The Effect of Exercise on the Growth of a Mouse Tumor*

There is considerable evidence to indicate that an inhibition of tumor growth is observed in animals maintained on a nutrit ionally adequate diet but limited in caloric intake (1, 5, 11, 12). This effect appears to be due entirely to the caloric restriction rather than to the lack of some specific growth factor. The result is especially significant since the animals maintained on the curtailed rations are generally in better health and outlive those allowed food ad libitum (5, 11). This caloric effect is not limited to laboratory animals but may pertain to human beings as well, since a review of insurance statistics concerned with the relationship of body weight to cancer incidence has shown that persons of average weight or less are not so likely to develop cancer as those who are overweight (10). It follows that the avoidance of overweight through restriction of food intake may aid in the prevention of human cancer or at least delay its onset. These observations indicate that neoplastic cells are not so likely to develop or to become established if little or no excess energy remains after the bodily requirements have been met. If this assumption is correct, it might be possible to inhibit tumor growth by subjecting animals to forced exercise and thus uti l izing the excess energy. To test this possibility the influence of forced exercise on the rate of tumor growth was studied on a series of mice bearing transplantable tumors.