EXERCISE: A help or Hindrance to Immune Defense?

Many people who exercise claims that they have fewer infections when they are in good aerobic conditions ,few studies have been conducted that can substantiate or refute this claim.  The bulk of the evidence indicates the moderate exercise may have beneficial effects on the immune system, whereas strenuous exercise may be accompanied by reduced immune -system activity.

Moderate exercise training results in an increase in the circulating numbers of granulocytes and lymphocytes and an increase in cytotoxic and natural killer cell acivity. On the other hand maximal exercise suppresses natural killer cells activity one to two hours after exercise. It is possible that intense physical activity induces the stress response, which in turn suppresses immune functions.

Athletes with long, difficult training schedules and intense competition have increased incident of respiratory infection. Because these athletes have lower resting salivary IgA levels compared with control subjects and that their mucosal immunoglobulins are decreased  after prolonged exhaustive exercise.  These levels return to normal after twenty four hours.

It is possible that the athlete who is in training with frequent bouts of exhaustive exercise may have a sustained reduction in mucosal immununity and therefore lower resistance to respiratory infection.