text: Polycythemia is an increase in red blood cell mass. It can be a normal  physiological increases in the Red Blood Count which can occur at high altitudes or after strenuous physical training. At high altitudes, less atmospheric weight pushes air into the lungs, causing a decrease in the partial pressure of oxygen and hypoxia. With strenuous physical training, increased muscle mass demands more oxygen.  It can also be due to a pathological reasons for an increased number of red blood cells like  Polycythemia vera which is a disease of unknown origin that results in an abnormal increase in red blood cells. \n\nThe term "anemia" is a general term that refers to a decrease in red blood cells. Anemia can occur from either a decrease in the number of red blood cells, a decrease in the hemoglobin content, or both.♥