What is behind "I'm so tired"? Fatigue experiences and their relations to the quality and quantity of external stimulation

In the present study, it is hypothesized that both low quality and high qua ntity of external stimulation are related to elevated levels of fatigue. Th is is proposed by the Quality-Quantity model for understanding fatigue (QQu F model). The relations between the quality and quantity of external inform ation and the Multidimensional Fatigue Inventory (MFI-20) are examined. Mor eover, the role of depression (measured with the CES-D) in relation to the QQuF model is explored. The results show low quality of external stimulatio n, that is, low "attractiveness of external stimulation," relating to all f ive dimensions of fatigue. A high quantity of external stimulation, that is , high "experienced overload," related primarily to general and mental fati gue. The QQuF model was only slightly moderated by depression, but depressi on directly and strongly related to all dimensions of fatigue. It is conclu ded that fatigue related to low quality of external stimulation can be dist inguished from fatigue related to a high quantity of external stimulation. This distinction is useful when considering theoretical issues and treatmen t of fatigue. (C) 1999 Elsevier Science Inc.