All participants were recruited by convenience sampling method. SUI patients were diagnosed using a urodynamic test by urogynecologists at the Urogynecology Outpatient Clinic of Imam Khomeini and Hashemi Nezhad hospitals located in Tehran. If mixed symptoms were present, such as frequency, urgency or nocturia, patients with predominately SUI as a chief complaint were included in the study. Healthy individuals without any form of urinary incontinence using the International Consultation on Incontinence Questionnaire-short form (ICIQ-UI SF) with a score of zero, were recruited from staffs of the same two hospitals where patients were selected. All eligible women aged between 20–55 years, prior to menopause were included in the study. The exclusion criteria for all participants were as follow: body mass index (BMI) > 30 kg/m2, cesarean labor, pregnant or had delivered in the previous 6 months, diabetes, nervous system problems, urogenital prolapse above grade 2, hysterectomy, pelvic floor surgery in the previous 6 months, taking medications related to UI, breathing disorders such as asthma and chronic obstructive pulmonary disease (COPD), being infected with coronavirus infection which had led to lung damage, smoking, and being a professional athlete [13 ].
Before the study, all the participants received verbal information about the methods and aims of the study. They filled out the informed consent forms, and were assured that their data would be confidential and that they could leave the study at any time. Ultrasonic evaluations were performed in a center at the School of Rehabilitation Sciences of Iran University of Medical Sciences (IUMS).