Mean Motor Unit Action Potential Research Articles

Neural control properties of the external anal sphincter in young and elderly women.

The prevalence of fecal incontinence (FI) increases with age and affects more than 15% of the elderly population. Sarcopenia, skeletal muscle structural, and functional decline with aging, is known to be caused by neuromuscular dysfunction. However, age-related alterations of the neuromuscular function of the external anal sphincter (EAS) have not been studied. This study aims to quantitatively characterize the effect of aging on the EAS by assessing the firing patterns and size of motor unit action potential (MUAP) using high-density surface electromyography (HD-sEMG) recording and analysis techniques. Thirteen young (31.0 ± 3.6 years) and 14 elderly (64.3 ± 6.2 years) healthy women were recruited for this study. EMG activity of the EAS during maximal voluntary contraction was recorded by a 64-Channel, HD-sEMG intra-rectal probe. HD-sEMG signals were decomposed into MUAP spike trains to extract the firing rate and amplitudes thereof. HD-sEMG decomposition was successfully performed. For the young and elderly groups, mean motor unit (MU) firing rates of 11.4 ± 2.1 pulses per second (PPS) and 9.6 ± 2.3 PPS, and mean MUAP amplitudes of 45.2 ± 14.3 µV and 61.9 ± 21.2 µV were respectively obtained. Both the MU firing rate and MUAP amplitude were significantly different between two groups (P < .05). Moreover, the MUAP firing rate and amplitude correlated with age with a linear regression model (P < .05). This study represents the first effort to examine the effect of aging on the neuromuscular function of EAS. Results suggest an age-related impairment of lower motor neuron descending excitation to the EAS with a compensatory increase in mean MU size.

Motor Unit Characteristics after Targeted Muscle Reinnervation.

Targeted muscle reinnervation (TMR) is a surgical procedure used to redirect nerves originally controlling muscles of the amputated limb into remaining muscles above the amputation, to treat phantom limb pain and facilitate prosthetic control. While this procedure effectively establishes robust prosthetic control, there is little knowledge on the behavior and characteristics of the reinnervated motor units. In this study we compared the m. pectoralis of five TMR patients to nine able-bodied controls with respect to motor unit action potential (MUAP) characteristics. We recorded and decomposed high-density surface EMG signals into individual spike trains of motor unit action potentials. In the TMR patients the MUAP surface area normalized to the electrode grid surface (0.25 ± 0.17 and 0.81 ± 0.46, p < 0.001) and the MUAP duration (10.92 ± 3.89 ms and 14.03 ± 3.91 ms, p < 0.01) were smaller for the TMR group than for the controls. The mean MUAP amplitude (0.19 ± 0.11 mV and 0.14 ± 0.06 mV, p = 0.07) was not significantly different between the two groups. Finally, we observed that MUAP surface representation in TMR generally overlapped, and the surface occupied by motor units corresponding to only one motor task was on average smaller than 12% of the electrode surface. These results suggest that smaller MUAP surface areas in TMR patients do not necessarily facilitate prosthetic control due to a high degree of overlap between these areas, and a neural information—based control could lead to improved performance. Based on the results we also infer that the size of the motor units after reinnervation is influenced by the size of the innervating motor neuron.

A preliminary evaluation of surface electromyography as a tool to measure muscle fatigue in the National Hunt racehorse

Background: Within equestrian sports, training is commonly based on historic and anecdotal good practice. Telemetric surface electromyography (sEMG) systems facilitate assessment of muscle recruitment including mean motor unit action potential (mM-UAP). Mean EMG frequency (mEMGF) provides an objective measure of fitness levels while a shift in the median EMG frequency (MeEMGF) over time can illustrate fatigue. Aim: This study aimed to investigate if sEMG could be used in the field to evaluate muscle activity of the Gluteus superficialis in a cohort of National Hunt racehorses during one canter interval training session. Method: Sensors were secured bilaterally to horses' Gluteal superficialis prior to exercise and data were collected over a standardised 10 metre interval. A repeated measure ANOVA assessed differences in mEMGF between runs across the cohort and between runs for individual horses. A Pearson's correlation identified if mEMGF was related to perceived fitness level as assessed by the trainer. mEMGF and MeEMGF for individual horses were plotted over time (0.25 second intervals) to assess fitness and fatigue. Results: Individual horses exhibited a wide variety of mMUAP values. No differences were found between runs for the overall cohort (p&gt;0.05) however significant differences were found between runs within some individual horses (p&lt;0.01). No relationship between fitness level and mEMGF was found (p&gt;0.05), mEMGF varied throughout runs and MeEMGF for most horses remained consistent indicative of a lack of fatigue. Conclusion: The results suggest that this technology exhibits potential to be used to aid analysis of efficacy of training programmes for individual horses.

