BBC News

The race to keep up with blood doping sports cheats

Scientists have developed tests to detect nearly every type of doping in sport, but they have not yet perfected a way to prevent all forms of the banned practice of blood doping.

It involves athletes storing and transfusing their own blood - or the blood of others - before exercise or competition, to increase the number of red blood cells in the body.

By manipulating their oxygen-carrying capacity, cheats can increase their stamina and speed.

It is possible to detect some - but not all - types of blood doping.

Video produced by Thomas Hannen.