How does altitude affect power output?
The effects of altitude on VO2 uptake (and hence aerobic power) are highly individual, so it is difficult to predict to what extent any one person will be affected, although as a general rule it has been shown that elite athletes, as compared to normal individuals, have a greater decline in VO2max under conditions of reduced ambient pO2 (partial oxygen pressure). This is caused by their higher cardiac output, which results in a decreased mean transit time for the erythrocytes (red blood cells) within the pulmonary capillary, and thus less time for equilibration between alveolar air and blood in the pulmonary capillary. These equations from Bassett et al.1 were generated from 4 groups of highly trained or elite runners, so they are population-specific to that group, but can be used to estimate aerobic power at a given altitude as a percentage y of what is normally available at sea level, where x = elevation above sea level in km: acclimatized athletes (several weeks at altitude): y = -1
