Exercise-based pad tests have been used to evaluate the effectiveness of conservative interventions on exercise-induced urinary incontinence. We hypothesized that perspiration and vaginal secretions contribute to pad weight gain and its variability during these tests. Therefore, among continent females who performed a treadmill-based pad test, we aimed to determine the contribution of fluids other than urine on, assess the test-retest reliability of, and determine the influence of temperature and humidity on pad weight gain.

This observational cohort study was approved by the local institutional ethics board. Inclusion criteria were females aged ≥18 years, no history of any urinary incontinence (UI), and self-reported ability to complete a 38-minute treadmill running protocol. Exclusion criteria were pregnancy or within the postpartum year, neuromuscular disorders affecting voiding control, and diagnosed pelvic floor disorder. After providing written informed consent, participants completed either two (n=20) or three (n=10) laboratory assessments. Participants completing two sessions were tested in a standard laboratory set to 21°C. Those completing three sessions performed all visits in an environmentally controlled chamber with temperature/humidity set at 21°C/35% for the first two trials and 27°C/65% for the third. Before each trial, participants were asked to void their bladder, then the bladder was confirmed to be empty (<50mL) using 2D transabdominal ultrasound. Participants were weighed with clothes off, and their running clothes and shoes were weighed separately. After donning a pre-weighed incontinence pad, participants walked or jogged at an intensity rated “somewhat hard” (Borg 12–14) for 5 minutes, then increased their pace to one rated as “hard” (14–16), which was maintained for 30 minutes, followed by a 3-minute cool down. Participants removed the pad and returned it for reweighing, were weighed again without clothing, then again had their clothes and shoes weighed. All study visits occurred within two weeks and at a similar time of day. Pad weight distributions were determined and tested for normality. Intra-class correlation coefficients (ICCs, model 3) and Bland-Altman analyses were used to determine the reliability between days 1 and 2 across all participants. A general linear mixed model evaluated the impact of higher ambient temperature/humidity on pad weight gain among those who ran in the environmental chamber. A linear regression examined the relationship between clothing weight gain (reflecting overall perspiration rate) and pad weight gain.

Thirty females participated (Table 1); 20 completed two visits and ten completed three visits; none perceived urine leakage during the running protocol. Pad weight gains were normally distributed while clothing weight gains were not. For pad weight gain, the ICC showed moderate between-day reliability (ICC 0.69; 95% CI 0.348–0.854) and the Bland–Altman analysis showed a mean difference of −0.1 g, with 95% limits of agreement from −4.11 to 3.91g. Perspiration loss was higher on day 3 compared to days 1 and 2, but pad weight gain was not (Table 2). No association was found between sweat loss and pad weight gain (p = 0.216).

Pad weight gains of up to 8g (95% CI) during a 38 min treadmill protocol may be attributed to fluids other than urine. Despite that pad weight gain demonstrated moderate between-day reliability, there was considerable variability across testing days (95% CI up to 4g), limiting the ability to adjust for perspiration or to set a meaningful cut-off score for detecting changes in urine leakage.

Pad weight gain and between-session changes in pad weight gain during exercise should be interpreted cautiously as an outcome measure in clinical practice or research, as they may reflect variability related to fluids other than urine.