Adaptation and validation of the muscle dysmorphic disorder inventory in a population of French athletes (MDDI-Fr).

Introduction: Muscle dysmorphia, a theme mainly investigated by Anglo-Saxon research, is a specific body dysmorphic disorder that characterizes individuals who think they are insufficiently muscular and lean. Understudied in francophone countries, tools translated and validated in French to measure the symptomatology of muscle dysmorphia remain rare.

Objectives: The aim of this study was the translation into French and the psychometric validation of a tool evaluating muscle dysmorphia, the Muscle Dysmorphic Disorder Inventory (MDDI-Fr), through 13 items divided into three dimensions: the "Drive For Size" (DFS), the "Appearance Intolerance" (AI) and the "Functional Impairment" (FI).

Methodology: A first translation step was conducted, followed by two cross-sectional studies conducted in France. In both of the latter studies, a sociodemographic questionnaire and the Muscle Dysmorphic Disorder Inventory - French version (MDDI-Fr) were administered. The first study included 342 university students (Mage=20.9; SDage=2.9), and 1822 athletes for the second study (Mage=23.9; SDage=5.9). Validation was performed using internal consistency measures and confirmatory factor analysis.

Results: The correlation matrices showed good significant results between items and dimensions. The three dimensions appeared distinct from each other with significant intra-dimension correlations. The internal consistency of the tool and its three dimensions show valid Cronbach's alphas (study 1: DFS=0.79, AI=0.74, FI=0.75, MDDI=0.74; study 2: DFS=0.72, AI=0.75, FI=0.83, MDDI=0.75). In addition, the tri-factor analysis shows significant and promising scores for the tool in three dimensions and 13 items for study 1 (χ/df=4.67, CFI=0.85, TLI=0.83, RMSEA=0.10, SRMR=0.00), as for study 2 (χ/df=16.08, CFI=0.87, TLI=0.84, RMSEA=0.09, SRMR=.06). Gender analyses were conducted on study 2, which showed that the DFS subscale (items 1, 4, 5) and the AI subscale (items 6 and 9) presented the greatest differences in factor loadings between genders.

Conclusion: The translation, as well as the validation of the MDDI-Fr structured with 13 items and three dimensions, showed significantly satisfying results for its adaptation in French in a population of French men and women practicing weight training. However, the "Appearance Intolerance" dimension shows moderate links with the global tool, which should be investigated in future studies. Although the psychometric properties of the MDDI-Fr are promising, additional research is needed to gain a better understanding of gender differences in the results, especially for the DFS dimension.