The hypothesis to be investigated in this study is that the oxygen content of Active O2 may - at least in part - compensate the hypoxic situation in the surface of the gut wall, when ingested during and after exercise. Luminal supply of oxygenated water potentially might protect mucosal tissue from ischemia related damage and could modulate immune responses. As a consequence, the overall situation of the immune system might improve. Such an effect should be reflected in the pharmacodynamic parameters determined in this study.