These studies on mucosal immunity in athletes are representative of a very small number of studies that have established a relationship between some surrogate measure of immune function and infection incidence in athletes.
A few studies on soldiers during intensive periods of military training have also reported a negative relationship between s-IgA concentration and occurrence of URTI (6), although others have not (17, 53).
In one recent study, an increased URTI incidence during 4 wk of intense military training was significantly correlated with
decreased numbers of circulating NK cells (17). However,
in these situations, the training often involves not only
strenuous physical activity, but also dietary energy deficiency, sleep deprivation, and psychological challenges.
These multiple stressors are likely to induce a pattern of
immunoendocrine responses that amplify the exercise-induced alterations