Fatigue, depression, and physical activity in relapsing-remitting multiple sclerosis: Results from a prospective, 18-month study

Background: Fatigue, depression, and physical inactivity are common in multiple sclerosis (MS), but there is limited information on the hi-directional associations among those variables over a long period of time. Objective: This study examined the hypothesis that fatigue and depression would predict change in physical activity and that physical activity would predict changes in fatigue and depression over an 18-month period of time in persons with MS, even after controlling for disability status, disease duration, sex, and age. Methods: This longitudinal study collected data on fatigue, depression, physical activity, and confounding variables from the same sample of persons with relapsing-remitting MS on two occasions that were separated by 18 months. Results: The cross-lagged path coefficient between baseline fatigue and follow-up physical activity was statistically significant (path coefficient=-.26, p<.0001) as was the cross-lagged path coefficient between baseline physical activity and follow-up fatigue (path coefficient=-.11, p<.05). Those bi-directional associations were independent of depression, disability status, disease duration, sex, and age. There were no statistically significant cross-lagged path coefficients between depression and physical activity. Conclusions: This study identified bi-directional associations between fatigue and physical activity over an 18-month period of time. The nature of such associations opens the door for research on fatigue management as an approach for sustaining or promoting physical activity over time. (C) 2011 Elsevier B.V. All rights reserved.