Hypothesis / aims of study
To investigate the potential cumulative effect of running on the female pelvic floor we compared pelvic floor morphology and pelvic floor muscle (PFM) function between experienced runners and women who do not exercise. We hypothesized that runners (both with and without running-induced (RI) stress urinary incontinence (SUI) would have less bladder neck support, larger hiatal areas, and lower stiffness of their PFMs than sedentary women.
Study design, materials and methods
The study was approved by the local ethics board (H-06-18-759) and all participants provided written consent prior to participating. Females over 18 years of age who run at least 5 km in under 50 min, twice a week, and who have maintained an average running distance over 10 km per week for a minimum of 1 year and those who do not exercise beyond daily life activities and who did not previously participate in high impact activities were invited to participate. Runners who did not leak urine while exercising or during activities of daily living were classified as continent and those who frequently experienced UI while running (self-reporting ≥ 1 episode per week) were classified as having RI-SUI. Participants were ineligible if they had undergone major urogenital surgery, had pelvic organ prolapse (POP-Q> stage 2), had BMI > 30kg/m2, were pregnant or had given birth in the previous year. Runners with UI were excluded if they reported leakage associated with urgency during running or if they experienced ≥1 urine leakage episode per month not associated with exercise.
Trans‐abdominal ultrasound was used to standardize estimated bladder volume between 100 and 200 mL before data collection. In a standing position, pelvic floor morphology was assessed using 2D and 3D transperineal ultrasound (GE Voluson S6, Toronto Canada) imaging. Levator hiatus area (LHA), bladder neck height (BNH) and levator plate length (LPL) at rest as well as changes in BNH and LPL during a maximum voluntary contraction (MVC) were measured. Still in standing, PFM contractile force was assessed using an intravaginal dynamometer (IVD). Participants performed a MVC with the IVD arms opened to an anterior-posterior diameter of 35mm and were instructed to contract as strongly and as quickly as possible, then to hold for 5 seconds. Contractile force outcomes included resting baseline force (N), rate of force development (N/s), relative peak force (N) and the time before the peak force decreased by 35% (endurance – s). Passive forces were recorded in supine as the IVD arms opened from 15mm to 40mm at a constant speed of 50mm/s and were held there for 7 seconds. The outcomes included baseline force (N), relative peak resistance to passive stretch, rate of force development (stiffness), and the stress relaxation coefficient measured from the stress relaxation curve. Each measure was repeated three times, with the average retained for analysis. All outcomes were tested for normality using the Shapiro-Wilk test. Group differences were tested as appropriate using either one-way ANOVA or the Kruskal-Wallis test, with effect sizes based on partial squared or epsilon, respectively. Based on a previous study (1), we estimated (α=0.05, Power=0.8) that at least 62 participants per group would be needed to detect between-group differences in LHA at rest, and 14 per group would be needed to detect between-group differences for BNH.
Results
This is a preliminary analysis. To date, thirty runners with RI-SUI, 49 runners without RI-SUI and 17 sedentary women (n=6 with UI and n=11 without UI symptoms) have participated. Data from the sedentary women with and without UI are pooled because of the current small sample. The groups were similar regarding body mass index (BMI), waist/hip ratio and parity. However, the runners with RI-SUI were older than runners without RI-SUI and sedentary participants (Table 1). Runners with and without RI-SUI had similar weekly training time and years of running experience (Table 1). Runners with RI-SUI showed a larger LHA at rest compared to runners without RI-SUI, as well as a lower bladder neck position at rest compared to both runners without RI-SUI and sedentary women (Table 2). No significant differences were found among groups for the other morphological outcomes, nor for any active and passive IVD outcomes (Table 2). The effect sizes were moderate for LHA and BNH at rest, and small for all other outcomes (Table 2).
Interpretation of results
No differences in pelvic morphology or pelvic floor muscle function were observed between continent runners and sedentary women. These findings suggest that running itself may not reduce pelvic floor support. Yet runners with RI-SUI showed less pelvic floor support than runners without RI-SUI (larger LHA and lower BNH), despite that running experience and training distance was similar between the two groups. The runners with RI-SUI also had larger LHA than sedentary women. While the runners with RI-SUI were older than the other two groups, age is not an independent risk factor for female UI in general and is unlikely to be a causal factor for RI-SUI, yet based on these findings, it should be investigated further. Other potential causes of reduced pelvic floor support (parity, BMI, menopause status) were not different among the groups. Details on biomechanical and kinematic running factors and other daily activities that may load the pelvic floor were not recorded but may help explain UI symptoms during exercise. The results of this study should be interpreted with caution due to the preliminary nature of the analysis, the cross-sectional design, and the multiple statistical comparisons. In addition, data from sedentary women with and without UI were pooled due to the small sample recruited to date; we plan to explore these cohorts separately once we reach our target sample size.