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Gregory J. Crowther, PhD, Research Scientist in the Department of Medicine at the University of Washington, wrote in his Sep. 2000 article "Living High and Training Low," published in Northwest Runner magazine:
"The term 'blood doping' refers to the practice of increasing the number of red blood cells (RBCs) in one's circulatory system, either by receiving a blood transfusion or by taking erythropoietin ('epo' for short), a hormone that promotes RBC production. Since RBCs carry oxygen from the lungs to the rest of the body, adding more of them to one's circulation should enhance the delivery of oxygen to one's muscles. Improved oxygen delivery, in turn, might help the muscles perform better."
Dan Kois, journalist for Slate and New York Magazine, stated in his Sep. 23, 2004 Slate article titled "What Is Blood Doping?":
"'Blood doping' refers to any illicit method of boosting an athlete's red blood-cell supply in advance of competition. The typical adult male's hematocrit--the percentage of his blood that is composed of red blood cells--hovers around 45. Since red blood cells carry oxygen through the bloodstream, increasing the number of them allows an athlete's blood to deliver oxygen to muscles more efficiently, reducing fatigue and giving the athlete an edge. Endurance athletes often train at high altitude for precisely this reason. The lower air pressure and diminished atmospheric oxygen at altitude spur the body to generate extra red blood cells, and can bump the hematocrit up two or three (non-illicit) percentage points.
Athletes can get a bigger--and illegal--boost by injecting themselves with erythropoietin (EPO), a hormone that stimulates RBC production. A urine test for artificial EPO was introduced in 1997, but it's not foolproof; while testable traces of artificial EPO disappear from an athlete's body within four days, the hormone's effects are strongest three weeks after injection."
Mark Jenkins, MD, Director of the Student Health Service at Rice University, wrote in a Feb. 2005 article "Erythropoietin," published on his website SportsMed Web:
"EPO is a protein hormone produced by the kidney. After being released into the blood stream it binds with receptors in the bone marrow, where it stimulates the production of red blood cells (erythrocytes). [..]
Blood doping is the process of artificially increasing the amount of red blood cells in the body in an attempt to improve athletic performance. In the past this was accomplished by transfusion. The athlete would 'donate' a unit of blood into storage and then 3 weeks later, after the body had completely replaced the blood loss, transfuse the unit back into the body. This would occur just before a big race, effectively giving the athlete an 'extra' unit of blood. This enables performance improvements in endurance sports because of the extra oxygen carrying capacity. [...]
EPO has put a whole new spin on blood doping. No need for messy transfusions, just shoot up with EPO to increase your circulating erythrocyte mass. Until recently accurate testing has been difficult because the recombinant human EPO made in the lab is virtually identical to the naturally occurring form and there are no firmly established normal ranges for EPO in the body."
MedicineNet.com, an online medical dictionary, stated in a Feb. 12, 2001 article titled "Definition of Erythropoietin (EPO)," posted on its website:
"Erythropoietin (EPO): A hormone produced by the kidney that promotes the formation of red blood cells in the bone marrow. EPO is a glycoprotein (a protein with a sugar attached to it). [...]
The kidney cells that make EPO are specialized and are sensitive to low oxygen levels in the blood. These cells release EPO when the oxygen level is low in the kidney. EPO then stimulates the bone marrow to produce more red cells and thereby increase the oxygen-carrying capacity of the blood."