International Urogynecology Journal

, Volume 25, Issue 8, pp 1097–1103

Characterization of the motor units of the external anal sphincter in pregnant women with multichannel surface EMG

  • Corrado Cescon
  • Eleonora Ester Raimondi
  • Vita Začesta
  • Kristina Drusany-Starič
  • Konstantinos Martsidis
  • R. Merletti
Original Article

DOI: 10.1007/s00192-014-2356-3

Cite this article as:
Cescon, C., Raimondi, E.E., Začesta, V. et al. Int Urogynecol J (2014) 25: 1097. doi:10.1007/s00192-014-2356-3


Introduction and hypothesis

Locating the innervation zones (IZs) of the external anal sphincter (EAS) is helpful to obstetricians to identify areas particularly vulnerable to episiotomy in pregnant women. The aim was to investigate the motor unit (MU) properties of the EAS during voluntary contractions.


Electromyographic signals were detected, from 478 pregnant women, by means of an intra-anal cylindrical probe carrying a circumferential array of 16 electrodes. The signals were decomposed into the constituent MU action potential trains and 5,947 templates were extracted and analyzed in order to identify the IZ position.


MUs innervated at one end are concentrated in the dorsal portion of the sphincter, while MUs innervated in the middle are distributed symmetrically in the left and right portions of the EAS. The angular propagation velocity was estimated for each MU resulting in 260 ± 45 rad/s, corresponding to 1.8 m/s on the probe surface and to about 4 m/s at a radial depth of 10 mm from the probe surface.


A novel method for identification and classification of MUs of the EAS is proposed and applied to a large-scale study. It is possible to distinguish MUs of the EAS in a minimally invasive way and identify their IZs. This information should be used to plan episiotomies and minimize risks of EAS denervation.


Innervation zone External anal sphincter Multichannel surface electromyography EMG 

Copyright information

© The International Urogynecological Association 2014

Authors and Affiliations

  • Corrado Cescon
    • 1
    • 7
  • Eleonora Ester Raimondi
    • 2
  • Vita Začesta
    • 3
  • Kristina Drusany-Starič
    • 4
  • Konstantinos Martsidis
    • 5
  • R. Merletti
    • 1
    • 6
  1. 1.Laboratory for Engineering of the Neuromuscular System, Department of ElectronicsPolitecnico di TorinoTorinoItaly
  2. 2.Ospedale S. Anna Como, Presidio CantùComoItaly
  3. 3.Riga Stradins UniversityRigaLatvia
  4. 4.University Medical CentreLjubljanaSlovenia
  5. 5.University of CagliariCagliariItaly
  6. 6.LISiN. Department of ElectronicsPolitecnico di TorinoTorinoItaly
  7. 7.Department of Health SciencesUniversity of Applied Sciences and Arts of Southern SwitzerlandMannoSwitzerland

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