Test-retest reliability of the different dynamometric variables used to evaluate pelvic floor musculature during the menstrual cycle

The aim of this study was to evaluate the reliability of different dynamometric variables of the pelvic floor muscles (PFM) in healthy women during different periods of menstrual cycle.

Vaginal dynamometric equipment was developed by the authors and its reproducibility was tested. The PFM contractions of 20 healthy women were collected by two independent examiners over three consecutive weeks, always on the same day, with a seven-day interval between readings, starting from the first day after the end of the menstrual period. For the measurements, the branch of the dynamometer was positioned first on the sagittal plane and then on the frontal plane. Baseline, peak time, maximum PFM strength, impulse contraction, and average contraction force were calculated. Reproducibility was tested using the intra-class correlation coefficient (ICC) and standard error of measurement. Repeated-measures ANOVA was used to compare the data from different days.

For intra-day and inter-day reliability between examiners, all the parameters collected on the sagittal plane presented good and excellent reproducibility (ICC_2,1  = 0.60 to 0.98), whereas reproducibility on the frontal plane was respectively poor and excellent (ICC_2,1  = 0.23 to 0.97). The ANOVA revealed significant differences between sessions only for the impulse of contraction for the sagittal (P = 0.005) and frontal (P = 0.03) planes.

Time and contraction force parameters of the PFM are not influenced by hormonal alterations that occur during the menstrual cycle. The impulse of contraction was the only variable to demonstrate a significant difference between the first and second week of the data collection protocol. The baseline, maximum strength value, impulse of contraction, and average contraction force variables presented good to excellent reproducibility and can be safely used as a method of PFM evaluation.