Using high-altitude training to prepare for sports entails living and training at a high altitude, living at a high altitude while training at a lower altitude, living at a lower altitude while training at a higher altitude or living at a high altitude while training at both high and low altitudes. There are also face masks and tents that simulate changes in altitude by controlling oxygen levels.
While at a high altitude, the body compensates for the decrease in oxygen found at higher elevations by making extra red blood cells, which are used to transport oxygen in the blood, and by making them more efficient at unloading the oxygen. The theory is that coming back down to sea level to perform gives athletes a competitive edge because they have an excess of red blood cells for the current environment, making it easier to get oxygen to the cells. Therefore, the heart has to pump less, and the lungs have to breath less rapidly to perform.
However, there are drawbacks to training at elevation such as the need to cut back on training while the body adapts to the lower oxygen levels, losing muscle, not being able to train as strenuously under low-oxygen conditions and a lack of resistance during training. Consequently, some athletes choose to train at lower elevations while sleeping at higher elevations. Eating a diet high in carbohydrates and salt, drinking plenty of fluids and avoiding alcohol help the athlete adjust to higher elevations more quickly.