I heard from somewhere that in blood doping, the athletes, blood is taken out and put in a freezer. Then close to the day of the competition the blood is simply put back (without any external chemicals).
I heard that this works because it improves your red blood cell count. And if your to combine it with fitness & workouts "you could do some damage".
How do the detect transfusion of your won blood? When it doesn't have any external chemicals?