Validation study of the muscle dysmorphic disorder inventory and the drive for muscularity scale in cisgender lesbian and bisexual Brazilian women.

Muscle dysmorphia is characterized by a persistent concern with being insufficiently muscular, a construct increasingly relevant among women, particularly those from sexual minority groups. This study aimed to validate the Muscle Dysmorphic Disorder Inventory (MDDI) and the Drive for Muscularity Scale (DMS) in Brazilian cisgender lesbian and bisexual women. A total of 1501 women, including 563 lesbian and 938 bisexual participants aged 18-50 years, were included in this cross-sectional study. Data were collected online via the REDCap platform. Participants completed a sociodemographic questionnaire, the MDDI, the DMS, and the Muscularity-Oriented Eating Test (MOET). Confirmatory factor analyses, reliability estimates (McDonald's ω), measurement invariance testing, convergent validity, and group comparisons were conducted. The MDDI replicated its original three-factor structure with good model fit (CFI = 0.972; TLI = 0.964; RMSEA = 0.086; SRMR = 0.078) and reliability (ω = 0.788-0.851). The DMS showed a better fit with the two-factor structure (CFI = 0.990; TLI = 0.988; RMSEA = 0.075; SRMR = 0.064), with adequate reliability for both Muscularity-oriented Attitudes (ω = 0.894) and Behaviors (ω = 0.809). Configural, metric, and scalar invariance were supported for both instruments across sexual orientation groups. Moderate-to-strong correlations with the MOET demonstrated convergent validity. A slightly higher score was found only among lesbian women for the DMS Behaviors subscale. The MDDI and DMS showed good evidence of validity and reliability for assessing muscularity-related constructs in Brazilian cisgender lesbian and bisexual women, supporting their use in both research and clinical contexts.