The Role of Sleep Quality and Sleepiness in the Relationship Between Cognitive Flexibility and Fatigue

TL;DR

This study shows that sleep quality and sleepiness play key roles in how cognitive flexibility affects fatigue in healthy adults.

Contribution

The study reveals sleep quality and sleepiness act as serial mediators between cognitive flexibility and fatigue.

Findings

Cognitive flexibility has both direct and indirect effects on fatigue.

Sleep quality and sleepiness each independently mediate the relationship between cognitive flexibility and fatigue.

The serial mediation effect of sleep quality followed by sleepiness is statistically significant.

Abstract

This study aimed to determine the pathways linking cognitive flexibility to fatigue through the serial mediation effect of sleep quality and sleepiness in 564 healthy adults using various scales, including the Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, Chalder Fatigue Scale, and Cognitive Flexibility Inventory. Analysis was performed using two mediating variables (sleep quality and sleepiness) with age and gender as covariates. The simple mediation effect was evaluated using the Causal Step. The indirect effect was examined using bootstrap method and Sobel test. The total and direct effects of cognitive flexibility on fatigue were both found to be statistically significant. The research model revealed three significant indirect effects: cognitive flexibility affecting fatigue through sleep quality, cognitive flexibility affecting fatigue through sleepiness and cognitive flexibility affecting fatigue through both sleep quality and sleepiness. Additionally, serial mediation analysis showed that the relationship between cognitive flexibility and fatigue is sequentially mediated by sleep quality and sleepiness (B = -0.064, SE = 0.013, 95% CI: -0.070 to -0.017). All effects were confirmed through the 95% confidence intervals, which did not include zero, and with significant p values. These findings highlight the role of sleep quality and sleepiness as serial mediators of the relationship between cognitive flexibility and fatigue. The study's major contribution is to provide insight on the independent and serial mediating role of sleep quality and sleepiness in the relationship between cognitive flexibility to fatigue.

The online version contains supplementary material available at 10.1007/s11126-025-10135-9.

Figures