative relationships between five motor unit action potential (MUAP) parameters (amplitude, duration, area, thickness, and size index) and the recruitment threshold of the motor units recruited up to 50% of the maximum voluntary contraction in the first dorsal interosseous, biceps brachii, rectus femoris, and tibialis anterior muscles of 5 healthy young men. In each muscle, the amplitude, duration, area, and size index had significant, positive high correlations with the motor unit recruitment thresholds. We conclude that the size principle applies to recordings made with concentric needle EMG electrodes under special recording conditions, and therefore that more importance should be attached to the patient's contraction force during EMG examinations in order to evaluate MUAPs for electrodiagnostic purposes.     

Comparative effects of topical perfusions of pentylenetetrazol in the mesencephalon and cerebral cortex of cats

Push-pull perfusions of pentylenetetrazol (PTZ) were carried out in the mesencephalon and cerebral cortex (orbitofrontal, motor, and suprasylvian) of “encéphale isolé” cats, while EEG recordings from motor cortices and EMG of facial muscles were obtained. There were significant differences between perfusions in the mesencephalic reticular formation (MRF) and in the cerebral cortex: (i) EEG spikes not accompanied by muscular contractions occurred during perfusion of cerebral cortex (motor cortex included), but never with perfusions in MRF. (ii) In some instances muscular tonic and clonic contractions occurred in the absence of EEG spikes when perfusing the mesencephalon, but never with cortical perfusions. (iii) Both MRF and cortical perfusions induced EEG spikes accompanied by myoclonic seizures; however, muscular seizures were practically of the same amplitude in both sides after perfusion of the MRF and were predominant in the contralateral side after cortical perfusions. In addition, significantly less perfusion time (total dose) of PTZ was needed to induce such events in the MRF than in the cerebral cortex. (iv) Generalized seizures induced by cortical perfusions showed a clear predominance of contractions in the muscles contralateral to the perfusion site, whereas perfusions in the MRF induced generalized seizures indistinguishable from those produced by i.v. administration of PTZ. Results suggest that PTZ generalized seizures, closely resembling the so called “primary generalized seizures,” result from activation of the MRF, whereas PTZ acting in the cerebral cortex produces a model of focal convulsions that may become secondarily generalized.     

fMRI analysis for motor paradigms using EMG-based designs: a validation study

The goal of the present validation study is to show that continuous surface EMG recorded simultaneously with 3T fMRI can be used to identify local brain activity related to (1) motor tasks, and to (2) muscle activity independently of a specific motor task, i.e. spontaneous (abnormal) movements. Five healthy participants performed a motor task, consisting of posture (low EMG power), and slow (medium EMG power) and fast (high EMG power) wrist flexion-extension movements. Brain activation maps derived from a conventional block design analysis (block-only design) were compared with brain activation maps derived using EMG-based regressors: (1) using the continuous EMG power as a single regressor of interest (EMG-only design) to relate motor performance and brain activity, and (2) using EMG power variability as an additional regressor in the fMRI block design analysis to relate movement variability and brain activity (mathematically) independent of the motor task. The agreement between the identified brain areas for the block-only design and the EMG-only design was excellent for all participants. Additionally, we showed that EMG power variability correlated well with activity in brain areas known to be involved in movement modulation. These innovative EMG-fMRI analysis techniques will allow the application of novel motor paradigms. This is an important step forward in the study of both the normally functioning motor system and the pathophysiological mechanisms in movement disorders.     

Motor unit number estimation,isometric strength,and electromyographic measures in amyotrophic lateral sclerosis

Pathologic progression in amyotrophic lateral sclerosis (ALS) results from motor neuron death, while the clinical expression also reflects the compensatory effects of collateral reinnervation consequent to lower motor neuron loss. In a cross-sectional study of ALS subjects, we made comparisons between motor unit number estimation (MUNE) values and several measures reflecting collateral reinnervation, including isometric strength, compound muscle action potential (CMAP) amplitude, surface motor unit action potential (S-MUAP) amplitude, fiber density (FD), macro-EMG potential amplitude, turns-to-amplitude (T/A) ratio, and amplitude and recruitment pattern of low threshold voluntary motor units in elbow flexor muscles. Before comparisons were made, testretest reproducibility of these measures was assessed in ALS subjects, and is highest for isometric strength, and lower but similar for EMG measures. When the effects of multiple comparisons are considered, borderline significant correlations are found between MUNE values and isometric strength. Neither MUNE values nor isometric strength are significantly correlated with macro-EMG amplitude, FD, T/A ratio, or amplitude and recruitment rate of low threshold voluntary motor units. There are significant correlations of CMAP and S-MUAP with MUNE values, but these are statistical artifacts with no independent interpretation. We conclude that collateral reinnervation prevents isometric strength and EMG measures from accurately reflecting lower motor neuron death in ALS. MUNE measurements are better suited to provide insight into the true natural history of the disease process and may be clinically useful to follow progression and response in drug trials. © 1993 John Wiley & Sons, Inc.