Final answer:
Exercising at high altitudes is difficult due to lower oxygen levels as a result of reduced atmospheric pressure, which decreases the partial pressure of oxygen, leading to reduced oxygen delivery to muscles and potential hypoxia.
Step-by-step explanation:
Exercising at high altitudes is difficult for individuals who are not accustomed to it because A. Oxygen levels are lower, leading to reduced oxygen delivery to muscles. This happens due to a decrease in atmospheric pressure as altitude increases, which leads to a reduction in the partial pressure of oxygen. The proportion of oxygen relative to other gases in the atmosphere remains constant at 21 percent, but its partial pressure, and therefore its availability to the human body, decreases with altitude. This can result in hypoxia, an inadequate supply of oxygen to the body, and can trigger symptoms of acute mountain sickness (AMS), including headaches, disorientation, fatigue, nausea, and lightheadedness.
The body can adjust to high altitudes through a process called acclimatization, which includes increasing the production of hemoglobin and the release of oxygen into the tissues. Nevertheless, this adjustment takes time, and the immediate effect of high altitude is a lower level of hemoglobin saturation compared to that at sea level, making physical activities more challenging until acclimatization occurs.