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boring and you can hardly keep your eyes open. All you want to do is sleep. You also often feel like this when at home watching TV.

  • Climbing stairs has become progressively, though subtly, more difficult over the last two years.

  • Although at first, exertion is not bothersome, after 10-15 minutes, you experience constant cramping in your extremities.

  • These examples illustrate the multidimensionality of fatigue. Fatigue can occur in anticipation of a task and be influenced by both physical (e.g., the length of the run) and psychological factors (e.g., how rewarding it will be). Fatigue can also be interpreted as a sense of effort needed to perform a task, and both physical and mental tasks may result in fatigue. In conjunction with the sensation or perception of fatigue, the effort associated with a task may be manifested as a change in behavior, especially a decrement in performance (e.g., information processing declines when one feels tired). Fatigue is also most often acute, and in such cases typically resolves after completion of the task. In cases in which fatigue is more chronic and pervasive, it is frequently associated with illness, stress, and sleep disturbances. Finally, as the last two vignettes illustrate, fatigue must be distinguished from sleepiness or drowsiness and true muscle weakness since these symptoms are associated with a different array of conditions, usually primary sleep and muscle disorders.

    Thus, it is clear that a simple question regarding “fatigue” is not likely to be very informative or precise. Yet elements of fatigue can be ascertained if care is taken in questioning an individual or in constructing an instrument. However, complicating matters even more is the fact that patients often have additional meanings for fatigue. Sometimes, the word fatigue is used as a synonym for other complaints while at other times it becomes a general term to encompass an array of symptoms that occur together.

    Patients will often equate fatigue with weakness, dizziness, lack of coordination or stamina, feeling “spacey,” poor concentration/cognitive abilities, having “rubber legs,” boredom, lack of motivation, malaise, or feeling blue or depressed. Despite the further ambiguity introduced by these descriptors, it is clear that fatigue has distinct physical and mental aspects that must be considered in measurement.

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