Reversible physiological adaptations to high altitudes. Although a number of environmental factors change with altitude, the adaptations are mainly in response to lower oxygen partial pressures. Early adaptations include hyperventilation and increases in submaximal heart rate, which raise the cardiac output. Major long-term adaptations improve the oxygen-carrying capacity of the blood by increasing the haemoglobin content and haematocrit, polycythaemia, and a decrease in plasma volume. Muscles develop more capillaries, and their myoglobin content and 2,3-diphosphoglycerate content increases with altitude. Acclimatization to avoid altitude sickness, generally takes 1–3 days at a given altitude. For example, if a person goes to 10,000 feet (3048 m) and spends several days at that altitude, their body acclimatizes to 10,000 feet (3048 m). If the person then climbs to 12,000 feet (3658 m), the body needs to acclimatize once again, taking another 1–3 days. For athletes preparing for competition at altitude, full acclimatization to medium altitudes (greater than 1829 m above sea level) may take about 2 weeks and will probably be longer for higher altitudes. Effects persist for about 3 weeks on return to sea level.
Subjects: Sports and Exercise Medicine.