High altitude are regions on the Earth's surface (or in its atmosphere) that are high above mean sea level. The composition and temperature of the atmosphere at high altitude is substantially different than at sea level. These differences can affect living organisms, including humans. High altitude is sometimes defined to begin at 1500 m above sea level.
At high altitude, atmospheric pressure is lower compared to sea level. This is due to two competing physical effects: gravity, which causes the air to be as close as possible to the ground; and the temperature of the air, which causes the molecules to bounce off each other and expand.
The lower atmospheric pressure affects animals and humans, due to the decrease in the partial pressure of oxygen.
Because of the lower pressure, the air expands as it rises, which causes it to cool. Thus, high altitude air is cold, which causes a characteristic alpine climate. This climate dramatically affects the ecology at high altitude.
Effects on humans
Oxygen saturation in hemoglobin affects our ability to use the vital gas. After the body reaches around 7000 feet above sea level, the saturation of oxyhemoglobin begins to plummet. At approximately 60% saturation, most people lose consciousness.
Altitude acclimatization, the physiological adaptions to altitude, can have immediate and long term effects.
Long Term Effects
- Lower lactate production (because reduced glucose break down decreases the amount of lactate formed).
- Alkaline loss
- Decrease in plasma volume
- Increased Hemocrit
- Increase in RBC mass
- Higher concentration of capillaries in striated muscle tissue
- Increase in myoglobin
- Increase in mitochondria
- Increase in aerobic enzyme concentration
- Decrease in 2,3 DPG
Altitude and Athletic Performance
In the athletic arena, it is thought that acclimatization to high altitudes enhances performance compared to training at sea level. However, these assumptions have not been backed with any significant evidence. Contrary to these beliefs, studies have shown that athletes may not be able to train with as much intensity at high altitudes compared to sea level.
Yet, for those determined to adjust to high altitudes, without being at high altitudes, inventors have cranked out state-of-the-art altitude acclimatization devices. Chambers that reduce barometric pressure, hydrobaric chambers with increased nitrogen concentration (which reduces oxygen), and tents that supply a limited amount of oxygen are used by athletes to acclimatize to high altitudes.
Finally, it is important to realize that to benefit from altitude acclimatization, one must stay in that altitude for a long period of time. Any benefits of altitude acclimatization are lost quickly by those who only dwell in high altitudes, or simulated circumstances, for a short amount of time.
Please see altitude sickness for more information.