Enhanching Athletic Performance through Endurance Training
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.
Higher VO2max is entirely related to the expansion of red blood cell volume.
In a recent study, scientists determined red blood cell volume, maximal cardiac output and skeletal muscle capillarization and mitochondrial content before and after an eight week exercise training intervention.
The subjects exercise for 60 min 3-4 times/ week at an average intensity of 65%. Following the training intervention red blood cell volume had increased by about 200 ml and total blood volume by 400 ml. Cardiac output was increased by 1.5 l/min and capitalization and mitochondrial content increased by 20 and 40% respectively. This resulted in an increased VO2max of 10%.
On the very last day of the study RBCV was restored to pre-training levels by means of blood donation and the exercise tests were repeated. Very surprisingly, and despite maintaining the skeletal muscle adaptations, both cardiac output and VO2max returned to pre-training values. This suggests that improvements in VO2max with exercise training are entirely related to adaptations in red blood cell volume.