Potential impact of physical activity and sport on the immune system--a brief review.

Description is given of methods that can evaluate the main functional elements of the immune system. Acute responses to exercise depend on the intensity and duration of the required activity relative to the individual's fitness level. Moderate endurance exercise causes either no change or an enhancement of such indices as total leucocyte count, granulocyte, monocyte, lymphocyte and natural killer cell count, total T cell count, helper:suppressor cell ratio, cell proliferation in response to mitogens, serum immunoglobulin levels, and in vitro immunoglobulin production. However, exhausting exercise tends to produce adverse changes in these same indices, particularly if the physical activity is accompanied by environmental or competitive stress. Moderate, appropriately graded training reduces reactions to any given absolute intensity of exercise. When pursuing a more demanding training regimen, it is important that the exerciser optimize immune responses. If athletic preparation is pursued to the level of staleness and/or muscle damage, it can have substantial negative implications for many aspects of immune function, including resistance to acute infections, HIV infections, ageing, cancer and other conditions influenced by the immune system.