The effect of exercise on the increase of red blood cells

During exercise the cardiovascular system has to warrant substrate supply to working muscle. The main functionof red blood cells in exercise is the transport of O۲ from the lungs to the tissues and the delivery of metabolicallyproduced CO۲ to the lungs for expiration. Hemoglobin also contributes to the blood's buffering capacity, and ATPand NO release from red blood cells contributes to vasodilation and improved blood flow to working muscle.These functions require adequate amounts of red blood cells in circulation. Trained athletes, particularly inendurance sports, have a decreased hematocrit, which is sometimes called “sports anemia.” This is not anemia ina clinical sense, because athletes have in fact an increased total mass of red blood cells and hemoglobin incirculation relative to sedentary individuals. The slight decrease in hematocrit by training is brought about by anincreased plasma volume (PV). The mechanisms that increase total red blood cell mass by training are notunderstood fully. Despite stimulated erythropoiesis, exercise can decrease the red blood cell mass by intravascularhemolysis mainly of senescent red blood cells, which is caused by mechanical rupture when red blood cells passthrough capillaries in contracting muscles, and by compression of red cells e.g., in foot soles during running or inhand palms in weightlifters. Together, these adjustments cause a decrease in the average age of the population ofcirculating red blood cells in trained athletes. These younger red cells are characterized by improved oxygenrelease and deformability, both of which also improve tissue oxygen supply during exercise.