# Associations of physical fitness and choice reaction time with chronic fatigue in working-age adults: a population-based study

## TL;DR

This study finds that chronic fatigue in working-age adults is linked to lower physical fitness and slower reaction times, suggesting that maintaining fitness can help reduce fatigue-related issues.

## Contribution

The study reveals that multidimensional physical fitness and cognitive-motor performance are independently associated with chronic fatigue in a large population sample.

## Key findings

- Chronic fatigue is associated with significantly slower choice reaction times and lower physical fitness.
- Higher physical fitness is strongly linked to lower odds of chronic fatigue in adjusted models.
- Choice reaction time shows moderate ability to discriminate chronic fatigue in both males and females.

## Abstract

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.

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.

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).

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.