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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences Advance Access published online on September 23, 2009
The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, doi:10.1093/gerona/glp137
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Published by Oxford University Press on behalf of The Gerontological Society of America 2009.

Ecological Measurement of Fatigue and Fatigability in Older Adults With Osteoarthritis

Susan L. Murphy1,2 and Dylan M. Smith3,4

1 Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor
2 Geriatric Research Education and Clinical Center, Veterans Affairs Ann Arbor Health Care System, Michigan
3 Department of Internal Medicine, University of Michigan, Ann Arbor
4 Veterans Affairs Ann Arbor Health Care System, Michigan

Address correspondence to Susan L. Murphy, ScD, OTR/L, 300 North Ingalls Street, 9th floor, Ann Arbor, MI 48109-2007; Email: sumurphy{at}umich.edu


  Abstract

Background: Fatigue is associated with loss of independence in older adults; however, little is known about optimal treatment or how fatigue manifests in daily life activities. "Fatigability" was recently proposed to clarify the fatigue–activity relationship. The purpose of this study was to present a new measurement method of fatigability and begin to test its validity.

Methods: Our sample included 40 adults with knee or hip osteoarthritis (OA) and 20 healthy controls. Fatigue was measured by ecological momentary assessment several times a day along with continuous measurement of physical activity using a wrist-worn accelerometer. Fatigability was measured as the fatigue increase after a period of high activity.

Results: Compared with controls, participants with OA were approximately four times more likely to have an increase in fatigue after a high activity interval (37.0% vs 9.8%). Among people with OA, average fatigue and fatigability were not highly related (r = .13). Fatigue was most strongly associated with reported physical function, pain, and vitality, whereas fatigability was most strongly associated with body mass index, OA severity, and knee strength.

Conclusions: Although fatigue among people with OA was more associated with subjective reports of physical function and symptoms, pairing fatigue reports with physical activity tapped objective factors that may be related to the biomechanical demands of daily life activities. Thus, fatigability measurement may help discern how symptoms relate to daily life function and help to refine treatment approaches in OA.

Keywords Fatigue; Measurement; Aged

Received: May 6, 2009; Accepted: August 10, 2009

Decision Editor: Luigi Ferrucci, MD, PhD


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