Athletes will typically experience two different types of effects upon their ability to perform at high-altitude venues. The first is physiological, determined by the body's reaction to a thin, less-oxygenated atmosphere. The second effect is impacts that are sport-specific but equally pronounced: how the physical components of a particular sport are altered in high altitude performance.
High altitude is the description given any locale where the athlete begins to experience the limitations that a reduced oxygen intake place upon the body. Scientists generally classify elevations of 6,500 ft (2,000 m) as high altitude because of the pronounced difference in oxygen content; the effect of altitude may be experienced at lower elevations. The human body has a built-in mechanism to counter the effects of low oxygen in the immediate atmosphere. When the body senses that it is not receiving its accustomed level of oxygen, it determines that it must produce a greater number of erythrocytes (red blood cells), which carry oxygen to the bloodstream. The increase of transportation capability means that the body will be optimizing the amount of available oxygen.
The process by which erythrocytes are increased commences with the release of a hormone in the kidneys known as erythropoietin (EPO), which acts as a trigger to the production of erythrocytes centered in the bone marrow of the long bones of the body, primarily the femur (thigh). The acclimatization of the body to an oxygen-reduced environment is not instantaneous; high altitude adaptations begin immediately. An athlete will be as much as 75% accustomed to the thin air within 7-10 days of exposure to the conditions, with full acclimatization within 15-20 days. High altitude training is a proven effective performance-enhancing tool, as the ability of an athlete to utilize greater amounts of oxygen will naturally support improved capabilities. The physiological benefits of high altitude training continue for between one to three months after the return of the athlete to sea-level training conditions conditions.
The physics of high altitude sports performance and the advantages derived by the competitors in such venues are as varied as they are emphatic. The 1968 Olympics held in Mexico City were the first games staged at a high altitude (7,349 ft [2,300 m]), and the number of world records set was indicative of the impact of the thinner air on performance. American Bob Beamon set a long jump event record of 29 ft 2 in (9.3 m), which shattered the then-existing standard by over 2 ft (.6 m), in a discipline where records are almost always broken in increments of fractions of an inch. Lee Evans of the United States set a world record of 43.86 seconds in the 400-m race, a mark that stood for almost 20 years. Records fell in almost every track event from the 100-m to the 1,500-m; the longer distances posed difficulties for the athletes that were not entirely accustomed to the high altitude effects.
Intense research conducted in the wake of the world record onslaught at Mexico City confirmed that the reduced wind resistance and drag upon the competitors' bodies in the thin air permitted the athletes to move with greater efficiency. So long as the event did not involve prolonged duress to the aerobic energy system and its dependency upon maximal amounts of oxygen, an athlete could expect better performances in higher altitude. Not only does the moving body encounter reduced air resistance, any objects thrown, such as a discus or javelin, would tend to travel further as well.
The effects of high altitude are well known in different professional team sports. The visiting soccer team to venues such as Mexico City and La Paz, Bolivia (where the stadium attitude of over 11,000 ft [3,400 m], is the highest in international soccer), will likely not be able to perform at a maximum level unless it has trained at altitude. To a lesser but measurable degree, Denver, Colorado's Mile High Stadium, situated at 5,500 ft above sea level (1,700 m), has been regarded as a difficult competitive environment for visiting American football teams since it was opened.
Altitude is a significant performance factor in the game of baseball, especially with respect to how far a batted ball will carry in the thinner air. The professional baseball stadium in Denver is known as a hitter's park for this reason, as are a number of National Collegiate Athletic Association (NCAA) venues in the western United States that are constructed at elevations greater than 5,000 ft (1,550 m). Research conducted at various times has concluded that a baseball will travel between 3% and 7% further in air at these altitudes than a similarly struck ball at sea level, assuming that the temperature is constant. An object will travel further in warmer, less dense air than it will in cold air.
In the sports of both American football and rugby, a ball can be kicked further in thinner high altitudes than at sea level. American football coaches and their specialist field goal kickers will be inclined