Exposure to altitude produces reactive changes which are only specific to altitude. Predominantly endurance performances at moderate altitude never reach levels that are possible at sea-level. The shorter the stay at altitude, the less marked and more transient will be any acclimatization changes. Physiological changes alone may be insufficient to fully enhance performance at altitude. The lower the altitude, the less marked will be the acclimatization response.
Individuals vary greatly in their responsiveness to altitude stress.
Some may never acclimate. These changes need to be qualified. Red blood cell volume may increase, if the exposure duration is greater than three to four weeks, but that association with an unchanged VO2max is not understood. Changes at the cellular level are likely to be moderated by the severity of the altitude exposure. Stages of acclimatization take time.