Reliability and validity of pelvic floor muscle displacement measurements during voluntary contractions


Introduction and hypothesis

Understanding the functioning of pelvic floor muscles (PFM) is crucial in female PFM rehabilitation. The aim of this study was to determine the intra-session retest reliability and validity to evaluate the quantity of PFM displacement.


This cross-sectional observational study examined the PFM displacement of 17 young healthy nulliparous women in the midsagittal plane. Three maximal voluntary contractions (MVCs) and five fast voluntary contractions (FVCs) were simultaneously examined with an electromagnetic tracking system (ETS) and transabdominal ultrasound (TAUS) and expressed in millimeters (mean, SD). To evaluate reliability and validity, the analysis of variance, intraclass coefficient (2,1), standard error of measurement (SEM), and minimal detectable difference (MDD) were calculated.


Maximal voluntary contractions and FVCs in supine position measured by an ETS (TAUS) showed a displacement of MVC: 3.5 ± 1.9 mm (7.8 ± 4.5 mm), FVC: 3.5 ± 2.4 mm (7.6 ± 5.3 mm), and during standing of MVC: 5.2 ± 1.6 mm (9.4 ± 3.8 mm) and FVC: 4.8 ± 2.5 mm (9.7 ± 4.1 mm). Intraclass correlation for the ETS (TAUS) measurement varied between 0.79 and 0.89 (0.61 and 0.74), SEM 0.52 and 1.03 mm (1.54 and 3.2 mm), and MDD 1.54 and 3.2 mm (6.64 and 7.53 mm). The correlation between an ETS and TAUS varied between 0.53 and 0.67.


For MVC and FVC, ETS measurements are highly reliable and TAUS measurements are moderately reliable for both contraction types. The correlation between the TAUS and ETS measurements is moderate. An ETS seems to be a reliable and valid measurement tool for evaluating PFM displacement during voluntary contractions. In future studies, the reproducibility and validity of ETS measurements need to be investigated in impact activities.

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Fig. 1
Fig. 2



Pelvic floor muscles


Maximal voluntary contraction


Fast voluntary contraction


Electromagnetic tracking system


Transabdominal ultrasound


Magnetic resonance imaging




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The authors thank Dr Martin Mueller and Dr Katja Duffe, Women’s Hospital, Urogynaecology, University Hospital and University of Bern, Switzerland, for the execution of the ultrasound measurements, Jean-Daniel Pourroy, private office of physical education and physiotherapy, Bern, Switzerland for assistance during the measurements, Michala Cadova, engineer, Centre of Dental Medicine, University of Zürich, Switzerland for setting up the custom-made MATLAB program, and Parsenn-Produkte AG (Küblis, Switzerland) for providing the vaginal surface EMG probes.

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H Moser: project development, data collection, manuscript writing; H Luginbuehl: project development, support of data collection, support of final draft; J-P Baeyens: adviser, support of final draft; L Radlinger: project development, contribution to study design, technical support, support of final draft.

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Correspondence to Helene Moser.

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Moser, H., Luginbuehl, H., Baeyens, J. et al. Reliability and validity of pelvic floor muscle displacement measurements during voluntary contractions. Int Urogynecol J 30, 2093–2100 (2019).

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  • Ultrasound
  • Reproducibility of results
  • Movement
  • Gynecology
  • Rehabilitation