HAMP and Hematuria: The etiology of such sports anemia is likely multifactorial, with proposed causes including dilution of erythrocytes secondary to plasma volume expansion as a beneficial adaptation to exercise (Eichner, 1992), hemolysis due to mechanical destruction of erythrocytes in plantar vasculature (similar to marching hematuria) (Hallberg and Magnusson, 1984), and iron-deficiency attributable to increased iron demand, loss iron, or blockage of iron absorption by stress-induced hepcidin (Clenin et al., 2015).