Motor Unit Count Research Articles

Recording of Motor Unit Potentials Count of Middle Trapezius in Children with Rounded Back

Background: Poor posture is unfortunately wide spreading not only among adults but also among children. Aim of Study: To detect the effect of rounded back posture on the Motor Unit Potentials (MUPs) count of middle trapezius. Patients and Methods: The right and left trapezius motor unit potentials countof 15 normal children (8.64±0.77 years) were compared with 15 children with rounded back (8.92±0.73 years) using electromyography apparatus (EMG). Results: There was a significant increase in the right trapezius motor unit count of the rounded back group compared with that of the normal group (p=0.02). There was no signif-icant difference in the left trapezius motor unit count between the normal and the rounded back groups (p=0.25). Conclusion: Rounded back posture affects the middle trapezius motor unit potential count.

Establishment of motor unit number index detection method

Objective: An electrophysiological technique was established to determine Motor Unit Number Index (MUNIX), and to investigate the stability of MUNIX. Methods: Fifty healthy subjects (25 males and 25 females) from the Outpatient Service of Peking University Third Hospital between December 2017 and September 2018 were included and divided into 5 groups according to age. The relevant parameters were detected in bilateral deltoid muscle (axillary nerve), double little finger abductor muscle (ulnar nerve), double quadriceps muscle (femoral nerve), double tibialis anterior muscle (peroneal nerve). The same muscle and the same healthy subjects were tested again three months later. Three-step detection were conducted: first, the surface electrode was attached to the muscle belly of each muscle, and the reference electrode was placed 2-3 cm away from the muscle belly. At the same time, the maximum compound muscle action potential (CMAP) of corresponding nerve was obtained, and the negative peak amplitude was measured. The second step was to collect the interference phase of the surface electromyography (SIP). There were 10 levels in total. And the measurement was repeated for three times, and the whole interference phase range was measured in the end. In the third step, the negative peak amplitude and SIP value of CMAP were substituted into the Excel table, and the MUNIX and motor unit number size (MUSIX) values were automatically calculated by the instrument through mathematical functions. Results: The mean MUNIX values of deltoid, extensor little finger, quadriceps femoris and tibial anterior were 193.2, 189.0, 159.7, 147.2, MUSIX were 46.9, 54.3, 49.6, 48.1 μV, respectively. The detection rates of MUNIX and MUSIX in the four muscles were 100%, respectively. With the increase of age, it could be seen that MUNIX declined, with statistically significant difference (P<0.05), but there was no significant change in MUSIX. There was no statistically significant difference in MUNIX and MUSIX between different gender, lateral sides and baseline and 3-month's reexamination results (P>0.05). Conclusions: MUNIX technology can improve the motor unit count of proximal upper limb and lower limb muscles. Its parameters are monitored using a mathematical model based on the composite muscle action potential and the interference phase of surface electromyography. Result is stable and reliable.

Motor unit number index (MUNIX) derivation from the relationship between the area and power of surface electromyogram: a computer simulation and clinical study

Objective. The motor unit number index (MUNIX) is a technique based on the surface electromyogram (sEMG) that is gaining acceptance as a method for monitoring motor neuron loss, because it is reliable and produces less discomfort than other electrodiagnostic techniques having the same intended purpose. MUNIX assumes that the relationship between the area of sEMG obtained at increasing levels of muscle activation and the values of a variable called ‘ideal case motor unit count’ (ICMUC), defined as the product of the ratio between area and power of the compound muscle action potential (CMAP) by that of the sEMG, is described by a decreasing power function. Nevertheless, the reason for this comportment is unknown. The objective of this work is to investigate if the definition of MUNIX could derive from more basic properties of the sEMG. Approach. The CMAP and sEMG epochs obtained at different levels of muscle activation from (1) the abductor pollicis brevis (APB) muscle of persons with and without a carpal tunnel syndrome (CTS) and (2) from a computer model of sEMG generation previously published were analysed. Main results. MUNIX reflects the power relationship existing between the area and power of a sEMG. The exponent of this function was smaller in patients with motor CTS than in the rest of the subjects. The analysis of the relationship between the area and power of a sEMG could aid in distinguishing a MUNIX reduction due to a motoneuron loss from that due to a loss of muscle fibre. Significance. MUNIX is derived from the relationship between the area and power of a sEMG. This relationship changes when there is a loss of motor units (MUs), which partially explains the diagnostic sensibility of MUNIX. Although the reasons for this change are unknown, it could reflect an increase in the proportion of MUs of great amplitude.

