Journal of Gerontology: MEDICAL SCIENCES Published by Oxford University Press on behalf of The Gerontological Society of America 2009.

doi:10.1093/gerona/gln017 IN older adults, fatigue is a commonly reported symptom. Different defi nitions have sought to represent fatigue ( 1, 2), and for use in the present study, it is conceptualized as “ the awareness of a decreased capacity for physical and/or mental activity due to an imbalance in the availability, utilization, and/or restoration of resources needed to perform activity ” ( 3). Typically, fatigue is studied in patient populations with an index condition such as cancer, HIV infection, or multiple sclerosis. Indeed, a review of symptoms associated with cancer, AIDS, heart disease, chronic obstructive pulmonary disease, and renal disease found that between 32 % and 90% of patients report fatigue ( 4). However, although fatigue is often attributed to underlying disease, in a large study of the general population only about one third of all fatigue cases could be explained by a diagnosed medical condition ( 5)