Blood itself can be a doping agent – transfusions are banned by the World Anti-Doping Agency except in medical emergencies. Blood transfusions boost counts of red blood cells which in turn allows the blood to carry more oxygen.

A related practice is doping with erythropoietin (EPO), a hormone that stimulates red blood cell production. Since 2008 when regulatory agencies introduced the “biological passport” program of testing, blood profiles indicate that both EPO use and blood transfusions have dropped off.

The cutting edge, however, is “gene doping,” in which additional copies of a naturally-occurring gene or modified copies may be inserted into an athlete’s genome using a virus carrier. This approach has drawn lots of attention for its ability to evade detection, since we all have varied genomes to begin with. Case in point: Finnish skiier Eero Mantyranta naturally carries a mutation in his EPO gene, elevating his blood cells’ oxygen-carrying capacity by 25 to 50 percent.