Diurnal variation of physical and mental fatigue

Diurnal effects on fatigue are well established. However, evidence exists that fatigue can be subdivided into physical and mental components. Diurnal effects on these subcomponents of fatigue are not known. The present study served to investigate diurnal influences on physical and mental signs of fatigue. A number of self-report measures of sleepiness, and physical and mental signs of fatigue were employed, including a specially developed questionnaire designed to assess current feelings of physical and mental fatigue. The responses from 40 subjects were assessed in the morning, at noon, and in the evening. Sleepiness as well as physical and mental signs of fatigue decreased from morning to evening. Indicators of physical and mental fatigue only differed at noon, with higher ratings of mental compared to physical fatigue. Repeated-measures anova of fatigue at each daytime session indicated an increase from the beginning to the end of each testing session. Since the diurnal courses of physical and mental fatigue differ, physical and mental fatigue are observed to diverge at noon.