Examining the role of physical activity in reducing postcancer fatigue
Persistent fatigue is a long-term adverse effect experienced in about a quarter of patients cured of cancer. It was shown that cognitive behavior therapy (CBT) especially designed for postcancer fatigue is highly effective in reducing severe fatigue. However, it is unclear by what mechanism the fatigue reduction is reached. In many fatigue reduction programs, an increase in physical activity is assumed to reduce fatigue. The purpose of the present study is to determine whether the effect of CBT on fatigue is mediated by an increase in physical activity. Data of a previous randomized controlled trial on the efficacy of CBT for postcancer fatigue were reanalyzed (CBT, n = 41; waiting list condition, n = 42). Actigraphy was used to assess the level of objective physical activity. Cancer survivors were assessed prior as well as after the CBT and waiting list period. The mediation hypothesis was tested according to guidelines of Baron and Kenny. A non-parametric bootstrap approach was used to test statistical significance of the mediation effect. Although CBT effectively reduced postcancer fatigue, no change in level of objective physical activity was found. The mean mediation effect was 1.4% of the total treatment effect. This effect was not significant. The effect of CBT for postcancer fatigue is not mediated by a persistent increase in objective physical activity.