A review of techniques employed to estimate the number of motor units in a muscle

Being the smallest functional units under neural control, motor units play an integral role in muscle physiology. However, at the present time, there does not exist any widely accepted technique for quantifying or estimating the number of motor units in a muscle. Specifically, the existing techniques are the increment-counting technique, a technique based on spike-triggered averaging, and a macro-EMG based technique which vary in invasiveness from noninvasive to highly invasive, respectively. We discuss each of these techniques, along with their associated shortcomings, in detail.     

Effect of small motor unit potentials on the motor unit number estimate

Small surface motor unit potentials (S-MUPs) may have a negative influence on the variability of the motor unit number estimate (MUNE). According to published consensus criteria S-MUPs with a negative peak amplitude smaller than 10 muV should be omitted. The effect of omitting small S-MUPs on the MUNE was evaluated using a simulation model. The model incorporated a healthy and amyotrophic lateral sclerosis (ALS) distribution formed with real S-MUPs. Using a random drawing process the MUNE was calculated with and without small S-MUPs. In the healthy population 27% of all S-MUPs were small. MUNE determined without these S-MUPs was marginally less variable. However, MUNE values dropped about 24% at a sample size of 20. In ALS, only 12% of the total population of 130 S-MUPs were small. MUNE dropped about 12% without the small S-MUPs. By omitting small S-MUPs the differences between the healthy and ALS distributions become smaller. Therefore, incorporating small S-MUPs in the estimate is suggested.     

Novel measurement for automated interference pattern analysis of the diaphragm

The automated interference pattern analysis for limb muscles was modified to take into account the unique features of the needle EMG of the diaphragm. The modification was successful in recording more accurately the number of small and large segments and the activity levels with inspiratory effort. “Clouds” were generated in ten healthy subjects. The techniques may prove useful in electrophysiological investigations. © 1997 John Wiley and Sons, Inc.     

Comparison of quantitative techniques in anal sphincter electromyography.

Data comparing results and utility of different quantitative electromyographic (EMG) techniques are limited. In the present study, we analyzed the EMG signal from the external anal sphincter (EAS) muscle using three techniques of motor unit potential (MUP) analysis, and a technique of interference pattern (IP) analysis. We examined 56 patients with damage to the cauda equina or conus medullaris, and 64 control subjects. Using manual-MUP and multi-MUP analysis about 20 MUPs, using a single-MUP technique about 10 MUPs, and using turn/amplitude (T/A) analysis about 20 IP samples were obtained. The sensitivities of these techniques in distinguishing neuropathic from control muscles were calculated. The single-MUP technique detected 63%, manual-MUP 57%, and multi-MUP analysis 62% of neuropathic muscles, and MUP parameters obtained by each of these differed significantly from the other. The sensitivity of T/A analysis of IP was 29%. Our results confirm the need for separate MUP normative data for each of the MUP analysis techniques, and favor them over the IP analysis technique. The normative data presented for the EAS muscle should improve and promote quantitative EMG in patients.     

Literature review of the usefulness of nerve conduction studies and electromyography for the evaluation of patients with carpal tunnel syndrome

The sensitivity and specificity of nerve conduction studies (NCS's) and electromyography (EMG) for the diagnosis of carpal tunnel syndrome CTS) were evaluated by a critical review of the literature. With a search of the medical literature in English through May 1991, 165 articles were identified and reviewed on the basis of six criteria of scientific methodology. The findings of 11 articles that met all six criteria and the results of 48 additional studies that met four or five criteria are presented. We concluded that median sensory and motor NCS's are valid and reproducible clinical laboratory studies that confirm a clinical diagnosis of CTS with a high degree of sensitivity and specificity. Clinical practice recommendations are made based on a comparison of the sensitivities of the several different median nerve conduction study (NCS) techniques.     

Standardization of anal sphincter electromyography: normative data.

