Also called erythrocytes, red blood cells are the important cells of the body that carry oxygen to the tissues. Like other cells of the blood, RBCs are produced in the bone marrow, but they develop a curved shape different from other types of blood cells. Red blood cells have a protein called hemoglobin, which binds to oxygen molecules. This capability is essential for maintaining oxygen levels during exercise.
RBCs and Hemoglobin
When RBCs pass through the circulation near the lungs, they pick up oxygen molecules, which bind to the hemoglobin that they carry. Together, the RBCs and hemoglobin transport oxygen molecules through the bloodstream. You need enough hemoglobin available for the RBCs to pick up the needed oxygen. Hemoglobin levels may be measured to determine the body's oxygen-carrying capacity. According to Sports Doctor, Inc., a normal level of hemoglobin is considered to be between 12 and 15 g/100 mL of blood.
Erythropoiesis
Because of their curved shape, RBCs do not contain a nucleus and therefore have a shorter lifespan, compared with other types of blood cells. The lifespan of an RBC is approximately 120 days, after which more of these cells must be produced by the body. Red blood cells are produced through a process in which the kidneys secrete a substance called erythropoietin, which stimulates the bone marrow to create more RBCs. When the body has lower levels of oxygen, such as during extended periods of exercise, the kidneys secrete erythropoietin to create more RBCs.
Oxygen During Exercise
When you exercise, you use your skeletal muscles for moving through your particular type of workout routine. The contraction of these muscles requires an increased need for oxygen in these tissues. Your body responds to this by increasing how fast your heart beats, which pumps more blood through circulation. As the blood is pumped faster, the RBCs are able to pass near the lung tissue and pick up extra oxygen molecules. They can then quickly carry the oxygen to the muscles and other parts of the body that need more oxygen due to exercise.
Anemia
The hemoglobin connected to RBCs is made up partly of iron molecules. If you have low levels of iron, such as in iron-deficiency anemia, you may have low levels of hemoglobin, resulting in less oxygen reaching the cells. If you have anemia caused by an iron deficiency, your exercise abilities may suffer because you may not be getting enough oxygen when you work out. Women may lose iron through blood loss of menstruation, and some performance athletes may have low iron counts due to sweat loss during heavy exercise. You can increase your iron intake by eating foods such as meat, fish, eggs or spinach.
