Abstract
OBJECTIVE: Although it has been well established that fatigue is common among older adults with osteoarthritis (OA), relatively little is known about how fatigue in daily life affects physical activity. The purposes of this study were to examine the relationship between momentary fatigue and subsequent physical activity among people with OA who reported clinically relevant levels of fatigue and to examine moderators of this relationship. METHODS: People with knee or hip OA and clinically relevant fatigue participated in physical performance assessments, completed questionnaires, and underwent a home monitoring period in which fatigue severity was measured 5 times/day over 5 days (n = 172). Physical activity was concurrently measured via a wrist-worn accelerometer. Multilevel modeling was used to examine the relationship of momentary fatigue and subsequent activity controlling for other factors (e.g., age, body mass index, pain, and depression). RESULTS: Fatigue was the strongest predictor of reduced subsequent activity. Only functional mobility (Timed Up and Go) moderated the relationship between fatigue and activity. The relationship between fatigue and activity was strongest for people with high functional mobility. CONCLUSION: Momentary fatigue is a robust and important variable associated with decreased physical activity. Further, the moderating effect of functional mobility suggests this factor should be considered when intervening on fatigue. While people with better functional mobility may benefit from an activity-based treatment approach (such as learning activity pacing techniques to reduce the impact of fatigue on activity), those with worse functional mobility may benefit from treatment focusing on underlying impairments.