Pain, Fatigue, and Physical Activity in Osteoarthritis: The Moderating Effects of Pain- and Fatigue-Related Activity Interference

Objective: To examine how self-reported pain- and fatigue-related activity interference relates to symptoms and physical activity (PA) in daily life among people with knee or hip osteoarthritis. Design: Cross-sectional study with a 7-day repeated-measures assessment period. Setting: General community. Participants: Participants (N=154; mean age, 65y; 60% women [n=92]) with knee or hip osteoarthritis and pain lasting >= 3 months. Interventions: Not applicable. Main Outcome Measures: Pain- or fatigue-related activity interference items on the Brief Pain Inventory or Brief Fatigue Inventory, respectively, from baseline survey, momentary pain and fatigue severity (measured 5times/d for 7d), and PA measured with a wrist-worn accelerometer over 7 days. We hypothesized that perception of pain- and fatigue-related activity interference would moderate the association between symptoms (pain or fatigue) and PA. People with higher pain- or fatigue-related activity interference were thought to have stronger negative associations between momentary ratings of pain and fatigue and PA than did those with lower activity interference. Results: Pain-related activity interference moderated the association between momentary pain and PA, but only in the first part of the day. Contrary to expectation, during early to midday (from wake-up time through 3 PM), low pain-related interference was associated with stronger positive associations between pain and PA but high pain-related interference was associated with a small negative association between pain and PA. Fatigue-related activity interference did not moderate the relation between fatigue and activity over the course of a day. Conclusions: Depending on a person's reported level of pain-related activity interference, associations between pain and PA were different earlier in the day. Only those with high pain-related activity interference had lower levels of PA as pain increased and only in the morning. High pain related activity interference may be important to address, particularly to maintain PA early in the day despite pain. (C) 2016 by the American Congress of Rehabilitation Medicine