How does lower air density at high altitudes affect breathing?

At high altitudes, the air density decreases, which results in a lower concentration of oxygen available for breathing. Oxygen is essential for human respiration; therefore, when individuals ascend to higher altitudes, the reduced air density means that each breath contains fewer oxygen molecules. This can lead to difficulty in obtaining sufficient oxygen, particularly during physical exertion or for those not acclimatized to the altitude. The body may struggle to meet its oxygen demand, causing symptoms such as shortness of breath, increased heart rate, and fatigue.

While the concept of air density impacting respiration is key to understanding the effects of high altitude, other choices like the assertion that breathing becomes easier or has no effect neglect the physiological realities of how oxygen levels change with elevation. Additionally, stating that it only affects swimmers is irrelevant, as the phenomenon is applicable to all individuals exposed to high-altitude environments, regardless of their activities.