OBJECTIVES: Electromyography (EMG) of the external anal sphincter (EAS) is important in the evaluation of conus/cauda lesions, the differential diagnosis of parkinsonism and anal incontinence. The aim of our study was to establish normative data in a sufficiently large group of healthy subjects, using a rigorously standardized examination technique. METHODS: Sixty-four subjects (aged 19-83 years) without pelvic or neurological disorders were included. Motor unit potentials (MUPs)/interference pattern (IP) samples were obtained from the EAS using multi-MUP and turn/amplitude analyses, respectively. The effect of age, gender, parity, and constipation on MUP/IP parameters was studied. For MUP parameters the lower/upper limits for mean values, and 'outlier' limits, and for IP parameters normal 'clouds' were calculated. RESULTS: From 112 muscles 15-30 MUPs were sampled. As no effect of evaluated factors on mean values could be demonstrated, common reference values were calculated. Lower/higher limits for mean values were: amplitude 148/661 microV, duration 3.2/7.8 ms, area 87/625 microVms, and number of phases 2. 3/3.7. 'Outlier' limits for individual MUPs were: amplitude 84/1315 microV, duration 1.6/13.8 ms, area 46/1222 microVms, number of phases 2/6. From 95 muscles 2706 IP samples were obtained. CONCLUSIONS: The presented normative data should allow valid quantitative EMG of the EAS muscle in patients.     

On the shape of the normal turns--amplitude cloud

Factors that affect the shape of the so-called "normal cloud" of the turns and amplitude measurements of the electromyographic interference pattern are investigated. As the force of voluntary contraction increases from low to moderate levels, the number of turns in the signal increase faster than does the mean amplitude change between turns. This results in a cloud that is concave downward. At higher force levels, the pattern is reversed. The overall shape of the cloud thus depends on the maximum effort at which recordings are made, which is determined by the procedure of muscle activation.     

Reversed bowel segments for the treatment of short bowel syndrome: assessment of their minimal length in correlation with electromyographic pattern in the rat

Reversal of a distal intestinal loop is a surgical therapy intended to cure rapid intestinal transit in short bowel syndrome. To be active, a reversed loop must present a retrograde propagation of electromyographic patterns and must not be so long as to cause total obstruction. The aim of the current study was to propose methods to calculate the minimal length of the intestinal reversed loop taking into consideration the two previous conditions. Intestinal electromyograms were recorded in 65 rats at short-term (4 days after surgery) and ten rats at long-term (50 days after surgery). Control rats demonstrated that the preprandial regular spiking activity (RSA) of the migrating myoelectrical complex (MMC) extended simultaneously a definite part of the intestine which corresponds to the minimal length to reverse. A similar result can be obtained from a trigonometric representation. Whatever the method, the minimal lengths allowing the recording of RSA decreased along the rat intestine from 6 cm (proximal jejunum) to 4 cm (distal ileum). The experiments demonstrated that shorter loops did not present the preprandial RSA. In conclusion, the minimal reversed length depends on intestinal electromyographic parameters and, thereby, on the intestinal level.     

Perceptual versus conceptual interference and pattern separation of verbal stimuli in young and older adults

Recently, several studies have strongly suggested that age‐related decline in episodic memory is associated with deficits in hippocampal pattern separation (orthogonalizing overlapping experiences using distinct neural codes). The same studies also link these deficits to neurobiological features such as dentate/CA3 representational rigidity and perforant path loss. This decline in pattern separation is thought to underlie behavioral deficits in discriminating similar stimuli on pictorial tasks. Similar pictorial stimuli invoke interference both in the perceptual and conceptual domains, and do not allow one to be disentangled from another. For example, it is very difficult to design a set of pictorial stimuli that are perceptually similar yet conceptually unrelated. Verbal stimuli, on the other hand, allow experimenters to independently manipulate conceptual and perceptual interference. We tested discrimination on conceptually similar (semantically related) and perceptually similar (phonologically related) verbal stimuli in young (mean age 20) and older adults (mean age 69), and find that older adults are selectively impaired in perceptual pattern separation. This deficit was not secondary to failure in working memory, attention, or visual processing. Based on past studies, we suggest that perceptual discrimination relies on recollection while conceptual discrimination relies more on gist. Our results fit well within the notion that recollection but not familiarity (i.e. gist) is impaired in older adults, and suggests that the impairment observed in pictorial tasks may be driven mostly by failure in perceptual and not conceptual pattern separation. © 2013 Wiley Periodicals, Inc.     

