Final answer:
Exercise at altitude feels more tiring due to decreased atmospheric pressure and lower oxygen levels, leading to decreased oxygen saturation and fatigue during exercise.
Step-by-step explanation:
Exercise at altitude is more tiring than at sea level due to the decreased atmospheric pressure and lower oxygen levels. The atmosphere at higher altitudes exerts less pressure, reducing the exchange of oxygen, which can lead to symptoms such as shortness of breath, confusion, headache, lethargy, and nausea. The lower atmospheric pressure also makes it more difficult for the body to achieve the same level of oxygen saturation, leading to decreased hemoglobin saturation. This decrease in oxygen availability can result in fatigue and a feeling of increased fatigue during exercise.