The connection between endurance training and enhanced red blood cell volume (RBCV) was first appreciated in the aftermath of World War II by Swedish scientists using the CO based methodology.
Since then, greater red blood cell volumes have consistently been demonstrated in athletes through cross-sectional studies. While recognized by most that an elevated red blood cell volumes are advantageous for athletic performance due to its oxygen carrying capacity, a second mechanisms may be just as important.
Red blood cell volume expansion augments the capacity to deliver oxygen, and thereby increasing VO2max, via two mechanisms:
- larger total BV facilitates venous return and cardiac filling, which by means of the Frank-Starling mechanism leads to increased stroke volume and Qmax
- higher number of circulating red blood cells and specifically, the hemoglobin inside them facilitates blood O2 carrying capacity. Besides these mechanisms it should also be noted that Hb functions as a buffer aiming to keep blood pH constant and thereby limit “muscle acidification”.
Besides blood and other cardiovascular adaptations, endurance athletes also carry a variety of other physiological traits such as an elevated number of skeletal muscle capillaries and mitochondria. With regular endurance exercise training also previously untrained individuals will enhance blood volume and skeletal muscle properties. A question is how important these are, respectively, to improvements in maximal oxygen uptake (VO2max) – which largely determines athletic performance.