The feasibility and reliability of using circular electrode for sphincter of Oddi electromyography in anaesthetised rabbits

Abstract  Sphincter of Oddi manometry (SOM) is the gold standard for assessing sphincter of Oddi dysfunction (SOD), but is considered a diagnostic sensitivity of 30–80% and associated with significant complications of pancreatitis. Electromyography (EMG) of sphincter of Oddi (SO) using a circular electrode (CE) may be useful in improving diagnostic accuracy and reducing complications. To evaluate the feasibility and reliability of the CE, we record myoelectric activity of SO in rabbits using the CE to compare with the traditional needle electrode (NE). The CE was prepared using a double-channel biogel catheter with two silver rings at the head of the catheter. The CE was then inserted into the lumen of the SO through the duodenal papilla, and myoelectric activity was recorded in the SO in 30 rabbits. An EMG recorded using an NE was performed at the same time, when the SO was in basal state, after injection of cholecystokinin and N-butylscopolamine bromide. Electromyographs recorded by the two methods were then evaluated. Satisfactory SO EMGs were acquired using the CE without any injury. Simultaneous recording revealed a very similar traces and one-to-one correspondence of SO spike bursts (SOSB). Linear regression analysis showed a significant direct correlation between the two methods for SOSB duration and amplitude. The results suggested that CE was comparable with NE in terms of recording efficacy. The CE also has advantages of easy fixation, accurate localisation, broad applicability and ease of achieving satisfactory outcomes without trauma, compared with the NE.     

Needle electromyography of the frontalis muscle in patients with amyotrophic lateral sclerosis

Introduction: We sought to determine which muscles to choose for better assessment of the craniobulbar region in establishing the diagnosis of amyotrophic lateral sclerosis (ALS). Methods: We studied the frontalis muscle in 83 controls and compared it with the tongue, sternocleidomastoid (SCM), and trapezius muscles in 105 definite or probable ALS patients (54 bulbar, 51 nonbulbar). Results: More patients achieved complete relaxation of the frontalis muscle than the tongue or SCM. Motor unit potentials were of longer duration and higher amplitude in ALS patients than in controls (P < 0.05). The frontalis had the same frequency of spontaneous potentials as the tongue, SCM, and trapezius muscles in bulbar ALS patients, but fewer than in the trapezius in nonbulbar patients. Conclusions: Examining the frontalis provides useful information in establishing the diagnosis of ALS by identifying clinically evident or subclinical abnormalities in the craniobulbar region. Muscle Nerve 54 : 1093–1096, 2016     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments

We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.     

Classification of the sleeping pattern of normal adults

A questionnaire concerning their sleep-related lifestyle and mental health was mailed to people aged in their twenties to fifties living in the Fukushima (North East), Tokyo (Central, Metropolitan) and Okayama (West) areas of Japan. We classified the sleeping pattern of 3642 people (1702 men, 1940 women; mean age 41.3+/-10.67) by multivariational analyses (factor analysis and cluster analysis). They were classified into six groups and defined as 'poor sleeper group' (30.0%), 'good sleeper group' (28.3%), 'long sleeper group' (8.2%), 'short sleeper group' (18.5%), 'irregular sleeper group' (11.3%), and 'Delayed Sleep Phase Syndrome group' (3.7%) based on their characteristics of the factor pattern.     

Motor unit number estimates in the tibialis anterior muscle of young, old, and very old men

The rate of motor unit (MU) loss and its influence on the progression of sarcopenia is not well understood. Therefore, the main purpose of this study was to estimate and compare numbers of MUs in the tibialis anterior (TA) of young men ( approximately 25 years) and two groups of older men ( approximately 65 years and >/=80 years). Decomposition-enhanced spike-triggered averaging was used to collect surface and intramuscular electromyographic signals during isometric dorsiflexions at 25% of maximum voluntary contraction. The mean surface-MU potential size was divided into the maximum M wave to calculate the motor unit number estimate (MUNE). The MUNE was significantly reduced in the old (91) compared to young (150) men, and further reduced in the very old men (59). Despite the smaller MUNE at age 65, strength was not reduced until beyond 80 years. This suggests that age-related MU loss in the TA does not limit function until a critical threshold is reached.     

