Fatigue mediates the relationship between physical fitness and quality of life in cancer survivors

ObjectivesThis study aims to investigate whether fatigue mediates the association between physical fitness and quality of life.DesignUncontrolled pre–post intervention design.MethodsPre- and post-intervention measurements were conducted in 119 patients who completed chemotherapy treatment for various types of cancer. The intervention was an 18-week exercise programme consisting of high-intensity resistance and interval training. We assessed physical fitness – peak oxygen uptake and peak power output – self-reported fatigue (Multidimensional Fatigue Inventory – subscales general fatigue, physical fatigue, reduced activity, reduced motivation, and mental fatigue-, and fatigue symptom scale of EORTC QLQ-C30) and quality of life (EORTC QLQ-C30, subscale global quality of life). Linear regression analyses were conducted on the residual change scores of the variables. The mediated effect of fatigue on the association between physical fitness and quality of life was examined using the products of coefficient method. Bootstrapping was used to calculate the confidence intervals.ResultsWe found significant associations between changes in physical fitness and global quality of life, between physical fitness and fatigue, and between fatigue and global quality of life. General fatigue mediated the positive association between peak power output and global quality of life, accounting for 82% of the total association. Physical fatigue, reduced activity, reduced motivation, and fatigue symptom were also mediators of this association. The mediation effects accounted for 91%, 76%, 38% and 71% of the total association, respectively. Reduced activity and reduced motivation mediated the association between peak oxygen uptake and global quality of life. Multiple mediation analyses showed that physical aspects of fatigue were stronger mediators than mental aspects.ConclusionsGeneral fatigue and physical aspects of fatigue mediate the relationship between physical fitness and quality of life in cancer survivors. We found no mediating effect of mental fatigue.