Modified motor unit number index (MUNIX) algorithm for assessing excitability of alpha motor neuron in spasticity

ObjectiveThe understanding of the spasticity mechanism is still a problem in the literature, as its definition can be made on the basis of more than one parameter. Therefore, we studied alpha motor neuron excitability, dynamic changes based on force production, and patellar tendon (T) reflex in spasticity and healthy control groups. MethodsAlpha motor neuron excitability, force production, and patellar T reflex were evaluated through three different test protocols. Motor Unit Number Index (MUNIX) measurement was applied for understanding motor neuron pool properties in the first protocol. Voluntary force production and patellar T reflex parameters were evaluated by voluntary force production and triggering patellar T reflex. Twenty spasticity and 20 healthy volunteers participated in the study. ResultsIn the spasticity group, both MUNIX numbers and Motor Unit Size Index (MUSIX) numbers were lower than those in the control group. The results for the Ideal Case Motor Unit Count (ICMUC) parameter show that there is no significant difference between spasticity and healthy individuals for low-level contractions, whereas there is a significant difference for high-level contractions (p < 0.05). In the spasticity group, an increase was observed in the ratio of maximal voluntary force to the T reflex triggered force production (Tf/Vf). ConclusionSpasticity and healthy subjects can be distinguished easily and clearly by evaluating the changes in both kinesiological and electrophysiological findings and the decreasing threshold in the alpha motor neuron pool. SignificanceThis study shows that such combined methods, which allow the evaluation of the alpha motor neuron pool, as well as kinesiological and electrophysiological parameters, are tools that cannot be overlooked in understanding spasticity.

Electrical stimulation of transplanted motoneurons improves motor unit formation.

Motoneurons die following spinal cord trauma and with neurological disease. Intact axons reinnervate nearby muscle fibers to compensate for the death of motoneurons, but when an entire motoneuron pool dies, there is complete denervation. To reduce denervation atrophy, we have reinnervated muscles in Fisher rats from local transplants of embryonic motoneurons in peripheral nerve. Since growth of axons from embryonic neurons is activity dependent, our aim was to test whether brief electrical stimulation of the neurons immediately after transplantation altered motor unit numbers and muscle properties 10 wk later. All surgical procedures and recordings were done in anesthetized animals. The muscle consequences of motoneuron death were mimicked by unilateral sciatic nerve section. One week later, 200,000 embryonic day 14 and 15 ventral spinal cord cells, purified for motoneurons, were injected into the tibial nerve 10-15 mm from the gastrocnemii muscles as the only neuron source for muscle reinnervation. The cells were stimulated immediately after transplantation for up to 1 h using protocols designed to examine differential effects due to pulse number, stimulation frequency, pattern, and duration. Electrical stimulation that included short rests and lasted for 1 h resulted in higher motor unit counts. Muscles with higher motor unit counts had more reinnervated fibers and were stronger. Denervated muscles had to be stimulated directly to evoke contractions. These results show that brief electrical stimulation of embryonic neurons, in vivo, has long-term effects on motor unit formation and muscle force. This muscle reinnervation provides the opportunity to use patterned electrical stimulation to produce functional movements.

Motoneuron replacement for reinnervation of skeletal muscle in adult rats.

Reinnervation is needed to rescue muscle when motoneurons die in disease or injury. Embryonic ventral spinal cord cells transplanted into peripheral nerve reinnervate muscle and reduce atrophy, but low motoneuron survival may limit motor unit formation. We tested whether transplantation of a purified population of embryonic motoneurons into peripheral nerve (mean ± SE, 146,458 ± 4,011 motoneurons) resulted in more motor units and reinnervation than transplantation of a mixed population of ventral spinal cord cells (72,075 ± 12,329 motoneurons). Ten weeks after either kind of transplant, similar numbers of neurons expressed choline acetyl transferase and/or Islet-1. Motoneuron numbers always exceeded the reinnervated motor unit count. Most motor end plate were simple plaques. Reinnervation significantly reduced muscle fiber atrophy. These data show that the number of transplanted motoneurons and motoneuron survival do not limit muscle reinnervation. Incomplete differentiation of motoneurons in nerve and lack of muscle activity may result in immature neuromuscular junctions that limit reinnervation and function.

