Mediators of Exercise Effects on HRQoL in Cancer Survivors after Chemotherapy

PURPOSE: We investigated the hypothesis that combined resistance and endurance exercise improves cardiorespiratory fitness and muscle strength, thereby reducing fatigue and improving global quality of life (QoL) and physical function among cancer survivors who completed curative treatment including chemotherapy. METHODS: Cancer survivors were assigned to a 12-wk exercise intervention (n = 186) or a wait list control group (n = 91). Data were collected at baseline and after 12 wk. Path analyses using follow-up values adjusted for baseline values, age, and gender were conducted to test if the exercise effects on global QoL and physical function (European Organization Research and Treatment of Cancer Quality of Life questionnaire-Core 30) were mediated by changes in cardiorespiratory fitness (peak V˙O2), hand-grip strength, lower body muscle function (30-s chair stand test), and fatigue (Multidimensional Fatigue Inventory). RESULTS: Compared with the wait list control, exercise increased cardiorespiratory fitness (β = 1.8; 95% confidence interval (CI), 1.0-2.6 mL·kg·min) and reduced general (β = -1.0; 95% CI, -1.8 to -0.2) and physical fatigue (β = -1.5; 95% CI, -2.3 to -0.6). The exercise effect on physical fatigue was mediated by change in cardiorespiratory fitness (β = -0.2; 95% CI, -0.4 to -0.1). Higher hand-grip strength was significantly associated with lower physical fatigue and better lower body muscle function with lower physical and general fatigue. Lower general fatigue and physical fatigue were significantly associated with higher global QoL (β = -1.6; 95% CI, -2.2 to -1.1; and β = -1.7; 95% CI, -2.3 to -1.1, respectively) and physical function (β = -1.0; 95% CI, -1.3 to -0.7; and β = -1.2; 95% CI, -1.6 to -0.9, respectively). The models explained 44%-61% of the variance in global QoL and physical function. CONCLUSION: Beneficial effects of exercise on global QoL and physical function in cancer survivors were mediated by increased cardiorespiratory fitness and subsequent reductions in fatigue.