Mild hemolysis with hematuria, hemoglobinemia, and hemoglobinuria produced by strenuous exercise, including running. The anemia may be caused by: 1) the destruction of red blood cells during repeated striking of the ground by the runner’s feet; 2) plasma volume expansion; and 3) intestinal blood loss. Blood may be lost in the feces, presumably due to transient ischemia of the gut during vigorous exercise.