Objective: Despite the numerous health benefits of physical activity, inactivity is endemic among adults with knee osteoarthritis (OA). Because sleep quality may be a target in order to improve physical activity behavior, we investigated the cross-sectional relationship between restless sleep and physical activity in participants with or at risk for knee OA. Methods: We analyzed accelerometer-measured physical activity and clinical data of participants included in the Osteoarthritis Initiative (OAI). We used multiple regression analysis to evaluate physical activity for participants, who were grouped by the reported frequency of restless sleep, and adjusted for demographic and medical confounders. Results: Of the 1,892 OAI participants for whom complete data were available, 300 participants (16%) reported restless sleep ≥3 days in the past week. Participants who reported restless sleep for much of the time (3–4 days/week) and most of the time (5–7 days/week) had 11.9% and 23.7% less weekly minutes of moderately vigorous activity, respectively, compared to participants who reported rarely restless sleep (<1 day/week) (P for trend 0.021). These differences persisted after accounting for age, sex, race, body mass index, medical comorbidity, and knee OA severity and pain (P for trend 0.023). Differences related to restless sleep were largely attenuated by the presence of high depressive symptoms and low energy levels. Conclusion: Poor sleep quality is associated with less physical activity in persons with or at risk for knee OA. Future studies are needed to determine the mechanisms of how poor sleep and physical activity are related, how energy and depression mediate these relationships, and whether interventions that improve sleep quality might result in increased physical activity.
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