Cancer-induced fatigue and skeletal muscle wasting: the role of exercise.

Fatigue is the most frequently reported symptom by cancer patients. Many of these patients perceive fatigue as the most distressing symptom associated with their illness because it imposes limitations on their physical activity level. Skeletal muscle wasting, which occurs as part of cancer cachexia, is one of the mechanisms that contribute to fatigue. Cancer-induced skeletal muscle wasting may occur despite normal food intake and is not prevented by nutritional supplementation. Evidence suggests that endurance exercise ameliorates cancer-related fatigue. There is no compelling evidence to support that exercise-induced reduction in fatigue is related to preservation of muscle mass. Resistance exercise attenuates muscle wasting associated with a variety of catabolic conditions. However, its effects on cancer-induced muscle wasting have not been adequately studied. This article describes the physiological mechanisms implicated in the induction of cancer-related muscle wasting, summarizes findings from endurance and resistance exercise studies in relation to fatigue and muscle wasting during cancer and selected clinical conditions, and proposes directions for future research.