This single-center diagnostic clinical trial aimed to detect the threshold of urine leakage in females with stress urinary incontinence as compared to normal controls by evaluating the vesical and abdominal pressures during weight pulling, pushing, and Valsalva maneuver.

The study was conducted from July 2017 to January 2018. Fifty-one female participants were enrolled. Exclusion Criteria included: pelvic organ prolapse/professional athletes/ diabetes/ hypertension/ history of any skeletal problems, recent pelvic surgery ,neurological or cardiovascular disease /BMI above 39/ urinary tract infection /dissatisfaction to enter or continue the study. Simple randomization was used to select participants from the target sample of healthy and incontinent women. The two groups were matched according to age, height, weight, BMI, parity, and menopausal situation.  Blinding was not possible for patients, but the performer and assessor were blind to the history of underlying incontinence. All participants completed the Incontinence Questionnaire-Urinary Incontinence Short Form (ICIQ-UISF). Modeling of Valsalva maneuver ,pulling and pushing heavy weights using a simulator device was used to understand the changes and involuntary leakage threshold with empty and full bladder. In all stages, the urodynamic system measured intra-abdominal pressure, intra-vesical pressure, and pressure of detrusor with anal and vesical sensors in full and empty bladder situations. In addition, Maximum Voluntary Contraction (MVC) (the greatest amount of tension a muscle can generate and hold) and urine leakage of participants were measured. Participants were asked to bend from their knees and hold their waist flat and lift the lever upward, which was connected to the device’s sensor on the floor by chains, flexible on the height of the participants, simulating the process of heavy lifting and holding. The participants were asked to increase their force gradually and eventually hold the lever with their maximum force within 10 seconds. The movement took place for 10 seconds, and it was asked to slow down the force and eventually reach its maximum and hold the lever.

The mean age of the 51 participants was 45.25±8 years (ranging from 30 to 65).  The mean BMI (Body Mass Index) was 28.96±3.81. Independent T-test showed a significant difference in MVC, intra-abdominal and vesical pressures in both full and empty bladders of patients as compared to healthy individuals (P˂0.001). Pearson test indicated that vesical pressure  and abdominal pressure were correlated with Valsalva maneuver in both empty and full bladder, even in healthy controls, but correlation of MVC with vesical pressure (p=0.005) and abdominal pressure (p=0.031) was significant only in the patient group while full bladder pulling but no urine leakage was observed even when reaching MVC. Significant correlation was found between vesical and abdominal pressure in both groups (p˂0.0001). The Patient group pushed or pulled weights with less force than the control group with no leakage; it can be hypothesized that incontinent patients were afraid of leakage, therefore they adjusted their MVC to the level that leakage did not occur, even if this threshold is higher than what they thought.

Utilizing  MVC force may not necessarily lead to urine leakage. Thus,  stress-causing factors like Valsalva maneuver are more important than weight-carrying in the occurrence of urinary incontinence, and recommendations should be individualized for weight carrying. Considering the potential of this device in recording  traction and compression forces in different positions such as squatting, crouching, pulling, and pushing, it can be helpful to identify the best position, in which there is minimum force on the pelvic floor structure, resulting in decreased urine leakage.

stress-causing factors like Valsalva maneuver are more important than weight-carrying in the occurrence of urinary incontinence, and recommendations should be individualized for weight carrying.