Mechanisms of pelvic floor muscle training for managing urinary incontinence in women: a scoping review

BACKGROUND: Pelvic floor muscle training is recommended as first line treatment for urinary incontinence in women based on three proposed theorized mechanisms: 'Enhanced Pelvic Floor Muscle Strength,' 'Maximized Awareness of Timing,' and 'Strengthened Core Muscles'. The purpose of this scoping review was to systematically map evidence for and against theorized mechanisms through which pelvic floor muscle training interventions work to reduce urinary incontinence in women. METHODS: The scoping review is based upon a comprehensive search of relevant literature published from 1990 to 2020 in PubMed, CINAHL, PsycINFO, ClinialTrials.gov, reference lists from review articles, and hand searches of articles by known researchers in the field. We included English-language, peer-reviewed articles on pelvic floor muscle training as an intervention for adult women if they provided empirical evidence to testing the theorized intervention mechanisms. Two independent reviewers screened articles for inclusion and extracted data to describe details of each study (author, year, country, design, sampling), measures of pelvic floor muscle strength and urinary incontinence, statistical analysis of linkage between changes in the measures, and pelvic floor muscle training regimens. Data were summarized to facilitate the integration of diverse evidence to draw conclusions on supporting or refuting the three proposed theorized mechanisms for managing urinary incontinence in women. RESULTS: Of the 278 articles identified with the search, 13 (4.7%) met inclusion criteria. There was weak to no evidence for the mechanism of enhanced pelvic floor muscle strength, equivocal support for maximized awareness of timing, and no evidence for strengthened core muscles. CONCLUSIONS: This review revealed extremely limited data supporting the proposed theorized mechanisms underlying pelvic floor muscle training programs to manage urinary incontinence in women. Such evidence is needed to help women and clinicians understand how, why and when a woman benefits from pelvic floor muscle training. Future studies should specifically state and report statistical analysis that relates the theorized mechanisms to the training outcomes observed.