Differences in pelvic floor muscle activation and functional output between women with and without stress urinary incontinence
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Introduction: The primary purpose of this research was to determine whether women with stress urinary incontinence (SUI) demonstrate pelvic floor muscle (PFM) strength or endurance deficits and/or changes in the motor control patterns used during maximum voluntary PFM contractions (PFM MVCs) and coughing. A secondary purpose was to determine the effect of age on these parameters. Methods: After first validating the use of vaginal pressure to study the functional output of the PFMs, three studies were carried out to address these objectives. In two studies vaginal pressure and PFM and abdominal muscle electromyography (EMG) data were recorded simultaneously during PFM MVCs and maximum effort coughs in continent women, women with mild SUI and women with moderate to severe SUI in both supine and standing. In the final study, the effect of continence status and age on PFM strength and endurance was measured with vaginal pressure. Results: Changes in vaginal pressure induced by PFM MVCs and coughing were found to reflect changes in urethral pressure. The women with SUI and the continent women were found to be equally able to produce peak PFM EMG and vaginal pressure amplitudes during PFM MVCs and coughs. Compared to the continent women, the women with SUI delayed activating their abdominal muscles during the PFM MVCs. During coughing, vaginal pressure and PFM EMG peaked simultaneously in the continent women, while in the women with SUI vaginal pressure peaked after PFM EMG. During both the PFM MVCs and the coughs, the EMG activity in all of the muscles tested was higher at the onset of vaginal pressure generation in the women with SUI compared to the continent women. No difference was found in PFM endurance between the women with and without SUI. The ability to generate peak vaginal pressure during coughing decreased with age. Conclusions: PFM weakness does not appear to play a significant role in SUI. Rather, the results of this research suggest that a combination of motor control deficits and delays in pressure transmission are associated with SUI in women.