This chapter proposes a number of exercise-generated mechanisms to influence the iron status of an athlete including hemolysis, hematuria, sweating, gastrointestinal bleeding, and injuries. The need to supplement athletes with iron was first suggested by the evidence of changes in blood cell counts and iron-associated parameters during periods of intense training or, even more accentuated, at the start of the training. This condition is known as “sports anemia” and is common in endurance athletes. The hematological changes that occur during intense training are paralleled by the fall in ferritin concentration, mirroring a depletion of the body iron stores, even though ferritin levels also depend upon a number of other factors such as liver disease, alcohol consumption, infections, cardiovascular disease, and aging. Other parameters that can be used to monitor the iron status include sTfR, red blood cells (RBC) protoporphyrin, and stainable bone marrow iron (hemosiderin).