What leads to increased erythropoiesis?

Excercise and tumors: Erythropoiesis is the process by which red blood cells (erythrocytes) are produced. It is stimulated by decreased O2 in circulation, which is detected by the kidneys, which then secrete the hormone erythropoietin. This hormone then stimulates proliferation and differentiation of red cells in the marrow. In certain diseases like kidney cancer, erythropoiesis also occurs outside the marrow.