Development of a dynamometer for measuring the isometric force of the pelvic floor musculature

The aim of this study was to design and develop a dynamometer providing a direct measurement of pelvic floor muscle (PFM) strength. Materials and Methods: Two pairs of strain gauges were mounted on the moveable branch of a dynamometric speculum allowing measurements at different vaginal apertures. Linearity, repeatability, independence of the site of application of the resultant force to the lower branch of the speculum, and hysteresis were tested by means of in vitro calibration studies. Results: The linearity proved excellent over a range of 0-15 N with regression coefficients close to unity between imposed loads and voltage outputs. The slopes and intercepts of the regression lines were not significantly different between repeated sessions, indicating the high reliability of these in vitro measurements. The slopes and intercepts of the calibrations, using the same repertoire of loads imposed at three locations on the moving branch of the dynamometer, were not significantly different, confirming that the force measurement is independent of the site of the force application. Hysteresis was considered to be minimal. Conclusions: This study demonstrates that the dynamometer provides reliable measurements. The new device thus appears to have conceptual and measuring advantages over conventional methods and seems to be a very promising instrument for measuring pelvic floor strength.