Infection, Immunity, and Exercise.

In brief How-and if-exercise alters immunity is open to debate. Research centers on changes in the number and function of granulocytes and lymphocytes and in levels of immunoglobulins. In general, these immune changes are mixed, mild, and brief. Clinical studies are inconclusive and fraught with confounders, especially the impact of psychological stress. Whether exercise enhances immunity or impairs it may, in fact, depend on whether the exercise is a joy or a stress.