title: Force-length relationship in the pelvic floor muscles under transverse vaginal distension: a method study in healthy women.
abstract: OBJECTIVE
  The purpose of this study was to investigate whether there is a relationship between changes in the diameter of the urogenital hiatus and force developed in pelvic floor musculature. In addition, we wanted to examine the reliability of the method that measures force development in the pelvic floor in the transverse direction of the urogenital hiatus.
  
  
  METHODS
  Passive and total force in the pelvic floor was measured with an intra-vaginal device in 20 healthy parous volunteers. The measurements were done with a consecutively increasing diameter in the transverse plane of the urogenital hiatus. The procedure was repeated with a few days interval.
  
  
  RESULTS
  The measurements show an increase in force with an increasing device-diameter. The results are reliable at all the diameters tested, estimated by the within-subject day-to-day variability which was non-significant. The 40 mm diameter device is most favourable, estimated by Bland Altman plots of the test-retest measurements.
  
  
  CONCLUSIONS
  Force development in pelvic floor muscles increased as a function of vaginal diameter when measured in the frontal plane. The measurements were reliable at all the different diameters chosen.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Tromsø, Norway. margareta.verelst@unn.no
authors.forename: M
authors.initials: M
authors.lastname: Verelst
authors.forename: G
authors.initials: G
authors.lastname: Leivseth
mesh_terms: D000328:Adult; D002138:Calibration; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D017773:Pelvic Floor / Q000502:physiology; D011312:Pressure; D012016:Reference Values; D015203:Reproducibility of Results; D012677:Sensation; D014551:Urinary Tract / Q000033:anatomy & histology; D014621:Vagina / Q000033:anatomy & histology / Q000502:physiology*