[Evaluation of mental stress and fatigue induced by performance of a mental task. 2. An experiment in 11-h self-paced calculating task].

An assessment of mental stress and fatigue was undertaken in 12 male students who did their best to perform a calculating task (addition and subtraction of 2-digit numbers) for 11 hours on a workday and rested without any task for 11 hours on a restday. During the work period, occipital midline beta-2 (Oz beta 2) amplitude, urinary adrenaline (A) and noradrenaline (NA) excretion, heart rate (HR), blood pressure (BP), subjective rating of tiredness (SRT), and subjective symptoms of fatigue (SSF) were higher than those during the rest period. Oz beta 2 amplitude, diastolic pressure (DP), critical flicker fusion value (CFF), and performance level (number answered, percent correct) remained unchanged over the rest/work period. Moreover, A and NA excretion, HR, and systolic pressure (SP) changed parallel with their resting level. With the lapse of working hours, SRT and SSF elevated. These results suggest that performance of calculating task causes mental stress which remains constant throughout the work period and that subjective fatigue increases with extension of working hours.