İdiyopatik Parkinson hastalığında motor ünite sayısı değişimi / Motor unit number estimation in Idiopathic Parkinson’s disease

Motor unit number estimation in Idiopathic Parkinson’s disease Objective: Motor neuron degeneration in parkinsonism is known to develop in Western Pacific (Guam) parkinsonism-amyotrophic lateral sclerosis complex, multisystem atrophy (MSA), postensefalitic parkinsonism, Creutzfeld-Jacob disease and dementia with parkinsonism linked to chromosome 17. Existence of motor neuron degeneration in these disorders brings up the question whether motor neuron degeneration develops in Idiopathic Parkinson Disease (IPD). Our study aims to answer this question. Methods: In this study, we estimated the motor unit counts in 24 patients diagnosed as IPD and 26 healthy control subjects with similar age (50-70) and gender, using threshold method. Results: Our study revealed the motor unit counts, done using threshold method, in IPD patients in thenar muscles were not different from the control group subjects. Conclusion: This result implied that there was not asymptomatic motor neuron degeneration in IPD, and IPD did not share the same physiological mechanism with other parkinsonism related disorders associated with motor neuron degeneration. However, since there are limited numbers of publications on this subject, to verify this conclusion, further studies using similar methods, with larger patient groups are needed.

Number of motor units in human abductor hallucis

Motor unit number was estimated for the human abductor hallucis (AH) muscle in 11 subjects by counting the number of increments in surface electromyographic responses to progressive increases in current-pulse amplitude applied to the muscle-nerve. The average motor unit count for AH (43) was substantially smaller than that estimated for other human muscles. Consequently, motor unit activity should be readily recordable up to high forces in AH, making it well suited for studies of recruitment and rate coding.

Mechanical properties and behaviour of motor units in the tibialis anterior during voluntary contractions.

The present work was carried out to analyse the properties and behaviour of Tibialis anterior motor units (MUs) during voluntary contractions in humans. A total of 528 single MU mechanical properties was recorded in 10 subjects by means of the spike-triggered averaging (STA) technique. MU recruitment thresholds and discharge frequencies were recorded during linearly increasing maximal voluntary contraction (MVC). The results indicate a mean (+/- SD) MU torque of 25.5 +/- 21.5 mN.m. and a mean time-to-peak of 45.6 +/- 13.6 ms. A comparison of the average MU twitch torque with that of the muscle allowed an estimate of about 300 MUs in the Tibialis anterior. A positive linear relationship was recorded between the MU twitch torque and the recruitment threshold. The mean minimal and maximal discharge frequencies of MUs were 8.4 +/- 3.0 Hz and 33.2 +/- 14.7 Hz, respectively. The results of the present work indicate that MU behaviour during voluntary contractions is different in the tibialis anterior and in the adductor pollicis.

Natural history of ALS: symptoms, strength, pulmonary function, and disability.

ALS is a disease that may have a preclinical and a clinical phase (see Appendix 1 Table 1). The low frequency of ALS suggests an inherent susceptibility in patients who are destined to develop the disease at a particular point in life subsequent to a possible initiating event. [1] View this table: Table 1. Appendix 1: Pathogenetic aspects of ALS. Neuropathological, neurophysiological, and clinical aspects of ALS in the preclinical and clinical stages. There is currently no clear-cut evidence of neuropathologic, neurophysiologic, or clinical abnormalities that would mark a patient as potentially susceptible to ALS during the susceptibility period. Initiating events may include severe electric shock exposure, which is a physical injury that is epidemiologically linked to the development of ALS, or dietary intake of particular substances that have, in isolated instances, been associated by case-control studies with the development of ALS. During the latent period of the development of the disease, there may be changes in motoneuron soma and dendritic size as the only neuropathologic features long before there is evidence of motoneuron loss or corticospinal tract degeneration. No clear-cut neurophysiologic signs have yet been described. [2] During the clinical period of the disease, there may be a presymptomatic period during which there are pathologic changes involving motoneuron size and loss as well as possible corticospinal tract degeneration. This hypothetical construct is based on pathologic studies. [3] Neurophysiologic changes during this time may include changes in single-fiber density, with variable changes in motor unit count. [4] The clinical examination at this point is characterized by patient reports of possible functional changes and by possible abnormalities in isokinetic muscle testing at a time when normal isometric strength is present. [5] During the stage of disease spread from focal onset to more symmetric generalization, there will be changes in motoneuron size and loss as …

A new approach to motor unit estimation with surface EMG triggered averaging technique.

