with the ACSM and issued a joint statement, warning athletes about both the prevalence and the potential risk factors of sickle cell trait. The NCAA has also recently encouraged athletes to become aware of their sickle cell trait status, as the trait itself does not typically result in symptoms under normal conditions but can become dangerous during extreme physical activity similar to the daily training that athletes undergo. Normal hemoglobin (and hemoglobin S in the presence of oxygen) contains a deformability characteristic that allows erythrocytes to essentially squeeze their way into smaller vessels, including those involved in microcirculation to the capillaries within muscle tissue as well as blood supply embedded within organ tissues. When hemoglobin S is deprived of oxygen, it can polymerize, which is what is proposed to cause the "sickled" cells. The sickled erythrocytes present a decreased deformability when compared to normal erythrocytes, leading to distress in circulation into the smaller vessels involved in microcirculation, particularly, in this case, the capillaries embedded in muscle tissue. The resulting microvasculatory distress in capillaries specific to muscle tissue can cause acute rhabdomyolysis and necrosis within the muscle cells. The inflammation and leakage of intracellular material resulting from muscle cell necrosis releases a particular protein, myoglobin, into the blood stream. While necessary in muscle tissue to bind iron and oxygen, myoglobin circulating through the bloodstream can break down into smaller compounds that damage kidney cells, leading to various complications, such as those seen in sickle cell trait athletes during high levels of physical exertion. Because of the link between deformability and sickled cells, deformability can be used to evaluate the amount of sickled cells in the blood. Deformability of the erythrocytes that cause the microcirculatory distress can be demonstrated through various other hemorheological characteristics. In order to determine the deformability of erythrocytes multiple factors including blood and plasma viscosity and hematocrit (a calculation of the percent of red blood cells present in the blood) are measured. Alpha-thalassemia Alpha-thalassemia, like sickle cell trait, is typically inherited in areas with increased exposure to malaria. It manifests itself as a decreased expression of alpha-globin chains, causing an imbalance and excess of beta-globin chains, and can occasionally result in anemic symptoms. The abnormal hemoglobin can cause the body to destroy red blood cells, essentially causing anemia. In endurance-trained individuals with sickle cell trait the presence of alpha-thalassemia has been shown to act protectively against microvasculatory distress