The data presented here document that exercise is associated with changes in immunological activity as assessed by a variety of in vitro assays. In general, these changes appear to be temporally associated with activity and are not persistent. In fact, most alterations are probably secondary to exercise-induced hormonal changes, with resultant effects on the intravascular composition of immunocompetent cells. Thus, changes in lymphocyte trafficking induced by hormonal effects lead to relative and absolute differences in cell numbers, which may be reflected in in vitro functional assays. These data argue against any profound impact of exercise on the immune system, which might impact on overall health. Furthermore, there is little information about exercise decreasing the number of infectious illnesses or diminishing the likelihood of immunologically mediated conditions or malignancies. Nevertheless, these results should not be construed as an argument against the tangible health benefits of exercise. The changes in life-style which often accompany exercise programmes, as well as the documented benefits for cardiovascular health, are reasons enough to support these activities.
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