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Remarkably, given that fatigue has been studied formally for well over 100 years, there is still no scientifically mature theory of its origins and functions. A major reason for the failure to understand fatigue has, I would argue, been the irresistible tendency to think of it in terms of a loss of energy resources (e.g., batteries running down, feeling spent). This view emerged during the 19th century, when the rapid spread of steam engines dramatically changed working life and gave rise to a widespread, enthusiastic adoption of the energy conservation metaphor as the basis for understanding human work and fatigue. Rabinbach (1990) observed that inadequacies of work had previously been considered a failure of will or desire; now, they could be explained as a result of a running down of the supply of whatever fuel the body (or mind) used. On this view, fatigue was the direct effect of doing work.What seems to have happened over the past 150 years is that the metaphor has been assumed as reality, and we have come to think of both the body and the mind-brain primarily as energy-transforming systems. Although the energy story is clearly relevant to fatigue from muscular activity, it is known that physical endurance is limited primarily by a willingness to exert effort (Holding, 1983). The argument is even less appropriate for mental fatigue. It has long been known that the brain uses very high amounts of glucose (around 20% of that available for all body activity) and that this level is very stable (Kety & Schmidt, 1945; Van den Berg, 1986). Whereas a number of recent studies have reported an increase in glucose oxidation during more demanding mental tasks (Fairclough & Huston, 2004;Gailliot & Baumeister, 2007), others have found no effects, even of extreme demand differences sustained over 90 minutes (Marcora, Staiano, & Manning, 2009). It is likely that increases in glucose oxidation under some conditions are integral to the effectiveness of brain operations (depending on the density of the neural structures involved). However, this is a quite separate issue from concluding that fatigue is the result of glucose depletion; there is no evidence for this (Marek, 2006;Warburton, 1986).As others have commented (e.g., Bartley & Chute, 1947), there is little doubt that the energy-depletion perspective has been a source of distraction in the search for a theory of fatigue. The most persistent view has been that fatigue is caused by the exhaustion of (bodily or mental) resources from carrying out

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How does negative mood affect risk taking? A brief questionnaire was used to measure state anxiety, depression, and fatigue, and a daily mood diary allowed state and trait (average level) mood to be separated. Studies 1 and 2 used natural moods and Study 3 a mood induction procedure. Risk was assessed using hypothetical everyday choice scenarios. Study 1 showed that riskiness was affected by state fatigue, but not by anxiety and depression. Study 2 showed that increased riskiness over a two-week period was predicted by fatigue changes, after controlling for riskiness and trait and state mood at time 1. Fatigue effects were stronger for more important scenarios, and when state anxiety was also high. In Study 3, covariance analyses showed that the observed increased in riskiness was related to induced fatigue, rather than to anxiety or depression. The effects are discussed in relation to the literature on fatigue effects, and models of mood and cognition.

The effects of loud noise are examined by observing its influence upon a combined tracking and multi-source monitoring task. Tracking (the primary task) improves in noise, as does the detection of centrally located signals in the monitoring task. Peripheral signals are detected less often in noise. The data are interpreted in terms of increased selectivity of attention with arousal.