Detection of individual motor units of the puborectalis muscle by non-invasive EMG electrode arrays

Cescon, Corrado and Bottin, Andrea and Fernandez Fraga, Xose Luis and Azpiroz, Fernando and Merletti, Roberto (2008) Detection of individual motor units of the puborectalis muscle by non-invasive EMG electrode arrays. Journal of Electromyography and Kinesiology, 18 (3). pp. 382-389. ISSN 1050-6411

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Purpose: The purpose of the study was to demonstrate that anatomical features of individual motor units of the puborectalis muscle can be detected with non-invasive electromyography (EMG) and to evaluate differences in electrophysiological properties of the pubo- rectalis muscles in a small group of healthy and pathologic subjects. Methods: Multichannel EMG was recorded by means of a flexible probe applied on the gloved index finger and carrying an array of eight equally spaced (1.15 mm) electrodes. A multichannel EMG amplifier provided seven outputs corresponding to the pairs of adjacent electrodes. Tests were performed in three different positions (dorsal, left and right) over the puborectalis muscle on 20 subjects (nine healthy, seven constipated and four incontinent patients). Motor unit action potentials (MUAPs) generated at the innervation zone of aMU and propagating along the muscle fibers generated repetitive characteristic patterns on the seven output channels allowing iden- tification of anatomical features of the motor units. Results: MUAPs were observed travelling in either one or both directions with the array in dorsal position, and mainly in ventral-to-dorsal direction in either lateral position. MUAP amplitude was lower in constipated and incontinent patients with respect to healthy subjects. The conduction velocity estimated on the identified MUAPs was lower for constipated patients with respect to healthy subjects suggesting different mechanical properties of the active motor units. Conclusions: This technique allows the extraction of relevant information about the anatomical features (innervation zone position and overlapping of motor unit branches) of the puborectalis muscle and its electrophysiological properties and maybe can be applied as an novel methodology for assessing the anorectal function in patients.

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