The Cross-Cultural Adaptation, Validation and Psychometric Properties of the Mental Fatigue Scale in Turkish Athletes

<b>Background/Objective</b>: This study aimed to adapt the Mental Fatigue Scale (MFs) to evaluate the psychometric properties in adult and adolescent athletes. <b>Methods</b>: A total of 491 adolescent and adult athletes (n = 491) consisting of 204 adults (men = 115; female = 90; age = 24.38 ± 3.18 year) and 287 adolescents (men = 178; female = 109; age = 14.97 ± 1.55 year) who actively participated in various sports branches voluntarily participated in this study. The MFs consists of fifteen (15) items and a single-factor structure and is a measurement tool used to measure the general mental fatigue level of athletes. Two experts used a four-point Likert scale to assess the content validity of each of the fifteen MFs items, which were aligned with the provided definition of mental fatigue in a sports context. Drawing on these findings, a confirmatory factor analysis was conducted on the survey data collected to assess the construct validity of this measure. <b>Results</b>: The outcomes of the confirmatory factor analysis provided acceptable support for factorial validity (χ²/sd = 1.52; <i>p</i> < 0.01, SRMR = 0.05, RMSEA = 0.08, GFI = 0.94, CFI = 0.89, NNFI = 0.87). Additionally, multi-group confirmatory factor analysis supported measurement invariance, indicating that the scale functions equivalently across adolescent and adult athletes. Furthermore, the analysis demonstrated favorable internal consistency (α = 0.88), confirming the reliability of the MFs. Test-retest after two weeks revealed an intra-class correlation of 0.90. <b>Conclusions</b>: Collectively, these results suggest that the MFs is a dependable and valid instrument that is particularly valuable for gauging overall mental fatigue in athletes. Coaches and sports scientists can use this assessment tool to evaluate athletes' general mental fatigue effectively.