What is EPO?
Erythropoietin (EPO) is a hormone which occurs naturally in the body. It controls a process known as erythropoiesis, the production of red blood cells.
Red blood cells play a key role in exercise as they transport oxygen from the lungs to the working muscles around the body. Therefore an increased red blood cell count could be beneficial in sports which require high levels of aerobic fitness, such as; cycling, long distance running and rowing.
As increased levels of EPO would lead increased red blood cell production some athletes began taking synthetically produced EPO in order to achieve a higher red blood cell count. This led to EPO being placed on the WADA (World-Anti Doping Agency) list of banned substances, despite it occurring naturally within the body.
Altitude training can have a similar effect on red blood cell levels to taking EPO but only lasts for a few days.