Loss of motor unit size and quadriceps strength over 10 years in post-polio syndrome

ObjectiveTo investigate whether strength decline in post-polio syndrome (PPS) results from excessive distal axonal degeneration of enlarged motor units. MethodsWe assessed changes over 10years in isometric quadriceps strength, mean motor unit action potential (MUAP) size, root mean squared (RMS) amplitude, and level of interference (LOI) in 47 patients with PPS and 12 healthy controls, using high density surface EMG. At baseline, all patients had symptomatic quadriceps dysfunction, evidenced by transmission defects on single-fibre EMG. ResultsMU size and strength declined significantly by 20% and 15%, respectively in patients with PPS. Those with the largest initial MU sizes exhibited the greatest losses of mean MU size (27%) and proportional decreases in quadriceps strength (23%). Initial strength, change in LOI and change in RMS amplitude together explained 35% of the variability in strength changes in patients. MU size of controls did not change, although they lost 29% strength. ConclusionsMU size and strength declined concomitantly in a homogeneous cohort of patients with PPS and quadriceps dysfunction. SignificanceThis long term follow-up study provides evidence that size diminution of enlarged MUs combined with a reduced number of active MUs contributes to the gradual strength decline in PPS.

Electromyographic evaluation of approach stride, jump stride and intermediate stride in selected superficial muscles of the jumping horse: a preliminary study

The horse's ability to execute the diverse physical demands of jumping is greatly influenced by muscular adaptations to training. The aim of the study was to provide preliminary insight into potential differences in the functional activity of muscles recruited during phases of the equine jumping effort. An exploratory case study was conducted to investigate muscle activity and recruitment in one jumping horse, experienced in 1.40 m competition. Wireless sEMG electrodes were utilised to quantitatively investigate the degree of muscle activation by recording potentials from the Superficial gluteal (SG), Triceps brachii (TB) and Longissimus dorsi muscles. Data were collected as the horse executed a related combination of fences with a maximum height of 1.25 m. Mean motor unit action potential (mMUAP) and mean peak amplitude frequency (PAF) were determined for each muscle during approach, jump and intermediate strides, and were analysed using Friedman and Wilcoxon Signed Rank tests to establish whether significant differences occurred between strides. Statistical analyses did not reveal significant differences between mMUAP values for muscles investigated across strides (P≯0.05). However, significant differences were found for mean PAF values in the left SG between approach and jump strides (P&lt;0.025), and between jump and intermediate strides (P&lt;0.025) in the left TB. The lack of significant differences between strides may reflect the theory that the jump stride is a form of extended suspension incorporated into the canter stride and may support current anecdotal training methods of the jumping horse, which place emphasis on developing a regular and collected canter. However, results from this study were based on one horse and therefore application to the wider population of jumping horses should be undertaken with caution until further research in more subjects is conducted to support the results from this preliminary study.

Quantitative analysis of motor unit action potentials in the subclavian muscle of healthy horses.

To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses. 10 healthy adult Dutch Warmblood horses. Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses. Mean +/- SD duration of insertional activity was 471.7 +/- 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 RV (95% confidence interval [CI], 349 to 410 microV). Mean MUAP duration of the subclavian muscle was 727 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP defined as MUAP with > 4 phases, was 77%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP CONCLUSIONS AND CLINICAL RELEVANCE: This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses.

Needle electromyography of bulbar muscles in patients with amyotrophic lateral sclerosis: evidence of subclinical involvement.

