Human Fatigue in Prolonged Mentally Demanding Work-Tasks: An Observational Study in the Field

Worker fatigue has been the focus of research for many years. However, there is limited research available on the evaluation and measurement of fatigue for prolonged mentally demanding activities. The objectives of the study are (1 )to evaluate fatigue for prolonged, mentally demanding work-tasks by considering task-dependent, task-independent and personal factors, (2) to identify effective subjective and objective fatigue measures, (3) to establish a relationship between time and factors that affect fatigue (4) to develop models to predict fatigue. A total of 16 participants, eight participants with western cultural backgrounds and eight participants with eastern cultural backgrounds, currently employed in mentally demanding work-tasks (e.g., programmers, computer simulation experts, etc.) completed the study protocols. Each participant was evaluated during normal working hours in their workplace for a 4-hour test session, with a 15-minute break provided after two hours. Fatigue was evaluated using subjective questionnaires (Borg Perceived Level of Fatigue Scale and the Swedish Occupational Fatigue Index (SOFI)); and objective measures (change in resting heart rate and salivary cortisol excretion). Workload was also assessed using the NASA-TLX. Fatigue and workload scales were collected every 30 minutes, cortisol at the start and finish of each 2-hour work block, and heart rate throughout the test session. Fatigue significantly increased over time (p-value \u3c0.0001). All measures, except cortisol hormone, returned to near baseline level following the 15-minute break (p-value \u3c0.0001). Ethnicity was found to have limited effects on fatigue development. Poor to moderate (Rho = 0.35 to 0.75) significant correlations were observed between the subjective and objective measures. Time and fatigue load (a factor that impacts fatigue development) significantly interact to explain fatigue represented by a hyperbolic relationship. Predictive models explained a maximum of 87% of the variation in the fatigue measures. As expected, fatigue develops over time, especially when considering other factors that can impact fatigue (e.g. hours slept, hours of work), providing further evidence of the complex nature of fatigue. As the 15-minute break was found to reduce all measures of fatigue, the development of appropriate rest breaks may mitigate some of the negative consequences of fatigue