Features Of Motor Unit Action Potentials Research Articles

A Deep CNN Framework for Neural Drive Estimation From HD-EMG Across Contraction Intensities and Joint Angles.

Previous studies have demonstrated promising results in estimating the neural drive to muscles, the net output of all motoneurons that innervate the muscle, using high-density electromyography (HD-EMG) for the purpose of interfacing with assistive technologies. Despite the high estimation accuracy, current methods based on neural networks need to be trained with specific motor unit action potential (MUAP) shapes updated for each condition (i.e., varying muscle contraction intensities or joint angles). This preliminary step dramatically limits the potential generalization of these algorithms across tasks. We propose a novel approach to estimate the neural drive using a deep convolutional neural network (CNN), which can identify the cumulative spike train (CST) through general features of MUAPs from a pool of motor units. We recorded HD-EMG signals from the gastrocnemius medialis muscle under three isometric contraction scenarios: 1) trapezoidal contraction tasks with different intensities, 2) contraction tasks with a trapezoidal or sinusoidal torque target, and 3) trapezoidal contraction tasks at different ankle angles. We applied a convolutive blind source separation (BSS) method to decompose HD-EMG signals to CST and segmented both signals into windows to train and validate the deep CNN. Then, we optimized the structure of the deep CNN and validated its generalizability across contraction tasks within each scenario. With the optimal configuration for the HD-EMG data window (overlap of 20 data points and window length of 40 data points), the deep CNN estimated the CST close to that from BSS, with a correlation coefficient higher than 0.96 and normalized root-mean-square-error lower than 7% with respect to the BSS (golden standard) within each scenario. The proposed deep CNN framework can utilize data from different contraction tasks (e.g., different intensities), learn general features of MUAP variants, and estimate the neural drive for other contraction tasks. With the proposed deep CNN, we could potentially build a neural-drive-based human-machine interface that is generalizable to different contraction tasks without retraining.

A simulation study on the relation between the motor unit depth and action potential from multi-channel surface electromyography recordings

To investigate the spatial information of individual motor unit (MUs) using multi-channel surface electromyography (EMG) decomposition. The K-means clustering convolution kernel compensation (KmCKC) approach was employed to detect the innervation pulse trains (IPTs) from the simulated surface EMG signals, and the motor unit action potentials (MUAPs) were evaluated using the spike-triggered average (STA) technique. The relationships between the features of MUAP and MU depth were determinated with a least square fitting method. The errors of peak-to-peak (PTP) amplitude of reconstructed MUAPs were less than 5.73%, even with 0 dB signal-to-noise (SNR). The fitting errors with nonlinear model were less than 5.55% for SNRs higher than 20 dB. The results show that it is possible to provide a useful method for estimating MU depth from surface EMG recordings. It is expected to extend the applicability of surface EMG technique to more challenging clinical applications.

S68 SFAP to MUAP: Temporal and spatial characteristics of MU

Motor unit action potential (MUAP) represents the summated activity of single fiber action potentials (SFAP) coming from individual muscle fibers those reside in the pick-up territory of recording needle. Calculated features of MUAP give reliable information concerning the architecture of motor unit under investigation but they also depend on the recording site and technique. In this presentation, features of SFAP will be discussed first as a measure of individual muscle fiber conductivity. Then, how MUAP features are changed by moving the needle near to tendon is questioned. Measuring the bioelectrical activity of motor unit across its territory by scanning EMG will be revisited. SFAP represents the moving quadrupole in near field recordings. The faster the quardupole moves, the quicker the phases of SFAP change and lead to shorter “spike duration” in turn. The distribution of “spike duration” shows less central tendency in myopathic muscle, which can be related to increased variability among the muscle fibers. Furthermore, moving the recording site near to tendon exaggerates this conduction difference and leads to more spiky and temporally dispersed MUAP, a finding that is especially detected in simulation studies. Scanning the electrical activity of motor unit from side to side informs the examiner about the motor unit structure. New algorithms and methods were developed for extracting features from scanning EMG signals. The recorded activity of motor unit during voluntary drive changes by the placement of needle electrode. As it changes, it teaches us a lot!

The effect of recording site on extracted features of motor unit action potential

Motor unit action potential (MUAP), which consists of individual muscle fiber action potentials (MFAPs), represents the electrical activity of the motor unit. The values of the MUAP features are changed by denervation and reinnervation in neurogenic involvement as well as muscle fiber loss with increased diameter variability in myopathic diseases. The present study is designed to investigate how increased muscle fiber diameter variability affects MUAP parameters in simulated motor units. In order to detect this variation, simulated MUAPs were calculated both at the innervation zone where the MFAPs are more synchronized, and near the tendon, where they show increased temporal dispersion. Reinnervation in neurogenic state increases MUAP amplitude for the recordings at both the innervation zone and near the tendon. However, MUAP duration and the number of peaks significantly increased in a case of myopathy for recordings near the tendon. Furthermore, of the new features, “number of peaks×spike duration” was found as the strongest indicator of MFAP dispersion in myopathy. MUAPs were also recorded from healthy participants in order to investigate the biological counterpart of the simulation data. MUAPs which were recorded near to tendon revealed significantly prolonged duration and decreased amplitude. Although the number of peaks was increased by moving the needle near to tendon, this was not significant.

