To great altitudes, there is a diminution in the oxygen saturation of the hemoglobin. In order to compensate this, the erythropoietin (EPO), a hormone secreted by the kidneys, stimulates the red globule production of the bony marrow to increase the saturation of the hemoglobin and the oxygen contribution. It is not known how long takes this adaptation, because diverse studies have found different conclusions on the base from the amount of time dedicated to high altitude.
Although the EPO takes place naturally in the body, also it is made of synthetic way to help to treat the patients who suffer of renal insufficiency and to treat to the patients during the chemotherapy. In the last thirty years, the OEP has become frequently object of abuse by competitive athletes through doping of blood and the injections with the purpose of obtaining advantages in resistance events. The EPO abuse, nevertheless, increases the count of erythrocytes beyond the normal levels (polycythemia) and increases viscosity of the blood, that can give rise to the hypertension and the increase of the probability that a sanguineous clot, attacks the heart or a cerebral spill. The natural secretion of EPO by the human kidneys can be increased the training in altitude, but the body has limits in the amount of the natural resources OEP that are secreted, avoiding therefore the negative indirect effect of the procedures of illegal doping.