Final answer:
VO2max starts to decline at approximately 1,500 meters above sea level due to reduced atmospheric pressure and lower oxygen availability, necessitating supplemental oxygen for high-altitude mountain climbers.
Step-by-step explanation:
The question is related to the physiological changes that occur in the human body in response to high altitudes, specifically concerning VO2 max and its decline at higher altitudes. VO2 max, or maximal oxygen uptake, begins to decline at approximately 1,500 meters above sea level. This decline is due to the reduced atmospheric pressure and lower oxygen concentration, which affects the body's ability to absorb and utilize oxygen, leading to decreased aerobic performance.
For mountain climbers, this would necessitate carrying bottled oxygen to supplement the decreased availability of oxygen in the air. The body compensates for hypoxia, or inadequate oxygen supply, by producing more hemoglobin over time, but acclimatization can take up to 10 days, and people living at high altitudes typically have a higher level of hemoglobin in their blood for this reason.