History of electromyography and nerve conduction studies: A tribute to the founding fathers

The early development of nerve conduction studies (NCS) and electromyography (EMG) was linked to the discovery of electricity. This relationship had been concluded by observing the effect of applying electricity to the body of an animal and discovering that nerves and muscles themselves could produce electricity. We attempt to review the historical evolution of NCS and EMG over the last three centuries by reviewing the landmark publications of Galvani, Adrian, Denny-Brown, Larrabee, and Lambert. In 1771, Galvani showed that electrical stimulation of animal muscle tissue produced contraction and, thereby, the concept of animal electricity was born. In 1929, Adrian devised a method to record a single motor unit potential by connecting concentric needle electrodes to an amplifier and a loud speaker. In 1938, Denny-Brown described the fasciculation potentials and separated them from fibrillations. Toward the end of World War II, Larrabee began measuring the compound muscle action potential in healthy and injured nerves of war victims. In 1957, Lambert and Eaton described the electrophysiologic features of a new myasthenic syndrome associated with lung carcinoma. Overall, research on this topic was previously undertaken by neurophysiologists and then later by neurologists, with Adrian most likely being the first neurologist to be involved. The field greatly benefited from the invention of equipment that was capable of amplifying small bioelectrical currents by the beginning of the 20th century. Significant scientific and technical advances were later made during and after World War II which provided a large patient population with nerve injuries to study.     

Cognitive inhibition of number/length interference in a Piaget-like task in young adults: evidence from ERPs and fMRI

We sought to determine whether the neural traces of a previous cognitive developmental stage could be evidenced in young adults. In order to do so, 12 young adults underwent two functional imaging acquisitions (EEG then fMRI). During each session, two experimental conditions were applied: a Piaget-like task with number/length interference (INT), and a reference task with number/length covariation (COV). To succeed at Piaget's numerical task, which children under the age of 7 years usually fail, the subjects had to inhibit a misleading strategy, namely, the visuospatial length-equals-number bias, a quantification heuristic that is often relevant and that continues to be used through adulthood. Behavioral data confirmed that although there was an automation in the young adult subjects as assessed by the very high number of accurate responses (>97%), the inhibition of the "length equals number strategy" had a cognitive cost, as the reaction times were significantly higher in INT than in COV (with a difference of 230 ms). The event-related potential results acquired during the first session showed electrophysiological markers of the cognitive inhibition of the number/length interference. Indeed, the frontal N2 was greater during INT than during COV, and a P3(late)/P6 was detected only during INT. During the fMRI session, a greater activation of unimodal areas (the right middle and superior occipital cortex) and in the ventral route (the left inferior temporal cortex) was observed in INT than in COV. These results seem to indicate that when fully automated in adults, inhibition processes might take place in unimodal areas.     

Comparative study of evoked electromyography and facial nerve latency test in the prognosis of idiopathic facial nerve palsy in childhood

We report our results from the application of evoked electromyography (EEMG) and facial nerve latency testing (FNLT) in 30 children aged 4–14 years with idiopathic facial palsy. Our aim was to define the value of these tests as prognostic tools in Bell's palsy. From the EEMG results we ascertained that, when the amplitude of the compound muscle action potential varied between 51% and 95% of the normal value, the neuronal damage is slight (neurapraxia). When the percentage value of muscle response decreases, the prognosis is worse. The results of the FNLT showed that, when the latency is within normal limits, the damage to the nerve is slight (neurapraxia). If the latency is prolonged, the prognosis is worse. Evaluation of our results and comparison with the index of facial nerve functional recovery showed that those two tests have a high percentage of correctness (100% for the EEMG and 96.7% for the FNLT) and a low percentage of error. We conclude that these tests are excellent for predicting the outcome of facial nerve palsy in childhood and we suggest that young patents undergo both so that the determination of the lesion may be as correct as possible.