Blood Doping: an illegal method of temporarily improving an athlete's performance in a race of competition by increasing the number of red blood cells in the body (Merriam-Webster).
In many cases, blood doping increases the amount of hemoglobin in the bloodstream. Hemoglobin is an oxygen-carrying protein in the blood. So increasing hemoglobin allows higher amounts of oxygen to reach and fuel an athlete's muscles. This can improve stamina and performance, particularly in long-distance events, such as running and cycling (WebMD).
In many cases, blood doping increases the amount of hemoglobin in the bloodstream. Hemoglobin is an oxygen-carrying protein in the blood. So increasing hemoglobin allows higher amounts of oxygen to reach and fuel an athlete's muscles. This can improve stamina and performance, particularly in long-distance events, such as running and cycling (WebMD).