A new method for estimating the number of motor units using a surface EMG triggered averaging technique is described. This method provides an estimation of mean motor unit potential (MUP) amplitude at different levels of contraction, which can be utilized to estimate the number of motor units in a given muscle. Motor unit count estimated in abductor pollicis brevis (APB) muscle of 11 normal healthy subjects ranged from 131 to 371 with a mean of 246 +/- 68. In our preliminary study of patients with lower motor neuron lesions, there was a significant reduction in the number of motor units. We believe our new noninvasive method of motor unit counting is a relatively simple and reproducible physiological technique.

Motor unit numbers and contractile properties after spinal cord injury

The number of motor units in the thenar muscle group was estimated in 11 patients with cervical spinal cord injuries. The surface electromyogram and twitch force, in response to maximal stimulation of the median nerve was divided by the average surface electromyogram and twitch of single units. The average single unit size was obtained by intramuscular microstimulation of motor nerve branches and by graded whole nerve stimulation, which provided three independent estimates, two based on the electromyogram and one based on force. The motor unit estimates from the patients covered a wide range. Some had essentially normal motor units both in numbers and contractile properties, while others had varying reductions in numbers of units. Those patients who showed a large reduction in motor unit numbers also had greatly enlarged units, which produced an average of up to sixfold the normal force. These enlarged units summed to produce maximal compound action potentials and twitches that were sometimes indistinguishable from normal. Magnetic resonance imaging scans of the cervical spine obtained from some patients provided independent evidence that patients with low motor unit counts had sustained direct injury to the anterior aspect of the spinal cord at the relevant segmental levels. Some patients showed a normal number of motor units long after the injury. No evidence of transneuronal degeneration could be demonstrated in the thenar group in these patients with the current techniques.

Estimation of the number of motor units based on macro-EMG.

The technique of the macro-EMG was used to estimate the number of motor units in the tibialis anterior muscles of healthy subjects in a wide range of ages, and of patients with myasthenia gravis and patients with amyotrophic lateral sclerosis or spinal muscular atrophy. The results obtained suggest a decrease in the number of motor units in the tibialis anterior muscle with increasing age in normal subjects. In myasthenic patients the motor unit count was within the normal range for their age group. Patients with motor neuron disorders on the average had a very low number of motor units.

Neuromuscular function in weight-trainers

Electrophysiologic measurements were made on the median-innervated thenar muscles and triceps surae in 17 weight-trainers (bodybuilders and weight-lifters) and in control subjects. In the median-innervated thenar muscles, the weight-trainers presented normal values for motor unit counts, reflex potentiation, and twitch contractile properties; however, the weight-trainers possessed a significantly greater (8%) median motor nerve conduction velocity. In the triceps surae, the weight-trainers exhibited significantly greater reflex potentiation (70%), which was interpreted as an increased ability to activate motor units during maximal voluntary contractions. Peak twitch tension (16%) and twitch contraction time (20%) of the triceps surae were significantly greater in the weight-trainers, whereas their twitch half-relaxation time and soleus motor unit counts were not significantly different from control values. The observed difference may reflect a combination of genetic endowment and the effects of training.

Neuromuscular adaptation in human thenar muscles following strength training and immobilization.

The effects of strength training and limb immobilization on the human thenar muscles were investigated in 11 healthy subjects. One group (n = 6) trained prior to immobilization and a second group (n = 5) underwent immobilization prior to training. Measurements made in the control condition and following the two experimental conditions included voluntary isometric strength, motor-unit counts, motor nerve conduction velocity, reflex potentiation, and isometric twitch-contraction properties. When the results of both groups were combined an average of 5 wk of immobilization was found to cause a significant decrease in voluntary strength (42%, P less than 0.05) and reflex potentiation (37%, P less than 0.01) in relation to the control condition. Training caused an increase (40%, P less than 0.05) in voluntary strength and a decrease in twitch tension (25%, P less than 0.01) and contraction time (8%, P less than 0.05). Training prior to immobilization provided a reserve of neuromuscular function, which attenuated the effect of immobilization in relation to the control condition. It was concluded that neural as well as muscular adaptation occurred in response to immobilization.

