Differences in pelvic floor muscle morphology and function between female runners with and without running-induced stress urinary incontinence

Objective: To investigate the differences in pelvic floor muscle (PFM) morphology and function between female runners with and without running-induced stress urinary incontinence (RI-SUI).

Design: This was a cross-sectional, observational study.

Methods: Experienced female runners were recruited into two groups: runners who regularly experience RI-SUI (n = 19) and runners who do not (n = 20). Active and passive pelvic floor muscle (PFM) properties were assessed using intravaginal dynamometry during maximal voluntary contractions (MVC) and during passive tissue elongation. The morphology of the urethra and PFMs was assessed using 2D and 3D transperineal ultrasound imaging. Independent t tests or Mann-Whitney U were used as appropriate to test group differences on all study outcomes, and Cohen's d effect sizes were calculated.

Results: The rate of force development during the MVC was significantly higher in participants reporting RI-SUI (p ≤ 0.05) and conversely, significantly lower during passive elongation of the PFMs (p ≤ 0.05) compared to runners with no history of leakage. Concurrently, the extent of bladder neck elevation between rest and maximum voluntary activation was significantly higher among those with RI-SUI compared to those without. Although not significant, small to moderate effect sizes were observed for other outcomes-active force outcomes measured during MVC tended to be higher in runners with RI-SUI, while passive force outcomes measured during passive tissue elongation tended to be lower. The cross-sectional area of the urethral wall and the area of the levator hiatus tended to be larger in runners with RI-SUI compared to those without.

Conclusion: Runners who experience RI-SUI demonstrate better PFM contractile function but lower passive support when compared to their continent counterparts.