A common feature of all HBOCs is their resistance to dissociate when dissolved in media, which contrasts hemoglobin of natural dissociation under non-physiological conditions. HBOCs may hypothetically supply greater benefits to athletes than those provided by the equivalent hemoglobin in traditional RBC infusion. Recent developments have shown that HBOCs are not only simple RBC substitutes, but highly effective O2 donors in terms of tissue oxygenation. Additional effects include increases in blood serum iron, ferritin, and Epo; up to 20% increased diffusion of oxygen and improved exercise capacity; increased CO2 production; and lower lactic acid generation in anaerobic activity. HBOCs have been shown in trials to be extremely dangerous in humans. Because HBOCs increase both the risk of death and risk of myocardial infarction clinical trials were ended. They are not commercially available in the US or Europe and there is no approved use for them.