ABSTRACT

Cancer and associated treatments such as chemotherapy and irradiation leave a patient with low aerobic power, weak, wasted muscles, and associated psychological reactions. It thus seems logical to recommend an appropriately adapted program of moderate exercise during and following the treatment of various types of neoplasia. However, there is as yet only limited objective data on the benefits from such treatment in human subjects. There are technical problems in comparing responses between small mammals and humans, particularly differences in the duration of exercise relative to lifespan of the organism. Moreover, there are important differences in responses to tumors that have been implanted, injected, or induced by massive doses of carcinogens and the slowly developing tumors of human experience. Nevertheless, a substantial volume of animal experimentation suggests that moderate exercise, preferably begun before tumor induction, can slow the growth of a variety of types of tumors, reducing the number of metastases. Some data suggest an associated increase in natural killer cell and phagocyte activity, but the main basis of benefit seems to come from the establishment of a better balance between energy intake and expenditure. In some instances, almost equal benefit has been gained by dietary restriction, without changing habitual physical activity. Both excessively vigorous exercise, and exercise that is begun at a late stage in the development of a tumor can have negative effects, increasing both tumor growth and metastasis, and accelerating catabolism and muscle wasting. Humans who have developed cancer generally show very low values for aerobic power, muscle strength and endurance, with an associated deterioration in self-image and self-efficacy. Measurement of fitness levels may be helpful in predicting overall prognosis and in determining the likely outcome of surgical treatment. Limited human experimentation suggests that light to moderate exercise can restore the patient's fitness, at least in the early stages of disease, with associated gains in the quality of life. However, chemotherapy has a negative impact on both physiological function and immune responses. There are also dangers associated with anemia, a low platelet count, and weakened bones. Any exercise program must therefore be introduced with considerable caution. Further research is needed to define the optimum intensity, frequency, and duration of exercise programs for the cancer patient, having regard for the type of tumor and the stage of disease.