Urinary symptoms during physical activity are commonly reported by females, which can limit their ability to fully engage in an active lifestyle. Despite the high prevalence, there are still knowledge gaps preventing us from fully understanding the role of physical activity on pelvic floor function [1]. There are two competing hypotheses regarding the impact of exercise on pelvic floor: on one hand, exercise may improve pelvic floor support and strength while on the other, it may induce strain on the structures that provide support. Both hypotheses are supported by findings suggesting that females who engage in physical activity are at higher risk of reporting urinary incontinence than sedentary females [2]. Yet, exercise, when done at mild to moderate intensity, was also shown to decrease the odds of females experiencing urinary incontinence [3]. 

To date, no studies have investigated the acute effects of running on pelvic floor function measured using intravaginal dynamometry and morphology measured using ultrasound imaging (USI) among females who experience running-induced stress urinary incontinence (RI-SUI) compared to those with equal exercise exposure who do not leak urine while running. By shedding light on the acute impact of physical activity on the pelvic floor, these findings will fill an important knowledge gap and will contribute to the implementation of targeted interventions.

This cross-sectional study received approval from the local institutional research ethics board. Adult females with no known risk factors related to physical activity (PAR-Q+), who run at least 5 km in under 50 minutes, twice per week and more than 10km a week, and who have done so for at least one year, were recruited into two cohorts: runners who regularly (≥ 1 per month) experience RI-SUI and those who do not. Runners were excluded if they reported a history of urogenital surgery, symptoms of energy deficiency using the LEAF-Q, dyspareunia, any neurologic disorder, were pregnant or had delivered a baby within the previous year. All eligible participants provided demographic information and were asked to complete several questionnaires (ICIQ-FLUTS, ICIQ-BS, ICIQ-Vaginal Symptoms, IPAQ-LF). 

The morphology of pelvic floor muscles (PFMs) was assessed using 2D and 3D USI. In a standardized standing position, static (3D) and dynamic (4D) volumes were acquired at rest and while the participant performed a maximum effort Valsalva maneuver (MVM). 2D ultrasound videos were then recorded during MVM and maximal voluntary contraction (MVC) of their PFMs. Next, participants were instrumented with an intravaginal dynamometer and performed a MVC against an anteroposterior diameter of 35mm. In supine, passive forces were recorded while the diameter moved from 15mm to 40mm. The elongation was held for 7 seconds before the arms return to their initial position. Three repetitions of each task were performed. Measures of PFM morphology in 3D included the area of the levator hiatus (LA) and its related antero-posterior (AP) and medio-lateral (ML) diameters both at rest and during peak MVM, as well as their relative displacement. The measures acquired in 2D included bladder neck (BN) height and levator plate (LP) length and their relative displacement during the MVC and MVM. Measures of PFM function acquired through dynamometry included baseline force, relative peak force, rate of force development, and static endurance measured as the time before the peak force achieved during the MVC decreased by 35%. Passive tissue forces measured during elongation included baseline force, relative peak resistance, rate of force development (stiffness), and the stress relaxation coefficient (SRc). The participants then ran on a treadmill for 37 minutes using a standardized protocol: 2 minutes at 7km/h, 10 km/h, and at 15 km/h, 30 minutes at a self-selected speed, followed by 30 seconds at 10 km/h then 7 km/h. Following the run, the ultrasound imaging and dynamometer protocols were repeated. Mixed-effects ANOVA models were used to compare all outcomes between groups (with or without RI-SUI) and within-groups (before and after the run) including the interaction between group and time. Effect sizes (Cohen’s d) were calculated using partial eta squared.

Thirty-nine runners (20 control, 19 RI-SUI) participated. The groups did not differ in terms of demographic outcomes; however, the controls were younger than the cases (mean=36.2 years SD=7.9; mean=43.9 SD=10.6, respectively (p≤0.01)). The ICIQ-FLUTS total score was significantly higher in participants who experienced SUI during running, which was driven by the results from the Urinary Incontinence subscale (mean=1.7/20 SD=2.0; mean=5.8/20 SD=2.3, respectively (p≤0.001)). The groups were similar in terms of running experience (years), weekly running distance, speed of running and the number of steps taken during the running protocol. 

Compared to before the run, changes in PFM function assessed using intravaginal dynamometry after the run were not different between groups. However, stiffness during passive elongation tended to be lower in the runners with RI-SUI both before and after the run when compared to the runners without RI-SUI (d=0.77) (Table 1). 

In terms of morphology measured using ultrasound imaging, significant and large within-group main effects were found. At rest, the area and AP diameter of the levator hiatus were larger after the run, the BN height was lower after the run, and the LP length was longer after the run. On peak MVM and MVC, the BN height was lower after the run than before the run. All outcomes had large effect sizes (d ranging from 0.84 to 2.09). Concurrently, the extent of LP shortening during MVC significantly increased after the run and the extent of LP lengthening and BN displacement decreased after the run during the MVM in both groups.

Significant acute changes in the morphology of the PFMs are caused by running. Specifically, running appears to strain the passive support system, as evidenced by the larger area and AP diameter of the levator hiatus, the more caudal position of the BN and the elongated LP observed in quiet standing after the run. These changes were observed in both groups. PFM function, as measured by intravaginal dynamometry during MVC and passive tissue elongation, was less affected by the run. Yet the observed changes in the morphology of the PFMs measured on USI after the run are consistent with the observed trends in relative peak force and stiffness measured using dynamometry after the run. While non-significant, runners with RI-SUI tended to demonstrate a reduction in their capacity to generate force rapidly (power) after the run while these same parameters tended to improve in runners without RI-SUI.

Running appears to strain the passive tissues within the pelvic floor – both runners with and without RI-SUI showed significant loss of pelvic floor support and trends towards reduced stiffness of the PFMs measured using intravaginal dynamometry. The unique approach used in this study adds to our knowledge regarding the acute effects of physical activity on the pathophysiology of RI-SUI.

K. Bo and I. E. Nygaard, “Is Physical Activity Good or Bad for the Female Pelvic Floor? A Narrative Review.,” Sports Med., vol. 50, no. 3, pp. 471–484, 2020, doi: https://dx.doi.org/10.1007/s40279-019-01243-1.
R. V. Teixeira, C. Colla, G. Sbruzzi, A. Mallmann, and L. L. Paiva, “Prevalence of urinary incontinence in female athletes: a systematic review with meta-analysis,” Int. Urogynecol. J., vol. 29, no. 12, pp. 1717–1725, 2018.
M. M. Kim, S.-S. Ladi-Seyedian, D. A. Ginsberg, and E. I. Kreydin, “The Association of Physical Activity and Urinary Incontinence in US Women: Results from a Multi-Year National Survey.,” Urology, vol. 159, pp. 72–77, 2022, doi: https://dx.doi.org/10.1016/j.urology.2021.09.022.

Continence 7S1 (2023) 100993
DOI: 10.1016/j.cont.2023.100993