Combining cognitive and physical work tasks: Short-term effects on fatigue, stress, performance and recovery

Sammanfattning: Background: Although combinations of physical and cognitive work tasks occurs in working life (both concurrent and alternating), no one has summarized the research regarding such combinations. Very few studies have investigated the effects of alternating physical and cognitive tasks, which have been suggested as an alternative to classic job rotation. The aim with this thesis was to investigate the effects of concurrent and alternating cognitive and physical work tasks on fatigue, stress, recovery, and performance and whether the task difficulty and the temporal pattern is important in this respect. Methods: In study I, 48 controlled studies comprising combinations of physical and cognitive work tasks was summarized in a systematic review. In two controlled experiments (study II, III and IV), participants performed alternations of a physical and a cognitive task. In study II and III, the difficulty levels of the cognitive task was varied between conditions, and in study IV, the temporal patterns and cognitive task difficulty was varied between conditions. During work, indicators of fatigue (study II and IV), stress (study III and IV) and performance (study II and IV) was assessed. Results: Concurrent physical and cognitive work tasks have a negative impact on biomechanical indicators, fatigue and performance, while the effect on stress seems mixed. Alternating physical and cognitive work tasks leads to some accumulated fatigue over time, with physical recovery taking place during the cognitive task. Indicators of stress did not increase over time, and neither fatigue nor stress was influenced by cognitive task difficulty. Conclusions: Concurrent physical and cognitive work should be avoided in working life and if they must be performed, employers should decrease task demands. Alternations on the other hand, could be carried out without excessive fatigue or stress, and with maintained performance. This thesis provides a basis for recommendations on how to properly organize job-rotation schemes.