Final answer:
Maximal exercise capacity is reduced at high altitude due to lower hemoglobin saturation with oxygen, as a consequence of decreased atmospheric pressure and the associated lower partial pressure of oxygen. This makes it difficult for the body to meet the oxygen demands of exercising muscles. Acclimatization over time can mitigate these effects, and supplemental oxygen is used by mountain climbers to improve exercise performance at high elevations.
Step-by-step explanation:
Maximal exercise capacity is reduced at higher altitude because of multiple physiological factors. The most critical factor is the decreased availability of oxygen that occurs as a result of the lower atmospheric pressure found at high altitudes. While the proportion of oxygen in the atmosphere remains at 21%, the partial pressure of this oxygen decreases with altitude. This lowered partial pressure of oxygen means that less oxygen is available to diffuse into the bloodstream and ultimately be delivered to the muscles that are being exercised.
At high altitudes, hemoglobin saturation with oxygen is significantly lower compared to sea level. For instance, while hemoglobin saturation reaches about 98 percent at sea level, it is only about 67 percent at an altitude of 19,000 feet. This reduced oxygen saturation makes it more challenging for the body to perform at the same level of intensity as it would at lower altitudes, as muscle and tissue demands for oxygen cannot be met as effectively. Moreover, the body may attempt to compensate by producing more hemoglobin and by increasing the release of oxygen from hemoglobin to the tissues, but these adaptations require time for acclimatization.
Acute mountain sickness (AMS) can also occur as a result of rapid ascent to high altitudes, further compounding difficulties with exercise. Symptoms of AMS include headaches, fatigue, and nausea, which also impair physical performance. For these reasons, mountain climbers often carry supplemental oxygen to help alleviate the effects of low atmospheric pressure and improve exercise tolerance at high altitudes.