Mechanisms Underlying Running-induced Stress Urinary Incontinence in Female Runners

Abstract

Background: Some females experience urinary incontinence primarily during exercise and the pathophysiology underlying this form of leakage remains poorly understood. Urine leakage during exercise is a barrier to physical activity and many females restrict and avoid their physical activities due to these symptoms. There is a need to better understand what the short- and long-term effects of running are on pelvic organ support to guide the development of interventions that mitigate urine leakage. Objectives: The main objectives were (i) to determine whether differences exist in the pelvic floor morphometry and function among females who experience running-induced stress urinary incontinence compared to their continent counterparts, (ii) to evaluate whether changes in pelvic floor morphometry or function occur after an acute bout of running, and whether these changes differ between females who do and do not leak urine while running, (iii) to investigate the feasibility of measuring pelvic floor loading exposure during running, and (iv) to evaluate whether the exposure of the pelvic floor to higher loads during running is associated with greater changes in pelvic floor morphometry or function after a run. Methods: This thesis involved a single cross-sectional, observational study which addressed all four objectives. Female runners with and without RI-SUI underwent ultrasound imaging to measure their urogenital morphometry and intravaginal dynamometry to assess pelvic floor muscle function. These measures were repeated after an acute bout of running. During the 37-minute running task, a sensor placed in the posterior fornix and an accelerometer placed over the lateral iliac crest were used to infer pelvic floor loading. Results: There appear to be deficits in pelvic floor passive support in runners with RI-SUI that may predispose them to urine leakage while running. Although an acute run reduced pelvic organ support in all runners, pelvic floor muscle function remained largely unchanged. The observed changes appear to be unrelated to the magnitude of pelvic floor loading experienced during the run. However, because of high variability in pressure measured by the sensor in the posterior fornix, future research should seek out other ways to study how running mechanics may affect pelvic floor loading. Conclusion: This work described in this thesis is original. It is the first to comprehensively assess intrinsic pelvic floor characteristics concurrently with pelvic floor loading exposure in runners with and without running-induced stress urinary incontinence, concurrently using state-of-the-art measurement tools including ultrasound imaging, intravaginal dynamometry, a posterior fornix pressure sensor, and a wearable accelerometer. These combined findings challenge current assumptions that urine leakage during running is a consequence of the magnitude of pelvic floor loading experienced while running, and points toward passive support deficits as key contributors to urine leakage. This thesis lays important groundwork for future research on the cause of athletic incontinence. Long-term studies are especially needed to explore how running affects pelvic floor health over time. These insights will ultimately lead to interventions that reduce fear of leakage and empower female runners to continue to participate in their chosen sport.