57 research outputs found
Scanning Electromyography
The study of the anatomy and physiology of the motor unit has important implications in
the diagnosis and follow-up of neuromuscular pathologies. Muscle action potentials allow
the use of electrophysiological techniques based on electromyography (EMG) to make
inferences about muscle structure, state and behaviour. Scanning EMG is one such
technique that can record the temporal and spatial distribution of electrical activity of a
single motor unit, allowing for deep insight into the structure and function of motor units.
In this chapter, we describe the scanning EMG technique in detail, both from a technical and
clinical point of view. A brief review of the motor unit anatomy and physiology is provided
in Section 2. The technique, the apparatus setup, the recording procedure and the signal
processing required are described in Section 3. Key results of studies using scanning EMG
are reviewed in Section 4, including findings related to motor unit organisation in normal
muscle and how changes due to pathology are reflected using this electrophysiological
technique. Finally, Section 5 provides some hints regarding the use of scanning EMG in
research.This work was supported by the Regional Health Ministry of the Government of Navarre
under the project 1312/2010
EMG Modeling
The aim of this chapter is to describe the approaches used for modelling electromyographic
(EMG) signals as well as the principles of electrical conduction within the muscle. Sections
are organized into a progressive, step-by-step EMG modeling of structures of increasing
complexity. First, the basis of the electrical conduction that allows for the propagation of the
EMG signals within the muscle is presented. Second, the models used for describing the
electrical activity generated by a single fibre described. The third section is devoted to
modeling the organization of the motor unit and the generation of motor unit potentials.
Based on models of the architectural organization of motor units and their activation and
firing mechanisms, the last section focuses on modeling the electrical activity of a complete
muscle as recorded at the surface
The filling factor of the sEMG signal at low contraction forces in the quadriceps muscles is influenced by the thickness of the subcutaneous layer
Introduction: It has been shown that, for male subjects, the sEMG activity at low contraction forces is normally âpulsatileâ, i.e., formed by a few large-amplitude MUPs, coming from the most superficial motor units. The subcutaneous layer thickness, known to be greater in females than males, influences the electrode detection volume. Here, we investigated the influence of the subcutaneous layer thickness on the type of sEMG activity (pulsatile vs. continuous) at low contraction forces.Methods: Voluntary surface EMG signals were recorded from the quadriceps muscles of healthy males and females as force was gradually increased from 0% to 40% MVC. The sEMG filling process was examined by measuring the EMG filling factor, computed from the non-central moments of the rectified sEMG signal.Results: 1) The sEMG activity at low contraction forces was âcontinuousâ in the VL, VM and RF of females, whereas this sEMG activity was âpulsatileâ in the VL and VM of males. 2) The filling factor at low contraction forces was lower in males than females for the VL (p = 0.003) and VM (p = 0.002), but not for the RF (p = 0.54). 3) The subcutaneous layer was significantly thicker in females than males for the VL (p = 0.001), VM (p = 0.001), and RF (p = 0.003). 4) A significant correlation was found in the vastus muscles between the subcutaneous layer thickness and the filling factor (p < 0.05).Discussion: The present results indicate that the sEMG activity at low contraction forces in the female quadriceps muscles is âcontinuousâ due to the thick subcutaneous layer of these muscles, which impedes an accurate assessment of the sEMG filling process
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