Abstract
BACKGROUND: Chronic fatigue is prevalent among working-age adults and has been linked to reduced physical capacity and impaired cognitive performance. While physical fitness is considered protective against fatigue-related dysfunction, few large-scale studies have examined how multidimensional fitness profiles relate simultaneously to chronic fatigue status and functional cognitive-motor outcomes. Clarifying these associations may improve risk stratification and functional assessment in occupational health settings. METHODS: In this cross-sectional study, 3,025 adults from the National Physical Fitness Health Test were evaluated. Chronic fatigue was defined using a standardized questionnaire cutoff. Physical fitness was assessed using an eight-component standardized battery and summarized as a composite Physical Fitness Index. Choice reaction time (CRT) was measured as a functional cognitive outcome. Multivariable logistic and linear regression models examined independent associations, adjusting for demographic, occupational, and anthropometric covariates. Sex-stratified ROC analyses evaluated discriminatory performance. RESULTS: Chronic fatigue was identified in 5.45% of participants and varied significantly across occupational groups. Individuals with chronic fatigue demonstrated slower CRT and lower overall physical fitness (both p < 0.001). In fully adjusted models (AUC = 0.725), higher physical fitness was strongly associated with lower odds of chronic fatigue. Chronic fatigue remained independently associated with slower CRT after adjustment, whereas higher fitness predicted faster reaction time (β = -11.66 ms per SD; p < 0.001). CRT showed moderate discriminatory ability for chronic fatigue in both males (AUC = 0.761) and females (AUC = 0.727). CONCLUSIONS: Chronic fatigue is associated with clinically meaningful slowing of cognitive-motor response and reduced multidimensional fitness. Overall fitness independently relates to both fatigue risk and reaction performance, underscoring the importance of maintaining physical fitness to mitigate functional impairment in working-age populations.