To determine if quantitative motor unit action potential (MUAP) analysis and peak ratio interference pattern analysis of the fifth, seventh, and eleventh cranial nerve innervated muscles are helpful in the assessment of subclinical bulbar involvement in ALS. With both electromyographic (EMG) techniques, electrical activity was recorded via needle electrodes from the right frontalis, masseter, and sternocleidomastoideus muscles of nine ALS patients without clinical bulbar signs (Frenchay score >85%) aged 40 to 87 years; 21 healthy subjects aged 27 to 74 years; and five ALS patients with clinical bulbar signs (Frenchay score <85%) aged 53 to 69 years. The normal mean (2 SD) MUAP duration of the frontalis muscle was 7.4 (2.2) milliseconds; masseter muscle, 9.3 (3.1) milliseconds; and sternocleidomastoideus muscle, 10.9 (4.1) milliseconds. The normal mean (2 SD) peak ratio of the frontalis was 2.3 (1.1) milliseconds; masseter, 1.2 (0.4) milliseconds; and sternocleidomastoideus, 1.5 (0.7) milliseconds. Quantitative MUAP analysis was interpreted as neuropathic if MUAP duration, MUAP amplitude, or both exceeded the mean (+2 SD). Peak ratio interference pattern analysis was interpreted as neuropathic if the peak ratio, the number of small time intervals, or both were below the mean (-2 SD). If a result of either EMG technique was neuropathic in at least one of the three investigated muscles, bulbar involvement was assumed. Subclinical bulbar involvement could be detected by quantitative MUAP analysis in six ALS patients without clinical bulbar signs, and by peak ratio interference pattern analysis in two. Conventional needle EMG of the fifth, seventh, and eleventh cranial nerve innervated muscles shows subclinical bulbar involvement quite frequently. Peak ratio interference pattern analysis is largely not helpful in detecting this involvement.

Automatic decomposition electromyography in idiopathic inflammatory myopathies.

Automatic decomposition electromyography (ADEMG) is a commercially available software package with installed reference values that enables the objective measurement of motor unit action potentials (MUAPs). To assess the diagnostic yield of this package in idiopathic inflammatory myopathies (IIM) we performed bicepts brachii ADEMG in 17 patients with polymyositis, dermatomyositis and inclusion body myositis. Results were compared with those in 12 controls, and with the results of conventional EMG of the biceps and other muscles. Decreased mean values for MUAP duration occurred significantly more frequently in IIM patients than in controls; other MUAP characteristics did not differ. In IIM patients, decreased mean amplitude and increased mean number of turns occurred significantly less frequently on ADEMG than did corresponding abnormalities on conventional biceps EMG. Decreased mean values for duration and amplitude, and increased mean values for number of turns were seen significantly less often on ADEMG than corresponding abnormalities on conventional EMG of four different, individually chosen muscles. Overall evaluation of ADEMG resulted in a diagnosis of "possible myopathy" in 1 and "probable myopathy" in 8 patients, whereas overall evaluation of conventional EMG led to a diagnosis "suggestive of IIM" in 13 patients. We conclude that, although measurement of mean MUAP duration might be valuable in IIM diagnosis, our results do not favour the use of biceps brachii ADEMG and the installed reference values for the diagnosis of IIM. We suggest modifications to improve ADEMG's applicability.

A comparison of turns analysis and motor unit analysis in electromyography

We compared the results of turns analysis and motor unit analysis on 4056 electromyographic interference patterns (IPs) from normal subjects and patients with neuromuscular disorders. The motor unit analysis involved decomposing the IPs into their component motor unit action potentials (MUAPs) using automatic decomposition electromyography (ADEMG). We checked the accuracy of the decompositions by attempting to reconstruct some of the IPs from their identified MUAPs using computer simulations. The simulations revealed that ADEMG typically identified more than 60% (but not all) of the MUAPs in a given IP. Both turns and MUAP properties showed regular and related changes with force, age, muscle, and recording electrode type. The number of turns in each IP was highly correlated with the number of active MUAPs ( r = 0.65), the mean MUAP firing rate ( r = 0.72), the mean number of turns per MUAP ( r = 0.34), and the product of these 3 properties ( r = 0.83). The mean amplitude change per turn was highly correlated with the mean MUAP amplitude ( r = 0.82), but also depended on the number of turns per MUAP. Due to the lack of a one-to-one relationship between the turns analysis properties and the MUAP properties, the turns analysis properties by themselves did not provide sufficient information to infer unambiguous physiological information about motor unit morphology or firing behavior.

