What happens to the respiratory process in a man going up a hill?

As a man goes up a hill, his respiratory rate and depth increase to meet the higher oxygen demand of his muscles. The air at higher elevations has lower oxygen pressure, so his lungs must work harder to take in enough O₂. This triggers faster breathing (hyperventilation) and increased heart rate. Over time, if the altitude is high enough, the body starts producing more red blood cells to carry oxygen more efficiently—a process called acclimatization.

At very high altitudes, the drop in oxygen can cause altitude sickness, with symptoms like headache, dizziness, and fatigue.