Nov.2010 Running Times has an article by Pete Magill about hormones.
http://runningtimes.com/Print.aspx?articleID=21172
He writes about EPO:
Erythropoietin (EPO) stimulates bone marrow to produce red blood cells. Red blood cells carry oxygen from our lungs to our cells. Because it increases our oxygen-carrying capacity, EPO is the drug of choice for many endurance athletes -- 1500m runner Rashid Ramzi was stripped of his Beijing gold medal for use of CERA (advanced EPO).
Runners use altitude training and altitude tents (which simulate hypoxia) to increase EPO naturally. "You can get a 10 to 15 percent increase," says Brown. [Jeffrey Brown, MD, endocrinologist]
But Brown has some words to the wise for runners who would go this route: There's no proof that elevated EPO works. "The oxygen that gets to the muscle is actually dissolved oxygen in the plasma," he says. "You go from red blood cell to plasma to tissue. There's a homeostatic mechanism in the body that maintains oxygen levels in the plasma. And plasma is not affected by EPO."
Brown believes the improved performances turned in by athletes on EPO might have a simple explanation: Elite runners tend to be anemic. "Pounding pavement with their feet breaks up red blood cells," he says, "and they lose them. So you bring somebody back to normal [with EPO], and they do remarkably better!"
If pounding causes anemia, wouldn't it make sense to do as most training runs in well-cushioned shoes, and save the lightweight shoes for racing?