ABSTRACT
This chapter seeks to define the concept of fatigue. It looks to approach the question of the definition and conceptualization of fatigue largely from an evolutionary perspective. The chapter identifies a candidate metabolic source of energy as the rate-limiting factor in fatigue and have suggested that this is strongly linked to the psychological construct of attentional resources. It shows that fatigue can be considered a chronic form of stress. The chapter discusses that the protestation of a single aspect of the overall biochemical balance of the brain is most probably a very simplistic representation of the situation. Cognitive fatigue, then, is a chronic state of attentional resource depletion very much related to the biochemical substrate energy that supports ongoing activity. Humans experience cognitive fatigue because they have developed very costly brains so that they can substitute cognitive search strategies for the eventually more costly physical search strategies.
