In scientific studies, a decrease in the number of circulating immune cells as well as a reduced host defence function after strenuous and sustained exercise has been demonstrated in-vivo and by application of immunological in-vitro methods. Significant decreases in T-lymphocytes, T-helper cells type 1 as well as in Natural Killer cells (NK) could be shown. However, B-cells and T-helper cells type 2 are not affected in a comparable magnitude [8-10].