Interestingly, not everyone agrees with this focus on red blood cell mass. Since the previous study (25) was published, there has been a “point counterpoint” debate on this issue (73), along with a series of letters to the editor in response to the debate (73), and an explosion of new research. Simply put, other studies have shown that six weeks of intermittent hypoxia during training improved VO2 mas and muscle oxidative potential and performance, without a change in red performance, without a change in red cell mass (37, 94, 151). A summary of potential mechanisms, other than red cell mass, linked to the improved performance following exposure to hypoxia was recently published (47). The focus inthis review was on improved mitochondrial function and increased buffering capacity.