Reliability, validity and responsiveness of pelvic floor muscle surface electromyography and manometry

Vaginal surface electromyography (sEMG) is commonly used to assess pelvic floor muscle (PFM) function and dysfunction but there is a lack of studies regarding the assessment properties. The aim of the study was to test the hypotheses that sEMG has good test-retest intratester reliability, good criterion validity and is responsive to changes compared to manometry.

PFM resting tone, maximum voluntary contraction (MVC) and endurance were measured in 66 women with pelvic floor dysfunction. One assessment by manometry was followed by two testing sessions with sEMG at baseline. After 4 to 42 weeks of supervised PFM strength training, 29 participants were retested with both devices.

Median age of the participants was 41 years (range 24-83) and parity 2 (range 0-10). Very good test-retest intratester reliability was found for all three sEMG measurements. The correlation between sEMG and manometry was moderate for vaginal resting tone (r = 0.42, n = 66, p < 0.001) and strong for MVC (r = 0.66, n = 66, p < 0.001) and endurance (r = 0.67, n = 66, p < 0.001). Following the strength training period, participants demonstrated increased MVC and endurance measured with manometry, but not with sEMG. A significant reduction in resting tone was found only with sEMG.

sEMG is reliable and correlates well with manometry. However, sEMG is not as responsive as manometry for changes in PFM MVC and endurance. For measurement of PFM resting tone, sEMG seems more responsive than manometry, but this requires further investigation.