Background <p>Muscle dysmorphia (MD) is characterized by an excessive concern of not being muscular enough. Sociocultural influences appear to play a central role in the internalization of muscular beauty ideals and the development of MD. No study has examined the potential mediating pathways from sociocultural pressure sources through internalized beauty standards to an algorithm-defined MD diagnosis in the general German population.</p> Methods <p>A cross-sectional survey was conducted among adults (≥ 18 years) in Germany via the Online Platform Prolific^®. Participants completed standardized questionnaires assessing sociocultural influences and internalization of different beauty standards (SATAQ-4R) and a clinically algorithm-defined MD, operationalized using criteria by Pope et al. [<CitationRef CitationID="CR4">4</CitationRef>], following the approach described by Mitchison et al. [<CitationRef CitationID="CR14">14</CitationRef>]. Data were weighted to approximate representativeness for the German population across the key demographics age and gender.</p> Results <p>In the total sample, a binary logistic regression indicated that internalization of the beauty standards Thin/Low body fat, Muscularity, and General Attractiveness significantly predicted algorithm-defined MD, whereas sociocultural pressure sources such as Family, Peers, Significant Others, and Media were not significant. In linear regression models, Media pressures predicted all forms of internalization, while Peer pressure predicted only Muscularity internalization. Mediation analyses indicated that internalization, particularly internalization of ideals of Muscularity, significantly mediated the relationship between Media and Peer pressures and algorithm-defined MD. Gender-specific analyses also showed Muscularity internalization as the key mediator for both men and women. In men, internalization of General Attractiveness ideals additionally mediated the relationship between Media pressure and MD. In women, only Family had a significant effect on algorithm-defined MD, mediated via Muscularity Internalization.</p> Discussion <p>Our findings highlight that internalization, particularly of the Muscularity ideal, appears to be a core mechanism linking sociocultural pressures to algorithm-defined MD. These results provide empirical evidence that interventions for MD need to focus on modifying internalized appearance ideals, especially the Muscularity ideal, to reduce MD symptoms in both men and women, with additional attention to General Attractiveness internalization in men.</p>