Is there any difference in measurement of pelvic floor muscle strength in supine and standing position?

Background. Traditionally, pelvic floor muscle function and strength have been measured in a supine position. However, stress urinary incontinence most often occurs in an upright position, and an important clinical question is whether measurement of pelvic floor muscle strength in the supine position reflects strength in standing. The purpose of the present study was to investigate whether there is a significant and clinical difference in pelvic floor muscle strength measurement in supine and standing position. Methods. Eighteen women, mean age 43.4 years (range 31-64 years), with symptoms of stress and mixed incontinence attending a pelvic floor muscle-training program participated in the study. Measurement of pelvic floor muscle strength was conducted with a fiberoptic microtip transducer connected to a balloon catheter inserted into the vagina (Camtech AS, Sandvika, Norway). Measurement of resting pressure, maximum squeeze pressure, and holding period in seconds, were assessed in random order in supine and standing position. Results. The mean difference between supine and standing resting pressure was 8.6 cmH(2)O (95% CI 4.9-12.3), p<0.001, between supine and standing maximum strength 0.3 cmH(2)O (95% CI-4.0 to 3.4), p=0.884, and between supine and standing holding period 0.9 s (95% CI-3.3 to 1.4), p=0.409. Conclusion. Vaginal resting pressure was significantly higher in the standing compared to the supine position. Neither maximal strength nor holding time was different when comparing the two positions. Measurement of vaginal squeeze pressure is easier to perform and standardize in the supine compared to the standing position, and seems to reflect pelvic floor muscle strength in the standing position.