The overall oxygen delivery system (blood oxygen levels, as well as heart stroke volume, vascularization, and lung function) is one of the major limiting factors to muscles ability to perform endurance exercise. Therefore, the primary reason athletes may use ESAs is to improve oxygen delivery to muscles, which directly improves their endurance capacity. With the advent of recombinant erythropoietin in the 1990s, the practice of autologous and homologous blood transfusion has been partially replaced by injecting erythropoietin such that the body naturally produces its own red cells. ESAs increase hematocrit (% of blood volume that is red cell mass) and total red cell mass in the body, providing a good advantage in sports where such practice is banned. In addition to ethical considerations in sports, providing an increased red cell mass beyond the natural levels reduces blood flow due to increased viscosity, and increases the likelihood of thrombosis and stroke.
In accordance with this decision, Tour organizers removed Armstrongs name and results from the races history.Witnesses testified that code words used for EPO included "Edgar", "Poe", "Edgar Allan Poe", and "Zumo" (Spanish for juice). Dynepo
Dynepo is the brand name for a form of EPO  developed by Shire Pharmaceuticals. The first development steps were performed by HMR and Aventis. Aventis obtained the license in Europe in 2002. The company expected to launch the product in Europe in 2006, although patents held by the American biotechnology company Amgen, Inc. may have precluded its sale in the United States.Dynepo was made in cultured human cells. It was therefore expected to have an authentic human form of sialic acid and other oligosaccharide residues. It was hoped that this would make a longer-acting product than existing brands. There were concerns that such production would also make Dynepo undetectable in the urine tests for EPO used, at that time, to detect doping by athletes. Dynepo was withdrawn from European markets on 17 February 2009, for commercial reasons. On July 1, 2009, professional cycling team Silence–Lotto announced that Thomas Dekker was tested positive for Dynepo on a test taken on December 24, 2007, while Dekker was riding for Rabobank. References
External links
 Media related to Erythropoiesis-stimulating agents at Wikimedia Commons
"Erythropoietin". Drug Information Portal. U.S. National Library of Medicine. "Epoetin alfa". Drug Information Portal. U.S. National Library of Medicine. "Epoetin beta". Drug Information Portal. U.S. National Library of Medicine. "Darbepoetin Alfa". Drug Information Portal. U.S. National Library of Medicine. "Methoxy polyethylene glycol-epoetin beta".