It has been said that one of the main differences between endurance athletes and nonathletes is their response to low pressures of oxygen (hypoxia) and higher levels of carbon dioxide (hypercapnia). In other words, endurance athletes are able to tolerate a greater concentration of carbon dioxide and lower concentration of oxygen in the blood during exercise. Intense physical exercise results in increased consumption of oxygen and increased production of carbon dioxide, so it is vitally important that athletes are able to cope well with changes to these gases.
