Vigorous physical activity at high altitude will:

Vigorous physical activity at high altitude significantly increases the body's oxygen demands due to the lower availability of oxygen in the environment. As altitude increases, the partial pressure of oxygen decreases, making it more difficult for the body to obtain sufficient oxygen. When engaging in vigorous physical activity in such conditions, the body's need for oxygen can quickly outstrip what is available, leading to an exacerbation of hypoxia.

This situation increases the risk of developing symptoms of altitude sickness and reduces the body's overall tolerance to hypoxia. Instead of adapting beneficially, the stress of vigorous activity under these circumstances can overwhelm the body's compensatory mechanisms, leading to more severe responses to the deficient oxygen levels. Therefore, under strenuous conditions at high altitudes, the ability of the body to cope with low oxygen is diminished, impacting performance and increasing the likelihood of hypoxia-related complications.