a1 Expert Centre Chronic Fatigue and Department of Medical Psychology, Radboud University Nijmegen Medical Centre, The Netherlands
Background Cognitive behaviour therapy (CBT) is known to reduce fatigue severity in chronic fatigue syndrome (CFS). How this change in symptomatology is accomplished is not yet understood. The purpose of the present study was to determine whether the effect of CBT on fatigue is mediated by an increase in physical activity.
Method Three randomized controlled trials were reanalysed, previously conducted to evaluate the efficacy of CBT for CFS. In all samples, actigraphy was used to assess the level of physical activity prior and subsequent to treatment or a control group period. The mediation hypothesis was analysed according to guidelines of Baron & Kenny [Journal of Personality and Social Psychology (1986)51, 1173–1182]. A non-parametric bootstrap approach was used to test statistical significance of the mediation effect.
Results Although CBT effectively reduced fatigue, it did not change the level of physical activity. Furthermore, changes in physical activity were not related to changes in fatigue. Across the samples, the mean mediation effect of physical activity averaged about 1% of the total treatment effect. This effect did not yield significance in any of the samples.
Conclusions The effect of CBT on fatigue in CFS is not mediated by a persistent increase in physical activity.
(Received January 28 2009)
(Revised August 24 2009)
(Accepted November 19 2009)
(Online publication January 05 2010)