Sports anemia refers to a period in early training when athletes may develop low blood hemoglobin for a while, and likely reflects a normal adaptation to physical training.
Aerobic training enlarges the blood volume and, with the added fluid, the red blood cell count per unit of blood drops. While true anemia requires treatment, the temporary reduced red blood cell count seen early in training goes away by itself after a time.
Physically active young women, especially those who engage in such endurance activities as distance running, are prone to iron deficiency. Research studies show that as many as 45% of female runners of high school age have low iron stores.
Iron status may be affected by exercise in a number of ways. One possibility is that iron is lost in sweat and, although the sweat of trained athletes contains less iron than the sweat of others, it is usually simply an adaptation to conditioning. Still, athletes sweat more copiously than sedentary people.
Another possible route to iron loss is red blood cell destruction is that blood cells are squashed when body tissues (as the soles of the feet) make high-impact contact with an unyielding surface (such as the ground). In addition, in some athletes at least, physical activity may cause small blood losses through the digestive tract.
Thirdly, the habitually low intake of iron-rich foods, combined with iron losses aggravated by physical activity, leads to iron deficiency in physically active individuals.
Iron deficiency impairs physical performance because iron is crucial to the body’s handling of oxygen. Since one consequence of iron deficiency anemia is impaired oxygen transport, aerobic work capacity is going to be reduced because the person is likely to tire very easily. Whether marginal deficiency without anemia impairs physical performance remains a point of continual debate among researchers.
Physical activity can also produce a hemolytic anemia caused by repetitive blows to the surfaces of the body. This condition was first noticed in soldiers after long forced marches (march hemoglobinuria). Today, it is more often seen in long-distance runners since soldiers are now better equipped with protective foot gear. March hemoglobinuria can also result from repeated blows to other body parts, and has been observed in martial arts and players of conga and bongo drums.