But, in terms of the total energy expenditure, all these performances pale somewhat when compared to that of Robert Falcon Scott’s Polar party during the 1911/12 British Antarctic Expedition. For most of 159 consecutive days, Scott’s team man-hauled for 10 hours a day to the South Pole and back covering a distance of 2 500 km. Their predicted total energy expenditure per individual would have been about 1 million kcal, making theirs, by some margin, the greatest sustained endurance athletic performance of all time. Interestingly, the dogs that provided the pulling power for Norwegian Roald Amundsen’s team that was the first to reach the South Pole, 35 days before Scott’s party, would have expended about 500 000 kcal in their 97 day trip, making theirs the greatest animal “sporting” performance on record. By contrast, mountain climbers expend only approximately4 000 kcal/day when climbing at extreme altitudes (above 4 000 m). This relatively low rate of energy expenditure results from the low exercise intensities that can be sustained at extreme altitude. Here I argue that this slow rate of energy expenditure is caused, not by either myocardial or skeletal muscle hypoxia as is usually argued, but is more likely the result of a process integrated HYPoXia and tHE CiRCulation Chapter 0 centrally in the brain, the function of which is to protect the body from harm. At extreme altitude the organ at greatest risk is the brain which must be protected from the catastrophic consequences of profound hypoxia. A key feature of this control is that it acts “in anticipation” specifically to insure that a catastrophic biological failure does not occur. The evidence for this interpretation is presented.