Evaluation of an automatic method of measuring features of motor unit action potentials

This study was performed to evaluate an automatic method of motor unit action potential (MUAP) analysis developed in our laboratory. MUAPs were recorded from the biceps brachii muscle of 68 normal subjects and 122 patients with nerve or muscle disease. The values of mean MUAP durations from normal subjects obtained by automatic analysis were similar to those reported in the literature. However, the normal range of MUAP amplitude and the incidence of polyphasic MUAPs were much higher. Normal ranges of mean MUAP area, area/amplitude ratio, and the number of turns were also defined. Automatic analysis demonstrated an abnormality of at least one MUAP feature in 70% of patients. There was concordance between automated analysis and visual assessment of MUAPs in 76% of patients with neuropathy but in only 50% of patients with myopathy. The relationships between different MUAP features seen in neuropathy and myopathy are explained in physiologic terms.

Influence of contractile force on properties of motor unit action potentials: ADEMG analysis

We have used automatic decomposition electromyography (ADEMG) to measure the configurational and firing properties of 13 206 motor unit action potentials (MUAPs) in the brachial biceps, brachial triceps and anterior tibial muscles of 30 healthy adults (22 men, 8 women; mean age 48.6 ± 16.9 years, range 20–76) at three levels of isometric contractile force: threshold, 10% of maximum voluntary contraction (MVC), and 30% MVC. In all muscles, the increment in contractile force from threshold to 10% MVC was associated with a significant ( P < 0.05, paired t-test) increase in mean MUAP firing rate and number of turns per MUAP. The increment from 10% to 30% MVC led to highly significant ( P < 0.005) increase in mean firing rate, number of turns, amplitude and rise rate. Each force increment was associated with an increase in the number of simultaneously-active MUAPs per recording site; and with a significant decrease in mean MUAP duration in all muscles, due to noise-dependency of the duration measurement. Quantitatively, the changes in MUAP properties with force were comparable to or exceeded the effects of age, gender differences, or intermuscular variability. Test-retest measurements 2 years apart in a subgroup of young adults showed good correspondence of mean MUAP properties with force standardization. These results demonstrate that contractile force is a major determinant of MUAP shape and behavior properties, and so must be precisely measured or controlled in clinical EMG studies.

Properties of motor unit action potentials recorded with concentric and monopolar needle electrodes: ADEMG analysis.

We compared the configurational and firing properties of 7270 motor unit action potentials (MUAPs) recorded with either concentric (CNE) or monopolar (MNE) needle electrodes from the brachial biceps and anterior tibial muscles of 10 healthy young adults (mean age 27 +/- 4.5 years) using automatic decomposition electromyography (ADEMG). In both muscles, mean MUAP amplitude, rise rate, and number of turns were significantly greater when recorded with MNE (paired t-test, P less than 0.001 in each case). Similar findings were observed at all three tested levels of isometric contractile force: threshold, 10% of maximum voluntary contraction (MVC), and 30% MVC. In contrast, there was no significant difference between electrode types on measurements of mean MUAP duration or firing rate (P greater than 0.05 in each case). These findings indicate that it is acceptable to generalize normative data on MUAP duration and firing rate from one electrode type to another, but that measures of MUAP amplitude and complexity require independent normative databases.

Age effects on properties of motor unit action potentials: ADEMG analysis.

We have measured the configurational and firing properties of 13,206 motor unit action potentials (MUAPs) from the brachial biceps, brachial triceps, and anterior tibial muscles in 10 young (20-40 years), 10 middle-aged (40-60 years), and 10 elderly (60-80 years) normal individuals, using an automatic method for decomposition of the electromyographic (EMG) interference pattern (ADEMG). Recording were made during stable isometric contractions at threshold, 10%, and 30% of maximum voluntary contraction using standard concentric needle electrodes. At supra-threshold forces, an average of 5.9 simultaneously active MUAPs were identified at each recording site. Mean amplitudes, durations, and numbers of turns all increased linearly with age in both low-threshold and high-threshold MUAPs (p less than 0.01), suggesting an ongoing process of progressive denervation and compensatory reinnervation. Mean MUAP firing rates decreased with age (p = 0.01) when force was measured proportionately, but not when measured absolutely. In a subgroup of 12 age-matched gender pairs, men had larger mean MUAP amplitudes, rise rates, and numbers of turns (p less than 0.05), probably reflecting larger muscle fiber diameters. These findings amplify previous observations from traditional analysis of lowest-threshold single MUAPs; establish a base of normative adult data for ADEMG; and further validate the clinical applicability of rapid, automatic EMG decomposition.