I don't know, but I have read that professional cyclists had easy access to EPO, which increases their level of oxygen carrying blood cells. This increased their endurance in long races, but was connected to a number of young, super fit cyclists dying in their sleep. Their resting pulse rate was so low, since they were so fit, that when it slowed too much, their heart wasn't able to pump their thickened blood through their veins. Obviously not a good use for the drug.