Electrophysiological evaluation of cross-face nerve graft in treatment of facial palsy.

A cross-face autogenous single graft was performed in eight patients with facial palsy. Several electrophysiological techniques have been used in a follow-up study of one to three years' duration. Clinical results are extremely disappointing. The only recovery observed could not be ascribed to the graft. The investigations and the motor unit count in the facial muscles led to the conclusion that the surgical technique employed is a failure. The orbicularis oculi muscle in particular has no chance whatsoever of being satisfactorily reinnervated. Various reasons for this poor recovery are analysed: too small a number of properly grafted axons, syncinesis, muscle degeneration and poor myelination. These observations nevertheless suggest some experimental fields which may lead to improvements in the technique to a point where it may become clinically useful.

Motor Unit Counting and the Caffeine Contracture Test in Malignant Hyperthermia

Motor unit counting, a neurophysiologic test, compares the sizes of the potentials of single motor units evoked by weak graded neural stimulation with the response of the whole muscle to a maximal neural stimulus. This test was performed on 1) individuals belonging to families afflicted with malignant hyperthermia (MH), and 2) individuals unrelated to malignant-hyperthermia-susceptible (MHS) patients. The MH status of the patients was confirmed by means of the skeletal-muscle caffeine contracture test. Two or more of the following muscles or muscle groups were examined in each subject: extensor digitorum brevis, hypothenar muscle groups, the thenar muscles supplied by the median nerve, and the soleus. Stimulating electrodes consisting of two silver discs were placed over the endplate zone of the muscle and a reference electrode at a distance. The repetition rate for the stimuli was approximately 0.7 Hz. When the potentials of 10 or more motor units had been identified on an oscilloscope their mean amplitude and the number of functioning motor units were calculated. Coaxial needle electromyography was carried out on the brachial biceps or the abductor pollicis brevis, and the vastus medialis or the extensor digitorum brevis. Motor unit counts were lower than the cut-off values corresponding to the selected probability levels in a high proportion of MHS subjects. The proportion was larger in tests utilizing pairs of muscles than in those involving the appropriate muscle types alone. A further increased proportion, and thereby more sensitive discrimination, was obtained by a triple combination of muscles. Concentric needle myopathy (EMG) was not as accurate a prognosticator of the MH trait as was motor unit counting. Motor unit counting confirms that the primary defect of human MH involves motor nerves as well as the skeletal muscle. Motor unit counting also serves as a noninvasive diagnostic test for MH and is only slightly less accurate than the caffeine contracture test.

The motor unit profile in two experimental chronic myopathies.

The motor unit profile of the rat soleus muscle has been studied in two types of experimentally induced chronic myopathy. Tetrabenazine administered for 6 weeks resulted in a moderate myopathy characterized by necrosis, regeneration, and hypertrophy of muscle fibers. This model was associated with a normal motor unit count. The twitch tension of the muscle remained normal, presumably because of hypertrophy of some of the soleus muscle fibers; however, tetanic tension was reduced. The twitch time to peak became very prolonged. Another myopathy, characterized only by regenerating muscle fibers, was produced 6 weeks after abdominal aortic ligation. In this model, the soleus motor unit count was also normal. Twitch and tetanic tensions were reduced, and the contraction time was prolonged. The findings are discussed in relation to the motor unit profile reported in human neuromuscular diseases.

Evidence for reversible motoneurone dysfunction in thyrotoxicosis.

Motor unit estimating techniques have been employed as part of a comprehensive electrophysiological survey of peripheral nerve and muscle in 20 patients with thyrotoxicosis. In all patients there was evidence of a loss of operational motor units; the selective nature of this involvement suggested that the motoneurone soma was the site of the primary lesion. The reversible nature of the postulated motoneurone dysfunction was demonstrated by the increased motor unit counts in six patients who were studied again after treatment of their thyrotoxicosis.

Functional compensation of human motor units in health and disease

The number of motor units in the human thenar muscles falls gradually over the first 6 decades of life. In healthy humans over 60 years of age and subjects with hemiplegic atrophy, motoneuron disease, diabetic neuropathy and the carpal tunnel syndrome, the loss may be more severe. Provided the motor unit count did not fall below 10–20% of the normal number of motor units, functional compensation could maintain muscle size and strength and mask the severity of motor unit loss.