What is the effect of altitude on oxygen availability for athletes?

At high altitudes, the atmospheric pressure decreases, which in turn lowers the partial pressure of oxygen. This reduction in the partial pressure means that there is less oxygen available for athletes to breathe. Consequently, even though the concentration of oxygen in the air remains the same at high altitudes, the body receives less oxygen due to the thinner air. This can significantly impact an athlete's performance because the body relies on oxygen to produce energy efficiently during physical exertion.

Additionally, as athletes perform at these altitudes, they may experience symptoms related to altitude sickness due to the lesser amount of oxygen accessible. This makes acclimatization important for athletes who are training or competing in such environments to improve their body's ability to utilize the limited oxygen available.

While hydration is indeed a concern at high altitudes, primarily due to increased respiratory water loss and lower humidity, it does not directly influence oxygen availability, which is the key focus of this question. Thus, the significant effect of altitude is the reduction in oxygen availability for athletes, confirming why this option is the correct choice.