Fatigue

 Fatigue may be considered to be a condition reflecting inadequate rest, as well as a collection of symptoms associated with displaced or disturbed biological rhythms. 

Acute fatigue is induced by long duty periods or by a string of particularly demanding tasks performed in a short term. 
Chronic fatigue is induced by the cumulative effects of fatigue over the longer term. 
Mental fatigue may result from emotional stress, even with normal physical rest. Like the disturbance of body rhythms, fatigue may lead to potentially unsafe situations and a deterioration in efficiency and well-being. Hypoxia and noise are contributing factors. 
Physical fatigue (e.g. muscle soreness, oxygen debt, or extreme tiredness caused by sleep deprivation, illness or poor nutrition), 
Mental fatigue (e.g. associated with tasks demanding intense concentration, rapid or complex information processing and other high level cognitive skills) 
Emotional fatigue (the wearying effect of working under trying conditions or performing psychologically disagreeable tasks). 
Concept of fatigue  It is not possible to measure fatigue directly, as one might measure blood pressure or the length of a person's hand.    
 Fatigue is indirectly measurable through its effects.
 For example,  number of errors committed per unit time on a particular task. If the person doing that task continues without rest long enough, the number of errors he or she commits increases.  
Working long hours, working during normal sleep hours, and working on rotating shift schedules all produce fatigue-like effects, although the mechanisms are different for each situation.
 Symptoms of fatigue may include:
• a lack of awareness;
• diminished motor skills;
• diminished vision;
• slow reactions;
• short-term memory problems;
• channelled concentration - fixation on a single possibly unimportant issue, to the neglect of others and failing to maintain an overview;
• easily distracted by unimportant matters, or, in the other extreme, impossible to distract;
• increased mistakes;
• poor judgement;
• poor decisions, or no decisions at all;
• abnormal moods - erratic changes in mood, depressed, periodically elated and energetic;
• diminished standard

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