Étude électromyographique paravertébrale dorso-lombaireAnalyse en mode multi-MUP et établissement de normes au sein d’une population de référence

Objective. The aim of this study was to contribute to draw up reference values relating to electromyographic (EMG) parameters in dorsal and lumbar paraspinal muscles. Materials and Methods. 75 healthy subjects without back pain underwent electromyography of multifidus bundles, which are innervated uni-segmentally by the dorsal ram of the spinal nerve. T8, L3, L4, L5 and S1 myotomes were systematically explored. Output variables were spontaneous denervation activity and quantitative EMG data obtained by multi-MUP (Motor Unit action Potential) analysis. Results. No abnormal insertional or spontaneous activity (such as fibrillation, positive sharp waves or fasciculation) was recorded at rest. Neither sex nor age influenced motor unit action potential features in our series. Reference values were drawn up for T8 and L5 segmental levels using the mean values of 20 motor unit potentials in each patient studied, the reference interval being defined by the lower and the upper outlier limits on individual values. Conclusion. This study offers reference data to electromyographers to help better identifying possible myogenic or neurogenic pathological changes, especially in lumbosacral radiculopathies.

Satellite potentials of motor unit action potentials in normal muscles: a new hypothesis for their origin

Objective: A satellite potential is a late component of the motor unit action potential (MUAP) that occurs both in pathologic and normal muscle. We investigated the physiological mechanisms responsible for satellite potentials in normal muscle by relating the latencies of MUAP features to the timing of the underlying electrical events.Methods: We analyzed 21 MUAPs with satellite potentials that had been recorded using a monopolar needle electrode from brachial biceps and tibialis anterior muscles in 10 normal subjects. We estimated the endplate-to-electrode, endplate-to-tendon, and satellite propagation times from the latencies, with respect to the MUAP onset, of the MUAP spike, terminal wave, and satellite.Results: Satellite latencies ranged from 8.8 to 32 ms, too long to be explained by mechanisms involving regenerating axons or atrophic muscle fibers. The spike-to-satellite time intervals approximated either twice the spike-to-terminal-wave interval (17 MUAPs) or twice the terminal-wave latency (4 MUAPs).Conclusions: These results are consistent with the hypothesis that satellite potentials are due to retrograde propagation in a non-innervated muscle fiber that is connected with an innervated muscle fiber at one of the muscle/tendon junctions. Such a configuration could arise as a result of longitudinal muscle-fiber splitting.

Global and detailed features of motor unit potential in myogenic and neurogenic disorders

Motor unit action potential (MUAP) may be characterized by two complementary features: global and detailed. The global feature is represented by the envelope of the curve while the detailed feature describes the fluctuations around the envelope. The global feature represents the magnitude of the signal and is related to the number of fibers contributing to the MUAP. The detailed feature indicates the single fiber potential's synchronization. The global feature is characterized by amplitude and duration and may be quantified by the following indexes: area/amplitude or size index, which is interpreted as the potential “thickness”. The detailed feature is characterized by the number of phases and turns. The irregularity coefficient, which is related to the “length” of the curve, combines the number of phases and turns with their amplitudes. The aim of this study was to analyze the relationship between the global and detailed features of MUAPs in various neuromuscular disorders. In neurogenic cases, with the exeption of the correlation between the duration and number of turns ( r=0.58), no correlation between any other parameters related to global and detailed features were significant ( r≤0.4). In myogenic cases, a significant correlation between the irregularity coefficient and duration ( r=0.71), irregularity coefficient and area/amplitude ( r=0.54) rather than that between the irregularity coefficient and area ( r=0.32), has been found. The correlations between parameters were more significant in more chronic processes.

P125 The reorganization of motor units (MUs) in amyotrophic lateral sclerosis (ALS) in comparison to spinal muscular atrophy (SMA)

Motor unit action potential (MUAP), which consists of individual muscle fiber action potentials (MFAPs), represents the electrical activity of the motor unit. The values of the MUAP features are changed by denervation and reinnervation in neurogenic involvement as well as muscle fiber loss with increased diameter variability in myopathic diseases. The present study is designed to investigate how increased muscle fiber diameter variability affects MUAP parameters in simulated motor units. In order to detect this variation, simulated MUAPs were calculated both at the innervation zone where the MFAPs are more synchronized, and near the tendon, where they show increased temporal dispersion. Reinnervation in neurogenic state increases MUAP amplitude for the recordings at both the innervation zone and near the tendon. However, MUAP duration and the number of peaks significantly increased in a case of myopathy for recordings near the tendon. Furthermore, of the new features, “number of peaks × spike duration” was found as the strongest indicator of MFAP dispersion in myopathy. MUAPs were also recorded from healthy participants in order to investigate the biological counterpart of the simulation data. MUAPs which were recorded near to tendon revealed significantly prolonged duration and decreased amplitude. Although the number of peaks was increased by moving the needle near to tendon, this was not significant.

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.